Preoperative CT-Based Segmentation of Psoas Muscle Area and Subcutaneous Fat Tissue: Associations With Perforation and Length of Hospital Stay in Pediatric Appendicitis

Preoperative CT-Based Segmentation of Psoas Muscle Area and Subcutaneous Fat Tissue: Associations With Perforation and Length of Hospital Stay in Pediatric Appendicitis | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Preoperative CT-Based Segmentation of Psoas Muscle Area and Subcutaneous Fat Tissue: Associations With Perforation and Length of Hospital Stay in Pediatric Appendicitis Celal Tacyildiz, Suna Yergin Tacyildiz This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8941099/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background Acute appendicitis is a leading cause of emergency abdominal surgery in children, and predicting postoperative length of hospital stay (LOS) is important for prognosis and resource planning. This study aims to assess the associations of LOS and appendiceal perforation with preoperative CT-derived measurements of psoas muscle area, attenuation, and subcutaneous fat tissue in children with appendicitis. Methods This retrospective study comprised 170 pediatric patients (< 18 years) surgically diagnosed with appendicitis between January 2022 and October 2025. At the L3-L4 intervertebral disc level, bilateral psoas muscles and subcutaneous adipose tissue were segmented using 3D Slicer. Right, left, and total psoas muscle area (tPMA), psoas muscle mean attenuation, tPMA Z-scores, subcutaneous fat tissue, inflammatory markers (WBC, neutrophils, and CRP), maximum appendiceal diameter, the presence of an appendicolith, appendiceal perforation status, surgical approach, and LOS were recorded. Results Of 170 patients, 51 had perforated appendicitis. Perforation correlated with elevated WBC/neutrophil/CRP levels, increased appendiceal max diameter, a higher incidence of appendicolith, reduced psoas muscle mean attenuation, and extended LOS (median 6.0 vs. 3.0 days; p < 0.001). CRP showed a moderate correlation with LOS (ρ = 0.435), while WBC (ρ = 0.302), neutrophils (ρ = 0.356), appendiceal max diameter (ρ = 0.233), and psoas muscle mean attenuation (ρ=−0.208) showed weak correlations. In multivariable negative binomial regression, perforation (IRR 2.287, p < 0.001) and neutrophil count (IRR 1.018 per 1×10⁹/L, p = 0.039) independently predicted extended LOS. Conclusions There is an association between post-appendectomy LOS and CT-derived psoas muscle attenuation, supporting segmentation-based prognostication and promising future studies. Psoas muscle area (PMA) Psoas muscle attenuation (HU) Subcutaneous fat tissue Pediatric Appendicitis CT-Based Segmentation Figures Figure 1 Introduction Acute appendicitis is one of the most common causes of emergency abdominal surgery in children. Obstruction associated with lymphoid hyperplasia is the most common cause of acute appendicitis in children. Clinical history, physical examination, laboratory values, and imaging play a crucial role in diagnosis. Ultrasound is primarily used for diagnosis; CT may be used when ultrasound is inadequate (e.g., obesity, atypical location, user- or patient-related factors, etc.). MRI is another imaging method used in pregnant women and children. Uncomplicated acute appendicitis can be treated with antibiotics. Laparoscopic and open surgical procedures can treat acute appendicitis with complications or cases that do not respond to antibiotic treatment. Laparoscopic appendectomy is currently preferred because it is less invasive and is generally associated with faster recovery and shorter hospitalization [ 1 , 2 ]. The length of hospital stay (LOS) following appendectomy surgery is important in terms of patient health and comfort, reducing costs, and increasing hospital bed utilization. According to studies, high WBC and CRP values (indicating severe inflammation), complicated appendicitis (perforated, gangrenous, etc.), the length of time between the onset of the disease and surgery, the presence of appendicolith, and increased surgery duration are factors that prolong hospital stay [ 3 ]. Additionally, studies indicate that the surgical method used to repair the stump (e.g., silk ligation, Endoloop ligation, Hem-o-lok vascular clamp occlusion, and endo-gastrointestinal anastomosis (Endo-GIA) stapling and closure) and the class of antibiotics used also affect the length of hospital stay [ 3 – 5 ]. Sarcopenia is a decrease in muscle mass and function. It is an important indicator of frailty [ 6 ]. Sarcopenia is one of the important indicators of morbidity and mortality in the elderly, chronic patients, and cancer patients. There are also studies showing that sarcopenia negatively affects the outcome of surgical procedures [ 7 ]. In children, body composition (adipose tissue, skeletal muscle, etc.) may be an important predictor of various health problems [ 8 ]. Skeletal muscle growth during childhood is influenced by factors such as maternal nutrition during pregnancy, genetic factors, nutritional intake, physical activity, cardiovascular and metabolic diseases, chronic diseases, and hormones [ 9 ]. It is difficult to assess skeletal muscle mass and function in children. This is because normative data for evaluating the results of methods measuring body muscle mass and function in children of different age groups are limited to a few studies. In our study, we used the normative data obtained by Aydın T. and colleagues in their research [ 10 ]. Muscle mass can be measured using dual-energy X-ray absorptiometry (DEXA), bioelectrical impedance analysis (BIA), and body composition analysis [ 7 ]. Currently, cross-sectional imaging (CT and MRI) has demonstrated that measurements of abdominal muscle and fat areas in axial planes reliably reflect total body muscle and fat mass [ 8 , 11 ]. The skeletal muscle area measured by CT scan at the L3-L4 vertebra level is generally accepted as a reliable indicator of total muscle volume [ 12 ]. These measurements can be obtained manually, using semi-automatic and fully automatic deep learning slice-based muscle segmentation. The aim of this study is to investigate the association between postoperative LOS and preoperative CT-derived measurements—obtained at the L3-L4 intervertebral disc level, using semi-automatic and manual segmentation—including psoas muscle area, psoas muscle density, and subcutaneous adipose tissue area, as well as laboratory parameters and surgical approach, in pediatric patients diagnosed with appendicitis who underwent appendectomy. Materials and methods Study Design Our study was conducted retrospectively between January 2022 and October 2025 and included patients under the age of 18 who underwent appendectomy surgery. The study was conducted in accordance with the Helsinki Declaration (as revised in 2013) and was approved by the Clinical Research Ethics Committee of our hospital with a waiver of consent (E-95531838-050.99-156362). Study Population Between January 2022 and October 2025, 784 children with appendicitis underwent appendectomy at our hospital. Our inclusion criteria were surgical confirmation of appendicitis and age < 18 years, with an available contrast-enhanced abdominal CT scan obtained within 48 hours before surgery when ultrasonography was non-diagnostic or when clinical suspicion persisted. Our exclusion criteria were contrast-enhanced abdominal CT scans with non-diagnostic motion artifacts, patients who underwent an additional surgical procedure concomitantly with appendectomy, children with malignancy or chronic disease, and cases with missing inflammatory marker data. Thus, 170 patients were included in this retrospective study. CT acquisition protocols CT images were obtained using a Toshiba Alexion 16-slice CT scanner. Intravenous contrast material was administered at a dose of 1 mL/kg at an injection rate of 0.5–1.5 mL/s. CT images were obtained in the portal venous phase with a slice thickness of 3 mm approximately 60 seconds after intravenous contrast administration. For children weighing less than 15 kg, the CT settings were 80 kV and 30 mA; for 16–30 kg, 100 kV and 30 mA; for 31–45 kg, 100 kV and 30 mA; and for more than 45 kg, 120 kV and 50 mA. CT-Derived Body Composition Measurements The patients' CT images were obtained in the picture archiving and communication system (PACS). CT images in the digital imaging and communications in medicine (DICOM) format were opened in 3D Slicer version 5.8.1 ( https://www.slicer.org/ ). The “Segment Editor,” “Segment Statistics,” and “Segment Cross-Section Area” modules in the 3D Slicer application were used. At the axial slice corresponding to the L3-L4 intervertebral disc level, the right and left psoas muscles were manually segmented from a single CT slice using the “Segment Editor” module. On the same CT slice, automatic segmentation was performed in the “Segment Editor” module for subcutaneous fat tissue segmentation using threshold values of -190 and − 30 HU. Visceral/intramuscular adipose tissue and regions erroneously segmented by 3D Slicer were manually removed, thereby completing the semi-automated segmentation process. After segmenting the psoas muscle and subcutaneous fat tissue axial slice at the L3-L4 intervertebral disc level, the average psoas muscle HU value, right and left psoas muscle areas, total psoas muscle area (tPMA), and subcutaneous fat tissue areas were measured using the “Segment Statistics” and “Segment Cross-Section Area” modules. Maximum appendiceal diameter was measured on axial images (outer wall to outer wall) at the most distended segment; appendicolith was defined as an intraluminal calcified focus with attenuation higher than adjacent soft tissue. Perforation status was determined based on operative findings, defined as a visible appendiceal wall defect with fecalith/spillage and/or purulent peritonitis, as documented in the surgical report. Whether the surgery was laparoscopic or laparotomy was recorded by checking the surgical notes. The LOS, intensive care unit requirement, postoperative oral intake day, presence of postoperative complications, and inflammatory markers were recorded for all patients. tPMA Z-scores were calculated based on the reference values reported by Aydın T et al. in their study establishing normative data for abdominal skeletal muscle compartments in Turkish children [ 10 ]. Segmentation and imaging measurements were performed by two radiologists (C.T. and S.Y.T., with 5 and 6 years of experience in abdominal imaging), blinded to clinical outcomes (LOS and perforation status). For interobserver analysis, 35 cases were randomly selected and re-segmented independently by the second reader. Intraclass correlation coefficients were calculated using a two-way random-effects model with absolute agreement (ICC[ 2 , 1 ]). Statistical Analysis All statistical analyses were performed using IBM SPSS Statistics, Version 28 (IBM Corp., Armonk, NY, USA). Normality of continuous variables was assessed using the Shapiro–Wilk test. As the majority of continuous variables were not normally distributed, continuous data are presented as median (IQR [25th–75th percentiles]) and were compared between groups using the two-sided Mann–Whitney U test. Categorical variables are summarized as counts and percentages and were compared using the Pearson chi-square test or Fisher’s exact test, as appropriate. Associations between length of hospital stay (LOS) and individual continuous predictors were evaluated using two-sided Spearman’s rank correlation (ρ). Where multiple simultaneous hypothesis tests were performed, multiplicity was controlled using the Benjamini–Hochberg false discovery rate (FDR) procedure, and FDR-adjusted q-values are reported; statistical significance for these analyses was defined as q < 0.05. LOS was analyzed as count data. Overdispersion was assessed by fitting a Poisson model and examining dispersion indices, including the variance-to-mean ratio and the Pearson chi-square statistic divided by degrees of freedom (χ²/df). Because overdispersion was present (variance-to-mean ratio = 2.26; Pearson χ²/df = 2.26), negative binomial regression models were used instead of Poisson regression. Univariable negative binomial models were first fitted for each candidate predictor, followed by a multivariable negative binomial model including clinically relevant covariates. Effect estimates are reported as incidence rate ratios (IRR) with 95% confidence intervals (CI) and two-sided p-values. Results Our study included a total of 170 patients under the age of 18 who underwent appendectomy surgery, comprising 119 cases of non-perforated appendicitis and 51 cases of perforated appendicitis. Of the patients included in our study, 58 (34.1%) were female and 112 (65.9%) were male. The median age of the female patients was 13.96 [10.46–15.90] years, and the median age of the male patients was 13.21 [11.08–15.77] years. The distribution of patients in our study according to age groups is as follows: 0–5 years: 2 individuals (1.2%); 5–10 years: 29 individuals (17.1%); 10–15 years: 85 individuals (50.0%); 15–18 years: 54 individuals (31.8%). In female patients, subcutaneous fat tissue and subcutaneous fat tissue/total psoas muscle area were significantly higher than in male patients, while total psoas muscle area was significantly higher in male patients. There was no significant difference in psoas muscle attenuation based on gender (Table 1 ). Table 1 Median CT segmentation values for female and male and their statistical comparison Variable Female (median [IQR]) Male (median [IQR]) p-value (MWU) q-value (FDR) Right psoas muscle area (mm²) 626.5 [508.3–721.0] 740.0 [547.3–1029.0] < 0.001 0.001 Left psoas muscle area (mm²) 616.5 [482.8–720.8] 719.0 [547.5–1047.8] < 0.001 < 0.001 Total psoas muscle area (mm²) 1244.0 [996.8–1421.3] 1440.0 [1116.3–2137.8] < 0.001 < 0.001 Subcutaneous fat tissue (mm²) 7281.8 [4430.5-15789.7] 3070.3 [1726.6–5971.8] < 0.001 < 0.001 Subcutaneous fat tissue / Total psoas muscle area 6.35 [4.03–12.10] 2.20 [1.40–4.30] < 0.001 < 0.001 tPMA Z-score -0.38 [-0.96–0.14] -0.30 [-0.78–0.24] 0.442 0.442 Psoas muscle mean attenuation (HU) 59.1 [54.6–62.0] 60.3 [56.2–63.9] 0.096 0.112 Data are presented as median (interquartile range). The Mann-Whitney U test was used to compare continuous variables between the two independent groups. To correct for multiple testing, q-values were adjusted using the Benjamini-Hochberg False Discovery Rate (FDR) method for 7 comparisons. tPMA Z-score, total muscle area Z-score In the comparison of non-perforated and perforated appendicitis groups, significant differences were observed in the variables WBC, neutrophils, CRP, appendix max diameter, appendicolith present, psoas muscle mean attenuation (HU), and LOS (Table 2 ). Age (years) was 13.25 [11.02–15.83] overall, 13.25 [11.04–15.88] in the non-perforated group, and 13.25 [11.00–15.33] in the perforated group (Table 2 ). Table 2 Clinical and CT segmentation values according to non-perforated and perforated appendicitis groups in the study population Variable Non-perforated (n = 119) (median [IQR]) Perforated (n = 51) (median [IQR]) p-value q-value (FDR) Age (years) 13.25 [11.04–15.88] 13.25 [11.00–15.33] 0.662 0.662 WBC (×10⁹/L) 14.5 [12.0–17.0] 17.0 [13.4–20.4] 0.001 0.004 Neutrophils (×10⁹/L) 11.3 [8.8–14.2] 14.2 [11.5–18.0] < 0.001 0.002 CRP (mg/L) 11.0 [2.3–35.5] 94.8 [25.3–144.2] < 0.001 < 0.001 Appendix max diameter (mm) 8.7 [7.1–10.0] 11.0 [9.2–12.4] < 0.001 < 0.001 Male sex 73 (61.3%) 39 (76.5%) 0.077 0.144 Appendicolith present 38 (31.9%) 29 (56.9%) 0.003 0.007 Right psoas muscle area (mm²) 686.0 [545.0–934.0] 683.0 [504.0–852.0] 0.621 0.662 Left psoas muscle area (mm²) 683.0 [549.5–938.5] 679.0 [512.0–838.0] 0.377 0.471 Total psoas muscle area (mm²) 1370.0 [1099.5–1857.0] 1348.0 [1008.5–1719.5] 0.540 0.624 Subcutaneous fat tissue (mm²) 4319.1 [2518.2–11774.7] 3435.4 [1650.9–10594.8] 0.170 0.254 Subcutaneous fat tissue / Total psoas muscle area 3.40 [2.05–8.00] 2.70 [1.40–8.45] 0.273 0.373 tPMA Z-score -0.11 [-0.82–0.57] -0.41 [-1.04–0.05] 0.156 0.255 Psoas muscle mean attenuation (HU) 60.4 [56.4–64.2] 58.0 [53.0–61.0] 0.018 0.038 LOS (days) 3.0 [2.0–3.0] 6.0 [5.5–8.0] < 0.001 < 0.001 Data are presented as median (interquartile range) or number (percentage). Continuous variables were compared using the Mann-Whitney U test, and categorical variables using the chi-square or Fisher’s exact test. To correct for multiple testing, q-values were adjusted using the Benjamini-Hochberg False Discovery Rate (FDR) method for 15 comparisons. WBC, white blood cell; CRP, C-reactive protein; tPMA Z-score, total muscle area Z-score; LOS, length of hospital stay Spearman correlation analysis between each continuous variable and LOS demonstrated a moderate correlation with CRP and weak correlations with WBC, neutrophil count, maximum appendiceal diameter, and psoas muscle mean attenuation (Table 3 ). After FDR adjustment, WBC, neutrophil count, CRP, appendix maximum diameter, and psoas muscle mean attenuation remained statistically significant (q < 0.05). Table 3 The relationship between single continuous variables and length of hospital stay (LOS) Variable Spearman ρ p-value q-value (FDR) Age (years) -0.073 0.346 0.377 WBC (×10⁹/L) 0.302 < 0.001 < 0.001 Neutrophils (×10⁹/L) 0.356 < 0.001 < 0.001 CRP (mg/L) 0.435 < 0.001 < 0.001 Appendix max diameter (mm) 0.233 0.002 0.007 Right psoas muscle area (mm²) -0.101 0.190 0.254 Left psoas muscle area (mm²) -0.126 0.102 0.205 Total psoas muscle area (mm²) -0.113 0.141 0.242 tPMA Z-score -0.107 0.164 0.246 Psoas muscle mean attenuation (HU) -0.208 0.006 0.016 Subcutaneous fat tissue (mm²) -0.075 0.331 0.377 Subcutaneous fat tissue / Total psoas muscle area -0.013 0.867 0.867 Associations between LOS and each continuous variable were assessed using two-sided Spearman’s rank correlation (ρ). P-values were adjusted for multiple testing using the Benjamini–Hochberg false discovery rate (FDR) procedure (m = 12), and FDR-adjusted q-values are reported. WBC, white blood cell; CRP, C-reactive protein; tPMA Z-score, total muscle area Z-score In the univariable negative binomial regression analysis performed to predict LOS, the variables WBC, neutrophil count, CRP, appendix maximum diameter, psoas muscle mean attenuation, presence of perforation, and surgical approach (laparoscopy vs laparotomy) were significant (Table 4 ). Table 4 Univariable negative binomial regression analysis in predicting length of hospital stay (LOS) Predictor IRR 95% CI p-value Age (per 1 year) 1.006 0.974–1.039 0.700 WBC (×10⁹/L) (per 1) 1.036 1.016–1.056 < 0.001 Neutrophil (per 1×10⁹/L) 1.047 1.026–1.068 < 0.001 CRP (mg/L) (per 10) 1.039 1.025–1.053 < 0.001 Appendix max diameter (mm) (per 1) 1.061 1.022–1.102 0.002 Male sex (vs Female) 1.095 0.883–1.358 0.408 Appendicolith present (vs absent) 1.160 0.945–1.424 0.156 Total psoas muscle area (per 100 mm²) 0.996 0.978–1.013 0.617 Subcutaneous fat tissue (mm²) (per 1000 mm²) 0.998 0.984–1.012 0.747 Subcutaneous fat tissue / Total psoas muscle area (per 1) 0.999 0.980–1.018 0.894 tPMA Z-score (per 1) 0.973 0.852–1.110 0.680 Psoas muscle mean attenuation (HU) (per 10) 0.836 0.700–0.998 0.048 Perforation present (vs absent) 2.557 2.175–3.005 < 0.001 Laparoscopy (vs Laparotomy) 0.756 0.618–0.925 0.007 Univariable associations with length of hospital stay (LOS) were evaluated using negative binomial regression models. Results are reported as incidence rate ratios (IRR) with 95% confidence intervals (CI) and two-sided p-values; continuous predictors were scaled as indicated in the table. WBC, white blood cell; CRP, C-reactive protein; tPMA Z-score, total muscle area Z-score In the multivariable negative binomial regression analysis performed to predict LOS, neutrophil count and the presence of perforation were significant (Table 5 ). Table 5 Multivariable negative binomial regression analysis in predicting length of hospital stay (LOS) Predictor IRR 95% CI p-value Neutrophil (per 1×10⁹/L) 1.018 1.001–1.036 0.039 CRP (mg/L) (per 10) 1.008 0.996–1.021 0.186 Appendix max diameter (mm) (per 1) 0.990 0.960–1.022 0.539 Psoas muscle mean attenuation (HU) (per 10) 1.014 0.875–1.175 0.857 Perforation present (vs absent) 2.287 1.880–2.783 < 0.001 Laparoscopy (vs Laparotomy) 0.865 0.732–1.022 0.089 Length of hospital stay (LOS) was modeled using multivariable negative binomial regression (log-link). Results are presented as incidence rate ratios (IRR) with 95% confidence intervals (CI) and two-sided p-values. Continuous predictors were scaled as shown in the table (CRP per 10 mg/L and psoas attenuation per 10 HU) Interobserver agreement Using ICC(2,1), interobserver agreement was good for the right psoas area (ICC = 0.82; 95% CI, 0.65–0.89), left psoas area (ICC = 0.83; 95% CI, 0.72–0.90), total psoas area (ICC = 0.83; 95% CI, 0.69–0.90), tPMA Z-score (ICC = 0.83; 95% CI, 0.70–0.90), and psoas muscle mean attenuation HU (ICC = 0.80; 95% CI, 0.69–0.85). Agreement was excellent for subcutaneous fat tissue (ICC = 0.999; 95% CI 0.998–0.999) and for the subcutaneous fat tissue-to-total psoas area ratio (ICC = 0.934; 95% CI 0.907–0.957). All ICC values were statistically significant (p < 0.001). Discussion Recently, numerous studies have been conducted measuring the psoas muscle area and average psoas muscle density at the L3-L4 intervertebral disc level in CT scans and investigating whether these have prognostic value. In children, there are no single standardized reference values for psoas muscle areas for girls and boys comparable to those used in adults. This fact has led to the establishment of age- and sex-specific reference values for psoas muscle areas in the pediatric population and to the calculation of tPMA Z-scores. Numerous studies have been conducted to calculate the tPMA Z-score [ 13 – 17 ]. Being able to predict the LOS for pediatric patients diagnosed with appendicitis preoperatively plays a critical role both in terms of the patient's prognosis and in terms of predicting and managing healthcare expenditures. In our study, subcutaneous fat area and the subcutaneous fat area-to-total psoas muscle area ratio were significantly higher in female patients than in male patients, whereas total psoas muscle area was significantly higher in male patients, consistent with the study by Samim et al. (Table 1 ) [ 18 ]. There were no significant differences in age, gender, tPMA, tPMA Z-score, subcutaneous fat tissue/total psoas muscle area ratio, and subcutaneous fat tissue area values between patient groups with perforated and non-perforated appendicitis (Table 2 ). tPMA, tPMA Z-score, and subcutaneous fat tissue were not significant predictors of LOS in the Spearman’s correlation analysis, and univariable regression analysis likewise showed no significant correlations between LOS and these variables (Table 3 and Table 4 ). The absence of a significant association between tPMA and tPMA Z-score and LOS may be explained by the characteristics of our cohort, which consisted of previously healthy children presenting to the emergency department with abdominal pain and without any known chronic disease or malignancy prior to symptom onset. In many pediatric studies in which tPMA was measured, a tPMA Z-score below − 2 has been defined as sarcopenia [ 19 – 21 ]. In our study cohort, only 1 of 170 patients had a tPMA Z-score below − 2. Due to the significantly low number of sarcopenic patients, we believe that we could not find a meaningful relationship between LOS and tPMA Z-score in our study. The mean HU values of the psoas muscle were significantly lower in patients with perforated appendicitis compared to those without perforation, suggesting lower muscle quality and a possible association with a tendency toward complicated disease (Table 2 ). The mean HU values of the psoas muscle showed a weak correlation with LOS (Table 3 ). Additionally, although the psoas muscle HU mean had a significant relationship with LOS in the univariate negative binomial regression analysis, this significant relationship was lost in the multivariate negative binomial regression analysis (Table 4 and Table 5 ). These results are important in that, among previously healthy pediatric patients without chronic disease, psoas muscle mean density—rather than tPMA, tPMA Z-score, or subcutaneous fat tissue area—appears to be associated with LOS and to discriminate appendiceal perforation. This situation showed that, apart from psoas muscle volume, the average density of the muscle, i.e., muscle quality, plays an important role in children. In addition, several studies supporting our findings have emphasized that muscle density may be more important than muscle index in predicting prognosis [ 22 , 23 ]. There are numerous studies in the literature in which mean muscle density has been assessed in addition to muscle area measurements. In the study by Yuan et al., muscle size and density measured at the T4 and T10 levels were shown to be reduced in children with osteogenesis imperfecta compared with the control group [ 24 ]. Hou et al. demonstrated that the psoas muscle index and muscle attenuation were positively correlated with functional status in patients with degenerative lumbar spinal stenosis [ 25 ]. Di Cola et al. conducted a multicenter study in patients with cirrhosis and reported that the 1-year cumulative mortality rate in patients with sarcopenia plus myosteatosis or isolated myosteatosis was more than twice that observed in patients with isolated sarcopenia. According to this study, myosteatosis—whether accompanied by sarcopenia or not—was significantly associated with worse outcomes in patients with cirrhosis [ 22 ]. According to the study by Yamashita et al., in patients undergoing cardiac surgery, psoas muscle attenuation was a significant indicator of poor muscle function and mortality, whereas the skeletal muscle index—calculated by dividing psoas muscle area by height squared—was not significantly associated with these outcomes [ 23 ]. In multivariate negative binomial regression analysis, neutrophil count and the presence of appendiceal perforation were significantly associated with LOS (Table 5 ). This finding is important because it highlights the critical role of perforation in determining patient prognosis. This study has several limitations, including the absence of data on height, weight, and BMI, precluding calculation of the psoas muscle index (tPMA/height²), as well as its single-center design. Finally, mean psoas muscle HU values on contrast-enhanced CT may be influenced by acquisition parameters and contrast timing. Therefore, our findings should be interpreted as an association rather than definitive evidence of myosteatosis, and protocol-standardized prospective studies are warranted. Conclusion Psoas muscle attenuation was lower in perforated cases and weakly correlated with LOS; however, in multivariable regression modeling, perforation and neutrophil count were the independent predictors. However, given the potential impact of numerous confounding factors on LOS, further comprehensive studies are warranted. Abbreviations CRP C-reactive protein FDR False discovery rate ICC Intraclass correlation coefficient IQR Interquartile range IRR Incidence rate ratio LOS Length of hospital stay MWU Mann–Whitney U test NB Negative binomial tPMA Total psoas muscle area WBC White blood cell Declarations Author Contribution Concept and study design: C.T. Data collection: C.T. and S.Y.T. Data analysis and interpretation: C.T. and S.Y.T. 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Comparison the effect of stump closure by endoclips versus endoloop on the duration of surgery and complications in patients under laparoscopic appendectomy: A randomized clinical trial. J Res Med Sci 2016; 21: 87. doi: 10.4103/1735-1995.192503 Talan DA, Saltzman DJ, DeUgarte DA et al. Methods of conservative antibiotic treatment of acute uncomplicated appendicitis: A systematic review. J Trauma Acute Care Surg 2019; 86: 722–736. doi: 10.1097/ta.0000000000002137 Namm JP, Thakrar KH, Wang CH et al. A semi-automated assessment of sarcopenia using psoas area and density predicts outcomes after pancreaticoduodenectomy for pancreatic malignancy. J Gastrointest Oncol 2017; 8: 936–944. doi: 10.21037/jgo.2017.08.09 Islam S, Kanavati F, Arain Z et al. Fully automated deep-learning section-based muscle segmentation from CT images for sarcopenia assessment. Clin Radiol 2022; 77: e363-e371. doi: 10.1016/j.crad.2022.01.036 Samim A, Spijkers S, Moeskops P et al. Pediatric body composition based on automatic segmentation of computed tomography scans: a pilot study. Pediatr Radiol 2023; 53: 2492–2501. doi: 10.1007/s00247-023-05739-x Inoue T, Wakabayashi H, Kawase F et al. Diagnostic criteria, prevalence, and clinical outcomes of pediatric sarcopenia: A scoping review. Clin Nutr 2024; 43: 1825–1843. doi: 10.1016/j.clnu.2024.06.024 Aydın T, Cingöz E, Durmuş A et al. Determination of reference values for abdominal skeletal muscle compartments in Turkish children. Journal of Back and Musculoskeletal Rehabilitation 2025. 10538127251407660 Shen W, Punyanitya M, Wang Z et al. Total body skeletal muscle and adipose tissue volumes: estimation from a single abdominal cross-sectional image. J Appl Physiol (1985) 2004; 97: 2333–2338. doi: 10.1152/japplphysiol.00744.2004 Smit KC, Derksen JWG, Kurk SA et al. Use of automated assessment for determining associations of low muscle mass and muscle loss with overall survival in patients with colorectal cancer - A validation study. Clin Nutr ESPEN 2024; 63: 572–584. doi: 10.1016/j.clnesp.2024.07.001 Metzger GA, Sebastião YV, Carsel AC et al. Establishing reference values for lean muscle mass in the pediatric patient. Journal of Pediatric Gastroenterology and Nutrition 2021; 72: 316–323 Lurz E, Patel H, Lebovic G et al. Paediatric reference values for total psoas muscle area. Journal of cachexia, sarcopenia and muscle 2020; 11: 405–414 Kim J, Lee M-J, Lim HJ et al. Pediatric reference values for total psoas muscle area in Korean children and adolescents. Frontiers in Pediatrics 2025; 12: 1443523 Marunowski K, Świętoń D, Bzyl W et al. Reference values for MRI-derived psoas and paraspinal muscles and macroscopic fat infiltrations in paraspinal muscles in children. Journal of Cachexia, Sarcopenia and Muscle 2022; 13: 2515–2524 Kudo W, Terui K, Hattori S et al. Establishment and validation of reference values for abdominal skeletal muscle compartments in children. Clinical Nutrition 2023; 42: 653–660 Samim A, Spijkers S, Moeskops P et al. Pediatric body composition based on automatic segmentation of computed tomography scans: a pilot study. Pediatric radiology 2023; 53: 2492–2501 Ritz A, Kolorz J, Hubertus J et al. Sarcopenia is a prognostic outcome marker in children with high-risk hepatoblastoma. Pediatric Blood & Cancer 2021; 68: e28862 Ritz A, Froeba-Pohl A, Kolorz J et al. Total psoas muscle area as a marker for sarcopenia is related to outcome in children with neuroblastoma. Frontiers in surgery 2021; 8: 718184 Wang Z, Zeng S, Liu L et al. Weak correlation between total psoas muscle area and sarcopenia index for children with brain tumor. Nutrition in Clinical Practice 2023; 38: 838–849 Di Cola S, D’Amico G, Caraceni P et al. Myosteatosis is closely associated with sarcopenia and significantly worse outcomes in patients with cirrhosis. Journal of Hepatology 2024; 81: 641–650 Yamashita M, Kamiya K, Matsunaga A et al. Prognostic value of psoas muscle area and density in patients who undergo cardiovascular surgery. Canadian Journal of Cardiology 2017; 33: 1652–1659 Yuan Y, Xu Y-f, Feng C et al. Low muscle density in children with osteogenesis imperfecta using opportunistic low-dose chest CT: a case-control study. BMC Musculoskeletal Disorders 2024; 25: 478 Hou X, Hu H, Kong C et al. Psoas muscle index and psoas muscle density are associated with functional status in patients with degenerative lumbar spinal stenosis. Journal of Back and Musculoskeletal Rehabilitation 2024; 37: 921–928 Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8941099","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":596962067,"identity":"217c5754-85eb-4985-9e64-fe5ba9b55723","order_by":0,"name":"Celal Tacyildiz","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABFUlEQVRIie2RsUoDQRCGBwIbizPbyRyC9woTDsIVgbzKXJPKIlWwkGClVWKr+Ag2ykHqhYA2e7E9SXN5AOEquUqym1xhccmlFNwPlh2G/2N2WACH4y+izMkh2tW5QJC24lGDwoC4rdko/o3t0JEKsAAg24EDSme1WOd8jRN5p7uKx9Eg/HiOi5wgkGeqVvGXw5D4DRH1JSleYquXfSVoHtZ9fOJahbQn0KyAkHmk4lsUvSx9sQrTaq/SLvkHMagUL3xIk7JBEWCSSJWCJKfzg1N8LUKMZ+i/6uHI7kKYnc4jJty7S0e31kXx3ZcX74ukKMaTgbxPk8/yqh/I83rlFyfVX+A2iU1xSzvf3VIdk3Y4HI5/xAYcoWCFX8248QAAAABJRU5ErkJggg==","orcid":"","institution":"Elazig Fethi Sekin City Hospital","correspondingAuthor":true,"prefix":"","firstName":"Celal","middleName":"","lastName":"Tacyildiz","suffix":""},{"id":596962068,"identity":"81573835-3227-4b8c-85ee-916246908247","order_by":1,"name":"Suna Yergin Tacyildiz","email":"","orcid":"","institution":"Elazig Fethi Sekin City Hospital","correspondingAuthor":false,"prefix":"","firstName":"Suna","middleName":"Yergin","lastName":"Tacyildiz","suffix":""}],"badges":[],"createdAt":"2026-02-22 19:23:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8941099/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8941099/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":103589710,"identity":"448e1b3d-3bb8-49d1-a6a5-b79ddf26dae1","added_by":"auto","created_at":"2026-02-27 11:57:09","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":762516,"visible":true,"origin":"","legend":"\u003cp\u003eAxial contrast-enhanced CT images and the corresponding post-segmentation CT images at the L3-L4 intervertebral disc level are shown for a 14-year-old female patient diagnosed with non-perforated appendicitis (a-b). Axial contrast-enhanced CT images and the corresponding post-segmentation CT images at the L3-L4 intervertebral disc level are shown for a 14-year-old male patient diagnosed with perforated appendicitis (c-d). \u003cem\u003eRed psoas muscles, yellow subcutaneous fat tissue\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8941099/v1/bba77ef68a621a2917043fe9.jpeg"},{"id":104401113,"identity":"b8cff7ec-c945-4b6e-bd3a-a61e3a176588","added_by":"auto","created_at":"2026-03-11 12:11:54","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1506138,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8941099/v1/f8caf727-59a3-4ce0-a831-12bed59a8f62.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Preoperative CT-Based Segmentation of Psoas Muscle Area and Subcutaneous Fat Tissue: Associations With Perforation and Length of Hospital Stay in Pediatric Appendicitis","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAcute appendicitis is one of the most common causes of emergency abdominal surgery in children. Obstruction associated with lymphoid hyperplasia is the most common cause of acute appendicitis in children. Clinical history, physical examination, laboratory values, and imaging play a crucial role in diagnosis. Ultrasound is primarily used for diagnosis; CT may be used when ultrasound is inadequate (e.g., obesity, atypical location, user- or patient-related factors, etc.). MRI is another imaging method used in pregnant women and children. Uncomplicated acute appendicitis can be treated with antibiotics. Laparoscopic and open surgical procedures can treat acute appendicitis with complications or cases that do not respond to antibiotic treatment. Laparoscopic appendectomy is currently preferred because it is less invasive and is generally associated with faster recovery and shorter hospitalization [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe length of hospital stay (LOS) following appendectomy surgery is important in terms of patient health and comfort, reducing costs, and increasing hospital bed utilization. According to studies, high WBC and CRP values (indicating severe inflammation), complicated appendicitis (perforated, gangrenous, etc.), the length of time between the onset of the disease and surgery, the presence of appendicolith, and increased surgery duration are factors that prolong hospital stay [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Additionally, studies indicate that the surgical method used to repair the stump (e.g., silk ligation, Endoloop ligation, Hem-o-lok vascular clamp occlusion, and endo-gastrointestinal anastomosis (Endo-GIA) stapling and closure) and the class of antibiotics used also affect the length of hospital stay [\u003cspan additionalcitationids=\"CR4\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSarcopenia is a decrease in muscle mass and function. It is an important indicator of frailty [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Sarcopenia is one of the important indicators of morbidity and mortality in the elderly, chronic patients, and cancer patients. There are also studies showing that sarcopenia negatively affects the outcome of surgical procedures [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. In children, body composition (adipose tissue, skeletal muscle, etc.) may be an important predictor of various health problems [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Skeletal muscle growth during childhood is influenced by factors such as maternal nutrition during pregnancy, genetic factors, nutritional intake, physical activity, cardiovascular and metabolic diseases, chronic diseases, and hormones [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. It is difficult to assess skeletal muscle mass and function in children. This is because normative data for evaluating the results of methods measuring body muscle mass and function in children of different age groups are limited to a few studies. In our study, we used the normative data obtained by Aydın T. and colleagues in their research [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Muscle mass can be measured using dual-energy X-ray absorptiometry (DEXA), bioelectrical impedance analysis (BIA), and body composition analysis [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Currently, cross-sectional imaging (CT and MRI) has demonstrated that measurements of abdominal muscle and fat areas in axial planes reliably reflect total body muscle and fat mass [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The skeletal muscle area measured by CT scan at the L3-L4 vertebra level is generally accepted as a reliable indicator of total muscle volume [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. These measurements can be obtained manually, using semi-automatic and fully automatic deep learning slice-based muscle segmentation.\u003c/p\u003e \u003cp\u003eThe aim of this study is to investigate the association between postoperative LOS and preoperative CT-derived measurements\u0026mdash;obtained at the L3-L4 intervertebral disc level, using semi-automatic and manual segmentation\u0026mdash;including psoas muscle area, psoas muscle density, and subcutaneous adipose tissue area, as well as laboratory parameters and surgical approach, in pediatric patients diagnosed with appendicitis who underwent appendectomy.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy Design\u003c/h2\u003e \u003cp\u003eOur study was conducted retrospectively between January 2022 and October 2025 and included patients under the age of 18 who underwent appendectomy surgery. The study was conducted in accordance with the Helsinki Declaration (as revised in 2013) and was approved by the Clinical Research Ethics Committee of our hospital with a waiver of consent (E-95531838-050.99-156362).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eStudy Population\u003c/h3\u003e\n\u003cp\u003eBetween January 2022 and October 2025, 784 children with appendicitis underwent appendectomy at our hospital. Our inclusion criteria were surgical confirmation of appendicitis and age\u0026thinsp;\u0026lt;\u0026thinsp;18 years, with an available contrast-enhanced abdominal CT scan obtained within 48 hours before surgery when ultrasonography was non-diagnostic or when clinical suspicion persisted. Our exclusion criteria were contrast-enhanced abdominal CT scans with non-diagnostic motion artifacts, patients who underwent an additional surgical procedure concomitantly with appendectomy, children with malignancy or chronic disease, and cases with missing inflammatory marker data. Thus, 170 patients were included in this retrospective study.\u003c/p\u003e\n\u003ch3\u003eCT acquisition protocols\u003c/h3\u003e\n\u003cp\u003eCT images were obtained using a Toshiba Alexion 16-slice CT scanner. Intravenous contrast material was administered at a dose of 1 mL/kg at an injection rate of 0.5\u0026ndash;1.5 mL/s. CT images were obtained in the portal venous phase with a slice thickness of 3 mm approximately 60 seconds after intravenous contrast administration. For children weighing less than 15 kg, the CT settings were 80 kV and 30 mA; for 16\u0026ndash;30 kg, 100 kV and 30 mA; for 31\u0026ndash;45 kg, 100 kV and 30 mA; and for more than 45 kg, 120 kV and 50 mA.\u003c/p\u003e\n\u003ch3\u003eCT-Derived Body Composition Measurements\u003c/h3\u003e\n\u003cp\u003e The patients' CT images were obtained in the picture archiving and communication system (PACS). CT images in the digital imaging and communications in medicine (DICOM) format were opened in 3D Slicer version 5.8.1 (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.slicer.org/\u003c/span\u003e\u003cspan address=\"https://www.slicer.org/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e). The \u0026ldquo;Segment Editor,\u0026rdquo; \u0026ldquo;Segment Statistics,\u0026rdquo; and \u0026ldquo;Segment Cross-Section Area\u0026rdquo; modules in the 3D Slicer application were used. At the axial slice corresponding to the L3-L4 intervertebral disc level, the right and left psoas muscles were manually segmented from a single CT slice using the \u0026ldquo;Segment Editor\u0026rdquo; module. On the same CT slice, automatic segmentation was performed in the \u0026ldquo;Segment Editor\u0026rdquo; module for subcutaneous fat tissue segmentation using threshold values of -190 and \u0026minus;\u0026thinsp;30 HU. Visceral/intramuscular adipose tissue and regions erroneously segmented by 3D Slicer were manually removed, thereby completing the semi-automated segmentation process. After segmenting the psoas muscle and subcutaneous fat tissue axial slice at the L3-L4 intervertebral disc level, the average psoas muscle HU value, right and left psoas muscle areas, total psoas muscle area (tPMA), and subcutaneous fat tissue areas were measured using the \u0026ldquo;Segment Statistics\u0026rdquo; and \u0026ldquo;Segment Cross-Section Area\u0026rdquo; modules.\u003c/p\u003e \u003cp\u003eMaximum appendiceal diameter was measured on axial images (outer wall to outer wall) at the most distended segment; appendicolith was defined as an intraluminal calcified focus with attenuation higher than adjacent soft tissue. Perforation status was determined based on operative findings, defined as a visible appendiceal wall defect with fecalith/spillage and/or purulent peritonitis, as documented in the surgical report. Whether the surgery was laparoscopic or laparotomy was recorded by checking the surgical notes.\u003c/p\u003e \u003cp\u003eThe LOS, intensive care unit requirement, postoperative oral intake day, presence of postoperative complications, and inflammatory markers were recorded for all patients.\u003c/p\u003e \u003cp\u003etPMA Z-scores were calculated based on the reference values reported by Aydın T et al. in their study establishing normative data for abdominal skeletal muscle compartments in Turkish children [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Segmentation and imaging measurements were performed by two radiologists (C.T. and S.Y.T., with 5 and 6 years of experience in abdominal imaging), blinded to clinical outcomes (LOS and perforation status). For interobserver analysis, 35 cases were randomly selected and re-segmented independently by the second reader. Intraclass correlation coefficients were calculated using a two-way random-effects model with absolute agreement (ICC[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]).\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eStatistical Analysis\u003c/h2\u003e \u003cp\u003eAll statistical analyses were performed using IBM SPSS Statistics, Version 28 (IBM Corp., Armonk, NY, USA). Normality of continuous variables was assessed using the Shapiro\u0026ndash;Wilk test. As the majority of continuous variables were not normally distributed, continuous data are presented as median (IQR [25th\u0026ndash;75th percentiles]) and were compared between groups using the two-sided Mann\u0026ndash;Whitney U test. Categorical variables are summarized as counts and percentages and were compared using the Pearson chi-square test or Fisher\u0026rsquo;s exact test, as appropriate.\u003c/p\u003e \u003cp\u003eAssociations between length of hospital stay (LOS) and individual continuous predictors were evaluated using two-sided Spearman\u0026rsquo;s rank correlation (ρ). Where multiple simultaneous hypothesis tests were performed, multiplicity was controlled using the Benjamini\u0026ndash;Hochberg false discovery rate (FDR) procedure, and FDR-adjusted q-values are reported; statistical significance for these analyses was defined as q\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003cp\u003eLOS was analyzed as count data. Overdispersion was assessed by fitting a Poisson model and examining dispersion indices, including the variance-to-mean ratio and the Pearson chi-square statistic divided by degrees of freedom (χ\u0026sup2;/df). Because overdispersion was present (variance-to-mean ratio\u0026thinsp;=\u0026thinsp;2.26; Pearson χ\u0026sup2;/df\u0026thinsp;=\u0026thinsp;2.26), negative binomial regression models were used instead of Poisson regression. Univariable negative binomial models were first fitted for each candidate predictor, followed by a multivariable negative binomial model including clinically relevant covariates. Effect estimates are reported as incidence rate ratios (IRR) with 95% confidence intervals (CI) and two-sided p-values.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eOur study included a total of 170 patients under the age of 18 who underwent appendectomy surgery, comprising 119 cases of non-perforated appendicitis and 51 cases of perforated appendicitis. Of the patients included in our study, 58 (34.1%) were female and 112 (65.9%) were male. The median age of the female patients was 13.96 [10.46\u0026ndash;15.90] years, and the median age of the male patients was 13.21 [11.08\u0026ndash;15.77] years. The distribution of patients in our study according to age groups is as follows: 0\u0026ndash;5 years: 2 individuals (1.2%); 5\u0026ndash;10 years: 29 individuals (17.1%); 10\u0026ndash;15 years: 85 individuals (50.0%); 15\u0026ndash;18 years: 54 individuals (31.8%).\u003c/p\u003e \u003cp\u003eIn female patients, subcutaneous fat tissue and subcutaneous fat tissue/total psoas muscle area were significantly higher than in male patients, while total psoas muscle area was significantly higher in male patients. There was no significant difference in psoas muscle attenuation based on gender (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMedian CT segmentation values for female and male and their statistical comparison\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFemale (median [IQR])\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMale (median [IQR])\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ep-value (MWU)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eq-value (FDR)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRight psoas muscle area (mm\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e626.5 [508.3\u0026ndash;721.0]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e740.0 [547.3\u0026ndash;1029.0]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLeft psoas muscle area (mm\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e616.5 [482.8\u0026ndash;720.8]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e719.0 [547.5\u0026ndash;1047.8]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal psoas muscle area (mm\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1244.0 [996.8\u0026ndash;1421.3]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1440.0 [1116.3\u0026ndash;2137.8]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSubcutaneous fat tissue (mm\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e7281.8 [4430.5-15789.7]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3070.3 [1726.6\u0026ndash;5971.8]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSubcutaneous fat tissue / Total psoas muscle area\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6.35 [4.03\u0026ndash;12.10]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.20 [1.40\u0026ndash;4.30]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003etPMA Z-score\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e-0.38 [-0.96\u0026ndash;0.14]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-0.30 [-0.78\u0026ndash;0.24]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.442\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.442\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePsoas muscle mean attenuation (HU)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e59.1 [54.6\u0026ndash;62.0]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60.3 [56.2\u0026ndash;63.9]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.096\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.112\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eData are presented as median (interquartile range). The Mann-Whitney U test was used to compare continuous variables between the two independent groups. To correct for multiple testing, q-values were adjusted using the Benjamini-Hochberg False Discovery Rate (FDR) method for 7 comparisons.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003etPMA Z-score, total muscle area Z-score\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eIn the comparison of non-perforated and perforated appendicitis groups, significant differences were observed in the variables WBC, neutrophils, CRP, appendix max diameter, appendicolith present, psoas muscle mean attenuation (HU), and LOS (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Age (years) was 13.25 [11.02\u0026ndash;15.83] overall, 13.25 [11.04\u0026ndash;15.88] in the non-perforated group, and 13.25 [11.00\u0026ndash;15.33] in the perforated group (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eClinical and CT segmentation values according to non-perforated and perforated appendicitis groups in the study population\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNon-perforated (n\u0026thinsp;=\u0026thinsp;119)\u003c/p\u003e \u003cp\u003e(median [IQR])\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePerforated (n\u0026thinsp;=\u0026thinsp;51)\u003c/p\u003e \u003cp\u003e(median [IQR])\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ep-value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eq-value\u003c/p\u003e \u003cp\u003e(FDR)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge (years)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e13.25 [11.04\u0026ndash;15.88]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e13.25 [11.00\u0026ndash;15.33]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.662\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.662\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWBC (\u0026times;10⁹/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e14.5 [12.0\u0026ndash;17.0]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e17.0 [13.4\u0026ndash;20.4]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.004\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNeutrophils (\u0026times;10⁹/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e11.3 [8.8\u0026ndash;14.2]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14.2 [11.5\u0026ndash;18.0]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.002\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCRP (mg/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e11.0 [2.3\u0026ndash;35.5]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e94.8 [25.3\u0026ndash;144.2]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAppendix max diameter (mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8.7 [7.1\u0026ndash;10.0]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e11.0 [9.2\u0026ndash;12.4]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMale sex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e73 (61.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e39 (76.5%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.077\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.144\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAppendicolith present\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e38 (31.9%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e29 (56.9%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.003\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.007\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRight psoas muscle area (mm\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e686.0 [545.0\u0026ndash;934.0]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e683.0 [504.0\u0026ndash;852.0]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.621\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.662\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLeft psoas muscle area (mm\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e683.0 [549.5\u0026ndash;938.5]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e679.0 [512.0\u0026ndash;838.0]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.377\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.471\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal psoas muscle area (mm\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1370.0 [1099.5\u0026ndash;1857.0]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1348.0 [1008.5\u0026ndash;1719.5]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.540\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.624\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSubcutaneous fat tissue (mm\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4319.1 [2518.2\u0026ndash;11774.7]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3435.4 [1650.9\u0026ndash;10594.8]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.170\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.254\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSubcutaneous fat tissue / Total psoas muscle area\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.40 [2.05\u0026ndash;8.00]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.70 [1.40\u0026ndash;8.45]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.273\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.373\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003etPMA Z-score\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e-0.11 [-0.82\u0026ndash;0.57]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-0.41 [-1.04\u0026ndash;0.05]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.156\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.255\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePsoas muscle mean attenuation (HU)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e60.4 [56.4\u0026ndash;64.2]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e58.0 [53.0\u0026ndash;61.0]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.018\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.038\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLOS (days)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.0 [2.0\u0026ndash;3.0]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.0 [5.5\u0026ndash;8.0]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eData are presented as median (interquartile range) or number (percentage). Continuous variables were compared using the Mann-Whitney U test, and categorical variables using the chi-square or Fisher\u0026rsquo;s exact test. To correct for multiple testing, q-values were adjusted using the Benjamini-Hochberg False Discovery Rate (FDR) method for 15 comparisons.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eWBC, white blood cell; CRP, C-reactive protein; tPMA Z-score, total muscle area Z-score; LOS, length of hospital stay\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eSpearman correlation analysis between each continuous variable and LOS demonstrated a moderate correlation with CRP and weak correlations with WBC, neutrophil count, maximum appendiceal diameter, and psoas muscle mean attenuation (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). After FDR adjustment, WBC, neutrophil count, CRP, appendix maximum diameter, and psoas muscle mean attenuation remained statistically significant (q\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe relationship between single continuous variables and length of hospital stay (LOS)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpearman ρ\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ep-value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eq-value (FDR)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge (years)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e-0.073\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.346\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.377\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWBC (\u0026times;10⁹/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.302\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNeutrophils (\u0026times;10⁹/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.356\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCRP (mg/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.435\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAppendix max diameter (mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.233\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.007\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRight psoas muscle area (mm\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e-0.101\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.190\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.254\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLeft psoas muscle area (mm\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e-0.126\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.102\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.205\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal psoas muscle area (mm\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e-0.113\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.141\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.242\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003etPMA Z-score\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e-0.107\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.164\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.246\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePsoas muscle mean attenuation (HU)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e-0.208\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.006\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.016\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSubcutaneous fat tissue (mm\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e-0.075\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.331\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.377\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSubcutaneous fat tissue\u003c/p\u003e \u003cp\u003e/ Total psoas muscle area\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e-0.013\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.867\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.867\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eAssociations between LOS and each continuous variable were assessed using two-sided Spearman\u0026rsquo;s rank correlation (ρ). P-values were adjusted for multiple testing using the Benjamini\u0026ndash;Hochberg false discovery rate (FDR) procedure (m\u0026thinsp;=\u0026thinsp;12), and FDR-adjusted q-values are reported.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eWBC, white blood cell; CRP, C-reactive protein; tPMA Z-score, total muscle area Z-score\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eIn the univariable negative binomial regression analysis performed to predict LOS, the variables WBC, neutrophil count, CRP, appendix maximum diameter, psoas muscle mean attenuation, presence of perforation, and surgical approach (laparoscopy vs laparotomy) were significant (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eUnivariable negative binomial regression analysis in predicting length of hospital stay (LOS)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePredictor\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIRR\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e95% CI\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ep-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge (per 1 year)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.006\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.974\u0026ndash;1.039\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.700\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWBC (\u0026times;10⁹/L) (per 1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.036\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.016\u0026ndash;1.056\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNeutrophil (per 1\u0026times;10⁹/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.047\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.026\u0026ndash;1.068\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCRP (mg/L) (per 10)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.039\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.025\u0026ndash;1.053\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAppendix max diameter (mm)\u003c/p\u003e \u003cp\u003e(per 1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.061\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.022\u0026ndash;1.102\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.002\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMale sex (vs Female)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.095\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.883\u0026ndash;1.358\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.408\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAppendicolith present (vs absent)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.160\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.945\u0026ndash;1.424\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.156\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal psoas muscle area (per 100 mm\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.996\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.978\u0026ndash;1.013\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.617\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSubcutaneous fat tissue (mm\u0026sup2;) (per 1000 mm\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.998\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.984\u0026ndash;1.012\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.747\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSubcutaneous fat tissue / Total psoas muscle area (per 1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.999\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.980\u0026ndash;1.018\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.894\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003etPMA Z-score (per 1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.973\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.852\u0026ndash;1.110\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.680\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePsoas muscle mean attenuation (HU) (per 10)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.836\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.700\u0026ndash;0.998\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.048\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePerforation present (vs absent)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.557\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.175\u0026ndash;3.005\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLaparoscopy (vs Laparotomy)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.756\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.618\u0026ndash;0.925\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.007\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eUnivariable associations with length of hospital stay (LOS) were evaluated using negative binomial regression models. Results are reported as incidence rate ratios (IRR) with 95% confidence intervals (CI) and two-sided p-values; continuous predictors were scaled as indicated in the table.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eWBC, white blood cell; CRP, C-reactive protein; tPMA Z-score, total muscle area Z-score\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eIn the multivariable negative binomial regression analysis performed to predict LOS, neutrophil count and the presence of perforation were significant (Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMultivariable negative binomial regression analysis in predicting length of hospital stay (LOS)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePredictor\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIRR\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e95% CI\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ep-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNeutrophil (per 1\u0026times;10⁹/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.018\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.001\u0026ndash;1.036\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.039\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCRP (mg/L) (per 10)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.996\u0026ndash;1.021\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.186\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAppendix max diameter (mm)\u003c/p\u003e \u003cp\u003e(per 1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.990\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.960\u0026ndash;1.022\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.539\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePsoas muscle mean attenuation (HU) (per 10)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.014\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.875\u0026ndash;1.175\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.857\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePerforation present (vs absent)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.287\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.880\u0026ndash;2.783\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLaparoscopy (vs Laparotomy)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.865\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.732\u0026ndash;1.022\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.089\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eLength of hospital stay (LOS) was modeled using multivariable negative binomial regression (log-link). Results are presented as incidence rate ratios (IRR) with 95% confidence intervals (CI) and two-sided p-values. Continuous predictors were scaled as shown in the table (CRP per 10 mg/L and psoas attenuation per 10 HU)\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003eInterobserver agreement\u003c/h3\u003e\n\u003cp\u003eUsing ICC(2,1), interobserver agreement was good for the right psoas area (ICC\u0026thinsp;=\u0026thinsp;0.82; 95% CI, 0.65\u0026ndash;0.89), left psoas area (ICC\u0026thinsp;=\u0026thinsp;0.83; 95% CI, 0.72\u0026ndash;0.90), total psoas area (ICC\u0026thinsp;=\u0026thinsp;0.83; 95% CI, 0.69\u0026ndash;0.90), tPMA Z-score (ICC\u0026thinsp;=\u0026thinsp;0.83; 95% CI, 0.70\u0026ndash;0.90), and psoas muscle mean attenuation HU (ICC\u0026thinsp;=\u0026thinsp;0.80; 95% CI, 0.69\u0026ndash;0.85). Agreement was excellent for subcutaneous fat tissue (ICC\u0026thinsp;=\u0026thinsp;0.999; 95% CI 0.998\u0026ndash;0.999) and for the subcutaneous fat tissue-to-total psoas area ratio (ICC\u0026thinsp;=\u0026thinsp;0.934; 95% CI 0.907\u0026ndash;0.957). All ICC values were statistically significant (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eRecently, numerous studies have been conducted measuring the psoas muscle area and average psoas muscle density at the L3-L4 intervertebral disc level in CT scans and investigating whether these have prognostic value. In children, there are no single standardized reference values for psoas muscle areas for girls and boys comparable to those used in adults. This fact has led to the establishment of age- and sex-specific reference values for psoas muscle areas in the pediatric population and to the calculation of tPMA Z-scores. Numerous studies have been conducted to calculate the tPMA Z-score [\u003cspan additionalcitationids=\"CR14 CR15 CR16\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eBeing able to predict the LOS for pediatric patients diagnosed with appendicitis preoperatively plays a critical role both in terms of the patient's prognosis and in terms of predicting and managing healthcare expenditures.\u003c/p\u003e \u003cp\u003eIn our study, subcutaneous fat area and the subcutaneous fat area-to-total psoas muscle area ratio were significantly higher in female patients than in male patients, whereas total psoas muscle area was significantly higher in male patients, consistent with the study by Samim et al. (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThere were no significant differences in age, gender, tPMA, tPMA Z-score, subcutaneous fat tissue/total psoas muscle area ratio, and subcutaneous fat tissue area values between patient groups with perforated and non-perforated appendicitis (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). tPMA, tPMA Z-score, and subcutaneous fat tissue were not significant predictors of LOS in the Spearman\u0026rsquo;s correlation analysis, and univariable regression analysis likewise showed no significant correlations between LOS and these variables (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The absence of a significant association between tPMA and tPMA Z-score and LOS may be explained by the characteristics of our cohort, which consisted of previously healthy children presenting to the emergency department with abdominal pain and without any known chronic disease or malignancy prior to symptom onset. In many pediatric studies in which tPMA was measured, a tPMA Z-score below \u0026minus;\u0026thinsp;2 has been defined as sarcopenia [\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. In our study cohort, only 1 of 170 patients had a tPMA Z-score below \u0026minus;\u0026thinsp;2. Due to the significantly low number of sarcopenic patients, we believe that we could not find a meaningful relationship between LOS and tPMA Z-score in our study.\u003c/p\u003e \u003cp\u003eThe mean HU values of the psoas muscle were significantly lower in patients with perforated appendicitis compared to those without perforation, suggesting lower muscle quality and a possible association with a tendency toward complicated disease (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The mean HU values of the psoas muscle showed a weak correlation with LOS (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Additionally, although the psoas muscle HU mean had a significant relationship with LOS in the univariate negative binomial regression analysis, this significant relationship was lost in the multivariate negative binomial regression analysis (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). These results are important in that, among previously healthy pediatric patients without chronic disease, psoas muscle mean density\u0026mdash;rather than tPMA, tPMA Z-score, or subcutaneous fat tissue area\u0026mdash;appears to be associated with LOS and to discriminate appendiceal perforation. This situation showed that, apart from psoas muscle volume, the average density of the muscle, i.e., muscle quality, plays an important role in children. In addition, several studies supporting our findings have emphasized that muscle density may be more important than muscle index in predicting prognosis [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThere are numerous studies in the literature in which mean muscle density has been assessed in addition to muscle area measurements. In the study by Yuan et al., muscle size and density measured at the T4 and T10 levels were shown to be reduced in children with osteogenesis imperfecta compared with the control group [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Hou et al. demonstrated that the psoas muscle index and muscle attenuation were positively correlated with functional status in patients with degenerative lumbar spinal stenosis [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Di Cola et al. conducted a multicenter study in patients with cirrhosis and reported that the 1-year cumulative mortality rate in patients with sarcopenia plus myosteatosis or isolated myosteatosis was more than twice that observed in patients with isolated sarcopenia. According to this study, myosteatosis\u0026mdash;whether accompanied by sarcopenia or not\u0026mdash;was significantly associated with worse outcomes in patients with cirrhosis [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. According to the study by Yamashita et al., in patients undergoing cardiac surgery, psoas muscle attenuation was a significant indicator of poor muscle function and mortality, whereas the skeletal muscle index\u0026mdash;calculated by dividing psoas muscle area by height squared\u0026mdash;was not significantly associated with these outcomes [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn multivariate negative binomial regression analysis, neutrophil count and the presence of appendiceal perforation were significantly associated with LOS (Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). This finding is important because it highlights the critical role of perforation in determining patient prognosis.\u003c/p\u003e \u003cp\u003eThis study has several limitations, including the absence of data on height, weight, and BMI, precluding calculation of the psoas muscle index (tPMA/height\u0026sup2;), as well as its single-center design. Finally, mean psoas muscle HU values on contrast-enhanced CT may be influenced by acquisition parameters and contrast timing. Therefore, our findings should be interpreted as an association rather than definitive evidence of myosteatosis, and protocol-standardized prospective studies are warranted.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003ePsoas muscle attenuation was lower in perforated cases and weakly correlated with LOS; however, in multivariable regression modeling, perforation and neutrophil count were the independent predictors. However, given the potential impact of numerous confounding factors on LOS, further comprehensive studies are warranted.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eCRP\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eC-reactive protein\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eFDR\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eFalse discovery rate\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eICC\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eIntraclass correlation coefficient\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eIQR\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eInterquartile range\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eIRR\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eIncidence rate ratio\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eLOS\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eLength of hospital stay\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eMWU\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eMann\u0026ndash;Whitney U test\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eNB\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eNegative binomial\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003etPMA\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eTotal psoas muscle area\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eWBC\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eWhite blood cell\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConcept and study design: C.T. Data collection: C.T. and S.Y.T. Data analysis and interpretation: C.T. and S.Y.T. Manuscript writing: C.T.All authors reviewed the manuscript and approved the final version for publication.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe authors of this manuscript confirm that the data supporting the results of this study are available within this manuscript. Additional details are available on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBorruel Nacenta S, Ib\u0026aacute;\u0026ntilde;ez Sanz L, Sanz Lucas R et al. Update on acute appendicitis: Typical and untypical findings. 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Journal of Hepatology 2024; 81: 641\u0026ndash;650\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYamashita M, Kamiya K, Matsunaga A et al. Prognostic value of psoas muscle area and density in patients who undergo cardiovascular surgery. Canadian Journal of Cardiology 2017; 33: 1652\u0026ndash;1659\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYuan Y, Xu Y-f, Feng C et al. Low muscle density in children with osteogenesis imperfecta using opportunistic low-dose chest CT: a case-control study. BMC Musculoskeletal Disorders 2024; 25: 478\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHou X, Hu H, Kong C et al. Psoas muscle index and psoas muscle density are associated with functional status in patients with degenerative lumbar spinal stenosis. Journal of Back and Musculoskeletal Rehabilitation 2024; 37: 921\u0026ndash;928\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Psoas muscle area (PMA), Psoas muscle attenuation (HU), Subcutaneous fat tissue, Pediatric Appendicitis, CT-Based Segmentation","lastPublishedDoi":"10.21203/rs.3.rs-8941099/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8941099/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eAcute appendicitis is a leading cause of emergency abdominal surgery in children, and predicting postoperative length of hospital stay (LOS) is important for prognosis and resource planning. This study aims to assess the associations of LOS and appendiceal perforation with preoperative CT-derived measurements of psoas muscle area, attenuation, and subcutaneous fat tissue in children with appendicitis.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eThis retrospective study comprised 170 pediatric patients (\u0026lt;\u0026thinsp;18 years) surgically diagnosed with appendicitis between January 2022 and October 2025. At the L3-L4 intervertebral disc level, bilateral psoas muscles and subcutaneous adipose tissue were segmented using 3D Slicer. Right, left, and total psoas muscle area (tPMA), psoas muscle mean attenuation, tPMA Z-scores, subcutaneous fat tissue, inflammatory markers (WBC, neutrophils, and CRP), maximum appendiceal diameter, the presence of an appendicolith, appendiceal perforation status, surgical approach, and LOS were recorded.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eOf 170 patients, 51 had perforated appendicitis. Perforation correlated with elevated WBC/neutrophil/CRP levels, increased appendiceal max diameter, a higher incidence of appendicolith, reduced psoas muscle mean attenuation, and extended LOS (median 6.0 vs. 3.0 days; p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). CRP showed a moderate correlation with LOS (ρ\u0026thinsp;=\u0026thinsp;0.435), while WBC (ρ\u0026thinsp;=\u0026thinsp;0.302), neutrophils (ρ\u0026thinsp;=\u0026thinsp;0.356), appendiceal max diameter (ρ\u0026thinsp;=\u0026thinsp;0.233), and psoas muscle mean attenuation (ρ=\u0026minus;0.208) showed weak correlations. In multivariable negative binomial regression, perforation (IRR 2.287, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and neutrophil count (IRR 1.018 per 1\u0026times;10⁹/L, p\u0026thinsp;=\u0026thinsp;0.039) independently predicted extended LOS.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eThere is an association between post-appendectomy LOS and CT-derived psoas muscle attenuation, supporting segmentation-based prognostication and promising future studies.\u003c/p\u003e","manuscriptTitle":"Preoperative CT-Based Segmentation of Psoas Muscle Area and Subcutaneous Fat Tissue: Associations With Perforation and Length of Hospital Stay in Pediatric Appendicitis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-27 11:55:31","doi":"10.21203/rs.3.rs-8941099/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"b7baad1e-6bb7-4844-981c-04278439c1b7","owner":[],"postedDate":"February 27th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-03-06T06:38:29+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-27 11:55:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8941099","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8941099","identity":"rs-8941099","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}