Understanding CT Resolution Timeline in Acute Pyelonephritis: A Framework for Clinical Practice

Understanding CT Resolution Timeline in Acute Pyelonephritis: A Framework for Clinical Practice | 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 Understanding CT Resolution Timeline in Acute Pyelonephritis: A Framework for Clinical Practice Steven S Chua, Leela Chaudhary, Blaine T Abraha, Jiries Ganim, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9390703/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract Purpose: Acute pyelonephritis is diagnosed based on clinical and laboratory signs. Computed tomography (CT) is typically reserved for detecting complications or alternative diagnoses. Current guidelines do not recommend routine follow-up imaging when abnormalities are found. The expected time to resolution (TTR) of CT abnormalities has not been clearly identified. This is the goal of our study. Methods: Retrospective study at an academic hospital in Harris County, Texas. Adult patients with a diagnosis of acute pyelonephritis who underwent at least two CT scans were included. Three board-certified radiologists independently reviewed CT studies performed within one year of the index scan and assessed for striated nephrogram, parenchymal edema, patchy hypodensities, perinephric fat stranding, and urothelial thickening. TTR was defined as the interval between the first positive CT sign and the first subsequent CT in which the sign was absent. TTR was calculated for individual signs and globally, provided clinical criteria for pyelonephritis were met. Sensitivity, specificity, and inter-rater agreement were also evaluated. Results: 288 CT scans from 93 patients were reviewed; 252 (88%) were of sufficient quality for analysis. The mean global TTR was 149 ± 100 days, with wide variation across individual signs. Moreover, imaging abnormalities persisted for 105 days despite clinical resolution. Conclusion: CT signs consistent with pyelonephritis may persist for several months after clinical recovery. Clinicians should interpret persistent imaging abnormalities appropriately to avoid unnecessary diagnostic or therapeutic interventions. computed tomography pyelonephritis perinephric fat stranding sensitivity and specificity diagnostic imaging Introduction Acute pyelonephritis is an infection of the renal parenchyma, renal pelvis, and calyces. The diagnosis is primarily clinical and is based on the presence of fever, flank or lumbar pain, costovertebral angle tenderness, and pyuria. Computed tomography (CT) is generally reserved for evaluating complications or associated features, such as gas formation, hemorrhage, urinary tract obstruction, nephrolithiasis, or abscess formation [ 1 , 2 ]. Characteristic CT signs in cases of pyelonephritis include a striated nephrogram, parenchymal edema, patchy hypodense areas, perinephric fat stranding, and smooth muscle urothelial thickening [ 3 – 8 ]. Magnetic resonance imaging (MRI) provides an alternative imaging modality, but its higher cost, longer scan times, claustrophobia, and availability limit routine use. Current recommendations from the American College of Radiology do not advise follow-up imaging after an episode of acute pyelonephritis [ 9 ]. However, these guidelines do not address the expected timeline for radiologic resolution or the duration of imaging abnormalities. The objective of this study was to determine, in patients with both clinical and radiological signs consistent with pyelonephritis, the time to radiologic resolution (TTR) on CT, provided that clinical resolution occurred concurrently. Methods This retrospective study was conducted at Lyndon B. Johnson Hospital, a safety-net academic hospital in Harris County, Texas, with previous approval by the Committee for the Protection of Human Subjects (HSC-MS-25-0660). Among approximately 48,000 CT scans performed between January 1, 2023, and December 31, 2023, about 1,000 reports described signs consistent with acute pyelonephritis. Patients aged 18 years or older with the International Classification of Diseases, Tenth Revision (ICD-10) code N10 (acute pyelonephritis), who underwent at least two CT scans (the first obtained during the study period), were screened for inclusion. Eligible cases were independently reviewed by three board-certified radiologists, who analyzed CT scans obtained within one year of the index study. For each scan, the radiologists recorded the presence or absence of the following signs: striated nephrogram, parenchymal edema, patchy hypodensities, perinephric fat stranding, and smooth urothelial thickening. Using these data, we calculated time to radiologic resolution (TTR), both globally (overall resolution of pyelonephritis signs) and individually for each radiologic sign on subsequent CTs. We recorded the clinical data available around the days of the subsequent CTs, such as fever, flank or lumbar pain, costovertebral-angle tenderness, and pyuria. Definitions: A clinical case of pyelonephritis was defined as the presence of pyuria plus at least one of the following: fever, flank or lumbar pain, or costovertebral angle tenderness, regardless of the results of the urine culture or antibiotic exposure. Clinical resolution represented cases where the clinical features were reportedly resolved, independent of residual pyuria. A true positive was defined as the presence of a positive radiologic sign in a patient meeting clinical criteria for pyelonephritis; a true negative was the absence of a radiologic sign in a patient who did not meet clinical criteria; a false positive was the presence of a radiologic sign in a patient without clinical pyelonephritis; and a false negative was the absence of a radiologic sign in a patient with clinical pyelonephritis. A striated nephrogram represents an appearance of discrete rays of alternating hypoattenuation and hyperattenuation radiating from the papilla to the cortex along the direction of the excretory tubules. This appearance is attributed to the decreased flow of contrast due to stasis in the infected tubules. This sign is not specific and is also seen in some other conditions, like renal vein thrombosis, ureteric obstruction, and contusion [ 10 ]. Parenchymal edema describes a focal or diffuse renal parenchymal enlargement with decreased attenuation relative to adjacent normal renal cortex and associated loss of corticomedullary differentiation [ 9 ]. Patchy hypodensities are defined as focal, ill-defined areas of decreased enhancement within the renal parenchyma relative to the surrounding cortex during the nephrographic phase [ 9 ]. Perinephric fat stranding refers to increased attenuation and linear streaking within the perirenal fat on CT, reflecting inflammation, edema, or fluid within the perirenal space. It occurs because inflammatory processes around the kidney increase vascular permeability and fat edema, producing the striated appearance in the surrounding fat. It carries reportedly low specificity, as it can be seen in pyelonephritis, renal or perinephric abscesses, ureteral obstructions, nephrolithiasis, renal infarction, renal vein thrombosis, renal contusion, perirenal hematoma, colonic or pancreatic inflammation involving the retroperitoneum, or after nephrostomy tube placement or renal biopsies [ 9 , 11 ]. Urothelial smooth muscle thickening is usually described in the renal pelvis or ureter. To be included in the TTR calculation, a given true-positive radiologic sign had to be present on an initial CT and subsequently absent on follow-up imaging. The interval between the first positive and the first negative scan was recorded, provided that clinical and laboratory data supported the diagnosis of pyelonephritis. The same approach was used for global radiologic resolution. Patients were excluded from TTR analyses if they did not meet clinical criteria for pyelonephritis or if imaging signs persisted without resolution on subsequent CT scans. We also excluded patients younger than 18 years old. We censored the cases without clinical pyelonephritis without CT resolution, as we could not ascertain if resolution might have been achieved beyond a 1-year follow-up. Statistical analysis We used MedCalc version 12.3.0 (MedCalc Software, Mariakerke, Belgium) for the statistical analysis. The correlation coefficient (Fleiss kappa) was calculated for each variable analyzed by the participating radiologists [ 12 ]. Sensitivity and specificity of each sign were calculated as previously described [ 13 ]. Results Ninety-three patients met the inclusion criteria; 26 (28%) were male. The mean age (± standard deviation) was 49 ± 14 years. Of the 288 initial CTs analyzed, 252 (88%) were of sufficient quality to evaluate the predefined radiologic signs. All patients had at least two CTs, 51 underwent a third scan, 29 a fourth, 17 a fifth, and 5 a sixth. Of the 288 encounters, pyelonephritis was clinically confirmed in 156 (54%) of the cases. Table 1 presents the interrater agreement among the three radiologists for the CT signs evaluated. Perinephric fat stranding, a nonspecific finding recognized both by our radiologists and in the literature, showed the highest level of agreement. Table 1 Correlation coefficient (Fleiss kappa) for the different signs assessed by the three participating radiologists sign kappa interpretation striated nephrogram 0.29 fair parenchymal edema 0.19 slight patchy hypodensities 0.33 fair perinephric fat stranding 0.5 moderate smooth urothelial thickening 0.33 fair global assessment 0.34 fair Table 2 summarizes the TTR of the individual and global signs consistent with pyelonephritis, along with their sensitivity and specificity. On average, CT signs resolved after 149 ± 100 days. Among individual features, parenchymal edema (133 ± 37 days), patchy hypodensities (134 ± 98 days), and perinephric fat stranding (155 ± 114 days) most closely approximated the TTR of the global assessment. In our series, perinephric fat stranding also showed the strongest correlation with the global assessment, and sensitivity and specificity were closest to it. Table 2 Time to resolution of individual and global signs consistent with pyelonephritis True positives striated nephrogram parenchymal edema patchy hypodensities perinephric fat stranding smooth urothelial thickening global assessment 45 33 35 34 35 49 Mean (days) 112 133 134 155 101 149 Median (days) 95 100 113 146 89 136 St dev. (days) 41 37 98 114 92 100 Range (days) 6 to 361 6 to 364 6 to 361 18 to 364 6 to 269 6 to 361 Sensitivity 42% 33% 48% 65% 43% 67% Specificity 79% 89% 59% 28% 59% 42% Table 3 details the number of studies in which signs persisted on follow-up CTs and the duration of these signs in patients with and without clinical pyelonephritis. Imaging abnormalities tended to persist longer in patients with clinical pyelonephritis; however, we could not determine whether clinical resolution occurred between episodes. In patients without clinical pyelonephritis, abnormalities persisted for a shorter period than that observed in the TTR analysis. Because imaging follow-up did not extend beyond one year, these cases were censored. Table 3 Time persistence of unresolved signs in patients with and without pyelonephritis Unresolved sign n pyelonephritis present persistence time in patients with pyelonephritis persistence time in patients without pyelonephritis striated nephrogram 28 5 (18%) 56 days 91 days parenchymal edema 51 10 (20%) 124 days 89 days patchy hypodensities 73 17 (23%) 115 days 95 days perinephric fat stranding 133 36 (27%) 156 days 122 days smooth urothelial thickening 50 17 (34%) 181 days 111 days global assessment 37 26 (70%) 101 days 105 days Discussion To our knowledge, this is the first study focused on the time to resolution of pyelonephritis based on CT signs. As important as these findings are, we also noted, as shown in Table 3 , that despite the clinical resolution of the pyelonephritis, the CT signs consistent with persistence were present for 105 days on average. This information may impact practice, as the low specificity of the signs or the global diagnosis can potentially lead to diagnostic and therapeutic interventions in people without pyelonephritis. Imaging is not routinely indicated in uncomplicated renal infections, as clinical signs and laboratory data are generally sufficient for making a diagnosis. However, imaging plays a crucial role under specific situations, including immunocompromised patients, treatment non-responders, equivocal clinical diagnosis, evaluation of existing anatomical anomalies, and assessment of disease extent [ 10 ]. Unfortunately, histologic specimens of the renal parenchyma in patients with pyelonephritis are seldom obtained, limiting the interpretation of the associated CT signs [ 9 ]. While both unenhanced and contrast-enhanced CT can identify urolithiasis, perinephric fluid, renal swelling, and hydronephrosis, only contrast-enhanced CT reliably demonstrates the parenchymal enhancement abnormalities that are characteristic of pyelonephritis. The American College of Radiology notes that in patients without a history of renal stones, the benefit of adding unenhanced CT to contrast-enhanced CT is negligible, as the contrast-enhanced phase alone achieved 96–99% accuracy for detecting urolithiasis in addition to its superior performance for diagnosing pyelonephritis [ 3 ]. The signs explored by our radiologists were previously found in 96% of 189 patients with the diagnosis of urinary tract infection, 62% of whom had two or more signs. A study using MRI to assess the resolution of imaging among patients with acute pyelonephritis showed that, in 30 women with full clinical resolution one month after the diagnosis, 43% showed image-based resolution at one month, and 74% showed resolution after three months [ 14 ]. These results, together with the cost of MRI, challenge its utility in defining cured cases or interpreting abnormal signs in patients with relapsed symptoms of pyelonephritis, as described in 44% of women who suffered 147 episodes of urinary infections [ 15 ]. Radionuclide-based scans have also been studied in patients with acute pyelonephritis. 99m Tc-DMSA scanning has detected changes consistent with acute pyelonephritis in 37 (46%) of 81 patients. The signs disappeared within three months in 18 of 24 of those patients who had adequate follow-up [ 16 ]. However, the relatively long waiting time after radiotracer injection, prolonged acquisition time, and high radiation dose may outweigh the benefits of this diagnostic test [ 17 ]. The main limitation of our study is its retrospective nature. Conducting this study prospectively would have required scheduling follow-up CTs at predetermined time points, an approach for which there is no currently clear clinical indication. Moreover, such a strategy would likely incur prohibitive costs and expose patients to potentially unacceptable risks from repeated radiation and contrast administration [ 18 ]. Follow-up CT examinations were obtained for a variety of clinical indications, including persistent symptoms, evaluation for complications, or unrelated clinical presentations. Because the timing of these studies was not standardized, variability in follow-up intervals likely contributed to the broad range of observed TTR values. Another limitation relates to case selection. Although there is broad agreement in the literature regarding the clinical diagnosis of pyelonephritis, other conditions, such as renal infarction, may present with similar defining features, leading to potential misclassification [ 19 ]. In addition, pyuria in the setting of a negative urine culture has been reported in up to 15% of patients with infections outside the urinary tract, which may further confound the diagnosis and result in an erroneous attribution to pyelonephritis [ 20 ]. Therefore, although diagnostic certainty cannot be fully assured for all patients included in our database, these considerations reflect real-world clinical practice and thus support the external validity of our signs. We opted not to consider in the TTR the patients with or without a clinical definition of pyelonephritis whose CT signs never resolved. Instead, we presented separately the duration of signs in Table 3 , which are, for the most part, shorter than those presented in Table 2 . Although including these cases in this calculation would have resulted in a shorter overall TTR, we censored these observations because we could not determine whether the abnormalities persisted beyond the one-year follow-up period [ 21 ]. Regarding the cases with clinical pyelonephritis but unresolved CT signs, we could not determine whether clinical resolution occurred between episodes. Knowing this information could have skewed the results towards a shorter TTR. Finally, since this study reflects the experience of a single hospital, the generalizability of the signs may be limited. We conclude that CT signs supportive of the diagnosis of pyelonephritis may persist for months and, in our series, frequently remain unresolved even when clinical and laboratory data suggest complete resolution. Awareness of this observation may help clinicians in interpreting persistent imaging abnormalities within the appropriate clinical context and may prevent potentially unnecessary investigations and treatments in patients without evidence of ongoing infection. Declarations Author Contribution JPH, SSC, and GMA were responsible for the study design.JG, YT, AH, and GMA were responsible for the acquisition of clinical data.SSC, LC, and JPH were responsible for the acquisition of radiological data.GMA analyzed the data.GMA and JPH generated the initial version of the manuscript. All authors approved the final version of the manuscript. References Zulfiqar M, Varela Ubilla C, Refky N, Menias CO. Imaging of Renal Infections and Inflammatory Disease. Radiol Clin N Am 2020; 58(5):909–923. doi: 10.1016/j.rcl.2020.05.004 Craig WD, Wagner BJ, Travis MD. Pyelonephritis: Radiologic-Pathologic Review. Radiographics 2008; 28(1):255–277. doi: 10.1148/rg.281075171 . Smith AD, Nikolaidis P, Khatri G, et al. ACR Appropriateness Criteria® Acute Pyelonephritis: 2022 Update. J Am Coll Radiol 2022; 19(11S):S224-239. doi: 10.1016/j.jacr.2022.09.017 Yano T, Takada T, Fujiishi R, et al. Usefulness of computed tomography in the diagnosis of acute pyelonephritis in older patients suspected of infection with unknown focus. Acta Radiol, 2022; 63(2):268–277. doi: 10.1177/0284185120988817 Rabushka LS, Fishman EK, Goldman SM. Pictorial Review: Computed tomography of renal inflammatory disease. Urology, 1994; 44(4):473–480. doi: 10.1016/s0090-4295(94)80042-1 Yu TY, Kim HR, Hwang KE, Lee JM, Cho JH, Lee JH. Computed tomography findings associated with bacteremia in adult patients with a urinary tract infection. Eur J Clin Microbiol Infect Dis, 2016; 35(11):1883–1887. doi: 10.1007/s10096-016-2743-4 El-Merhi F, Mohamad M, Haydar A, et al. Qualitative and quantitative radiological analysis of non-contrast CT is a strong indicator in patients with acute pyelonephritis. Am J Emerg Med, 2018; 36(4):589–593. doi: 10.1016/j.ajem.2017.09.026 Saunders HS, Dyer RB, Shifrin RY, Scharling ES, Bechtold RE, Zagoria RJ. The CT nephrogram: Implications for evaluations of urinary tract disease. Radiographics, 1995; 15(5):1069–1085. doi: 10.1148/radiographics.15.5.7501851 Kawashima A, Sandler CM, Goldman SM, Raval BK, Fishman EK. CT of renal inflammatory disease. Radiographics, 1997; 17(4):851–866. doi: 10.1148/radiographics.17.4.9225387 Das CJ, Ahmad Z, Sharma S, Gupta AK. Multimodality imaging of renal inflammatory lesions. World J Radiol, 2014; 6(11):865–873. doi: 10.4329/wjr.v6.i11.865 Heller MT, Haarer KA, Thomas E, Thaete FL. Neoplastic and proliferative disorderes of the perinephric space. Clin Radiol 2012; 67(11):e41-41. doi: 10.1016/j.crad.2012.03.015 Fleiss, J. L. Measuring nominal scale agreement among many raters. Psychological Bulletin, 1971; 76(5):378–382. doi.org/10.1037/h0031619 Trevethan R. Sensitivity, Specificity, and Predictive Values: Foundations, Pliabilities, and Pitfalls in Research and Practice. Front Public Health 2017; 5:307. doi: 10.3389/fpubh.2017.00307 Faletti R, Gatti M, Bassano S, et al. Follow-up of acute pyelonephritis: what causes the diffusion-weighted magnetic resonance recovery to lag clinical recovery? Abdom Radiol (NY), 2018; 43(3):639–646. doi: 10.1007/s00261-017-1242-0 Ikäheimo R, Siitonen A, Heiskanen T, et al. Recurrence of Urinary Tract Infection in a Primary Care Setting: Analysis of a 1-Year Follow-up of 179 Women. Clin Infect Dis, 1996; 22(1):91–99. doi: 10.1093/clinids/22.1.91 Bailey RR, Lynn KL, Robson RA, Smith AH, Maling TM, Turner JG. DMSA renal scans in adults with acute pyelonephritis. Clin Nephrol, 1996; 46(2):99–104. PMID: 8869786 Sarikaya I, Sarikaya A. Current Status of Radionuclide Renal Cortical Imaging in Pyelonephritis. J Nucl Med Technol, 2019; 47(4):309–312. doi: 10.2967/jnmt.119.227942 Brenner DJ, Hall EJ. Computed Tomography – An Increasing Source of Radiation Exposure. N Engl J Med, 2007; 357(22):2277–2284. doi: 10.1056/NEJMra072149 Piccoli GB, Priola AM, Vigotti FN, Guzzo G, Veltri A. Renal infarction versus pyelonephritis in a woman presenting with fever and flank pain. Am J Kidney Dis, 2014; 64(2):311–314. doi: 10.1053/j.ajkd.2014.02.027 Wise GJ, Schlegel PN. Sterile pyuria. N Engl J Med, 2015; 372(11):1048–1054. doi: 10.1056/NEJMra1410052 Lagakos SW. General right censoring and its impact on the analysis of survival data. Biometrics, 1979; 35(1):139–156. PMID 497332 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 11 May, 2026 Reviewers invited by journal 19 Apr, 2026 Editor assigned by journal 13 Apr, 2026 Submission checks completed at journal 13 Apr, 2026 First submitted to journal 11 Apr, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-9390703","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":625820580,"identity":"44f4ed5e-1286-4a71-a82f-0b7db3fa70ad","order_by":0,"name":"Steven S Chua","email":"","orcid":"","institution":"The University of Texas, John P and Kathrine G McGovern School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Steven","middleName":"S","lastName":"Chua","suffix":""},{"id":625820581,"identity":"efb95a4d-8eb9-4de0-876a-b1613a6b7a18","order_by":1,"name":"Leela Chaudhary","email":"","orcid":"","institution":"The University of Texas, John P and Kathrine G McGovern School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Leela","middleName":"","lastName":"Chaudhary","suffix":""},{"id":625820582,"identity":"1f08ee31-10b1-4f67-8c29-39c6108e21e2","order_by":2,"name":"Blaine T Abraha","email":"","orcid":"","institution":"The University of Texas, John P and Kathrine G McGovern School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Blaine","middleName":"T","lastName":"Abraha","suffix":""},{"id":625820583,"identity":"94e7ced3-bad8-4c29-8e18-f1acf0be01d9","order_by":3,"name":"Jiries Ganim","email":"","orcid":"","institution":"The University of Texas, John P and Kathrine G McGovern School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Jiries","middleName":"","lastName":"Ganim","suffix":""},{"id":625820584,"identity":"cab096e5-4c25-4e2f-abf1-a2dd0cb4fa1a","order_by":4,"name":"Yasmin A. Toy","email":"","orcid":"","institution":"The University of Texas, John P and Kathrine G McGovern School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Yasmin","middleName":"A.","lastName":"Toy","suffix":""},{"id":625820585,"identity":"f5869eca-3c41-4030-93e5-2acfe9c97afa","order_by":5,"name":"Areeba Hafeez","email":"","orcid":"","institution":"The University of Texas, John P and Kathrine G McGovern School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Areeba","middleName":"","lastName":"Hafeez","suffix":""},{"id":625820586,"identity":"5259f129-f145-41fe-8cb2-be424aec9000","order_by":6,"name":"Joseph P Hasapes","email":"","orcid":"","institution":"The University of Texas, John P and Kathrine G McGovern School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Joseph","middleName":"P","lastName":"Hasapes","suffix":""},{"id":625820587,"identity":"e03a5121-0ec3-434e-be1a-a68eaf5bd2d3","order_by":7,"name":"Gabriel M. Aisenberg","email":"data:image/png;base64,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","orcid":"","institution":"The University of Texas, John P and Kathrine G McGovern School of Medicine","correspondingAuthor":true,"prefix":"","firstName":"Gabriel","middleName":"M.","lastName":"Aisenberg","suffix":""}],"badges":[],"createdAt":"2026-04-11 22:23:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9390703/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9390703/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108181379,"identity":"392fd42a-7988-4928-83a4-58ecdd64957c","added_by":"auto","created_at":"2026-04-30 08:58:35","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":218540,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9390703/v1/b886062b-6cc1-44f1-a875-2ab0fe185a0c.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Understanding CT Resolution Timeline in Acute Pyelonephritis: A Framework for Clinical Practice","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAcute pyelonephritis is an infection of the renal parenchyma, renal pelvis, and calyces. The diagnosis is primarily clinical and is based on the presence of fever, flank or lumbar pain, costovertebral angle tenderness, and pyuria. Computed tomography (CT) is generally reserved for evaluating complications or associated features, such as gas formation, hemorrhage, urinary tract obstruction, nephrolithiasis, or abscess formation [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Characteristic CT signs in cases of pyelonephritis include a striated nephrogram, parenchymal edema, patchy hypodense areas, perinephric fat stranding, and smooth muscle urothelial thickening [\u003cspan additionalcitationids=\"CR4 CR5 CR6 CR7\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMagnetic resonance imaging (MRI) provides an alternative imaging modality, but its higher cost, longer scan times, claustrophobia, and availability limit routine use. Current recommendations from the American College of Radiology do not advise follow-up imaging after an episode of acute pyelonephritis [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. However, these guidelines do not address the expected timeline for radiologic resolution or the duration of imaging abnormalities.\u003c/p\u003e \u003cp\u003eThe objective of this study was to determine, in patients with both clinical and radiological signs consistent with pyelonephritis, the time to radiologic resolution (TTR) on CT, provided that clinical resolution occurred concurrently.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e This retrospective study was conducted at Lyndon B. Johnson Hospital, a safety-net academic hospital in Harris County, Texas, with previous approval by the Committee for the Protection of Human Subjects (HSC-MS-25-0660). Among approximately 48,000 CT scans performed between January 1, 2023, and December 31, 2023, about 1,000 reports described signs consistent with acute pyelonephritis.\u003c/p\u003e \u003cp\u003ePatients aged 18 years or older with the International Classification of Diseases, Tenth Revision (ICD-10) code N10 (acute pyelonephritis), who underwent at least two CT scans (the first obtained during the study period), were screened for inclusion. Eligible cases were independently reviewed by three board-certified radiologists, who analyzed CT scans obtained within one year of the index study.\u003c/p\u003e \u003cp\u003eFor each scan, the radiologists recorded the presence or absence of the following signs: striated nephrogram, parenchymal edema, patchy hypodensities, perinephric fat stranding, and smooth urothelial thickening. Using these data, we calculated time to radiologic resolution (TTR), both globally (overall resolution of pyelonephritis signs) and individually for each radiologic sign on subsequent CTs.\u003c/p\u003e \u003cp\u003eWe recorded the clinical data available around the days of the subsequent CTs, such as fever, flank or lumbar pain, costovertebral-angle tenderness, and pyuria.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eDefinitions:\u003c/h2\u003e \u003cp\u003eA clinical case of pyelonephritis was defined as the presence of pyuria plus at least one of the following: fever, flank or lumbar pain, or costovertebral angle tenderness, regardless of the results of the urine culture or antibiotic exposure. Clinical resolution represented cases where the clinical features were reportedly resolved, independent of residual pyuria.\u003c/p\u003e \u003cp\u003eA true positive was defined as the presence of a positive radiologic sign in a patient meeting clinical criteria for pyelonephritis; a true negative was the absence of a radiologic sign in a patient who did not meet clinical criteria; a false positive was the presence of a radiologic sign in a patient without clinical pyelonephritis; and a false negative was the absence of a radiologic sign in a patient with clinical pyelonephritis.\u003c/p\u003e \u003cp\u003eA striated nephrogram represents an appearance of discrete rays of alternating hypoattenuation and hyperattenuation radiating from the papilla to the cortex along the direction of the excretory tubules. This appearance is attributed to the decreased flow of contrast due to stasis in the infected tubules. This sign is not specific and is also seen in some other conditions, like renal vein thrombosis, ureteric obstruction, and contusion [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eParenchymal edema describes a focal or diffuse renal parenchymal enlargement with decreased attenuation relative to adjacent normal renal cortex and associated loss of corticomedullary differentiation [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePatchy hypodensities are defined as focal, ill-defined areas of decreased enhancement within the renal parenchyma relative to the surrounding cortex during the nephrographic phase [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePerinephric fat stranding refers to increased attenuation and linear streaking within the perirenal fat on CT, reflecting inflammation, edema, or fluid within the perirenal space. It occurs because inflammatory processes around the kidney increase vascular permeability and fat edema, producing the striated appearance in the surrounding fat. It carries reportedly low specificity, as it can be seen in pyelonephritis, renal or perinephric abscesses, ureteral obstructions, nephrolithiasis, renal infarction, renal vein thrombosis, renal contusion, perirenal hematoma, colonic or pancreatic inflammation involving the retroperitoneum, or after nephrostomy tube placement or renal biopsies [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eUrothelial smooth muscle thickening is usually described in the renal pelvis or ureter.\u003c/p\u003e \u003cp\u003eTo be included in the TTR calculation, a given true-positive radiologic sign had to be present on an initial CT and subsequently absent on follow-up imaging. The interval between the first positive and the first negative scan was recorded, provided that clinical and laboratory data supported the diagnosis of pyelonephritis. The same approach was used for global radiologic resolution.\u003c/p\u003e \u003cp\u003ePatients were excluded from TTR analyses if they did not meet clinical criteria for pyelonephritis or if imaging signs persisted without resolution on subsequent CT scans. We also excluded patients younger than 18 years old. We censored the cases without clinical pyelonephritis without CT resolution, as we could not ascertain if resolution might have been achieved beyond a 1-year follow-up.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eWe used MedCalc version 12.3.0 (MedCalc Software, Mariakerke, Belgium) for the statistical analysis. The correlation coefficient (Fleiss kappa) was calculated for each variable analyzed by the participating radiologists [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Sensitivity and specificity of each sign were calculated as previously described [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eNinety-three patients met the inclusion criteria; 26 (28%) were male. The mean age (\u0026plusmn;\u0026thinsp;standard deviation) was 49\u0026thinsp;\u0026plusmn;\u0026thinsp;14 years. Of the 288 initial CTs analyzed, 252 (88%) were of sufficient quality to evaluate the predefined radiologic signs. All patients had at least two CTs, 51 underwent a third scan, 29 a fourth, 17 a fifth, and 5 a sixth. Of the 288 encounters, pyelonephritis was clinically confirmed in 156 (54%) of the cases.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents the interrater agreement among the three radiologists for the CT signs evaluated. Perinephric fat stranding, a nonspecific finding recognized both by our radiologists and in the literature, showed the highest level of agreement.\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\u003eCorrelation coefficient (Fleiss kappa) for the different signs assessed by the three participating radiologists\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\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=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003esign\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ekappa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003einterpretation\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003estriated nephrogram\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003efair\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eparenchymal edema\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eslight\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003epatchy hypodensities\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003efair\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eperinephric fat stranding\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003emoderate\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003esmooth urothelial thickening\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003efair\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eglobal assessment\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003efair\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e summarizes the TTR of the individual and global signs consistent with pyelonephritis, along with their sensitivity and specificity. On average, CT signs resolved after 149\u0026thinsp;\u0026plusmn;\u0026thinsp;100 days. Among individual features, parenchymal edema (133\u0026thinsp;\u0026plusmn;\u0026thinsp;37 days), patchy hypodensities (134\u0026thinsp;\u0026plusmn;\u0026thinsp;98 days), and perinephric fat stranding (155\u0026thinsp;\u0026plusmn;\u0026thinsp;114 days) most closely approximated the TTR of the global assessment. In our series, perinephric fat stranding also showed the strongest correlation with the global assessment, and sensitivity and specificity were closest to it.\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\u003eTime to resolution of individual and global signs consistent with pyelonephritis\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTrue positives\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003estriated nephrogram\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eparenchymal edema\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003epatchy hypodensities\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eperinephric fat stranding\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003esmooth urothelial thickening\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eglobal assessment\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e45\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e35\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e34\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e35\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e49\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMean (days)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e112\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e133\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e134\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e155\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e101\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e149\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMedian (days)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e113\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e146\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e136\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSt dev. (days)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e114\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRange (days)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6 to 361\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6 to 364\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6 to 361\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18 to 364\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e6 to 269\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e6 to 361\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSensitivity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e42%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e48%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e65%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e43%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e67%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecificity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e79%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e89%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e59%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e28%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e59%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e42%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e details the number of studies in which signs persisted on follow-up CTs and the duration of these signs in patients with and without clinical pyelonephritis. Imaging abnormalities tended to persist longer in patients with clinical pyelonephritis; however, we could not determine whether clinical resolution occurred between episodes. In patients without clinical pyelonephritis, abnormalities persisted for a shorter period than that observed in the TTR analysis. Because imaging follow-up did not extend beyond one year, these cases were censored.\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\u003eTime persistence of unresolved signs in patients with and without pyelonephritis\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=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUnresolved sign\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003en\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003epyelonephritis present\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003epersistence time in patients with pyelonephritis\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003epersistence time in patients without pyelonephritis\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003estriated nephrogram\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5 (18%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e56 days\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e91 days\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eparenchymal edema\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10 (20%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e124 days\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e89 days\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003epatchy hypodensities\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17 (23%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e115 days\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e95 days\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eperinephric fat stranding\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e133\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36 (27%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e156 days\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e122 days\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003esmooth urothelial thickening\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17 (34%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e181 days\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e111 days\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eglobal assessment\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26 (70%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e101 days\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e105 days\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eTo our knowledge, this is the first study focused on the time to resolution of pyelonephritis based on CT signs.\u003c/p\u003e \u003cp\u003eAs important as these findings are, we also noted, as shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, that despite the clinical resolution of the pyelonephritis, the CT signs consistent with persistence were present for 105 days on average. This information may impact practice, as the low specificity of the signs or the global diagnosis can potentially lead to diagnostic and therapeutic interventions in people without pyelonephritis.\u003c/p\u003e \u003cp\u003eImaging is not routinely indicated in uncomplicated renal infections, as clinical signs and laboratory data are generally sufficient for making a diagnosis. However, imaging plays a crucial role under specific situations, including immunocompromised patients, treatment non-responders, equivocal clinical diagnosis, evaluation of existing anatomical anomalies, and assessment of disease extent [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Unfortunately, histologic specimens of the renal parenchyma in patients with pyelonephritis are seldom obtained, limiting the interpretation of the associated CT signs [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWhile both unenhanced and contrast-enhanced CT can identify urolithiasis, perinephric fluid, renal swelling, and hydronephrosis, only contrast-enhanced CT reliably demonstrates the parenchymal enhancement abnormalities that are characteristic of pyelonephritis. The American College of Radiology notes that in patients without a history of renal stones, the benefit of adding unenhanced CT to contrast-enhanced CT is negligible, as the contrast-enhanced phase alone achieved 96\u0026ndash;99% accuracy for detecting urolithiasis in addition to its superior performance for diagnosing pyelonephritis [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. The signs explored by our radiologists were previously found in 96% of 189 patients with the diagnosis of urinary tract infection, 62% of whom had two or more signs.\u003c/p\u003e \u003cp\u003eA study using MRI to assess the resolution of imaging among patients with acute pyelonephritis showed that, in 30 women with full clinical resolution one month after the diagnosis, 43% showed image-based resolution at one month, and 74% showed resolution after three months [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. These results, together with the cost of MRI, challenge its utility in defining cured cases or interpreting abnormal signs in patients with relapsed symptoms of pyelonephritis, as described in 44% of women who suffered 147 episodes of urinary infections [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eRadionuclide-based scans have also been studied in patients with acute pyelonephritis. \u003csup\u003e99m\u003c/sup\u003eTc-DMSA scanning has detected changes consistent with acute pyelonephritis in 37 (46%) of 81 patients. The signs disappeared within three months in 18 of 24 of those patients who had adequate follow-up [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. However, the relatively long waiting time after radiotracer injection, prolonged acquisition time, and high radiation dose may outweigh the benefits of this diagnostic test [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe main limitation of our study is its retrospective nature. Conducting this study prospectively would have required scheduling follow-up CTs at predetermined time points, an approach for which there is no currently clear clinical indication. Moreover, such a strategy would likely incur prohibitive costs and expose patients to potentially unacceptable risks from repeated radiation and contrast administration [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Follow-up CT examinations were obtained for a variety of clinical indications, including persistent symptoms, evaluation for complications, or unrelated clinical presentations. Because the timing of these studies was not standardized, variability in follow-up intervals likely contributed to the broad range of observed TTR values.\u003c/p\u003e \u003cp\u003eAnother limitation relates to case selection. Although there is broad agreement in the literature regarding the clinical diagnosis of pyelonephritis, other conditions, such as renal infarction, may present with similar defining features, leading to potential misclassification [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. In addition, pyuria in the setting of a negative urine culture has been reported in up to 15% of patients with infections outside the urinary tract, which may further confound the diagnosis and result in an erroneous attribution to pyelonephritis [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Therefore, although diagnostic certainty cannot be fully assured for all patients included in our database, these considerations reflect real-world clinical practice and thus support the external validity of our signs.\u003c/p\u003e \u003cp\u003eWe opted not to consider in the TTR the patients with or without a clinical definition of pyelonephritis whose CT signs never resolved. Instead, we presented separately the duration of signs in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, which are, for the most part, shorter than those presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Although including these cases in this calculation would have resulted in a shorter overall TTR, we censored these observations because we could not determine whether the abnormalities persisted beyond the one-year follow-up period [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Regarding the cases with clinical pyelonephritis but unresolved CT signs, we could not determine whether clinical resolution occurred between episodes. Knowing this information could have skewed the results towards a shorter TTR.\u003c/p\u003e \u003cp\u003eFinally, since this study reflects the experience of a single hospital, the generalizability of the signs may be limited.\u003c/p\u003e \u003cp\u003eWe conclude that CT signs supportive of the diagnosis of pyelonephritis may persist for months and, in our series, frequently remain unresolved even when clinical and laboratory data suggest complete resolution. Awareness of this observation may help clinicians in interpreting persistent imaging abnormalities within the appropriate clinical context and may prevent potentially unnecessary investigations and treatments in patients without evidence of ongoing infection.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eJPH, SSC, and GMA were responsible for the study design.JG, YT, AH, and GMA were responsible for the acquisition of clinical data.SSC, LC, and JPH were responsible for the acquisition of radiological data.GMA analyzed the data.GMA and JPH generated the initial version of the manuscript. All authors approved the final version of the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eZulfiqar M, Varela Ubilla C, Refky N, Menias CO. Imaging of Renal Infections and Inflammatory Disease. Radiol Clin N Am 2020; 58(5):909\u0026ndash;923. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.rcl.2020.05.004\u003c/span\u003e\u003cspan address=\"10.1016/j.rcl.2020.05.004\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCraig WD, Wagner BJ, Travis MD. Pyelonephritis: Radiologic-Pathologic Review. Radiographics 2008; 28(1):255\u0026ndash;277. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1148/rg.281075171\u003c/span\u003e\u003cspan address=\"10.1148/rg.281075171\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSmith AD, Nikolaidis P, Khatri G, et al. ACR Appropriateness Criteria\u0026reg; Acute Pyelonephritis: 2022 Update. J Am Coll Radiol 2022; 19(11S):S224-239. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.jacr.2022.09.017\u003c/span\u003e\u003cspan address=\"10.1016/j.jacr.2022.09.017\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYano T, Takada T, Fujiishi R, et al. Usefulness of computed tomography in the diagnosis of acute pyelonephritis in older patients suspected of infection with unknown focus. Acta Radiol, 2022; 63(2):268\u0026ndash;277. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1177/0284185120988817\u003c/span\u003e\u003cspan address=\"10.1177/0284185120988817\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRabushka LS, Fishman EK, Goldman SM. Pictorial Review: Computed tomography of renal inflammatory disease. Urology, 1994; 44(4):473\u0026ndash;480. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/s0090-4295(94)80042-1\u003c/span\u003e\u003cspan address=\"10.1016/s0090-4295(94)80042-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYu TY, Kim HR, Hwang KE, Lee JM, Cho JH, Lee JH. Computed tomography findings associated with bacteremia in adult patients with a urinary tract infection. Eur J Clin Microbiol Infect Dis, 2016; 35(11):1883\u0026ndash;1887. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s10096-016-2743-4\u003c/span\u003e\u003cspan address=\"10.1007/s10096-016-2743-4\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEl-Merhi F, Mohamad M, Haydar A, et al. Qualitative and quantitative radiological analysis of non-contrast CT is a strong indicator in patients with acute pyelonephritis. Am J Emerg Med, 2018; 36(4):589\u0026ndash;593. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.ajem.2017.09.026\u003c/span\u003e\u003cspan address=\"10.1016/j.ajem.2017.09.026\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSaunders HS, Dyer RB, Shifrin RY, Scharling ES, Bechtold RE, Zagoria RJ. The CT nephrogram: Implications for evaluations of urinary tract disease. Radiographics, 1995; 15(5):1069\u0026ndash;1085. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1148/radiographics.15.5.7501851\u003c/span\u003e\u003cspan address=\"10.1148/radiographics.15.5.7501851\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKawashima A, Sandler CM, Goldman SM, Raval BK, Fishman EK. CT of renal inflammatory disease. Radiographics, 1997; 17(4):851\u0026ndash;866. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1148/radiographics.17.4.9225387\u003c/span\u003e\u003cspan address=\"10.1148/radiographics.17.4.9225387\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDas CJ, Ahmad Z, Sharma S, Gupta AK. Multimodality imaging of renal inflammatory lesions. World J Radiol, 2014; 6(11):865\u0026ndash;873. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.4329/wjr.v6.i11.865\u003c/span\u003e\u003cspan address=\"10.4329/wjr.v6.i11.865\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHeller MT, Haarer KA, Thomas E, Thaete FL. Neoplastic and proliferative disorderes of the perinephric space. Clin Radiol 2012; 67(11):e41-41. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.crad.2012.03.015\u003c/span\u003e\u003cspan address=\"10.1016/j.crad.2012.03.015\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFleiss, J. L. Measuring nominal scale agreement among many raters. Psychological Bulletin, 1971; 76(5):378\u0026ndash;382. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003edoi.org/10.1037/h0031619\u003c/span\u003e\u003cspan address=\"10.1037/h0031619\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTrevethan R. Sensitivity, Specificity, and Predictive Values: Foundations, Pliabilities, and Pitfalls in Research and Practice. Front Public Health 2017; 5:307. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3389/fpubh.2017.00307\u003c/span\u003e\u003cspan address=\"10.3389/fpubh.2017.00307\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFaletti R, Gatti M, Bassano S, et al. Follow-up of acute pyelonephritis: what causes the diffusion-weighted magnetic resonance recovery to lag clinical recovery? Abdom Radiol (NY), 2018; 43(3):639\u0026ndash;646. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s00261-017-1242-0\u003c/span\u003e\u003cspan address=\"10.1007/s00261-017-1242-0\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIk\u0026auml;heimo R, Siitonen A, Heiskanen T, et al. Recurrence of Urinary Tract Infection in a Primary Care Setting: Analysis of a 1-Year Follow-up of 179 Women. Clin Infect Dis, 1996; 22(1):91\u0026ndash;99. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1093/clinids/22.1.91\u003c/span\u003e\u003cspan address=\"10.1093/clinids/22.1.91\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBailey RR, Lynn KL, Robson RA, Smith AH, Maling TM, Turner JG. DMSA renal scans in adults with acute pyelonephritis. Clin Nephrol, 1996; 46(2):99\u0026ndash;104. PMID: 8869786\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSarikaya I, Sarikaya A. Current Status of Radionuclide Renal Cortical Imaging in Pyelonephritis. J Nucl Med Technol, 2019; 47(4):309\u0026ndash;312. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.2967/jnmt.119.227942\u003c/span\u003e\u003cspan address=\"10.2967/jnmt.119.227942\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBrenner DJ, Hall EJ. Computed Tomography \u0026ndash; An Increasing Source of Radiation Exposure. N Engl J Med, 2007; 357(22):2277\u0026ndash;2284. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1056/NEJMra072149\u003c/span\u003e\u003cspan address=\"10.1056/NEJMra072149\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePiccoli GB, Priola AM, Vigotti FN, Guzzo G, Veltri A. Renal infarction versus pyelonephritis in a woman presenting with fever and flank pain. Am J Kidney Dis, 2014; 64(2):311\u0026ndash;314. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1053/j.ajkd.2014.02.027\u003c/span\u003e\u003cspan address=\"10.1053/j.ajkd.2014.02.027\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWise GJ, Schlegel PN. Sterile pyuria. N Engl J Med, 2015; 372(11):1048\u0026ndash;1054. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1056/NEJMra1410052\u003c/span\u003e\u003cspan address=\"10.1056/NEJMra1410052\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLagakos SW. General right censoring and its impact on the analysis of survival data. Biometrics, 1979; 35(1):139\u0026ndash;156. PMID 497332\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"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":"abdominal-radiology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"aima","sideBox":"Learn more about [Abdominal Radiology](http://link.springer.com/journal/261)","snPcode":"261","submissionUrl":"https://submission.springernature.com/new-submission/261/3","title":"Abdominal Radiology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"computed tomography, pyelonephritis, perinephric fat stranding, sensitivity and specificity, diagnostic imaging","lastPublishedDoi":"10.21203/rs.3.rs-9390703/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9390703/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003ePurpose: \u003c/strong\u003eAcute pyelonephritis is diagnosed based on clinical and laboratory signs. Computed tomography (CT) is typically reserved for detecting complications or alternative diagnoses. Current guidelines do not recommend routine follow-up imaging when abnormalities are found. The expected time to resolution (TTR) of CT abnormalities has not been clearly identified. This is the goal of our study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods: \u003c/strong\u003eRetrospective study at an academic hospital in Harris County, Texas. Adult patients with a diagnosis of acute pyelonephritis who underwent at least two CT scans were included. Three board-certified radiologists independently reviewed CT studies performed within one year of the index scan and assessed for striated nephrogram, parenchymal edema, patchy hypodensities, perinephric fat stranding, and urothelial thickening. TTR was defined as the interval between the first positive CT sign and the first subsequent CT in which the sign was absent. TTR was calculated for individual signs and globally, provided clinical criteria for pyelonephritis were met. Sensitivity, specificity, and inter-rater agreement were also evaluated.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults: \u003c/strong\u003e288 CT scans from 93 patients were reviewed; 252 (88%) were of sufficient quality for analysis. The mean global TTR was 149 ± 100 days, with wide variation across individual signs. Moreover, imaging abnormalities persisted for 105 days despite clinical resolution.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion: \u003c/strong\u003eCT signs consistent with pyelonephritis may persist for several months after clinical recovery. Clinicians should interpret persistent imaging abnormalities appropriately to avoid unnecessary diagnostic or therapeutic interventions.\u003c/p\u003e","manuscriptTitle":"Understanding CT Resolution Timeline in Acute Pyelonephritis: A Framework for Clinical Practice","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-27 15:43:10","doi":"10.21203/rs.3.rs-9390703/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"67049124259761898020081262609525964861","date":"2026-05-11T12:04:28+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-19T12:24:05+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-13T10:12:41+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-13T10:12:08+00:00","index":"","fulltext":""},{"type":"submitted","content":"Abdominal Radiology","date":"2026-04-11T22:19:27+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"abdominal-radiology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"aima","sideBox":"Learn more about [Abdominal Radiology](http://link.springer.com/journal/261)","snPcode":"261","submissionUrl":"https://submission.springernature.com/new-submission/261/3","title":"Abdominal Radiology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"64403984-bc1a-44f6-8854-d3d10e2a6fcf","owner":[],"postedDate":"April 27th, 2026","published":true,"recentEditorialEvents":[{"type":"reviewerAgreed","content":"67049124259761898020081262609525964861","date":"2026-05-11T12:04:28+00:00","index":15,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-27T15:43:10+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-27 15:43:10","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9390703","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9390703","identity":"rs-9390703","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}