{"paper_id":"a2d233b8-af32-481c-b0ee-6d9da723a34f","body_text":"Abdominal wall masses have a wide differential diagnosis, which includes\nendometriosis and other neoplastic and inflammatory etiologies. Abdominal wall\nendometriosis is commonly associated with scars related to Cesarean section,\nhysterectomy and other uterine surgery. However, in a substantial minority of cases,\nAWE does not arise in association with abdominal scarring or in the context of prior\nsurgery ( 1 ,  2 ). The condition may be detected incidentally on imaging or it may come\nto medical attention because of chronic abdominal or pelvic pain. As with the pelvic\nvariety, malignant transformation is a rare but recognized complication ( 3 ). Although the diagnosis may at times be made\nbased on clinical presentation, in many scenarios, clinical manifestations of AWE\nare nonspecific, and patients may complain only of vague abdominal pain, a tender\nmass, or they may be asymptomatic ( 3 ).\nMoreover, symptoms may not occur until years after uterine surgery (reported cases\nrange from 6 months to 20 years), and as such may not be recognized as being related\nto prior surgical treatment ( 4 ).\nAs CT scan is often part of the evaluation of patients with abdominal pain,\nawareness of potential differences and similarities in cross-sectional imaging\nfeatures between AWE and other abdominal wall masses is important. Furthermore, an\nabdominal wall soft tissue mass may be detected incidentally in an asymptomatic\npatient being evaluated with CT for an unrelated condition.\nThe literature regarding the imaging features of AWE is scarce, and\ndiscriminating imaging features are not well-defined. While some have studied\nsonographic features of AWE ( 5 , 6 , 7 , 8 , 9 , 10 ), the existing literature on CT is limited to case\nreports, with CT features often described as nonspecific with variable attenuation\nand enhancement characteristics ( 4 , 5 , 7 , 8 , 11 ).\nThere have been no studies evaluating the role of CT in distinguishing AWE from\nother abdominal wall masses. Thus, the purpose of this study is to assess the\nutility of morphologic and quantitative CT features in differentiating abdominal\nwall endometriosis from other masses of the abdominal wall.\n\nThis retrospective study was HIPAA-compliant and IRB approved with a\nwaiver of the requirement for written informed consent. Pathology databases of\ntwo institutions were searched for the terms “abdominal wall\nmass” and “pelvic wall mass” in female patients between\nages 18 and 55, from January 2000 through April 2014. Initially, 323 cases were\nidentified. Then, only cases with CT studies performed within 12 months prior to\nhistopathologic evaluation were considered, yielding a cohort of 111 cases. Of\nthese, 5 cases were excluded because the biopsied mass was along the pelvic\nsidewall and 1 case was excluded because the biopsied mass was in the left upper\nquadrant and not within the anterior abdominal or pelvic wall soft tissues. The\nfinal cohort included 105 patients with median age 41 years (range: 21-55\nyears); 24.8% (26/105) had histologically proven endometriosis.\nHistopathologic criteria for the diagnosis of endometriosis in our series\nincluded the presence of benign-appearing endometrial glands and stroma with\nevidence of fresh or remote hemorrhage. Occasional cases lacked either obvious\nendometrial stroma or hemorrhage, but not both. When endometrial stroma was not\napparent, a diagnosis of endometriosis required benign-appearing endometrioid\nglands and architectural features that were characteristic of endometriosis.\nSo-called “stromal endometriosis,” a lesion containing\nendometrial stroma, but no glands, was not encountered in this cohort.\nCT scans were performed on 16 or 64 detector row GE helical scanners (GE\nMedical Systems, Milwaukee, WI). Images were reconstructed at 2.5-mm or 5-mm\nintervals. Iodinated intravenous contrast material (120 – 150\ncm 3  Omnipaque-300) was administered to 76 of 105 patients\n(72.4%).\nTwo fellowship-trained radiologists (HAV and GY with 4 and 5 years of experience, respectively) blinded to the final histopathologic diagnoses\nindependently reviewed all CT scans. They assessed each study for the following\nqualitative CT features: border type (irregular, lobulated, or smooth), presence\nof calcifications, intramuscular versus subcutaneous fat location, homogeneous\nversus heterogeneous density, association with a scar, multiplicity, location\nabove or below the umbilicus, presence of coexisting intraperitoneal disease and\npresence of intraperitoneal extension. The presence of linear infiltration\nirradiating peripherally from a central soft tissue nodule, which we refer to as\nthe “gorgon sign”, was also recorded ( Figure 1 ). A mass was considered to have subcutaneous\nfat location if greater than 50% of the mass extended into the\nsubcutaneous soft tissues. Similarly, a mass was considered to have\nintraperitoneal extension if greater than 50% of the lesion bulged into\nthe peritoneal cavity. Both readers measured mass densities on all non-contrast\ncases by placing an ROI in the center of the mass, encompassing at least\n50% of the lesion. Seventy-six studies were performed following\nintravenous contrast administration only, precluding evaluation of pre-contrast\ndensity.\nClinical, pathologic and imaging characteristics were summarized using\nmedians and ranges for continuous variables and frequencies and percentages for\ncategorical variables ( Table 1 ).\nInter-reader agreement for CT features was assessed with Cohen's simple\nKappa statistic with 95% confidence intervals and percentage\nagreement.\nAssociations between CT features and endometriosis were tested using\nFisher's exact test for categorical variables ( Table 2 ). P-values were adjusted for multiple\ntesting using the false discovery rate approach and values less than 0.05 were\nconsidered statistically significant. The variables significant for both readers\nin the above analysis were combined into a feature scoring system ( Table 3 ). Scores could range from at least\n1 feature present to having all 3 features present. Diagnostic accuracy,\nincluding sensitivity, specificity, positive predictive value (PPV) and negative\npredictive value (NPV) were calculated for each of these levels along with exact\n95% CI. We then noted the differences between each of these levels.\nFor patients with non-contrast CTs (N=26), the densities in\nHounsfield units for patients with and without endometriosis were assessed with\ndescriptive statistics and box plots. Due to the small patient sample, formal\nhypothesis tests were not conducted. Lesions with obvious calcifications and\ngross fat were excluded from this part of the analysis. To assess the effect of\ncontrast on the appearance of mass heterogeneity in patients both with and\nwithout endometriosis, a logistic regression was performed with an interaction\nterm for contrast and heterogeneity; endometriosis was the independent outcome\nfor both readers 1 and 2.\n\nThe final cohort included 105 patients with median age 41 years (range\n21 – 55 years); 24.8% (26/105) showed histologically proven\nendometriosis. Of non-endometriosis diagnoses, there were 28 patients with\nadenocarcinoma (21%), 15 with desmoid (14.3%), 9 with\nleiomyosarcoma (8.6%), 3 with lymphoma (2.9%), 3 with lipoma\n(2.9%), 3 with squamous cell carcinoma (2.9%), 2 with blastoma\n(1.9%), 2 with abscess and/or fat necrosis (1.9%), 2 with\nfibromatosis (1.9%), 2 with gastrointestinal stromal tumor\n(1.9%) and 2 with synovial sarcoma (1.9%). Other diagnoses\nconstituted 1% each of the total number of cases and are listed in  Table 1 . Of the 28 adenocarcinomas, 5 were\nclear cell subtype and 1 was endometrioid subtype. Both entities have a known\nassociation with endometriosis ( 12 ).\nInter-reader agreement ranged from substantial for border type\n(85.7%, k=0.75, 95%CI: 0.64 - 0.87) and peritoneal\nextension (89.5%, k=0.71, 95% CI: 0.56 – 0.87)\nto almost perfect on calcifications (98.1%, k=0.85, 95%\nCI: 0.64 – 1.00), gorgon sign (99%, k=0.97, 95%\nCI: 0.91 – 1.00), mass location (93.3%, k=0.90,\n95% CI: 0.82 – 0.97), mass heterogeneity (95.2%,\nk=0.90, 95% CI: 0.81 – 0.98), association with scar\n(95.2%, k=0.88, 95% CI: 0.77 – 0.98), additional\nsimilar masses (98.1%, k=0.94, 95% CI: 0.87 –\n1.00), position above or below the umbilicus (99%, k=0.97,\n95% CI: 0.92 – 1.00), and coexisting intraperitoneal disease\n(99%, k=0.97, 95% CI: 0.90 – 1.00).\nFor both readers, gorgon sign (p<0.0001 for both), homogeneous\ndensity (p=0.0188 for both) and location above or below umbilicus\n(p=0.0188 for both) were significantly associated with endometriosis. A\nhigher proportion of patients with AWE had gorgon sign compared with patients\nhaving other diagnoses (R1: 73.1% vs. 3.8% and R2: 73.1%\nvs. 2.5%). Additionally, endometriosis patients had a higher proportion\nof homogeneous density masses (R1: 88.5% vs. 58.2% and R2:\n88.5% vs. 57%), and masses located below the umbilicus compared\nwith other patients (R1: 96.2% vs. 70.9% and R2: 96.2%\nvs. 69.6%). Border type was significant for reader 2 (p=0.0199),\nbut not for reader 1 (p=0.06), and peritoneal extension was significant\nfor reader 1 (p=0.0188) but not for reader 2 (p=0.06). No other\nfeatures, including calcifications, mass location, coexisting intraperitoneal\ndisease or additional similar masses were found to be significant\n(p=0.06-60) ( Table 2 ). No\nrelationship was found between the use of IV contrast and heterogeneity in\npredicting endometriosis (p=0.96-0.97). Patients with IV contrast\n(76/105 patients) did not display different profiles of heterogeneity.\nPatients with at least 1 feature present had the highest sensitivity in\ndiagnosing AWE (0.96, 95% CI: 0.80-1.00 for both), but the lowest\nspecificity (0.08, 95% I: 0.03-0.16 for R1 and 0.10, 95% CI:\n0.04-0.19 for R2). Patients with at least 2 features present also had a high\nsensitivity in assessing AWE (0.92, 95% CI: 0.75-0.99 for both), but\nmoderate specificity (0.62, 95% CI: 0.50-0.73 for R1 and 0.63,\n95% CI: 0.52-0.74 for R2). The highest combined sensitivity (0.69,\n95% CI: 0.48-0.86 for both) and specificity (0.97, 95% CI:\n0.91-1.00 for both) occurred for patients having all three features present,\nthough sensitivity in predicting endometriosis declined with the more stringent\nrequirement ( Table 3 ).\nTwenty-nine patients had non-contrast CT scans. Three of the 29 had\nextremely skewed densities (below -100 or above 100) and excluded from further\ndescriptive statistics. None of these three patients had AWE. In patients with\nendometriosis (N=5), the median density was 45 HU (range 39-54 HU),\nwhile for patients with other diagnoses, the median density was 38.5 HU (range\n15 – 58 HU) ( Table 4  and  Fig. 2 ).\n\nThis study compared a spectrum of CT features in cases of AWE and of other\nmasses of the abdominal wall, all with histopathologic verification. Significant\ndifferences were observed; the presence of “gorgon” sign, mass\nhomogeneity and location below the umbilicus were significantly associated with\nendometriosis. The presence of all three features provided the highest combined\nsensitivity and specificity for the diagnosis.\nWe defined the “gorgon” sign as the presence of linear\ninfiltration radiating peripherally to the adjacent subcutaneous fat from a central\nsoft tissue nodule ( Fig. 1 ). Upon\nhistopathologic evaluation, cases with the gorgon sign exhibited an appearance\nsimilar to that of deep pelvic endometriosis, in which there is a predominance of\nhistiocytic infiltration and fibrosis due to chronic hemorrhage, and few glands\n( Fig. 3 ). This appearance is in contrast\nwith the ovarian form of endometriosis in which there is classically a predominance\nof ectopic endometrial glands and/or an endometriotic cyst, with fibrosis not a\ndominating feature.\nThe literature regarding imaging features of AWE is scarce, with many\nauthors concluding that the usefulness of imaging is limited to determining the\nlocation and extent of involvement of the lesion with respect to the surrounding\ntissue. Interestingly, the few studies that consider the sonographic features of\nabdominal wall endometriosis have described specific features, including solid\nlesions with ill-defined blurred outer borders and the presence of a hyperechoic\nring. The latter correspond to adipose tissue that has become edematous and is\nfilled with cells of inflammatory origin ( 9 ,\n 10 ). Our findings are consistent with\nthese results, as the “gorgon” sign may be a CT correlate to the\nhyperechoic rim seen on ultrasound.\nAwareness of the discriminating imaging features that we describe may impact\nclinical management and the workup of abdominal wall masses. An understanding of the\nsignificance of these features could potentially facilitate appropriate diagnosis at\nthe time of initial image interpretation. This may in turn assist in patient\ncounseling and in selection of optimal management strategies ( 13 ). While hormonal suppression or surgical resection\nwill often be needed, especially for patients symptomatic for pain at the abdominal\nwall site, this valuable radiographic information could provide opportunity for a\nnon-operative approach. In a patient with history of primary malignancy, tissue\nsampling may be deemed appropriate regardless of CT appearance. However, if imaging\nfeatures are suggestive of AWE, this information may affect the radicality of\ndissection and the need for complex abdominal wall reconstruction.\nTreatment options for AWE have evolved. The hallmark of endometriosis\nmanagement is hormonal suppression and surgical resection, however treatments with\npercutaneous cryoablation and radiofrequency ablation have been reported ( 14 ,  15 ).\nThere is thus substantive impact on patient counseling and treatment planning as a\nresult of accurate initial interpretation of imaging.\nOur study had several limitations. First, it was retrospective and had a\nsmall sample size (26 cases of endometriosis among the 105 cases evaluated). Second,\nonly masses that were biopsied were included in the study, introducing a\nverification bias in the sample. Although this provided the most rigorous imaging to\npathology correlation possible, it must be acknowledged that in standard practice\nnot all abdominal wall masses require biopsy for clinical management, especially if\nlongstanding and asymptomatic. Third, due to lack of pre and post-contrast images in\nmost cases, we were not able to assess enhancement characteristics. In our\nassessment of lesion heterogeneity, we did not differentiate between those patients\nwho were given intravenous contrast and those who were not. However, a sensitivity\nanalysis revealed no relationship between contrast and heterogeneity in predicting\nendometriosis (p=0.96-0.97). Patients with contrast did not display\ndifferent profiles of heterogeneity; however, given the limited sample size of\nnon-contrast patients, this analysis should be repeated with a larger sample of\npatients with non-contrast CT.\nIn conclusion, our study showed significant differences between CT features\nof abdominal wall endometriosis and those of other abdominal wall masses. Increased\nawareness of this possible diagnosis and improved understanding of its\ndiscriminating imaging features may be valuable for assisting clinical\nmanagement.","source_license":"CC0","license_restricted":false}