Clear cell carcinoma arising from abdominal wall endometriosis: A case report with imaging findings and pathologic correlation

A woman in her 50s presented with a gradually enlarging, painful mass in the lower abdominal wall, localized to the pubic region. She had undergone a cesarean section in her 20s. Physical examination revealed a 7-8 cm midline mass in the pubic region, without overlying skin ulceration, erythema, or erosion. Pelvic examination revealed no vaginal erosion, and the uterus was normal in size. Laboratory tests, including tumor markers such as CA125, CA19-9, and CEA, were within normal limits. Transabdominal ultrasonography demonstrated a slightly hypoechoic, heterogeneous subcutaneous mass in the pubic region ( Fig. 1 A); color Doppler was not assessed. Transvaginal ultrasonography showed a normal-sized uterus and ovaries, with no evidence of ascites or endometrial thickening. Fig. 1 Ultrasound and CT findings. (A) Transabdominal ultrasound shows a slightly hypoechoic, heterogeneous subcutaneous mass in the pubic region (white arrow); color Doppler was not assessed. (B-D) Axial CT images demonstrate a subcutaneous mass in the pubic region composed of a hypoattenuating cystic component (white arrow) and an enhancing solid component (arrowhead). (E) The solid component extends into the rectus abdominis muscle (open arrow), suggesting muscular invasion, and the lesion is clearly separated from the pubic bone. (B) Noncontrast CT; (C) contrast-enhanced CT, arterial phase; (D and E) contrast-enhanced CT, venous phase. Fig 1 dummy alt text Ultrasound and CT findings. (A) Transabdominal ultrasound shows a slightly hypoechoic, heterogeneous subcutaneous mass in the pubic region (white arrow); color Doppler was not assessed. (B-D) Axial CT images demonstrate a subcutaneous mass in the pubic region composed of a hypoattenuating cystic component (white arrow) and an enhancing solid component (arrowhead). (E) The solid component extends into the rectus abdominis muscle (open arrow), suggesting muscular invasion, and the lesion is clearly separated from the pubic bone. (B) Noncontrast CT; (C) contrast-enhanced CT, arterial phase; (D and E) contrast-enhanced CT, venous phase. Contrast-enhanced computed tomography (arterial and venous phases) demonstrated a subcutaneous mass in the lower anterior abdominal wall, in the pubic region, clearly separated from the pubic bone. The lesion was composed of hypoattenuating cystic areas with minimal enhancement and an enhancing solid component with heterogeneous enhancement. The mass broadly abutted the overlying skin and extended into the rectus abdominis muscle, suggesting muscular invasion ( Fig. 1 B-E). No lymphadenopathy or distant metastasis was identified on contrast-enhanced CT. Magnetic resonance imaging (MRI) revealed an 80 × 38 mm subcutaneous mass anterior to the pubic bone. The lesion demonstrated a mixed cystic–solid architecture, with the solid component showing mildly hyperintense signal relative to skeletal muscle on T2-weighted images and slightly increased signal intensity on T1-weighted images. On diffusion-weighted imaging ( b -values: 0 and 1000 second/mm²), the solid component showed high signal with corresponding low signal on the apparent diffusion coefficient (ADC) map, consistent with restricted diffusion (minimum ADC: 0.401 × 10 −3 mm²/s). Dynamic contrast-enhanced MRI demonstrated progressively heterogeneous enhancement within the solid component ( Fig. 2 ). Fig. 2 MRI findings (A-D: axial images; E-H: sagittal dynamic contrast-enhanced images). (A-D) Axial MRI shows an 80 × 38 mm subcutaneous mass anterior to the pubic bone, with cystic areas (white arrow) and a solid component (arrowhead). The solid component demonstrates high signal on DWI ( b = 1000 second/mm²) (arrowhead in C) and low signal on the ADC map (arrowhead in D), consistent with restricted diffusion (minimum ADC: 0.401 × 10 −3 mm²/s). (E-H) Sagittal dynamic contrast-enhanced MRI shows progressively heterogeneous enhancement in the solid component (arrowheads). (A) T1-weighted image; (B) T2-weighted image; (C) DWI ( b = 1000 second/mm²); (D) ADC map; (E) precontrast; (F) 40 seconds; (G) 90 seconds; (H) 180 seconds after contrast injection. Fig 2 dummy alt text MRI findings (A-D: axial images; E-H: sagittal dynamic contrast-enhanced images). (A-D) Axial MRI shows an 80 × 38 mm subcutaneous mass anterior to the pubic bone, with cystic areas (white arrow) and a solid component (arrowhead). The solid component demonstrates high signal on DWI ( b = 1000 second/mm²) (arrowhead in C) and low signal on the ADC map (arrowhead in D), consistent with restricted diffusion (minimum ADC: 0.401 × 10 −3 mm²/s). (E-H) Sagittal dynamic contrast-enhanced MRI shows progressively heterogeneous enhancement in the solid component (arrowheads). (A) T1-weighted image; (B) T2-weighted image; (C) DWI ( b = 1000 second/mm²); (D) ADC map; (E) precontrast; (F) 40 seconds; (G) 90 seconds; (H) 180 seconds after contrast injection. Ultrasound-guided percutaneous needle biopsy was performed, and histopathological analysis revealed clear cell carcinoma. The differential diagnosis included malignant transformation of AWE vs metastasis or extension from another primary site, including a gynecologic origin or clear cell renal cell carcinoma. To achieve definitive local control and to exclude a gynecologic primary, the patient subsequently underwent wide excision of the abdominal wall mass together with total hysterectomy and bilateral salpingo-oophorectomy. The mass was resected en bloc with full-thickness resection of the rectus abdominis muscle, with a gross surgical margin of approximately 1.5-2.0 cm from the palpable border. The abdominal wall defect was reconstructed using a flap. Gross examination of the resected specimen revealed mixed cystic and solid components. Microscopically, the cystic wall was lined by endometrioid-type glands with endometrial-type stroma and associated hemorrhage, consistent with endometriosis. The solid component demonstrated malignant glands composed of tumor cells with clear cytoplasm, consistent with clear cell carcinoma. Benign endometriosis was identified in close proximity to the carcinoma within the same lesion, supporting an endometriosis-associated origin ( Fig. 3 ). The final pathological diagnosis was clear cell carcinoma arising from malignant transformation of AWE. The patient did not return for postoperative outpatient follow-up; therefore, long-term outcome data are unavailable. Fig. 3 Gross specimen and histopathology. (A) Gross specimen of the resected abdominal wall mass showing mixed cystic and solid components (cystic component, white arrow; solid component, arrowhead). (B) The cyst wall is lined by endometrioid-type glands (white arrows) with associated hemorrhage (asterisk), consistent with endometriosis (×200). (C and D) The solid component shows malignant glands composed of tumor cells with clear cytoplasm (arrowheads), consistent with clear cell carcinoma (C: ×20; D: ×400). (E and F) Endometrioid glands accompanied by endometrial-type stroma are seen adjacent to the carcinoma (white arrows), supporting origin from endometriosis (E: ×40; F: ×200). Fig 3 dummy alt text Gross specimen and histopathology. (A) Gross specimen of the resected abdominal wall mass showing mixed cystic and solid components (cystic component, white arrow; solid component, arrowhead). (B) The cyst wall is lined by endometrioid-type glands (white arrows) with associated hemorrhage (asterisk), consistent with endometriosis (×200). (C and D) The solid component shows malignant glands composed of tumor cells with clear cytoplasm (arrowheads), consistent with clear cell carcinoma (C: ×20; D: ×400). (E and F) Endometrioid glands accompanied by endometrial-type stroma are seen adjacent to the carcinoma (white arrows), supporting origin from endometriosis (E: ×40; F: ×200).

We explained the use of the specimens for clinical research to the individual patients and obtained their consent.

Although exceedingly rare, malignant transformation of AWE should be considered in the differential diagnosis of a scar-related abdominal wall mass in women with a history of cesarean section or other gynecologic surgery. Imaging features—particularly a mixed cystic–solid architecture, heterogeneous enhancement of the solid component, and restricted diffusion—may overlap with those of ovarian clear cell carcinoma arising from endometriosis. Recognition of these findings may facilitate earlier diagnosis and appropriate surgical management.

We report a woman in her 50s with a history of cesarean section who developed clear cell carcinoma arising from AWE. Ultrasound and cross-sectional imaging (CT and MRI) revealed a subcutaneous mass in the pubic region with mixed cystic and solid components; the solid component showed heterogeneous progressive enhancement and restricted diffusion on MRI. The lesion extended into the rectus abdominis muscle, and no lymphadenopathy or distant metastasis was identified on CT. Wide excision of the abdominal wall mass was performed together with total hysterectomy and bilateral salpingo-oophorectomy to exclude a gynecologic primary, and no malignancy was found in the uterus or adnexa, supporting the diagnosis of clear cell carcinoma arising from AWE. Because malignant transformation of endometriosis is rare, attribution of a carcinoma to an endometriotic origin requires explicit pathologic correlation. As summarized in the recent literature, the commonly applied diagnostic framework requires endometriosis in proximity to the tumor, absence of another primary tumor site, histopathologic features compatible with an endometrial origin, and morphologic contiguity between benign endometriosis and malignant tissue [ 4 ]. In our case, benign endometriosis was identified adjacent to the carcinoma within the resected lesion. In addition, no malignancy was identified in the uterus or adnexa at surgery, and the histopathologic findings were consistent with clear cell carcinoma arising in an endometriotic background. Taken together, these findings support an endometriosis-associated origin in the abdominal wall [ 4 ]. AWE is an uncommon form of extrapelvic endometriosis that typically occurs in surgical scars, particularly after cesarean section. Malignant transformation is rare, estimated to occur in approximately 0.7%-1.5% of endometriosis cases, and malignant transformation arising from the abdominal wall is even less frequent [ 3 ]. Previous reports suggest that malignant transformation of AWE usually occurs decades after the inciting uterine surgery, with an average latency of approximately two decades [ 4 ]. In this context, awareness of suspicious imaging findings is clinically important, because the long interval from prior surgery may reduce initial suspicion of malignancy. To our knowledge, no dedicated review has specifically focused on the imaging features of malignant AWE. Therefore, comparison with the established imaging features of ovarian clear cell carcinoma arising from endometriosis may provide a useful interpretive framework for the present case. Ovarian clear cell carcinoma associated with endometriosis is generally characterized by a cystic mass with enhancing mural nodules or papillary projections on CT and MRI [ 5 ]. On MRI, suspicious findings include heterogeneous enhancement of the solid component and restricted diffusion within mural nodules or solid portions; additional reported findings include loss of the typical T2 shading of an endometrioma and reduction or loss of high T1 signal in the cystic component [ 5 ]. Our case showed a similar imaging pattern, including mixed cystic–solid architecture, heterogeneous progressive enhancement of the solid component, mildly increased T2 signal relative to skeletal muscle, and restricted diffusion with low ADC values. Although the location was unusual, the radiologic phenotype of the lesion overlapped with that of ovarian clear cell carcinoma arising from endometriosis, which may reflect a shared histopathologic background of endometriosis-associated carcinogenesis. Ultrasound is typically the first-line imaging modality for suspected AWE. In our case, grayscale ultrasound demonstrated a slightly hypoechoic, heterogeneous subcutaneous mass, although color Doppler was not assessed. CT and MRI were subsequently useful for characterizing the cystic-solid architecture, evaluating rectus abdominis involvement, and excluding overt metastatic disease. From a practical standpoint, when a scar-related abdominal wall mass in a woman with a history of cesarean section demonstrates both cystic and enhancing solid components, particularly with restricted diffusion in the solid portion, malignant transformation of AWE should be considered in the differential diagnosis. Recognition of this imaging pattern may prompt timely biopsy, appropriate staging work-up, and surgical planning. This study has several limitations. First, as a single case report, it cannot define the full imaging spectrum of malignant transformation arising from AWE. Second, because malignant AWE is extremely rare, radiologic descriptions in the literature remain limited. Third, the ultrasound images at our institution were archived as printed films rather than DICOM data, which may reduce image quality despite careful digitization and anonymization. Finally, long-term outcome assessment was not possible because the patient did not return for postoperative follow-up. Despite these limitations, the present case suggests that a scar-related abdominal wall mass with mixed cystic–solid architecture, heterogeneous enhancement, and restricted diffusion should raise suspicion for malignant transformation of AWE.

Endometriosis typically occurs in the pelvic peritoneum, ovaries, and rectovaginal septum, affecting 6% to 10% of women of reproductive age [ 1 ]. In contrast, abdominal wall endometriosis (AWE) is a rare condition, most commonly found at surgical scar sites, particularly following cesarean section [ 2 ]. Malignant transformation is exceedingly uncommon, estimated to occur in 0.7%-1.5% of endometriosis cases [ 3 ], and abdominal wall origin is even less frequent. Because malignant transformation is rare, attributing a carcinoma to an endometriotic origin requires explicit histopathologic correlation. As summarized in a recent literature review of clear cell carcinoma arising from AWE, the commonly applied diagnostic framework (often referred to as Sampson’s criteria with Scott’s additional criterion) requires: (1) endometriosis in proximity to the tumor, (2) absence of another primary tumor site, (3) histologic features consistent with an endometrial origin, and (4) morphologic contiguity between benign endometriosis and malignant tissue [ 4 ]. In this report, we describe a case of clear cell carcinoma arising from AWE, focusing on imaging findings with pathologic correlation and comparison with the established imaging features of ovarian clear cell carcinoma associated with endometriosis.