Primary sclerosing epithelioid fibrosarcoma of the iliac fossa: a case report.

Sclerosing epithelioid fibrosarcoma (SEF) is an exceedingly rare and aggressive fibroblastic malignancy. Primary involvement of the retroperitoneal iliac fossa is exceptionally uncommon in the literature, and its nonspecific clinical features and overlapping imaging findings pose significant diagnostic challenges. This case report describes a 53-year-old man who presented with a large, painful, palpable mass in the right lower quadrant. Imaging revealed a well-circumscribed lesion in the right iliac fossa. Non-contrast-enhanced computed tomography (CT) showed heterogeneous low density, while contrast-enhanced CT demonstrated characteristic progressive enhancement. On magnetic resonance imaging (MRI), the lesion exhibited iso- to slightly hypointense signals on T1-weighted imaging, mixed hyperintensity on T2-weighted imaging, and remarkable heterogeneous restricted diffusion on diffusion-weighted imaging. The patient underwent radical surgical resection, and the diagnosis of SEF was confirmed by histopathological and immunohistochemical examinations. No evidence of recurrence or metastasis was observed during the short-term follow-up period. The uniqueness of this case lies in the primary iliac fossa location, which has been reported only once previously in the pathological literature. Preoperatively, differential diagnoses included solitary fibrous tumor, low-grade fibromyxoid sarcoma, and schwannoma, which were ruled out based on characteristic imaging and histopathological features. During 10 months of short-term follow-up, there was no evidence of local recurrence or distant metastasis. A deep-seated soft-tissue mass displaying heterogeneous T2 signal with hypointense collagenous areas and progressive enhancement should raise suspicion for sclerosing epithelioid fibrosarcoma, especially in atypical locations such as the iliac fossa. Definitive diagnosis requires histopathology and immunohistochemistry (MUC4), while long-term follow-up is essential to monitor late recurrence or metastasis.