Proximal-Type Epithelioid Sarcoma in Skull Base: a Pathological Diagnosis Challenge with Other Intracranial Tumors

Proximal-type ES (PES) is a rare and aggressive sarcoma originated from soft tissues with uncertain differentiation. It mainly affects middle-aged patients and often locates in proximal extremity and deep-seated tissues. Only one case of PES located in the skull base has been reported to date. Herein, we report two cases of PES occurred in the middle cranial fossa in two middle-aged Chinese women. Microscopically, the tumors were consisted of epithelial-like cells with or without rhabdoid cells. And frequent mitotic activity and coagulation necrosis were present. Immunohistochemically, tumor cells in the two cases were positive for vimentin, AE1/AE3, epithelial membrane antigen (EMA), CD34, and synaptophysin. A few number of tumor cells expressed CD56. They were completely negative for integrase interactor-1 (INI1). Besides, TP53 positive cells were observed (>50%) in the two cases. The MIB-1 proliferation index was high up to 50-70%. Fluorescence in situ hybridization showed the monoallelic deletions of INI1. Intracranial PES is needed to identify with other mimic tumors, especially rhabdoid meningioma, epithelioid MPNST and adult AT/RT. The prognosis of the two patients was very poor. They died respectively less than a month and half a month after surgery. Tumor grew rapidly and was easy to infiltrate into the surrounding tissues. It may suggest that the prognosis of PES occurred at the base of skull was worse than in other sites.