Malignant hemangiopericytoma of the omentum presenting as an ovarian tumor.

Malignant hemangiopericytomas are usually found in the musculature of the extremities, the retroperitoneum, and the pelvis. Malignant hemangiopericytoma arising in the omentum is extremely rare. We recently experienced such a case, in which a malignant ovarian tumor was suspected preoperatively on the basis of the sonogram, CT scan, magnetic resonance image, and increased CA-125 value. Microscopically, the tumor showed many mitoses, increased cellularity, and cytologic atypia. The patient was treated with CAP combination therapy following resection of the tumor; however, an intraperitoneal recurrence probably due to implantation was recognized 11 months later.