Hyalinizing spindle cell tumor with giant rosettes of the omentum.

We report the first case of a hyalinizing spindle cell tumor with giant rosettes of the omentum. The mesenchymal tumor arises from a multiplication of fibroblastic cells containing large rosette-like structures composed of a central collagen core surrounded by plump oval to spindle tumor cells. A 38-year-old woman exhibited the symptom of abdominal pain in the right side, with a correlated sensation of a mass in the same area. A tumor consisting of both solid and cystic cytologic features was subsequently diagnosed, on the right side of the uterus. Her serum level of CA-125 was only slightly elevated. Surgical intervention indicated that the tumor originated from lower pole of the omentum and the histological diagnosis was hyalinizing spindle cell tumor with giant rosettes. The metastatic potential of this type of tumor is considered similar to that of the metastatic low-grade fibromyxoid sarcoma, which indicated the need for careful clinical follow up of this case.