Synovial sarcoma involving the head: analysis of 36 cases with predilection to the parotid and temporal regions.

Synovial sarcoma involving the head is rare, and data on the clinicopathologic characteristics of such tumors are scant. In this study, we examined 36 synovial sarcomas of the head excluding tumors in the oral cavity, sinonasal tract, submandibular area, neck, and intracranial space. There were 19 men and 17 women with a mean age of 35 years (range: 4 to 85 y). There was a marked predilection for the parotid (n=14) and temporal regions (n=9), and cheek (n=4). Other locations included mastoid area (n=2), infratemporal fossa (n=2), and one each from the supra-auricular scalp, maxillary, submaxillary, mandibular, and nasolabial regions. Histologically, 25 examples were of monophasic type, 10 were biphasic. Five of these cases contained a poorly differentiated Ewing sarcoma-like component and 1 was purely poorly differentiated. Histologically, 9 tumors involved skeletal muscle, 4 parotid gland (focally or in the interlobular septa), and 1 intertrabecular spaces of bone; the others involved subcutis or fascia and rarely skin. The tumor size ranged from 0.6 to 7.0 cm (median: 3.5 cm) and mitotic activity varied from <1 to 85 per 10 high-power fields (HPFs) (median, 6/10 HPFs). Keratin-positive tumor cells were detected in 19 of 19 monophasic and 1 of 1 of poorly differentiated tumors that were examined. SS18 gene rearrangement was confirmed in all 14 cases examined (3 biphasic and 11 monophasic tumors). Follow-up on 29 patients revealed that 11 were alive without disease from 2 to 31 years (median, 14 y). Ten patients died of disease 1 to 18 years after the diagnosis (median, 3 y); most of these patients had a tumor >5 cm and 6 of 10 had mitotic counts >10/10 HPFs. One patient died of an unrelated cause (metastatic melanoma) and 7 died of unknown causes. Four other patients had subsequent malignancies, including carcinomas of the breast, esophagus, rectum, and parotid gland. The latter was possibly radiation-induced, diagnosed 30 years after the synovial sarcoma. Synovial sarcoma of the head has a striking predilection for the parotid and temporal regions and the prognosis varies with many patients having long tumor-free survivals.