Dumb-bell shaped poorly differentiated pelvic synovial sarcoma with molecular confirmation: a rare presentation of an uncommon disease entity.

Pelvic localization of synovial sarcoma is a rare phenomenon and to the best of our knowledge its presentation as a large "dumb-bell"-shaped abdomino-pelvic mass showing extension to the thigh has never been reported in the literature. We report a case of a young adult presenting with retention of urine and was found to have a large abdomino-pelvic mass causing bony destruction and compression of pelvic viscera. A biopsy revealed a cellular tumor composed of spindle to oval cells arranged in a hemangiopericytomatous pattern. Histopathology was suggestive of poorly differentiated synovial sarcoma. Immunohistochemistry (IHC) was positive for vimentin, CD 99, Bcl2, Mic2 and focally for EMA and negative for CD 34, CK, desmin, synaptophysin, and WT1. Due to equivocal IHC findings molecular analysis was done which confirmed the diagnosis as synovial sarcoma.