MYOEPITHELIOMA OF THE RETROPERITONEUM

An abdominal mass detected in a 36-year-old man was thought from radio logic studies to be a renal neoplasm, but at surgery the kidney was fo und to be uninvolved. The 9.5-cm retroperitoneal tumor was resected to tally and found to be encapsulated, and it appeared to be benign by li ght microscopy. The pattern of the spindle cells throughout the tumor suggested a cellular schwannoma, but immunocytochemical and ultrastruc tural studies did not support schwannian differentiation and instead r evealed epithelial and smooth muscle features compatible with a myoepi thelioma.