Endometrial stromal nodule with smooth and skeletal muscle components simulating stromal sarcoma

A stromal nodule was found in a hysterectomy specimen from a 29-year-old woman with a history of menometrorrhagia. Endometrial curettings had revealed stromal cells admixed with well-defined bundles of smooth muscle cells, a finding that had led to the erroneous diagnosis of stromal sarcoma invading the myometrium. Ultrastructural and immunohistochemical studies demonstrated several components: stromal cells, smooth muscle cells, sex-cord-like structures, and a hitherto undescribed component of skeletal muscle cells.