Myxoid variant of epithelioid smooth muscle tumor.

The light-microscopic and ultrastructural features of a paravaginal epithelioid smooth muscle tumor that contained prominent myxoid stroma are reported. Because of its prominent myxoid component and the soft tissue location, this tumor was difficult to classify by histologic features alone. The ultrastructural studies demonstrated a constellation of features that have been accepted to be indicative of smooth muscle origin. The histogenesis and differential diagnosis are discussed. The elucidation of the biologic behavior of this peculiar variant of smooth muscle tumor awaits accumulation of further cases.