Intramuscular Myxoma

**Semantic type:** Neoplastic Process

**Definition:** A benign, painless soft tissue tumor that arises in a muscle, usually in a large muscle of the thigh, buttocks, shoulder, or upper arm. It is associated with point mutations of the GNAS gene. Grossly it is characterized by a gelatinous and lobulated cut surface. Morphologically it is composed of uniform spindled and stellate-shaped cells without atypia. The cells are separated by myxoid stroma. No recurrences have been reported.