Painless giant angioleiomyoma in the subfascia of the lower leg.

Angioleiomyoma is rare, benign vascular smooth muscle tumor originating from the tunica media of the veins and arteries. It usually presents as a slow-growing, small, and painful mass arising from the cutaneous or subcutaneous tissue. We report an unusual case of angioleiomyoma that was located in the subfascia of the lower leg and had grown to massive size (≤5 cm in diameter) during a 3-year period without pain. A 57-year-old female presented with a 3-year history of a slowly growing pain-free mass on the anterior portion of her right lower leg, just above the ankle joint. Magnetic resonance imaging revealed a well-demarcated lesion, measuring approximately 5 × 4 cm, located deep to the fascia of the anterior compartment of the lower leg and adjacent to the tibia, fibula, and interosseous membrane. The mass was isointense to skeletal muscle on T(1)-weighted images, hyperintense and heterogeneous on T(2)-weighted images, and enhanced intensely and heterogeneously after the intravenous administration of contrast medium. We performed an excision, and histologic analysis revealed smooth muscle cells surrounding blood vessels of various sizes. From these histologic findings, the tumor was diagnosed as a solid form of angioleiomyoma. The present case was unique in that the tumor grew to a massive size without pain and was located deep to the fascia.