Myopericytoma of the hand.

Myopericytoma is a rare benign smooth-muscle cell neoplasm of the subcutaneous soft tissues that is primarily found in young adults with a male predominance. We present the clinical, radiologic, and histopathologic features of a longstanding myopericytoma of the hand. We emphasize the features that help the radiologist and pathologist to accurately characterize this entity. Radiologic evaluation, particularly MRI, plays a crucial role in differentiating myopericytoma from other soft tissue masses. Characteristic MR features include a well-demarcated lesion with intense post-contrast enhancement, isointensity to muscle on T1-weighted imaging, and hyperintensity on T2-weighted imaging, often with a central vascular pedicle. Histopathologic examination reveals a concentric perivascular growth pattern, which helps to distinguish myopericytoma from other soft tissue tumors. Immunohistochemically, these myoid cell neoplasms stain positive for alpha-smooth muscle actin and h-caldesmon, lack nuclear atypia, and are not highly proliferative (relatively low Ki-67 index and very low mitotic activity). The vast majority stain negative for desmin and CD34. Treatment typically involves complete surgical resection, with excellent prognosis and rare recurrence. Despite its rarity, awareness of this entity is important for clinicians who encounter soft tissue masses of the extremities.