Soft tissue myoepithelioma arising over the scalp: Rare case report

Myoepithelioma is a well-known tumour in the salivary glands and breasts in adults. It is exceptionally rare in soft tissue and in children.Myoepithelial tumours of soft tissue are categorised as tumours of uncertain differentiation (WHO Classification of Tumours 5ed-Soft Tissue and Bone Tumours). They are a group of uncommon neoplasms with equal sex predilection and a wide age range (median age:40years). These tumours show extensive spectrum of cytological, architectural, and heterogenous immunophenotypic profile. This case report presents a 36-year-old male who visited surgery OPD with complaints of a gradually increasing painless swelling over the scalp for 5 years. Clinical examination showed a well demarcated, irregular, soft to firm, non-compressible and non-reducible swelling over left side of scalp measuring 11x3cm. No signs of inflammation/pulsations/punctum over the swelling. Skin over the swelling appeared normal. Pre operative diagnosis of venous malformation or sebaceous cyst was made. Radiological assessment was not done. Mass was excised keeping the capsule intact and the specimen was sent for histopathological assessment. Final diagnosis of Soft Tissue Myoepithelioma (Scalp) was made.Immunohistochemistry showed diffuse strong positivity for S-100 protein & myogenic marker Calponin. Myoepithelial tumours of soft tissue arise on the limbs and limb girdles (75%; lower more frequently than upper); others arise on the trunk. They are rarely located over scalp (head & neck region). Myoepitheliomas lack tubulo-ductal differentiation histologically. Because of the variable appearance of myoepithelial cells and their phenotype, the histopathological diagnosis is challenging. Most myoepithelial tumours are benign, show indolent behaviour, rarely metastasize; showing recurrence in 20% cases. Myoepithelial carcinomas recur and metastasize (40-50% of cases); with disease related death in 13-43% of patients. Therefore, prompt identification using histopathology and immunohistochemistry becomes necessary.