Scalp epithelioid glomus tumor: a rare location.

A 35-year-old Japanese woman was referred to our hospital with a small, asymptomatic tumour on her scalp. The lesion had been present for approximately 3 years and was not associated with any pain or tenderness. Physical examination revealed a 1-cm diameter, firm, and slightly reddish subcutaneous tumour on her scalp (Fig. 1). Clinically, the lesion was initially thought to be a pilomatricoma, epidermal or trichilemmal cyst, osteoma cutis, angiosarcoma or other adnexal tumour, and an excisional biopsy was performed. At biopsy, a well-circumscribed ovoid mass was isolated at the interface of the dermis and subcutis. At low magnification, there were sheets of tumour cells and numerous stenopeic blood vessels, which were embedded in a fibrous stroma (Fig. 2a). There were no “staghorn” branching capillaries, which are regarded as a characteristic diagnostic feature of haemangiopericytoma (1). Connective tissue was focally hyalinized and small aggregates of tumour cells were isolated. Individual tumour cells were polygonal shaped with indistinct cell borders and abundant, pale, eosinophilic cytoplasm. Most of the nuclei were round-to-oval and had delicate, marginated chromatin and distinct small basophilic nucleoli (Fig. 2a inset). Abnormal mitoses were not observed. There was no striking concentric pattern around the numerous blood vessels implicating myopericytoma (2, 3). Immunohistochemically, the tumour cells were positive for alpha smooth muscle actin (Fig. 2b), and negative for CD34, CD31, Factor 8 and desmin (Fig. 2c). From these findings, the diagnosis of epithelioid glomus tumour was finally made. The patient has since had no evidence of recurrence or other complications half a year following her surgery.