An asymptomatic pedunculated nodule on the scalp: nodular hidradenoma

Hidradenoma is a relatively rare tumor of appendageal origin. It is clinically characterized by a slow-growing dermal nodule and histologically by well-circumscribed dermal epithelial lobules composed of polygonal clear cells and small darker cells. Pedunculated type and ulceration are rare in hidradenoma.
Here, we report a case of a nodular hidradenoma, pedunculated variety, affecting the scalp in a male patient.
A case of 25-year-old man presented with an asymptomatic solitary nodule on the scalp. It had begun as an asymptomatic papule 1 year ago, gradually progressing to reach its present size of 1 × 2 cm. Occasional history of serous discharge from the nodule was noted since 3 months. On examination, a single, pedunculated, flesh-colored, non-tender, firm nodule was seen (fig. 1). The surface of the nodule was lobulated with a few crusted erosions. His general physical examination was normal. There was no regional lymphadenopathy.
Excisional biopsy was done and sent for histopathological examination. Light microscopic examination revealed a well-circumscribed tumor in the dermis showing a connection to the epidermis focally. Tumor tissue was arranged in lobules separated by fibrovascular septa (fig. 2). Within the lobules, tubular lumina of various sizes, cystic spaces and many proliferating blood vessels were noted. Individual tumor cells were round to polygonal with round to oval nuclei, fine chromatin, inconspicuous nucleoli and abundant eosinophilic to clear cytoplasm (fig. 3). Mucinous material was noted in a few cystic spaces.
Hidradenoma is a rare benign adnexal neoplasm that differentiates towards the eccrine and apocrine apparatus [1]. It is also known as nodular hidradenoma, nodulocystic hidradenoma and acrospiroma. It can occur at all ages, with female preponderance. There is no site predilection [2]. It is sub-divided into two types: apocrine (clear cell hidradenoma) and eccrine (poroid) differentiation. Clear cell hidradenoma is the most common type. Clinically it presents as a slow-growing, asymptomatic, solitary, freely mobile and firm dermal nodule. The lesions may be flesh-colored, red, blue or brown in color. Hidradenomas may be solid or cystic in varying proportions. Uncommonly they are pedunculated like the index case or ulcerated [3]. Local recurrences are common but malignant transformation is very rare [2].
Histopathologically, it is characterized by a well-circumscribed, encapsulated nodular,...


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