Solitary nodule over the labia majora

Histopathology showed tubular and cystic structures in the dermis [Figure - 2]. The tubules and glands were lined by tall columnar cells with decapitation secretion [Figure - 3]. The cystic structures were lined by apocrine cells with abundant eosinophilic cytoplasm [Figure - 4]. The features were suggestive of hidradenoma papilliferum.

Discussion

Hidradenoma papilliferum is a rare, benign, cystic, papillary apocrine gland tumor that occurs almost exclusively in the skin of the anogenital region in women. ^[1] It occurs between the ages of 25 and 40 years. ^[2] It usually presents as an asymptomatic nodule measuring 1 to 40 mm in size. The most common site is the labia majora, but it may occur elsewhere on the vulva or perianal area. Other ectopic sites include eyebrow, eyelid, nose, chest and external auditory canal. ^[3] Ectopic hidradenoma papilliferum occurs more frequently in the head and neck region. It is rarely associated with Paget′s disease and invasive squamous cell carcinoma. ^[4]

The tumor represents an adenoma with apocrine differentiation. Hidradenoma papilliferum can also originate from recently described anogenital mammary-like glands. ^[5] Located in the dermis, it is well circumscribed and surrounded by a fibrous capsule. The tumor is usually partly cystic and comprises of both papillary and glandular areas. The lumina are lined by single or double layer of cells consisting of a luminal layer of secretory cells, which show active decapitation secretion, and an outer layer of small cuboidal cells. ^[6]

The tumor is usually mistaken for a cyst, polyp or an angioma. The histopathological differential diagnosis includes tubular apocrine adenoma, syringocystadenoma papilliferum, apocrine hydrocystoma and apocrine fibroadenoma. ^[6] Simple excision is curative.