Abstract

Mammary-type tissue in the vulva was first described in 1872, and has been rarely reported in the literature. This tissue was previously considered as ectopic breast tissue that occurs due to incomplete regression of the milk line. Similar to native breast tissue, ectopic mammary tissue is hormone-sensitive and can develop benign changes, like fibroadenoma, as well as malignant changes. A more recent theory suggests that these benign and malignant mammary-type entities are arising from mammary-like anogenital glands, which constitute normal vulvar components. We report a case of a 41-year-old woman, who presented with a chronic asymptomatic cyst on the left vulva that eventually became uncomfortable, especially on standing. The cyst was located in the labia minora measuring 1.0 x 0.5 cm with no erythema or other skin abnormalities identified. Excision of the lesion and subsequent microscopic examination showed a circumscribed intracanalicular stromal proliferation around compressed branching glandular structures resembling a mammary fibroadenoma. The epithelial component comprised normal luminal glandular cells and subjacent myoepithelial cells.  The stromal cells were normochromatic spindle cells without significant hypercellularity, atypia, or mitotic activity. Architecturally, the spindled stromal cells lined short pseudovascular spaces reminiscent of pseudoangiomatous stromal hyperplasia (PASH) of the breast, a feature that can be seen in fibroadenomas.  We bring to attention this rare diagnosis and the importance of considering it in the presence of a vulvar lesion. The malignant and recurrence potential of mammary-type tissue necessitates excision with clear margins and close monitoring of these patients.