[Ectopia of mammary tissue]

Ectopic breast tissue may represent the complete breast (accessory breast), glandular tissue without areola or nipple (aberrant breast tissue), or exclusively the nipple (polythelia). Localization is along the embryonic milk ridge extending from the axilla to the vulva. Only rarely, is ectopic tissue found outside of the milk ridge. Most frequently affected are the axilla, the breast itself, and its close neighbourhood. Ectopic breast tissue may rarely give rise to tumours such as fibroadenoma or carcinoma.