Polythelia (Supernumerary Nipple): Clinicopathological Characterization of an Atavistic Lesion

Polythelia refers to the presence of additional nipples typically located along the "milk line." While its atavistic nature and associations with congenital anomalies are well documented, its clinicopathological features are less defined. This retrospective study reviewed 131 lesions diagnosed as polythelia in 112 patients from 1999 to 2024. The median age of patients at the time of excision was 28 years (range: 6 months to 72 years). Most (101, 90.2%) patients were female. Lesions were located around the breast (42%), chest (28%), axilla (15%), inframammary fold (8%), and abdomen (6%). Histopathology of 107 lesions showed breast glandular tissue in 83 (77.6%). Sixty (72.3%) of these also exhibited nipple-type smooth muscle, and 24 (22.4%) contained smooth muscle only. Among lesions with glandular tissue, 66/83 (79.5%) had ducts, and 17/83 (20.5%) exhibited lobules. In addition, 54 lesions, initially misdiagnosed as accessory nipples, were reclassified as "clinical pseudo-polythelia." The latter included nevi (48.1%), seborrheic keratosis (13.0%), and hemangiomas (3.7%). Based on our study, polythelia (when encountered in routine practice) is typically a benign and solitary lesion, excised for cosmetic reasons in younger females. Although one lesion of ductal carcinoma in situ in polymastia, under a polythelia, was encountered, no tumor with any nipple or breast lesion was identified in polythelia per se. No other congenital diseases or medical condition was identified in our cohort; however, there were ipsilateral or contralateral malignancies in the native breast in 7.6% of the lesions. Recognition of polythelia is essential to distinguish it from other skin lesions.