Accessory breast tissue, also known as supernumerary breasts, refers to the presence of additional breast tissue beyond the usual two. This common congenital anomaly is present from birth, though often noticeable later in life. It involves the development of extra breast tissue, extra nipples, or a combination of both, appearing in various locations on the body. While generally harmless, understanding this variation provides clarity.
What Are Accessory Breasts?
Accessory breasts encompass different forms, primarily polymastia and polythelia. Polymastia is additional glandular breast tissue, which may or may not include a nipple and areola. Polythelia is extra nipples or areolae without underlying glandular breast tissue. These conditions can occur independently or together, presenting a spectrum of appearances.
The appearance of accessory breast tissue can vary significantly. It might manifest as a fully developed breast, although this is rare, or simply as a small, palpable lump of tissue. Some individuals may observe just a pigmented patch of skin or a distinct, extra nipple that can resemble a mole. This variation in presentation stems from its embryological origins.
Accessory breasts develop from remnants of the embryonic “milk line” (mammary ridge) during fetal development. This structure forms as a band of ectodermal cells, extending from the armpit to the groin, typically around the fourth to sixth week of gestation. Normally, most of this milk line regresses, leaving behind only the two primary breast areas on the chest. Accessory breast tissue results from the incomplete regression or displacement of these embryonic cells.
Classification systems categorize accessory breast tissue types. Kajava’s classification, established in 1915, is widely used. It describes eight categories based on the presence of glandular tissue, nipple, areola, or even a patch of hair. For instance, Class I includes a complete breast with all three components, while Class IV represents only glandular tissue without a nipple or areola. Class VI, known as polythelia, involves only an extra nipple.
Common Locations of Accessory Breasts
The most common locations for accessory breast tissue are found along the embryonic “milk line.” This line extends from the axilla (armpit) down the chest and abdomen, reaching towards the groin and inner thigh. The axilla is the most frequent site for polymastia, accounting for about 60-70% of cases, often presenting as a palpable thickening. Other common areas along this line include the inframammary fold (below the regular breast), the upper abdomen, and the groin region, sometimes adjacent to the vulva.
While most accessory breast tissue appears along this predictable milk line, rarer instances of “ectopic” breast tissue can occur. Ectopic tissue develops outside the typical milk line, appearing in less common body areas. These unusual locations might include the back, thigh, face, neck, buttocks, ear, knee, hip, shoulder, or upper extremities. Such occurrences are less frequent but highlight the diverse possibilities of this variation.
Addressing Health Concerns and Treatment
Accessory breast tissue is often asymptomatic, with many unaware of its presence unless detected incidentally. Because this tissue contains normal breast components, it responds to hormonal fluctuations, similar to regular breast tissue. This hormonal sensitivity may lead to symptoms like swelling, tenderness, or pain, particularly during menstruation, pregnancy, or lactation. Some individuals may also experience milk secretion from an accessory nipple.
Like typical breast tissue, accessory breasts can develop various benign conditions, including cysts or fibroadenomas. Though rare, cancer can also arise in accessory breast tissue. Ductal cancer is the most common malignancy found in these extra tissues, with infiltrating ductal carcinoma representing a significant percentage of cases. While the risk of cancer is generally low, it is present, and any suspicious changes warrant evaluation.
Diagnosis of accessory breast tissue typically begins with a physical examination to identify any palpable abnormalities. If uncertainty or suspicion of underlying issues exists, imaging techniques may be employed. Ultrasound is commonly used to confirm glandular tissue, and in complex cases, magnetic resonance imaging (MRI) may be performed. These imaging studies help differentiate accessory breast tissue from other conditions like swollen lymph nodes or benign fatty lumps.
Treatment for accessory breast tissue depends on symptoms or health concerns. If asymptomatic and causing no discomfort, observation may be recommended. For persistent pain, discomfort, or cosmetic concerns, surgical removal is the primary treatment option. If the tissue primarily consists of fullness, liposuction may be used. Excision of excess tissue is often recommended if there is associated loose skin. Management of cancer in accessory breast tissue generally follows the same guidelines as for cancer in normally positioned breasts.