It is possible for a person to have three or more breasts, a condition known as supernumerary breast tissue or accessory breasts. This is a congenital anomaly, meaning it is present from birth, and is a relatively common variation in human anatomy. The extra tissue can range from a small, barely noticeable patch of skin to a fully formed extra breast, complete with glandular tissue and a nipple-areola complex. This phenomenon is found in an estimated 2 to 6% of women and 1 to 3% of men, though many remain unaware they have the condition until puberty or pregnancy.
Polymastia and the Embryological Origin
The existence of extra breast tissue is rooted in human embryonic development. During the fourth and fifth weeks of gestation, thick ridges of specialized skin tissue, known as the mammary ridges or “milk lines,” form on the embryo’s ventral surface. These two ridges extend from the armpit down to the inner thigh region. Typically, the tissue along these lines regresses, leaving only the two main breast buds on the chest.
When this regression process is incomplete, remnants of the mammary ridge tissue persist, resulting in accessory breast tissue. The specific medical term for the presence of extra glandular breast tissue is Polymastia, which describes a complete extra breast. Conversely, Polythelia refers only to the presence of an extra nipple or areola without underlying glandular tissue, which is the most common form of this anomaly. These accessory tissues can develop anywhere along the original milk lines.
Common Locations of Ectopic Breast Tissue
Ectopic breast tissue is most frequently located along the path of the original embryonic milk line. This line extends bilaterally from the axilla down to the groin area. The most common site for accessory breast tissue (Polymastia) is the axilla, often presenting as an extension of the main breast tissue.
This tissue in the armpit often presents as a bulge or thickening and may not be noticed until it enlarges. Other common locations along the milk line include the chest wall below the typical breast, the abdomen, and occasionally the vulva. While rare, accessory breast tissue has been reported in locations entirely outside this established line, such as the face, neck, back, and thigh.
Functional Characteristics and Associated Symptoms
Ectopic breast tissue containing glandular elements is functionally identical to normal breast tissue and is hormonally responsive. The tissue can swell, become tender, or feel painful in response to hormonal fluctuations of the menstrual cycle. This accessory tissue often becomes more noticeable during periods of high hormonal activity, such as menarche, pregnancy, or breastfeeding.
The glandular tissue can produce milk, especially when located in the axilla, leading to unexpected milk secretion. Furthermore, this tissue is subject to the same health risks as normally positioned breasts, including the formation of benign conditions like cysts and fibroadenomas. Although rare, accessory breast tissue can also develop breast cancer, making regular monitoring important for those with significant glandular presence.
Diagnosis and Treatment Options
Diagnosis is often made clinically during a physical examination, particularly if the tissue is symptomatic or visually prominent. Since the tissue can sometimes be mistaken for a normal fat deposit or a swollen lymph node, imaging techniques are frequently used for confirmation. An ultrasound can help determine if the mass contains actual breast glandular tissue, which appears indistinguishable from regular breast tissue on the scan.
If the accessory tissue is asymptomatic, small, and purely a cosmetic concern, observation is often recommended. Surgical excision is the treatment of choice if the tissue causes significant discomfort, pain, or restriction of movement, especially in the armpit. Removal is also warranted if there is concern for underlying pathology, such as a suspicious mass, or if the tissue is cosmetically undesirable to the patient.