Polymastia, or supernumerary breasts, is the medical term for extra breast tissue beyond the typical two. These formations are congenital, present from birth, though often unnoticeable until puberty or hormonal changes.
The appearance of supernumerary breasts can vary considerably. They can range from a fully formed breast, complete with glandular tissue, nipple, and areola, to a small patch of glandular tissue without them. Sometimes, only an extra nipple (polythelia) or just an areola is present. This diverse presentation means “three breasts” can manifest in various ways, from a fully developed extra breast to a subtle additional nipple or tissue.
Causes and Forms of Supernumerary Breasts
Supernumerary breasts develop during early fetal development, specifically between the fourth and sixth weeks of embryogenesis. At this stage, thickened ectoderm strips, known as “mammary ridges” or “milk lines,” form symmetrically on the embryo, extending from the armpit to the groin. Normally, these ridges largely regress, with only pectoral portions developing into typical breasts.
Polymastia occurs when remnants of these mammary ridges fail to regress completely. This incomplete regression leads to extra breast tissue or nipples forming anywhere along this embryonic milk line, though occurrences outside this line are possible. Supernumerary breasts are relatively rare, affecting an estimated 1-6% of the population, with rates varying by ethnicity and gender. For instance, some studies suggest a prevalence of 2-6% in females and 1-3% in males.
Supernumerary breast forms are categorized using a classification system developed by Kajava in 1915, still in use today. These classifications describe the completeness of the extra breast tissue. Type I, for example, is a complete breast with glandular tissue, nipple, and areola, representing what is often considered a “third breast.” Other types include glandular tissue and nipple without an areola (Type II), glandular tissue and areola without a nipple (Type III), or solely glandular tissue (Type IV). The most common type is polythelia (Type VI), involving only an extra nipple.
Associated Health Considerations
Supernumerary breast tissue behaves like normal breast tissue. This means it is susceptible to the same hormonal influences and potential health issues. During hormonal fluctuations like puberty, menstruation, or pregnancy, accessory breast tissue can enlarge, become tender, or cause pain. In cases where glandular tissue is present, it can even lactate during pregnancy or breastfeeding.
Beyond physiological responses, supernumerary breasts can develop various benign and malignant conditions found in typical breast tissue. These include benign growths like fibroadenomas and cysts, or inflammatory conditions such as mastitis and abscesses. Breast cancer can also, though rarely, develop within supernumerary breast tissue, sometimes diagnosed later due to its unusual location. Extra breast tissue can also lead to cosmetic concerns or psychological distress for some individuals.
Diagnosis and Management
Diagnosis typically begins with a physical examination, especially since supernumerary breasts often appear along the embryonic milk line. However, because some forms may be subtle or resemble other skin anomalies like moles, further investigation may be necessary. Imaging techniques like ultrasound or mammography can confirm glandular tissue within the extra formation, especially if not outwardly obvious.
Management strategies vary based on their characteristics and individual concerns. If the tissue is asymptomatic and poses no health risks, observation may be chosen. However, surgical removal can be considered for several reasons, including cosmetic concerns, discomfort, or functional issues like pain or lactation. Surgical intervention is also recommended if there is concern for malignancy or if the tissue causes significant physical or psychological distress.