Accessory breast

Accessory breast (also known as polymastia or supernumerary breast) refers to the presence of additional breast tissue beyond the normal two breasts. This tissue develops from remnants of the embryonic mammary ridge (milk line), which extends from the axilla to the inguinal region bilaterally.

Key Features

• Prevalence: Reported in approximately 1–6% of the general population, with higher rates in certain ethnic groups. It is more common in women but can also occur in men.

• Location: Most commonly found in the axillary region, but can occur anywhere along the milk line. Rarely, ectopic breast tissue may appear outside the milk line.

• Classification: Ranges from a complete accessory breast with nipple, areola, and glandular tissue to isolated findings such as:

  • Polythelia — supernumerary nipple only (most common variant)

  • Polymastia — supernumerary glandular tissue with or without a nipple