Polymastia: More than Just a Benign Accessory in the Axilla

Background: Accessory breast tissue (polymastia) typically occurs anywhere along the thoracoabdominal region of the milk line, such as the axilla (most common), chest wall, and vulva. Accessory breast tissue itself is a normal variant and is subject to the same benign and malignant processes that occur in normal breast tissue. Although it is present in about 2 – 6% of females and 1 – 3% of males, it is commonly misdiagnosed in clinical medicine. While ectopic breast cancer is rare, accounting for only 0.3% of all breast neoplasms, it is important for the radiologist to be familiar with its imaging appearance. It is also important to know that the axilla can be a challenging location for imaging, often better assessed on ultrasound compared to mammography and breast MRI. This exhibit presents a pictorial review of the benign and malignant pathologies that occur in accessory axillary breast tissue.

Learning Objectives: 1. List the common locations of accessory breast tissue.
2. Recognize the typical imaging appearance of accessory breast tissue in the axilla.
3. Understand and recognize benign and malignant processes that affect accessory breast tissue.

Abstract Content/Results: Pictorial review which includes:
1. Normal appearance of accessory breast tissue on ultrasound, mammogram, and MRI.
2. Case series reviewing benign processes in accessory breast tissue, including lactational change and benign masses like fibroadenomas and hamartomas.
3. Cases series reviewing malignant processes involving accessory breast tissue, including ductal carcinoma in situ, invasive ductal carcinoma, and invasive lobular carcinoma.

Conclusion: Upon completion of this educational exhibit, participants will be able to recognize accessory breast tissue in the axilla and consider it when evaluating patients who present with a palpable axillary mass, thus potentially avoiding an unnecessary biopsy. The reader will also understand that the same benign and malignant pathologies found in normal breast tissue are also seen in accessory breast tissue. Compared to the normal breast, imaging of the axilla often relies on ultrasound rather than mammography and MRI. When assessing the axilla, a focused clinical history with a detailed evaluation of a patient’s risk factors can help ensure prompt and accurate diagnosis.