History:

 A 30-year-old female presents with a soft, palpable mass in the left axilla. The patient reported discomfort during her menstrual cycle. No significant family history of breast cancer.

She was referred to ultrasound to evaluate the axillary region.

Ultrasound Findings and Description:

●      A well-defined, hypoechoic tissue extending into the axillary region, measuring 3.0 cm x 2.0 cm. The echotexture resembles normal breast parenchyma.

●     Homogeneous echotexture similar to that of normal glandular breast tissue.

●     Minimal vascularity noted within the tissue.

●     No abnormal or enlarged lymph nodes visualized in the axilla.

●     No signs of surrounding edema or infiltration.

Diagnosis: Accessory axillary breast tissue (polymastia).

Differential Diagnosis:

1. Lipoma: A benign, well-defined, echogenic fatty mass, usually compressible on ultrasound, differing in echotexture from breast tissue.
2. Lymphadenopathy: Enlarged, hypoechoic lymph nodes, but lymph nodes generally appear more oval with central hilar fat and typically do not mimic breast tissue.
3. Sebaceous Cyst: Well-circumscribed, round, and hypoechoic, but without the internal tissue architecture resembling breast parenchyma.

Discussion:

●     Accessory breast tissue, also known as polymastia, occurs due to incomplete regression of the mammary ridge during embryonic development. It is most commonly found in the axilla and can be hormonally responsive, causing discomfort or swelling during menstruation or pregnancy.

●     Ultrasound findings of well-defined, homogeneous, hypoechoic tissue resembling breast parenchyma confirm the diagnosis.

●     While typically benign, excision may be considered if symptomatic or for cosmetic reasons. Follow-up imaging is not usually required unless new symptoms arise.

●     It is essential for radiologists to be aware of the imaging appearance and clinical presentations of accessory breast tissue to avoid misdiagnosis of this normal variant.