Case 1: A 23-year-old black woman (gravida 2, para 2) presented two weeks postpartum with painless swelling of her left axilla. Her medical history was notable for sickle cell anemia. Her pregnancy was unremarkable, resulting in the spontaneous vaginal delivery of a healthy infant. Her immediate postpartum course was unremarkable, and she was currently breast-feeding. She denied fever. On physical examination, a mobile 3 × 4 cm non-tender swelling was noted in the left axilla (see Figure 1). There were no signs of local, regional or systemic infection.
Case 2: A 22-year-old white woman (gravida 1, para 1) presented three days following spontaneous vaginal delivery with painless swelling of her right axilla. She had an unremarkable medical history, and her prenatal course was unremarkable. She denied any fever or signs of systemic infection. On physical examination, a 3 × 3 cm mobile, painless swelling was noted in the right axilla (see Figure 2). A small amount of cloudy fluid was expressed through a central punctum within the swelling.
The answer is A: accessory mammary tissue. In structural anomalies or anatomic variants of the breast, the presence of a supernumerary nipple is more common than the presence of supernumerary breast tissue with or without an associated nipple-areolar. Accessory mammary tissue is more common in women (2 to 6 percent) than in men (1 percent).1 Incidence also varies among ethnic groups; accessory mammary tissue is more common in Asian women than in black or white women.2
Hidradenitis suppurativa is an infection of the apocrine glands, most commonly of the axillae and groin. Drainage and scarring are common sequelae, and the process is often bilateral.
Lipomas are common subcutaneous fatty tumors. They are often hard to see but easy to palpate. Most are asymptomatic and, on physical examination, appear as rubbery, mobile lesions, most commonly on the trunk, neck and upper extremities.
Sebaceous cysts are less commonly found in the axillae, appearing most often on the scalp, face and trunk. Often, a central punctum is visible. Rapid growth is usually due to infection and presents as an inflamed, tender mass.
Axillary adenopathy most commonly accompanies an infectious process. Neither patient presented with a history consistent with infection. The large size of these masses would also be unusual for adenopathy.
Embryologically, mammary development occurs during the fourth and fifth weeks of gestation in primitive galactic bands that extend from the axilla to the groin. As gestation progresses, the galactic band enlarges to form the mammary ridge, and the remainder of the primitive galactic band regresses. If the regression is incomplete or if residual cells remain along the milk line, the possibility exists for the formation of supernumerary nipples and/or breast tissue.3
Accessory nipples are often overlooked as moles or nevi on the anterior chest wall. Patients with accessory axillary mammary tissue often present with complaints of pain or swelling in the involved axilla. Axillary breast tissue can also undergo monthly premenstrual changes. Symptoms may be exacerbated during pregnancy and lactation as well.4
Clinically, ectopic breast tissue has the same occurrence of benign and cancerous change as normal breast tissue and should be managed as such. While most patients can be managed conservatively, surgical excision is an option for those patients with persistent pain or swelling, or those who desire excision for cosmetic reasons.5