In the fourth week of gestational development, a pair of epidermal “mammary ridges” develops along either side of the body from the area of the future axilla to the future inguinal region and medial thigh. These ridges normally regress, except at the normal location of the adult breasts. The remnant of the mammary ridge produces the primary bud in the fifth gestational week. This bud grows into the underlying dermis and in the tenth week begins to branch. By the twelfth week, several secondary buds form, which lengthen and branch throughout the remainder of gestation. Ultimately, the ducts canalize and, at birth, the mammary glands consist of 15 to 25 lactiferous ducts that open onto a small depression known as the mammary pit. Proliferation of the underlying mesoderm usually converts this pit to an everted nipple within a few weeks after birth (1).

The breasts of many normal male and female infants are transiently hypertrophied at birth, sometimes producing small amounts of clear or white fluid, termed witch’s milk. This hypertrophy normally regresses by 2 to 3 months of age. This hypertrophy is presumed a consequence of persistent circulating maternal hormones (2). Many pubertal boys have transient unilateral or bilateral firm, sometimes painful, subareolar masses that disappear within a year of onset. A girl’s pubertal breast development is frequently asymmetric and proceeds through several stages, starting with an increase in the areolar diameter between ages 8 and 13, with full breast development completed between ages 12 and 19.

It is not infrequent for one or more supernumerary nipples (polythelia) or supernumerary breasts (polymastia) to form along the line of the mammary ridges (1). The most common location is just caudad to the normal breast. Supernumerary nipples are equally common in males as females. More rarely, an ectopic nipple forms off the line of the mammary ridges as a consequence of migration of the mammary tissue. Supernumerary breasts most frequently become evident at puberty or during pregnancy, when they enlarge or even lactate. Although uncommon, ectopic breast tissue may be identified distant from the mammary ridge or milk line, (i.e., the buttock, back, or thigh). Abnormally located breast tissue may not only be cosmetically and psychologically distressing, but may cause significant functional deformity as well, particularly if located in the axilla. Both supernumerary nipples and breasts have been reported to undergo malignant transformation (3). For these listed reasons, excision of the supernumerary breast and/or nipple is usually indicated.

The absence of the breast (amastia) is uncommon but of considerable concern to the parents when identified. A more common and extensive form of aplasia, termed Poland syndrome, includes deficits of the chest wall, including muscle, cartilage, ribs, and soft tissue in addition to the breast and/or nipple (4). The embryologic or genetic events responsible for Poland syndrome are unknown (5), and a discussion of reconstruction is not pursued here. Bilateral absence of the breast may occur in ectodermal dysplasia patients. When unilateral amastia alone is identified, reconstruction of the breast via augmentation mammaplasty is best pursued following adolescent breast development so long-term satisfactory symmetry can be best achieved.

Inflammation or infection of breast tissue may occur in the neonatal period, this condition referred to as mastitis neonatorum. It typically presents as a subareolar abscess in the second or third week of life manifested by erythema, swelling, tenderness, and occasionally discharge at the location of the breast bud, accompanied by fever and agitation. The responsible microorganism is usually Staphylococcus aureus (6). Although the precise etiology is unclear, it is likely in part a consequence of breast stimulation by maternal hormones. The degree of physiologic breast enlargement does not, however, correlate with the incidence (7). The preferred management of mastitis neonatorum includes antibiotics and needle aspiration of any abscesses. Aggressive surgical treatment such as incision and drainage or excision, should be avoided because this can result in undesirable disturbed growth of the breast bud, potentially causing significant hypoplasia, deformity, and/or asymmetry in subsequent years. If there is recurrence of the abscess, then repeat aspiration should be performed rather than aggressive surgical drainage. Close follow-up is essential to ensure response because insufficient therapy may result in further destruction of normal tissue.

Infection and abscess in the postpartum lactating breast is a well-described entity (8). Presentation typically includes local pain, tenderness, erythema, and occasionally purulent discharge. Ultrasound examination can sometimes be helpful to identify abscesses. Treatment employs adequate surgical drainage for abscess formation and antibiotics for cellulitis. The concerns relating to future breast development are less important. Illicit use of intravenous drugs may also lead to infections of the breast. A choice of injection site might include the superficial vessels of the breast, and the lack of aseptic technique or the use of nonsterile hypodermic needles can result in breast abscess at the site of injection. Incision and drainage in conjunction with antibiotics for cellulitis, and counseling to avoid recurring episodes are indicated.

Significant blunt trauma to the breast may result in fat necrosis in adolescents. Treatment is usually conservative, and observation alone is typically adequate. Occasionally, infection in the form of abscess or cellulitis is treated with antibiotics and drainage. Undrained abscesses may lead to additional destruction of normal breast tissue; if extensive, cosmetic deformity and asymmetry may ensue.

Fibrocystic change of the breast, and its associated symptoms referred to as cyclical mastopathy, is a frequent finding in premenopausal women (30% to 40%), but is only occasionally present in adolescent girls (9). It manifests as breast swelling and tenderness occurring primarily in the luteal phase of the menstrual cycle. Examination may reveal no abnormalities, there may be discrete cysts, or the breast may be diffusely nodular. Cysts may be aspirated in the office setting or under ultrasound guidance. Only cyst fluid that is bloody or serosanguineous requires cytopathologic examination. If the cyst does not recur following 2 to 4 months of observation, the patient can simply be followed by serial examinations. However, if a single dominant nodule persists over several months and is not clearly a fibroadenoma, excisional biopsy may be necessary. Histologic findings in fibrocystic breast tissue been classified into prognostic categories: nonproliferative, proliferative change without atypia, and proliferative change with atypia. Most young women with fibrocystic change possess nonproliferative histology and are at no increased risk for breast cancer. Only patients with both proliferative changes and atypia appear to have a clearly increased risk of breast cancer (10).