Abnormal Breast Development

Congenital Abnormalities
The most frequently observed abnormality seen in both sexes is an accessory nipple (polythelia). Ectopic nipple tissue may be mistaken for a pigmented nevus, and it may occur at any point along the milk streak from the axilla to the groin. Rarely, accessory true mammary glands develop. These are most often located in the axilla (polymastia).

During pregnancy and lactation, an accessory breast may swell; occasionally, if it has an associated nipple, the accessory breast may function.

Hypoplasia is the underdevelopment of the breast; congenital absence of a breast is termed amastia. When breast tissue is lacking but a nipple is present, the condition is termed amazia. A wide range of breast abnormalities have been described and can be classified as follows:

• Unilateral hypoplasia, contralateral normal
• Bilateral hypoplasia with asymmetry
• Unilateral hyperplasia, contralateral normal
• Bilateral hyperplasia with asymmetry
• Unilateral hypoplasia, contralateral hyperplasia
• Unilateral hypoplasia of breast, thorax, and pectoral muscles (Poland's syndrome)

Most of these abnormalities are not severe. The most severe deformity, amastia or marked breast hypoplasia, is associated with hypoplasia of the pectoral muscle in 90% of cases, but the reverse does not apply. Of women with pectoral muscle abnormalities, 92% have a normal breast. Congenital abnormalities of the pectoral muscle are usually manifested by the lack of the lower third of the muscle and an associated deformity of the ipsilateral rib cage. The association among absence of the pectoral muscle, chest wall deformity, and breast abnormalities was first recognized by Poland in 1841. The original description, however, did not note the concomitant abnormalities of the hand (synbrachydactyly, with hypoplasia of the middle phalanges and central skin webbing), and considerable controversy has evolved concerning the validity of the eponym for this congenital syndrome.

Acquired Abnormalities
The most common - and avoidable - cause of amazia is iatrogenic. Injudicious biopsy of a precociously developing breast results in excision of most of the breast bud and subsequent marked deformity during puberty. The use of radiation therapy in prepubertal girls to treat either hemangioma of the breast or intrathoracic disease can also result in amazia. Traumatic injury of the developing breast, such as that caused by a severe cutaneous burn, with subsequent contracture, can also result in deformity.

M. P. Osborne: Department of Surgery, Joan and Sanford I. Weill Medical College, Cornell University