Supernumerary nipples (SNs) are a common minor congenital malformation that consists of nipples and/or related tissue in addition to the nipples normally appearing on the chest. SNs are located along the embryonic milk lines. Ectopic SNs are found beyond the embryonic milk lines. The embryonic milk line is the line of potentially appearing breast tissue as observed in many mammals. In humans, the embryonic milk line extends bilaterally from a point slightly beyond the axillae on the arms, down the chest and the abdomen toward the groin, and is generally thought to end at the proximal inner sides of the thighs, although SN has been described on the foot. SNs can appear complete with breast tissue and ducts and are then referred to as polymastia, or they can appear partially with either of the tissues involved.
The classification established by Kajava in 1915 is still valid :
Although this classification is clear, encountering interchangeable terms and misnomers when dealing with the SN complex is not surprising because of the variability in morphologic patterns.
The paucity of descriptions of SNs in medical writings is probably due to its relatively minor clinical significance. However, the subject of SNs has been very popular in the last 2 decades because of the dilemma of possible associated malformations and diseases. The occurrence of SNs has been documented since Roman times and featured in legends and ethnic mythology prior to that time. SNs, and particularly polymastia, were attributed to increased femininity and fertility. Ancient artists depicted the goddess of Artemis of Ephesus and the Phoenician goddess of fertility, Astrate, like other ancient deities, as having row upon row of breasts on their chests. Anne Boleyn, the wife of King Henry VIII, was known to have a third breast. SNs in men were a sign of virility and endowed them with divine powers. Nowadays, film stars expose their SNs in the cinema with this same effect.
The first medical report dates back to 1878 when Leichtenstern estimated the prevalence of SNs to be 1 in 500 (0.2%).
SN features are found in a number of syndromes, but, in most cases, it is probably a chance finding. These syndromes include Turner syndrome, Fanconi anemia, and other hematologic disorders ; ectodermal dysplasia; Kaufman-McKusick syndrome; Char syndrome; Simpson-Golabi-Behmel syndrome; and epibulbar lipodermoids associated with preauricular appendages syndrome. Numerous sporadic publications linked SNs to an association with anomalies or diseases, but such an association is probably only a chance finding. Such associations of SNs include the following:
In 1979, Méhes drew attention to the association of SNs and other anomalies. The claim that 40% of SNs investigated also had renal involvement was striking. This figure was later corrected to 23-27%.[8, 9] The renal involvement was infectious, a malformation, or neoplastic but mainly due to an obstructive disturbance.
In the following decade, numerous publications supported the claim for a close association of SNs and a renal anomaly, but many others could not find evidence to support such an association, which remains controversial.
The Medscape Reference article Disorders of the Breast may be of interest.
Saint-Hilaire in 1836 and Darwin in 1871 advanced the concept of development of the human race from primitive animals; thus, they also considered the supernumerary nipple as an atavistic structure deriving from the milk line of mammals. Similarly, ectopic supernumerary nipple found on the vulva may express an atavistic structure because the breasts of dolphins and whales are in that location, or ectopic supernumerary nipple on the back, the scapula, and the shoulder[31, 32, 33] is reminiscent of the nutria and hutia (rodents) with a similar location of the breasts.
Between the fourth and fifth weeks of embryogenesis, an ectodermal thickening forms symmetrically along the ventral lateral sides of the embryo. This epidermal ridge extends from the axillary region to the inner side of the thigh to form the embryogenic milk (or mammary) line. During the second and third embryogenic months, the glandular elements of the breasts are formed near the fourth and fifth ribs, with regression of the rest of the thickened ectodermal streaks. In the case of failure of a complete regression, some foci may remain to result in a supernumerary nipple. This can develop into a supernumerary complete breast (polymastia) or into any other supernumerary nipple variant according to the Kajava classification.
The prevalence of supernumerary nipples varies with different reports. The prevalence is 0.22% in a Hungarian population, 1.63% in black American neonates, 2.5% in Israeli neonates, 4.7% in Israeli Arabic children, and 5.6% in German children. These variabilities are attributed at least partially to differences in geographic regions, ethnic groups, and methodology, including methods of physical examination, as well as the age groups participating in the studies.
The male-to-female ratio for supernumerary nipples differs in various studies, but, most often, the studies show a male predominance as high as 1.7:1.
Usually, the supernumerary nipple remains undetected or asymptomatic. Occasionally, the supernumerary nipple is noticed only when hormonal changes during adolescence, menstruation, or pregnancy cause increased pigmentation, fluctuating swelling, tenderness, or even lactation.
The supernumerary nipple is often overlooked at the first examination of the neonate. It appears as a small pigmented or pearl-colored mark or as a concave or umbilicated spot (note the image below).
Supernumerary nipple in a neonate. Courtesy of Dr P. Merlob.
In 75% of patients, it measures no more than 30% of the diameter of the normal nipple (at times no more than 0.2-0.3 cm in diameter). In the other 25% of patients, it is of medium size, as large as 50% of the normal size of the nipple. Rarely, a supernumerary nipple is as large as a normal nipple. It can be mistaken for many other small lesions, most of them hardly noticeable. Note the image below.
Supernumerary nipple in an adolescent boy. Courtesy of Dr B. Fisher.
Most supernumerary nipples are single, and, when 2 or more (as many as 8) supernumerary nipples are present, they are distributed bilaterally or unilaterally, symmetrically or not. Most supernumerary nipples are located below the regular nipple, while approximately 13% appear above it along the milk line.
When examining adolescent girls (note the image below), the normally developed breast may hide the supernumerary nipple. A number of studies have indicated a preponderance of supernumerary nipples on the right side.
Supernumerary nipple (bilateral) in an adolescent girl.
For easier detection of the supernumerary nipple, a wet gauze pad is passed along the mammary line (milk line) from the axillary region to the upper part of the thigh on each side. This technique is particularly helpful in the dry and desquamating skin of full-term and postterm infants. When the suggested lesion is concave, folding it between fingers shows a typical wrinkling.
A dermoscopic examination of supernumerary nipple shows a pattern similar to dermatofibroma, with both showing central, white, scarlike areas and a peripheral fine-pigment network. Supernumerary nipple also has a cleftlike appearance in the central area, thus allowing differentiation from dermatofibroma. For a more precise examination one can resort to a reflectance confocal microscopy.
Approximately 5% of supernumerary nipples are ectopic, located outside of the milk line, such as on the back, the shoulder (note the image below), the limbs, the neck, the face, and the vulva and perineum.
Ectopic supernumerary nipple on the shoulder. Courtesy of Dr B. Fisher.
Familial cases of supernumerary nipple were recorded as parent-child transmission, including 1 report of a family who had supernumerary nipples in 4 successive generations; therefore, autosomal dominant with incomplete expressivity is the accepted transmission of inheritance.
The histologic features of a supernumerary nipple are identical to that of the regular nipple, including hyperpigmentation, slight hyperkeratosis with epidermal thickening, pilosebaceous structure of Montgomery areolar tubercles, smooth muscle bundles typical of the areola, and possible mammary glands and intradermal straight ducts. A significant increase in the number of clear cells of Toker has been found in supernumerary nipple tissue, indicating supernumerary nipple may be a precursor of extramammary Paget disease.
A protruding (or erectile) supernumerary nipple that causes the patient embarrassment can be easily removed surgically, if desired. Removal using liquid nitrogen cryotherapy has been described. The removal of polymastia or a complete ectopic supernumerary nipple (with breast) is more involved but is indicated in women at high risk of developing breast cancer. To avoid an unsightly scar after the removal of a complete ectopic supernumerary nipple, the tumescent liposuction technique has been suggested.
The Medscape Dermatologic Surgery Resource Center may be of interest.
A sporadic supernumerary nipple typically does not present an indication for a thorough workup for other malformations. Exceptions are a supernumerary nipple accompanied by additional minor malformations, a prominent ectopic supernumerary nipple, or an established familial supernumerary nipple. In these instances, consultations for ultrasonography and nephrography investigation are indicated, bearing in mind that kidney and urinary tract pathologic findings can be present but silent.
Most supernumerary nipples can be ignored; occasionally, a cosmetic blemish occurs. A sporadic supernumerary nipple typically does not present an indication for a thorough workup for other malformations (see Consultations).