Polythelia: extra nipples along the milk line
Polythelia means one or more extra nipples, typically along the milk line, the line from the armpit to the groin where breast tissue develops in the embryo.
Remember
An extra nipple is called polythelia, and it typically lies along the milk line from the armpit to the groin because part of that line did not regress (disappear) as it should.
Polythelia is one or more extra nipples. It is a developmental variant, present from birth.
In the embryo, two lines of thickened skin run from the armpit (axilla) to the groin, one on each side, and breast tissue develops along them. These are the mammary ridges, also called milk lines. Normally most of each ridge disappears (regresses), and only the part at chest level goes on to form a breast.
If a patch of ridge fails to regress, a small area of nipple or breast tissue remains, giving an extra nipple or extra breast tissue. Extra breast tissue without a nipple is the less common form. It is called accessory (ectopic) breast tissue, meaning breast tissue in an area not normally associated with the breast.
Extra nipples typically lie along the milk line. They are found most often around the breast, chest and armpit, and sometimes on the abdomen, so the armpit is only one site along it.
Polythelia is usually benign. It can swell during pregnancy because it responds to hormones, and it may become tender or even release milk. Moles can look like an extra nipple, so careful examination matters.
Key facts
- What it is
- one or more extra nipples, a developmental variant present from birth
- Where
- typically along the milk line, from the armpit to the groin
- Cause
- part of the mammary ridge fails to regress (disappear) as it should
- How common
- the commonest developmental disorder of the breast
- Course
- usually benign and often needs nothing but reassurance, and it may be removed if it troubles the person
- Pregnancy
- it can swell, become tender and even leak milk with pregnancy hormones
- Look-alike
- moles can mimic an extra nipple but contain no nipple tissue
Exam traps
- Extra nipples do not point to breast cancer, because polythelia is usually a benign, isolated finding.
- Extra nipples are not restricted to the armpit, because the armpit is only one site along the milk line, and they are also found on the chest and abdomen.
- Extra nipples do not lie in a horizontal band across the chest at nipple level, because the milk line runs from the armpit down towards the groin.
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