As a medical student, I was doing an abdominal exam on a fifteen-year-old girl in the emergency department when I noticed four small, tan papules running down her lower chest and abdomen. Two were in line with her right nipple, two with her left.
"How long have you had these?" I asked her.
"Oh, my birthmarks?" she responded. "My whole life."
I suddenly realized, with that exhilaration peculiar to a medical student connecting book knowledge with an actual living patient, what they were.
Supernumerary nipples (polythelia) are extra nipples present in 1-5% of the population. They typically follow the embryonic milk lines, which run from the underarm, through the regular nipples, down the chest and abdomen, into the groin and end on the upper inner thigh. (Think of the row of nipples on a cat or pig.) However, ectopic supernumerary nipples have even been reported on the foot and face.
Polythelia can present with just one extra nipple, or as many as eight. The nipples can range from a subtle nodule a fraction of the size of a regular nipple, to a miniature breast complete with glandular tissue, nipple and areola (polymastia). The extra breast tissue can change in size and tenderness and even lactate in response to hormones.
I wasn't sure if I should tell my patient this. I doubted a teenage girl would greet my diagnosis with the same enthusiasm I felt. I kept quiet and passed my observations on to my resident instead.
You might want to reexamine those "moles" on your belly.