Spontaneous endometriosis in an umbilical skin lesion.

Cutaneous endometriosis of the umbilicus is an unusual condition with unclear pathogenetic mechanisms that might be mistaken for a malignant condition. A 46-year-old woman presented with a cutaneous black mass in the umbilicus. The lesion was removed surgically and histological analyses revealed that it consisted of endometrial tissue. There was no recurrence at 18-month follow-up. Endometriosis of the umbilicus is a rare condition and the pathogenesis is not completely elucidated. According to one theory, intraperitoneal endometrial tissue is translocated during endoscopic surgery or other surgical procedures that involve the umbilicus. However, in this case there was no history of abdominal wall surgery. We conclude that endometriosis is important to consider in cases of unclear skin lesions of the umbilicus, even in cases with no previous abdominal surgery. Moreover, umbilical endometriosis of the skin can have different appearances that resemble malignant tumors, and radical surgery with histology is therefore indicated.