Rectus abdominis endometrioma.

A 31-year-old woman presented with complaints of increasingly severe right lower quadrant discomfort that had occurred for several days each month over the course of the previous 6 months. A tender mass of the abdominal wall was palpated on physical examination, and subsequent ultrasonography and magnetic resonance imaging disclosed a discrete mass of the body of the right rectus abdominis muscle which was confirmed as endometrial tissue on biopsy. Rectus abdominis endometrioma is a relatively rare cause of abdominal pain which may mimic an acute abdomen. Clinical clues to the diagnosis include previous uterine or gynecological surgery/invasive procedure (with preservation of ovarian function), cyclical nature of the discomfort, and the presence of a palpable mass with or without associated skin color changes.