An embryologic structure, the urachus is the canal joining the fetal urinary bladder to the allantois. The urachus, when obliterated normally, forms the median umbilical ligament. Persistent remnants are uncommon but may still manifest clinically as a vesicocutaneous fistula, urachal cyst or umbilical sinus. The presence of urothelium within the persistent urachus has been reported to result in malignant transformation.
A recent article in the American Journal of Surgery retrospectively examined abdominal wall endometriomas and found that the mean age of presentation was at 29.4 years. Presenting symptoms were noted to include abdominal mass, cyclical and non-cyclical pain with dysmenorrhea [3, 4]. Although rather uncommon, endometriosis can occur in the postmenopausal (oestrogen-deprived) state , and usually occur in women who undergo unopposed oestrogen replacement therapy . Previous case reports have described umbilical endometriosis with periodic bleeding from the umbilicus without prior pelvic or abdominal surgery .
As demonstrated in our patient, however, endometriosis may masquerade as a tumour arising from the urachus . Endometriosis can display local aggression, with urinary bladder endometriosis previously reported to extend into the adjacent bowel . Endometriosis of the abdominal wall scars is rare, especially in postmenopausal woman. However, it must be considered as a possible cause of any abdominal wall mass in a woman who has had previous pelvic surgery and who is of reproductive age or taking exogenous hormones. Malignant transformation has been described in abdominal wall endometriosis, with clear cell carcinoma and endometrial carcinoma being the most common reported variants. As such, radical surgery is the most common treatment applied .