Myxoid change in nondecidualized cutaneous endometriosis resembling malignancy

Cutaneous endometriosis infrequently arises in the absence of pelvic disease. Rare features such as myxoid change can resemble malignancy and may pose a challenging histological diagnosis. We are not aware of any previous cases involving nondecidualized cutaneous endometriosis with myxoid change associated with an abdominal surgical scar. We report the first such case in which a 24-year-old woman presented with a steadily growing, firm, tender, painful, subcutaneous cicatrical mass that had appeared shortly after cesarean section 1 year previously. The mass was removed and permanent sections revealed foci of large, irregular endometrial glands embedded within prominent myxoid stroma and acellular mucin pools, with fibrosis and pseudoinfiltration of the fascia. No evidence of malignancy was identified. This case demonstrates that nondecidualized cutaneous endometriosis with myxoid change should be considered in the differential diagnosis of histologically similar malignancies such as mucinous adenocarcinoma and pseudomyxoma peritonei.