Pregnancy-related decidualization of subcutaneous endometriosis occurring in a post-caesarean section scar: Case study and review of the literature

Endometriosis of surgical scars is a rare complication of caesarean sections (incidence: 0.03-0.4%) and other surgical procedures. As endometriosis could be responsive to hormonal stimulation, decidualization and other secondary changes may occur during pregnancy or progestin therapy, sometimes causing a clinically-evident increase in the size of the endometriotic nodules, which could be mistaken for malignant tumors. To our knowledge, we report the 8th subcutaneous case of a pregnancy-related decidualization occurring in a post-caesarean section scar endometriosis. A 33-year-old woman showed a painless, firm, subcutaneous nodule (size: 1 cm) located near the scar of a caesarean section performed 3 years before. Ultrasound examination revealed a well-delimited, hypoechogenic nodule showing perilesional inflammatory reaction without vascular signals. The nodule was considered a post-surgical granuloma: its size did not increase during 4 years of follow-up. Finally, the nodule was totally excised during a second caesarean section performed at 39 weeks of gestation. Histological examination showed nodules of decidualized stromal cells surrounding rare, small, atrophic endometrial glands. Nuclear atypia and mitoses were absent. On immunohistochemical examination, the epithelial cells were pan-CK(AE1/AE3)+/ER+/PR+/S100-/Calretinin-/Vimentin-, while the stromal cells were pan-CK(AE1/AE3)-/Vimentin+/ER+/PR+/CD10+/S100-/Calretinin-. We reviewed the literature, discussing the main clinic-pathological diagnostic pitfalls and the possible differential diagnoses.