A case of deep endometriosis with cyst formation as a differential diagnosis of rectal duplication cyst in the presacral space.

Cysts occurring in the presacral space may become malignant and therefore require surgical removal. A wide variety of cystic lesions can occur in the presacral space, such as tailgut cysts, dermoid cysts, and duplication cysts. However, deep endometriosis with cyst formation in the presacral space is extremely rare. Here, we report a case of deep endometriosis that presented characteristic imaging and pathological findings and required a differential diagnosis of rectal duplication cyst. A 49-year-old female was referred with a chief complaint of lower abdominal pain. Magnetic resonance imaging (MRI) revealed a cystic lesion with a three-layered wall structure on the right side of the rectum, suggesting a rectal duplication cyst. The lesion had a maximum diameter of 8 cm and extended from the lower end of the second sacral vertebra to the levator ani muscle. The cystic lesion was removed laparoscopically, and intraoperative findings revealed no communication between the cystic lesion and the rectum. We found that the wall of the deep endometriosis with cyst formation had a histopathological three-layered structure and considered that the layered structure closely resembled the intestinal wall on MRI. Deep endometriosis should be recognized as a differential diagnosis of cystic lesions in the presacral space.