[Incidental finding of an intestinally differentiated adenocarcinoma in a tailgut cyst after robotic-assisted resection].

Due to pelvic symptoms, a diagnostic sectional imaging was initiated in a 52-year-old female patient. This revealed a cystic, retrorectal mass, suspected to be a tailgut cyst. Due to the symptoms and the unclear dignity after several frustrating endosonographic punctures, a robotic-assisted resection of the cystic Tumor was performed after careful interdisciplinary consultation.The histological examination confirmed the diagnosis of a tailgut cyst but also revealed parts of an intestinally differentiated adenocarcinoma.Due to the unclear metastatic behaviour, robotic-assisted low anterior resection with total mesorectal excision was performed as oncological resection, similar to rectal carcinomas. No residuals or lymph node metastases were detectable in the histological examination, so that follow- up monitoring was recommended.Retrorectal tumours are an extremely rare entity, worldwide only 28 cases of an intestinally differentiated carcinoma in a tailgut cyst have been described so far. Since there are no clear recommendations in the literature regarding the diagnostic or therapeutic procedure, we would like to discuss a possible algorithm in case of a proven retrorectal mass in our case study.