Summary

A 67-year-old man with a slow-growing, asymptomatic perianal lesion was presented to the colorectal clinic. Physical examination and radiological investigation were suggestive of an externally prolapsing colonic polyp. However, intraoperative findings of a cystic lesion containing a thick brown substance questioned the initial diagnosis. After complete surgical resection of the encapsulated lesion, histological examination revealed a tailgut cyst (cystic hamartoma). These uncommon lesions originate from an embryological remnant of the hindgut. They are generally benign but may have extremely rare malignant potential which warrants complete surgical resection. Throughout the literature, they are described to present with various symptoms and may be found in several anatomical locations, most commonly within the retrorectal space. In very rare instances, with only two other documented cases, they can be found externally at the anorectal junction. Although very rare, an anal tailgut cyst should be taken into account in differential diagnosis.