An Unusual Perianal Presentation of a Tailgut Cyst.

Tailgut cysts or retrorectal cystic hamartomas are rare, congenital, development lesions arising from the remnants of the hindgut during embryogenesis. It is most often misdiagnosed due to its rarity, variable clinical presentation, and malignant potential. The following report describes an unusual case of a tailgut cyst in a 60-year-old male with a history of a perianal mass for 12 years. Surgical resection was done, and histopathological examination revealed a multiloculated cyst filled with brownish fluid, grossly, and a cyst lined by various epithelia such as stratified squamous epithelium, pseudostratified columnar epithelium, and flattened to cuboidal and mucin-secreting columnar epithelium along with cyst wall made up of bundles of smooth muscles, microscopically. Several lesions mimic a tailgut cyst and need to be excluded from the differentials. Although no malignancy was documented in this case, these cysts have been known to undergo malignant transformation into adenocarcinoma and neuroendocrine carcinoma, to name a few. This warrants a thorough and accurate histopathological assessment and mandatory follow-up.