RESUMO
BACKGROUND: Tailgut cyst [retrorectal hamartomas] is an unusual cystic lesion, located in the retrorectal space. It develops from post anal foetal gut remnants, present anterior to the sacrum and posterior to the rectum. A high index of clinical suspicion is required to diagnose this rare tumour. This malformative lesion should be distinguished from teratomas, mullerian cysts, anal gland cysts and duplication cysts of the rectum. The treatment of choice is complete surgical excision. CASE: A tailgut cyst is hereby reported, which had undergone malignant transformation, with development of an adenocarcinoma. Only 16 additional cases of tailgut cysts with adenocarcinoma were recovered, in an extensive search of world literature. CONCLUSION: The identification of this rare entity provides an opportunity to examine this pathological rarity in the context of the few previously reported cases of this type.