Retrorectal cystic hamartoma diagnosed by fine-needle aspiration biopsy.

A 17-yr-old postpartum female presented with a large multicystic mass posterior to the rectum, thought clinically to be an abscess. Fine-needle aspiration biopsy revealed numerous squamous cells. The diagnosis of retrorectal cystic hamartoma was considered and subsequently confirmed by the surgical resection specimen. The cytologic and histologic findings are presented along with a discussion of the entity "retrorectal cystic hamartoma," including a differential diagnosis of presacrococcygeal cysts.