Adenocarcinoma arising in a tailgut cyst with prominent meningothelial proliferation and thyroid tissue: case report and review of the literature.

Tailgut cysts (retrorectal cystic hamartomas) are rare lesions occurring in the retrorectal/presacral space of young women, considered to be of developmental origin. In this study, we report the clinicopathological characteristics of an adenocarcinoma developing in an unusual tailgut cyst. A 47-year-old female presented with a 3-month history of an enlarging presacral mass, extending into the gluteal area. The patient underwent surgical resection. Microscopic examination revealed a mucinous adenocarcinoma with intestinal features arising in a tailgut cyst. In addition to the usual components previously described in this lesion (cuboidal, columnar, ciliated or squamous epithelial lining with scattered smooth muscle fibers in the wall), our case was unique in that it was associated with a meningothelial proliferation and benign thyroid tissue with oncocytic changes. These additional features bring into question the proposed hindgut origin of tailgut cysts.