Retrorectal cystic hamartoma. Report of three cases, including one with a perirenal component.

Retrorectal cystic hamartomas (RCHs) are uncommon lesions of controversial pathogenesis that arise in the presacrococcygeal space. We describe the clinicopathologic features of RCHs from three adult patients. Two were asymptomatic women; the third was a man who had a pelvic abscess. All three specimens were multiloculated cysts lined by squamous, transitional, and glandular epithelium. Poorly organized collections of smooth muscle were present in the surrounding connective tissue, but no well-formed smooth-muscle coat was seen. Although RCHs possess elements of three germ-cell layers, their histologic features are similar to those of the embryonic tailgut. The male patient also had a perirenal mass that was grossly and histologically identical to the RCH. The associated kidney was malrotated. A portion of the embryonic tailgut may have been pulled cephalad by the developing kidney, inhibiting its rotation. Clinicopathologic features distinguish RCH from other retrorectal cystic lesions, including teratoma, dermoid, epidermal cyst, rectal duplication, anal duplication, and anal gland cyst.