Caudal appendage derived from a vestigial remnant of the tailgut.

The presence of smooth muscle at the basal portion of a caudal appendage is very rare. We report a 3-month-old girl in which a caudal appendage is associated with smooth muscle bundles at the perianal region. Immunohistochemistry was performed for NCAM (neural cell adhesion molecule) to identify smooth muscle. NCAM immunoreactivity was observed within the presumptive circular and/or longitudinal muscle layers of the muscularis propria. NCAM is expressed by smooth muscle during the early stages of human embryonic gut development, suggesting that the caudal appendage in the present case may be derived from a tailgut remnant.