Ossifying Pilomatrixoma of the Eyelid.

Pilomatrixoma, an uncommon, usually benign cutaneous appendageal tumor, shows differentiation toward the hair follicle matrix cell. It undergoes various histopathologic stages, early on displaying epithelial and shadow cells along with granulomatous inflammation. In later stages, illustrated by this unusual case, epithelial cells disappear and are replaced by calcification and ossification. Immunohistochemistry in the current case showed transitional cell reactivity for β-catenin, probably linking the tumor to a mutation in the β-catenin gene CTNNB1. There was also transitional cell positivity for cyclin D1, a marker found in matrical cells of the human hair follicle. While pilomatrixoma occurs occasionally in the eyelid, the ossified eyelid variant in the current case is very rare, with only one preceding description in the literature.