A Rapidly Enlarging Recurrent Eyebrow Pilomatrixoma in a Nonagenarian

A rapidly growing, large (horizontal diameter of 3.1 cm) eyebrow lesion in a nonagenarian patient was found on pathologic examination to demonstrate an admixture of islands of anucleated, washed out eosinophilic "ghost" cells with surrounding nucleated, small germinal basaloid cells. Further analysis disclosed adipophilin granular positivity in the necrotic zones, negative nuclear staining for androgen receptor and strong nuclear positivity for Ki67 in the basaloid cells (proliferation index of 50%). These findings are consistent with a highly mitotically active pilomatrixoma. The lesion recurred after initial resection but returned the same histopathologic features as the primary. Several clinical features were notably atypical for pilomatrixoma-specifically, the age of the patient, rapid lesion growth and recurrence, and clinical appearance and large size of the mass. The immunohistochemical findings can help to distinguish this tumor from other skin neoplasms, especially sebaceous carcinoma in an older individual.