Pilomatrixoma: clinicopathologic study of 51 cases with emphasis on cytologic features

The clinical and pathologic features of 51 cases of pilomatrixoma found in our archives from 1990-1999 were reviewed, with emphasis on the cytopathologic features of the 22 cases that were sampled by fine-needle aspiration (FNA) biopsy prior to excision. Although uncommon, almost 20% of the pilomatrixomas in this series occurred in adults over age 30. Of the commonly reported features, the presence of basaloid cells and ghost cells in FNA smears, associated with a cutaneous location of the lesion, was sufficient for a confident cytologic diagnosis of pilomatrixoma. The presence of foreign body-type giant cells, nucleated squamous cells, and calcification, alone or in combination, was less specific, but supported a diagnosis of pilomatrixoma. Although infrequently reported, prominent nucleoli in basaloid cells and smears containing refractile keratin clumps were very useful clues in the diagnosis of pilomatrixoma. Finally, the routine use of cell blocks is recommended because in many of the cases presented ghost cells were fragmented or obscured in smears, but were more readily identified in cell block sections.