Pilomatrixoma (PMX) is a benign skin neoplasm of hair matrix origin. The fine-needle aspiration (FNA) features of PMX frequently lead to a misdiagnosis of carcinoma.
Nine cases of PMX in which a preoperative FNA was performed were reviewed. The cytologic features were compared with the histologic appearance of corresponding surgical specimens as well as with cytologic features of tumors that arose in the differential diagnosis.
Unequivocal benign diagnoses were rendered in three cases; the correct preoperative diagnosis of PMX was rendered in two of these cases and considered in an additional case. In four additional cases, carcinoma was diagnosed or could not be excluded. A noncommittal diagnosis of epithelial tumor, most likely of skin adnexal origin, was rendered in an additional single case. Retrospective review of the FNA smears in all nine instances disclosed cytologic features that corresponded well with the histologic components of PMX. Diagnostic cytologic features included cellular aspirates; clusters of small, primitive-appearing basaloid epithelial cells; a high nuclear-cytoplasmic ratio; evenly dispersed chromatin; prominent nucleoli; pink, fibrillary material enveloping clusters of basaloid cells; multinucleated giant cells; and sheets of ghost cells.
The FNA cytologic diagnosis of PMX may be extremely difficult; its distinction from various primary cutaneous carcinomas is most problematic. Recognition of a unique constellation of cytologic features in FNA smears in the appropriate clinical context is most helpful in making this distinction.