Mimics of pilomatrixomas in fine-needle aspirates.

This is a review of the fine-needle aspirates (FNAs) of nine pilomatrixomas (PMs) found in a series of 1,500 FNAs performed on skin nodules. The objective is to determine and list the cytologic findings that might mislead the less-experienced cytopathologist and to give him advice on how to avoid such errors. The following recommendations are made: 1) The FNAs should be carried out and the smears interpreted by the same person. 2) Clinical data, particularly age and location, are of paramount importance. 3) Shadow cells are pathognomonic of PMs. 4) Basaloid nuclei with prominent nucleoli should not be overdiagnosed. 5) Use both Papanicolaou and Diff-Quik stains. 6) Think of PM when performing and interpreting aspirations from subcutaneous growths located in the head and neck of young persons.