Limits of Fine-Needle Aspiration Cytology in Diagnosing Pilomatrixoma: A Series of 25 Cases with Clinico-Pathologic Correlations

BACKGROUND: Pilomatrixoma (PMX) is a benign, quite uncommon, skin neoplasm, which is frequently misdiagnosed by clinicians. AIM: We have analyzed 25 PMX to determine the agreement between clinical diagnosis, preoperative FNA characteristics, and corresponding histopathological specimens; moreover, reliable cytologic criteria for PMX and the differential diagnosis to avoid cytological pitfalls have been emphasized. MATERIALS AND METHODS: By fine-needle aspiration (FNA) cytology a series of consecutive cases of PMX collected during last 5 years were studied. Smears were stained by Papanicolau and May-Grünwald-Giemsa. RESULTS: Patients affected by PMX were 11 males, 14 females (ratio 1:1.27); the mean age was 32.72 years with age range 3-78 years, being 72% (18/25) of patients 40 years or less. PMX was mainly distributed in the head-neck region (52%), scalp (16%), upper/lower arms (28%), and chest (4%). The observed diagnostic cytological features were represented by clusters of basaloid epithelial cells, shadow or ghost cells, inflammatory background, calcification, and giant cells. Unfortunately, not all these morphological aspects were always disclosed in smears, thus making the cytological preoperative diagnosis questionable and problematic. CONCLUSIONS: The experience of a well-trained cytopathologist should distinguish the relevant FNA features in terms of smear background, architecture, and cell morphology. The most dangerous mistake in FNA diagnosis of PMX regards a diagnosis of primary malignant or metastatic cutaneous lesions.