Additional cytomorphological criteria in diagnosis of pilomatricoma--benign tumor with bad reputation.

Pilomatricomas (PM) are benign skin appendageal tumors, with differentiation towards hair-forming cells, usually found in children. They are frequently misdiagnosed by clinicians, and there are also many reports of false positive diagnoses made on fine needle aspiration (FNA) cytology. PM are often mistaken for "small round blue cell" tumors in children, or for Merkel cell carcinoma, basalioma and metastatic small cell carcinoma in adults, with possible over-aggressive therapeutic approach. We present 6 cases of PM, correctly diagnosed preoperatively by FNA. Clinical, cytomorphologic and basic morphometric features were analyzed, and compared with 4 cases of malignant tumors with similar clinical presentation. Morphometric data (longest nuclear diameter) did not prove to be helpful, while basophilic cytoplasmatic protrusions, observed in all 6 analyzed cases, could be useful additional cytomorphologic feature of PM. We concluded that cytomorphologic characteristics of PM are reliable enough for correct preoperative diagnosis in adequate specimens, however the best results are achieved when FNA is performed by an experienced cytologist, and when all relevant clinical data are obtained.