Discussion

Pilomatricoma is a rarely encountered lesion in cytopathology. While its’ histologic features are easily recognized on surgically resected specimen, FNA samples often lead to a misdiagnosis,  as a malignant lesion.5-8 Other commonly mistaken diagnosis are epidermal inclusion cyst, adnexal tumor, and salivary gland neoplasm when occurring in/near parotid glands.1 Clinically, the diagnosis is also challenging, since one study of 209 cases determined that only 54 cases (21%) were correctly diagnosed in clinical setting.2 Diagnostic morphologic features on histology are sheets of basaloid cells, sheets of shadow or ghost cells, and intervening stroma that may contain foreign body giant cells, mixed inflammatory cells, calcification, and hemosiderin.9 These features are also seen on FNA smears. which yield a highly cellular sample composed of sheets of anucleated squames (ghost cells) with clusters of basaloid cells. There are usually multinucleated giant cells and mixed inflammatory cells associated with these cells. The background may show keratin or stromal debris that may be mistaken for necrosis. These features maybe mistaken for a malignant neoplasm, e.g. squamous cell carcinoma, basal cell carcinoma, etc; however, careful review of the cells will reveal that the cells are uniform with no atypia. Knowing the clinical history is important since a majority of pilomatricomas occur in the head and neck and during the first 2 decade of life. When a young patient presents with a suspicious nodule on head or neck, the differential diagnosis of pilomatricoma should be kept in mind. While there are no specific cytomorphologic features of pilomatricoma, a good clinical history and a sound working differential diagnosis should aid in correctly diagnosing the lesion.