Pilomatrixoma: A Benign Appendageal Tumor not Uncommon in Children.

Pilomatrixoma is a benign appendageal tumor, accounting for 1% of all benign skin lesions (1). It is mostly seen in children and young adults up to 20 years of age, the second peak being in the sixth and seventh decade of life. Pilomatrixoma usually manifests as a solitary, asymptomatic nodule on the head and less frequently on the upper and lower extremities. The diagnosis is commonly based on biopsy and histological findings of basaloid cells with calcium deposits within a fibrin capsule. The therapy of choice is complete surgical excision with a wide peripheral edge, which has a low probability of recurrence. A 10-month-old male infant was referred to pediatric oncologist due to the formation located in the left temporal region, observed by his parents a month ago and associated with insect bite. The mass was painless, occasionally reddish-bluish, and had not changed in size. On examination a superficial, well circumscribed, and moderately firm lesion 1.5 cm in diameter was seen and palpated in the left temporal region (Figure 1). Plain radiography revealed no bone lesions. Ultrasonography demonstrated an ovoid, well-defined hypoechoic formation 1 cm in diameter, suggesting granuloma. Fine needle aspiration (FNA) was performed. Cytomorphologic analysis revealed the presence of abundant clusters of small cells with denting nuclei and basophilic cytoplasmic protrusions surrounded by extracellular pink fibrillary substance, some phagocytes, lymphocytes, granulocytes, scantily calcificated detritus, and scarce squamous cells, characteristic for pilomatrixoma. A complete surgical resection was done. Histopathological findings confirmed the diagnosis (Figure 2). Eight months after the excision there were no signs of local recurrence. Calcifying epithelioma was first described by Malherbe and co-workers in the 19th century (2). The tumor was later called pilomatrixoma to reflect the more accurate description of the origin from the hair follicle germinal matrix center. Pilomatrixoma is a benign solitary tumor usually occurring on the head. Multiple presentations have been described, sometimes in more family members, mainly in association with myotonic dystrophy (3). Pilomatrixoma typically presents as a firm, hard mass, with reddish purple discoloration of the skin resulting from intrinsic hemorrhage. It usually manifests as an asymptomatic nodule and rarely causes pain or itching due to ulceration and inflammation. The growth is rather slow, up to a