Pilomatrical neoplasms in children and young adults

Pilomatrixoma, a neoplasm of hair germ matrix origin, is one of the most common cutaneous appendage tumors in patients 20 years of age or younger. Our review of cutaneous adnexal tumors in the first 2 decades of life showed that pilomatric lesions accounted for ~75% of cases. We examined 76 tumors from 69 patients between the ages of 8 months and 19 years (average age, 8 years). The female-to-male ratio was 3:1. We noted a predilection for the head and neck region, as has also been reported by other investigators. Sixty-nine tumors were examples of typical or classic pilomatrixoma; four of them showed the unusual histologic feature of transepidermal elimination or perforation. None of the tumors in the typical category recurred during a follow-up period that averaged 8.7 years. Seven of the lesions with atypical histologic features were examples of aggressive pilomatrixoma (three cases) and pilomatrical carcinoma (four cases). The average age of these seven patients was similar to that of the overall group. The pilomatrical carcinomas were characterized by invasive nests of tumor cells with irregular borders, large vesicular nuclei, prominent nucleoli, multiple mitotic figures, and focal necrosis. A desmoplastic stroma surrounded the infiltrating nests of tumor. Two of the four pilomatrical carcinomas recurred 2 and 6 months, respectively, after initial excision. The aggressive pilomatrixomas had a similar infiltrative growth pattern, but they did not exhibit the same degree of worrisome cytologic features. Single cell necrosis, identifiable mitotic figures, and prominent nucleoli differentiated the atypical from the typical pilomatrixomas. One of the three aggressive pilomatrixomas recurred after 2 months. Tumors of hair germ matrix or pilar derivations show a spectrum of pathologic findings that correlate with prognosis.