Abstract
A 16-year-old girl with proliferating trichilemmal cyst (PTC) was admitted to hospital with a complaint of a painless lump on the nucha. It had gradually enlarged during the past two years. The excised 5×4×4 cm tumor weighed 30 gr and was well demarcated from the surrounding tissue by a thin fibrous capsule. Microscopically, the tumor was composed of squamous epithelium proliferating in irregularly-shaped and various-sized lobules with central areas of trichilemmal keratinization and foci of calcification. Epithelial cells were small and palisaded at the periphery of the lobules, and in the inner layer they are large and clear with glycogen in the cytoplasm. Foci of inflammatory reaction with foreigh-body giant cells were present. There was no evidence of malignancy. Eighty-six reported cases of PTC collected from the Japanese literature were reviewed, together with the present case. There were 65 benign PTCs and 22 malignant PTHs. More than a half the number of patients with benign PTC were elderly women (55%), whereas the majority of the patients with malignant PTC were males (73%). The benign PTCs occurred mostly on the scalp (82%), but the malignant lesions were often present in sites other than the scalp (73%). Although benign PTCs were sharply demarcated and often encapsulated, malignant PTCs showed invasive growth, cellular atypia and frequent mitoses, occasionally metastasizing to the regional lymph nodes.
