Abstract: 【Abstract】 Objective To analyze clinical and pathological features of childhood perforating pilomatricoma, and to explore its pathogenesis. Methods A retrospective analysis was conducted on clinical and histopathological data from 29 children with perforating pilomatricoma in Department of Dermatology, Beijing Children′s Hospital from 2014 to 2020. Results Among the 29 patients, 11 were males, and 18 were females, with a male-to-female ratio of 1∶1.64. Their age at onset ranged from 3 months to 14 years and 10 months, and the median age at onset was 4.58 years. The disease duration ranged from 2 months to 2 years, with an average of 8.72 months. The perforation occurred 2 days to 1 year and 6 months after the onset of pilomatricoma, with an average of 1.85 months. Ulceration occurred in 1 patient after the treatment with ichthammol, as well as in 3 patients after local scratching or bumping, and spontaneous ulceration without definite precipitating factors occurred in the remaining 25 patients. The average duration from the onset of disease to tumor perforation was 6.87 months. Skin lesions occurred on the face in 15 cases, on the lateral neck in 8, on the upper limb in 4, as well as on the scalp in 2. Perforating pilomatricoma clinically manifested as indurated subcutaneous nodules with crusts or ulcers, and was classified into 3 subtypes: ulcerative type （19 cases）, horny type （8 cases）, and crusted type （2 cases）. The tumor diameter ranged from 0.3 to 2.5 cm, with an average of 1.2 cm. Histopathological examination showed that the tumor was located in the superficial to middle dermis, and mainly consisted of basophils and ghost cells; in 19 cases, the tumor mass was extruded onto the skin surface through a perforated epidermal channel, and the epidermis around the perforation site was hyperplastic and invaginated into the dermis, forming epithelial tunnels surrounding the tumor; in 4 cases, the skin on the tumor surface was thinned and ruptured; in 6 cases, the perforation site could not be observed due to surgical separation of the epidermis and tumor. All lesions were resected, and no infection or recurrence was observed during the postoperative follow-up. Conclusions Childhood perforating pilomatricoma mostly occurs on the face and neck, usually with rapid progress, and can be classified into ulcerative type, horny type and crusted type. Histological findings suggest that transepithelial elimination is an important mechanism underlying the occurrence of perforation in pilomatricoma.

Key words: Pilomatrixoma, Child, Skin manifestations, Pathologic processes, Perforating pilomatricoma, Transepithelial elimination