Fibrous hamartoma of infancy is a benign myofibroblastic proliferation that typically occurs in the axillary or shoulder region of male infants. We describe 15 cases of this condition, which involved the inguinal region in 5, scrotum in 5, spermatic cord in 1, perineum in 1, labium majus in 1, the suprapubic region in 1 and the pubic area in 1. Patient median and mean ages were 10 and 6.7 months, respectively (range 2 to 24). No case was reported to be congenital. Median and mean tumor size was 3 cm. (range 0.5 to 6). The microscopic features were identical to those seen in fibrous hamartoma of infancy occurring in more typical sites and consisted of 3 components: 1) fascicles of myofibroblasts, 2) disorganized mature adipocytes and 3) small rounded primitive mesenchymal cells. Immunohistochemically, the myofibroblastic component expressed muscle specific actin and vimentin, and the primitive component expressed vimentin only. There was no evidence of increased cellular proliferation in the primitive cell component using proliferating cell nuclear antigen antibodies. Of the 15 lesions 1 recurred locally and 14 were apparently cured by local excision. Awareness of this presentation of fibrous hamartoma of infancy may avert misdiagnosis of more aggressive lesions, especially infantile fibromatosis or rhabdomyosarcoma.
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