Infantile digital fibromatosis occurring outside the digit.

This report illustrates an extradigital fibromatosis located in the right upper arm. The clinical, light-, and electron-microscopic features were identical to those found in the recurrent digital fibromatosis of childhood. As is typical for infantile digital fibromatosis, this reported lesion recurred once. Light microscopy showed eosinophilic, perinuclear inclusions which by electron microscopy were nonmembrane-bound, compact fibrillary structures. Whereas major reviews state that infantile digital fibromas occur exclusively on the digits, this unique case describes the rare occurrence outside the digit.