A report of three cases of pediatric proliferative fasciitis.

Proliferative fasciitis is a rapidly growing myofibroblastic proliferation that more commonly presents in adults as a subcutaneous mass. Cases in children can cause diagnostic difficulty, as histological features often differ from classic proliferative fasciitis. We present three cases of pediatric proliferative fasciitis, in children age 5-7. Case 1 involved the subcutis and resembled conventional proliferative fasciitis. The lesion was focally positive for desmin. Case 2 involved the subcutis and was more cellular with focal sheet-like areas of ganglion-like fibroblasts. Case 3 involved the dermis and subcutis with a diffuse, solid sheet-like pattern of ganglion-like myofibroblasts with numerous mitotic figures (4 per 10 high power fields), necrosis and foci of acute inflammation. This case had a circumscribed pushing border rather than the more common infiltrating border seen in proliferative fasciitis. The cells were positive for desmin but negative for cytokeratin and had retained SMARCB1 expression. Proliferative fasciitis in childhood can have a varied histological appearance that can cause confusion with malignancies. Awareness of these histological pitfalls is critical to avoid potentially serious diagnostic errors.