Superficial malignant peripheral nerve sheath tumor arising from diffuse neurofibroma in a neurofibromatosis type 1 patient.

Malignant peripheral nerve sheath tumors (MPNST) are regarded as sarcomas that arise from peripheral nerves or that display differentiation along the lines of the various elements of the nerve sheath. These tumors occur in deep soft tissues, but superficial primary MPNST with a cutaneous or subcutaneous origin have rarely been reported. A 70-year-old woman presented with a 3-4-year history of a slowly enlarging soft nodule on the left side of her neck. The histopathological diagnosis of the nodule was low-grade MPNST arising from diffuse neurofibroma. There was increased cellularity, but no necrosis or mitotic activity. These histopathological findings pose difficulties in differential diagnosis from a neurofibroma with atypical histological features. We report a rare case of superficial MPNST arising from diffuse neurofibroma associated with underlying occipital bone dysplasia in a neurofibromatosis type 1 patient.