DISTINCTIVE FEATURES

Two major types of peripheral nerve tumors are the Schwannomas and neurofibromas.

Schwannomas are benign tumors of schwann cells.

Schwannomas may arise from the eighth nerve at the cerebellopontine angle (acoustic neuroma), from dorsal roots or from a peripheral major nerve trunk.
Grossly, these tumors are well circumscribed, encapsulated, with a gray-white cut surface. The tumors arising from the dorsal root may extend from the vertebral foramen and become dumb-bell shaped. The nerve is attached to the tumor, however, it may be entrapped in the tumor capsule.
Microscopically, the tumor consists of two growth patterns. In Antoni A areas, the cells are elongated and more densely packed with little intervening stroma. In Antoni B areas, the tumor cells are less densely packed and are separated by a myxoid stroma. Malignant Schwannoma (Malignant nerve sheath tumor) is a higly malignant, locally infiltrating, poorly circumscribed tumor which consists of elongated cells with bipolar processes and nuclear atypia. These tumors arise de novo or originate from plexiform neurofibroma.

Three types of neurofibromas is recognized; cutaneous neurofibroma, solitary neurofibroma and plexiform neurofibroma.

Grossly, cutaneous neurofibroma appears as raised, nodular and sometimes pedunculated skin lesions that may be associated with hyperpigmentation. These tumors exist in the dermis and extend into the subcutaneous tissue. These tumors are well demarcated but are not encapsulated.
Microscopically, these tumors consist of spindle cells in a collagen rich stroma.

The solitary neurofibromas arising from peripheral nerves resemble the cutaneous neurofibromas.

Plexiform neurofibromas occur in association with the neurofibromatosis and have a risk of becoming malignant.
Grossly, these tumors are intimately associated with the nerve and unlike Schwannomas can not be separated from the nerve from which they arise.
Microscopically, these tumors consist of a hypocellular and loose myxoid stroma containing Schwann cells, perineural cells, fibroblasts, and inflammatory cells including mast cells. Axons can be visualized within the tumor.