Page 821 - Robbins Basic Pathology by Vinay Kumar, Abul K. Abbas, Jon C. Aster

associated with multiple schwannomas in which vestibular Peripheral Nerve Sheath Tumors 807
schwannomas are absent. Some cases have recently been
linked to loss-of-function mutations in a tumor suppressor Neurofibromas
gene on chromosome 22 that encodes a protein that regu-
lates chromatin structure. Neurofibromas are benign peripheral nerve sheath tumors.
Three important subtypes are recognized:
MORPHOLOGY • Localized cutaneous neurofibromas arise as superficial

On gross inspection, most schwannomas appear as circum- nodular or polypoid tumors. These occur either as soli-
scribed masses abutting an adjacent nerve. On microscopic tary sporadic lesions or as often multiple lesions in the
examination, these tumors often show an admixture of dense context of neurofibromatosis type 1 (NF1).
and loose areas referred to as Antoni A and B, respectively • Plexiform neurofibromas grow diffusely within the con-
(Fig. 21–7, A and B). They are comprised of a uniform pro- fines of a nerve or nerve plexus. Surgical enucleation of
liferation of neoplastic Schwann cells. In the dense Antoni A such lesions is therefore difficult and is often associated
areas, bland spindle cells with buckled nuclei are arranged with lasting neurologic deficits. Plexiform neurofibro-
into intersecting fascicles. These cells often align to produce mas are virtually pathognomonic for NF1 (discussed
nuclear palisading, resulting in alternating bands of nuclear later on). Unlike other benign nerve sheath tumors,
and anuclear areas called Verocay bodies. Axons are largely these tumors are associated with a small but real risk of
excluded from the tumor. Thick-walled hyalinized vessels malignant transformation.
often are present. Hemorrhage or cystic change are also seen • Diffuse neurofibromas are infiltrative proliferations that
sometimes. can take the form of large, disfiguring subcutaneous
masses. These also are often associated with NF1.

AB

CD

Figure 21–7 Schwannoma and plexiform neurofibroma. A and B, Schwannoma. As seen in A, schwannomas often contain dense pink Antoni A areas
(left) and loose, pale Antoni B areas (right), as well as hyalinized blood vessels (right). B, Antoni A area with the nuclei of tumor cells aligned in palisad-
ing rows. C and D, Plexiform neurofibroma. Multiple nerve fascicles are expanded by infiltrating tumor cells (C), which at higher power (D) are seen
to consist of bland spindle cells admixed with wavy collagen bundles likened to carrot shavings.