Neural tumors

Neurofibroma

• Loose arrangement with pale myxoid stroma

• Haphazard spindle cells with small wavy or S-shaped nuclei

Neurofibromas may occur as solitary lesions. Multiple widespread neurofibromas characterize neurofibromatosis (von Recklinghausen’s disease) in which they are seen in association with café-au-lait macules, axillary freckling, and pigmented hamartomas of the iris (Lisch nodules).

Fig 22-1 Neurofibroma

Fig 22-2 Neurofibroma

Diffuse neurofibroma

Key features

• At scanning magnification, diffuse replacement of dermis and infiltration of fat

• Higher magnification shows features typical of neurofibroma

Differential Diagnosis

Dermatofibrosarcoma protuberans has a similar growth pattern and can be myxoid, bearing a considerable resemblance to diffuse neurofibroma. Both may be CD34 positive, but S100 staining of the neurofibroma can distinguish the two. Spindle cell lipoma can appear similar, but occurs as an encapsulated nodule.

Plexiform neurofibroma

Key features

• Large fascicles of neurofibroma surrounded by perineurium

• Often embedded within a diffuse neurofibroma

Plexiform neurofibroma clinically resembles a “bag of worms” and is considered pathognomonic of neurofibromatosis. Both diffuse and plexiform neurofibromas probably result from loss of heterozygosity, where segmental loss of the remaining normal allele for the NF1 gene results in a localized complete lack of tumor suppressor protein.

Fig 22-3 Plexiform neurofibroma

Fig 22-4 Plexiform neurofibroma

Schwannoma (neurilemmoma)

Key features

• Deep dermal or subcutaneous tumors with perineural capsule

• Arise within a nerve, displacing axons to the periphery, causing pain

• Antoni A tissue contains parallel rows of nuclei separated by acellular areas (Verocay bodies)

• Antoni B tissue represents a degenerative change with edematous stroma, typically just below the capsule

Fig 22-5 Schwannoma

Fig 22-6 Schwannoma (Verocay bodies)

Fig 22-7 Psammomatous melanotic schwannoma

Fig 22-8 Ancient schwannoma

Psammomatous melanotic schwannoma is a variant with psammoma bodies and melanin. It is associated with Carney’s complex (myxomas, spotty pigmentation, and endocrinopathy).