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Neurofibroma


KEY FACTS

Terminology

  • Neoplasm containing Schwann cells, fibroblasts, myxoid material, and peripheral nerve fibers

Imaging

  • Locations: Extradural/paraspinal, intradural extramedullary

  • Variable involvement of spinal root, neural plexus, peripheral nerve, or end organs

  • Different neurofibroma morphologies

    • Localized

    • Diffuse

    • Plexiform

  • Size varies from small circumscribed mass to large plexiform neurofibroma (NF) involving multiple body compartments

  • Plexiform neurofibroma pathognomonic for neurofibromatosis type 1 (NF1)

  • Target sign on T2WI suggestive but not pathognomonic for NF

  • May see bone remodeling due to tumor

  • PET avidity suggests malignant degeneration

Top Differential Diagnoses

  • Schwannoma

  • Meningioma (“dumbbell” with intra-, extraspinal components)

  • Perineural root sleeve cyst

  • Chronic inflammatory demyelinating polyneuropathy

  • Malignant nerve sheath tumors

Pathology

  • Neoplastic Schwann cells + fibroblasts

  • Tumor, nerve fascicles intermixed

    • Presence of axons characteristic of NF

  • 90% of neurofibromas are sporadic

Clinical Issues

  • Malignant transformation of plexiform NF to MPNST in 10% of NF1 patients

Diagnostic Checklist

  • Rapidly growing NF or atypical pain concerning for malignant transformation to MPNST

  • Solitary spinal lesion more likely schwannoma than NF

Axial graphic portrays bilateral lobulated plexiform neurofibromas
in neurofibromatosis 1. There is erosion of the left pedicle
by the tumor.

Axial T2* MR shows a mass widening the right neural foramen
and scalloping the adjacent cervical vertebral body
. The intraspinal extradural component of the mass
causes severe canal stenosis. The mass is predominantly hyperintense with some whorled hypointensity centrally
(so-called target sign not specific for neurofibroma).

Coronal T1WI C+ MR shows an enhancing paraspinal mass on the left at L1-2 extending into the left neural foramen, with minimal impact on the thecal sac
. Remodeling causes enlargement of the left L1-2 neural foramen with thinning of the L1 pedicle
.

Axial T2WI in the same patient shows central areas of T2 hypointense signal
with peripheral rim of hyperintensity. This target sign is not specific but is seen more commonly with neurofibroma than with schwannoma.

TERMINOLOGY

Abbreviations

  • Neurofibroma (NF)

Synonyms

  • Nerve sheath tumor (NST)

    • Category of NST also includes schwannomas

Definitions

  • Neoplasm containing Schwann cells, fibroblasts, myxoid material, and peripheral nerve fibers

IMAGING

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