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Schwannoma


KEY FACTS

Terminology

  • Neurinoma, neurilemmoma (outdated terms)

  • Neoplasm of nerve sheath (Schwann cells)

Imaging

  • 70-75% intradural extramedullary

    • Most common intradural extramedullary mass

  • 15% completely extradural

  • 15% transforaminal, “dumbbell” masses

  • Size varies from small intradural mass to large intraspinal or paravertebral mass (“giant schwannoma”) extending ≥ 2 vertebral segments

  • Bone remodeling due to large intraspinal or intraforaminal tumor common

  • Cystic change common

  • Calcifications, hemorrhage are rare

  • Uniform, heterogeneous, or peripheral enhancement patterns

Top Differential Diagnoses

  • Neurofibroma

  • Perineural root sleeve cyst

  • Myxopapillary ependymoma

  • Meningioma

  • Leptomeningeal carcinomatosis

  • Neuroblastic tumor

Pathology

  • WHO grade I

  • Neurofibromatosis type 2 (NF2): Loss of tumor suppressor (merlin) on chromosome 22

  • Sporadic schwannoma more common than NF2

    • Inactivating mutations of merlin gene in ~ 60%

Clinical Issues

  • Pain, weakness, paresthesias most common clinical findings

  • Typically solitary unless part of inherited tumor syndrome

Diagnostic Checklist

  • Schwannoma most likely when solitary enhancing “dumbbell-shaped” spinal lesion present

Axial graphic portrays a right-sided dumbbell-shaped spinal nerve root schwannoma, enlarging the neural foramen
and compressing the spinal cord
. Both intra- and extradural components (“dumbbell”) are present.

Axial CECT shows a hypodense transforaminal mass
enlarging the right neural foramen. The intraspinal component effaces the thecal sac
and causes canal stenosis.

Axial NECT demonstrates a large soft tissue mass
enlarging the right L1-2 neural foramen. There is conspicuous scalloping of the vertebral body
. The full intraspinal component is not seen.

Axial T2WI MR in the same patient reveals heterogeneous mass
signal intensity. Foraminal enlargement and vertebral body scalloping are again seen
. The extradural component within the spinal canal is causing significant canal stenosis
.

TERMINOLOGY

Abbreviations

  • Neurofibromatosis type 2 (NF2)

    • Multiple inherited schwannomas, meningiomas, and ependymomas (MISME)

Synonyms

  • Neurinoma, neurilemmoma (outdated terms)

  • Nerve sheath tumor (NST)

Definitions

  • Neoplasm of nerve sheath (Schwann cells)

IMAGING

General Features

  • Best diagnostic clue

    • Well-circumscribed, “dumbbell-shaped' transforaminal mass

    • Solitary or multiple enhancing cauda equina nodules

  • Location

    • 70-75% intradural extramedullary

      • –

        Most common intradural extramedullary mass

    • 15% completely extradural

    • 15% “dumbbell”

      • –

        Both intra- and extradural

    • Rare intramedullary

    • Thoracic > cervical = lumbar

  • Size

    • Most are small: Few millimeters in diameter

    • Giant schwannoma

      • –

        Extend ≥ 2 vertebral segments

      • –

        Paraspinal extension > 2.5 cm

      • –

        Posterolateral extension into myofascial planes: Giant invasive schwannoma

      • –

        Lumbosacral spine most common

  • Morphology

    • Round

    • Lobulated

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