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Spinal nerve sheath tumours

Spinal nerve sheath tumours are the most common intradural extramedullary mass.

They include, in order of decreasing frequency:

Most nerve sheath tumours arise from the dorsal sensory roots. Seventy percent are intradural/extramedullary in location, 15% are purely extradural and a further 15% have both intradural and extradural components (“dumbbell” lesions). Less than 1% are intramedullary 2.

This article is an overview of spinal nerve sheath tumours. For a discussion on the epidemiology, clinical presentation, pathology and treatment/prognosis of spinal schwannomas and neurofibromas, please refer to spinal schwannoma and spinal neurofibroma.

Associations

35-45% of patients with nerve root tumours have neurofibromatosis 2. Multiple lesions are common in these patients. Neurofibromas are associated with NF1, whereas schwannomas are associated with NF2.

Radiographic features

Schwannomas and neurofibrommas are often indistinguishable radiographically.

Plain film
  • bony changes can be common on plain film and can include
    • enlarged neural foraminaen
    • pedicle erosion
CT (non-contrast)
  • density varies from hypodense to to slightly hyperdense
  • widened neural exit foramina
  • bone erosion
  • vertebral body scalloping
  • paraspinous soft tissue mass: (“dumbbell” and extradural lesions)
  • calcification and haemorrhage are rare
MRI

Schwannomas are frequently associated with haemorrhage, intrinsic vascular changes (thrombosis; sinusoidal dilatation), cyst formation and fatty degeneration. These findings are rare in neurofibromas 4.

Neurofibromas tend to encase the nerve roots, in contrast to schwannomas which commonly displace the nerve root due to their asymmetric growth.  

Schwannomas are usually round, whereas neurofibromas are more commonly fusiform.

Signal characteristics include:

  • T1: 75% are isointense, 25% are hypointense 2
  • T2: > 95% are hyperintense 2
    • schwannomas may have mixed signal intensity on T2
    • a hyperintense rim and central area of low signal resulting in a target sign, may be seen in neurofibromas and occasionally also in schwannomas; this is thought to be due to a dense central area of collagenous stroma
  • T1 C+ (Gd)
    • virtually 100% enhance
    • heterogenous enhancement with areas of low signal is more characteristic of a neurofibroma

Differential diagnosis

  • meningioma
    • broad dural base
    • dural tail sign
    • usually located posterolaterally (compared to nerve sheath tumours which are typically located anteriorly)
    • neural exit foraminal widening is less commonly seen with meningiomas than with nerve sheath tumours
  • paraganglioma
    • usually seen as a well-circumscribed mass inferior to the conus
    • flow voids are typically seen along the surface of and within the tumour nodule
    • haemorrhage is common, leading to a "cap sign" on T2 weighted images
    • the characteristic “salt-and-pepper” appearance of neck and skull base paragangliomas may be seen
  • myxopapillary ependymoma
    • occur almost exclusively in the conus medullaris and filum terminale
    • haemorrhage is common
  • intradural extramedullary metastases
    • an important differential for multiple neurofibromas
    • cord oedema may be seen with more extensive disease, especially if there is an intramedullary component
    • sugar coating” of the spinal cord and nerve roots may be seen
  • perineural root sleeve cyst
    • CSF density on CT; CSF intensity on T1 and T2 weighted images
    • no contrast enhancement
  • epidermoid or dermoid
    • epidermoid
      • similar intensity to CSF on T1 and T2 weighted images
      • typically non-enhancing, however a thin rim of contrast enhancement may be seen
      • diffusion restriction on DWI
    • dermoid
      • presence of fat is suggestive
      • usually present in younger patients (<20 years)
      • associated dermal sinus may be present
  • intradural disc herniation
    • no enhancement

See also

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