Schwannomatosis

Last revised by Dr Francis Deng on 24 Jun 2021

Schwannomatosis, also known as neurilemmomatosis, is a condition characterized by multiple schwannomas, and occasionally meningiomas, but without meeting criteria for neurofibromatosis type 2 (NF2). Some consider this as a variant of NF2 1, but this article considers schwannomatosis an independent disease.

The disease is rare, with an incidence of 1 in 40,000-70,000 5. The incidence peak occurs between the ages of 30 and 60 years 4.

Patients frequently present with pain that can, sometimes, be disabling, resulting in a diminished quality of life. 

The clinical diagnosis of schwannomatosis requires either of the following 6:

  • at least 2 non-intradermal schwannomas, including at least 1 with pathological confirmation, AND no evidence of bilateral vestibular schwannomas
  • pathologically confirmed schwannoma or intracranial meningioma AND an affected first-degree relative

Patients are excluded if any of the following criteria are met 6:

Schwannomatosis is characterized by multiple schwannomas, which are pathologically similar to sporadic/isolated schwannomas. About 5% of schwannomatosis patients also have meningiomas (see meningiomatosis).

The majority of patients demonstrate schwannomas confined to one limb or within five or fewer contiguous spinal segments (segmental schwannomatosis) 5.

Meningiomas are predominantly located along the falx cerebri 6.

The combined clinical and molecular diagnosis of schwannomatosis requires either of the following 6:

  • at least 2 pathologically confirmed schwannomas or meningiomas with chromosome 22q loss of heterozygosity and 2 different somatic NF2 mutations
  • a pathologically confirmed schwannoma or meningioma and germline SMARCB1 or LZTR1 pathogenic mutation (or the identification of two identical SMARCB1 or LZTR1 mutations in different tumors in a patient)

Patients are excluded if they have a germline pathogenic NF2 mutation.

Schwannomatosis appears as multiple discrete, round or tubular lesions situated along the course of peripheral nerves 5. These can involve cranial nerves, spinal nerve roots, or nerves in the neck, limbs, or torso. 

The larger a schwannoma is, the more likely it is to show heterogeneity because of cystic degeneration or hemorrhage.

  • schwannomas usually slightly hypo- to isodense to skeletal muscle with varying degrees of enhancement
    • small tumors show homogeneous enhancement
    • larger tumors may show heterogeneous enhancement
  • adjacent bone remodeling may be seen
  • calcification is rare

MRI is the preferred modality for its soft tissue contrast and has two roles in suspected schwannomatosis: to exclude vestibular schwannomas (which requires a high-quality MRI of the internal auditory canals with slices no more than 3 mm thick 6) and to identify lesions involving the other cranial nerves or peripheral nervous system. Schwannomas have the following typical appearance:

  • T1: isointense or hypointense
    • T1 hyperintense components indicating hemorrhage or fatty degeneration occurs in a small fraction
  • T2: hyperintense
    • cystic degeneration is common
    • peripheral arachnoid cysts may be associated with intradural lesions
  • T1 C+ (Gd): intense enhancement

Symptom control consists of pain relief. Asymptomatic patients are followed and observed.

When symptoms of spinal cord compression occur clearly secondary to a schwannoma, surgical intervention is indicated.

When multiple schwannomas are observed, the main differential diagnosis is neurofibromatosis type 2.

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