schwannoma (neurilemoma, neurinoma)

Epidemiology

• 7% of primary intracranial neoplasms
• 29% of primary spinal nerve root tumors
• rare central nervous system schwannoma
• generally occurs in patients 40-50 years of age

Pathology

• may arise from any cranial, spinal or peripheral nerve
• commonly involves
  • cranial nerve VIII (most common)
    • arise from vestibular division of nerve
    • enlarging vestibular tumors may compress the cerebellum, pons or facial nerve (CN VII)
  • cranial nerve V
  • dorsal root of spinal nerves (seen in patients with neurofibromatosis type I)
• bilateral acoustic schwannomas are the hallmark of neurofibromatosis type II
• corresponds to WHO grade I

Microscopic pathology

• encapsulated sometimes cystic tumor composed of spindle-shaped Schwann cells
• histopathology:
  • variants: cellular, plexiform, melanotic, epithelioid
  • Antoni A pattern: compact areas of elongated cells with pallisading pattern, Verocay bodies
  • Antoni B pattern: less cellular, loosely textured
  • clusters of lipid laden cells
  • large atypical appearing nuclei considered to be degenerative change
  • occasional mitotic figures may be seen

Immunophenotype

• S100: + strong, diffuse, cytoplasmic, nuclear
• EMA: -
• CD34: - in cellular areas, may be seen associated with degenerative areas
• vimentin: +
• CD68: may be + due to high lysosomal content
• keratin (AE1): commonly +

Clinical manifestations

• progressive unilateral hearing loss
• symptoms from compression of CN VII, pons, cerebellum
  • impaired physical function
  • disfigurement
  • diminished quality of life

Diagnostic procedures

• audiometry
• brainstem auditory evoked potential

Radiology

• magnetic resonance imaging (MRI)
  • dense, uniformly enhancing lesions
  • vestibular schwannomas enlarge in the internal auditory canal*

* distinguishing feature from other cerebellar-pontine angle masses

Management

• surgical excision
  • generally possible to preserve hearing
• stereotactic radiation therapy with gamma-knife
• selumetinib (Koselugo) FDA-approved for symptomatic inoperable plexiform neurofibromas in patient ages 2-17 with neurofibromatosis type 1
• mirdametinib is investigational
• prognosis:
  • schwannomas are clinically benign
  • rarely limits life expectancy

More general terms

• nerve sheath tumor

More specific terms

• vestibular schwannoma (acoustic neuroma)

Additional terms

• facial nerve (CN VII)
• gamma knife radiosurgery (stereotactic radiosurgery)
• neurofibromatosis (central) type 2
• neurofibromatosis (classic) type 1
• neuroma
• trigeminal nerve (CN V)

Patient information

schwannoma patient information