vestibular schwannoma (acoustic neuroma)

Introduction

schwannoma or neurilemmoma of 8th nerve; acoustic neuroma is misnomer.

Etiology

• idiopathic sporadic unilateral 95%
• cancer susceptibility syndromes
  • neurofibromatosis type 2
  • schwannomatosis

Epidemiology

• 8% of all intracranial neoplasms
• lifetime prevalence of 1 in 500 persons
• increasing incidence due to enhanced detection
• most common in 6th or 7th decade in life
  • 20 cases per 100,000 person years

Pathology

• arise from myelinating Schwann cells of vestibular division of cranial nerve VIII
• compressive growth with the internal auditory canal/meatus results in unilateral tinnitus & hearing loss
• compromise of cranial nerves VII & VIII, the brain stem & the cerebellum may occur

Clinical manifestations

• sensorineural hearing loss
  • tinnitus &/or vertigo may be presenting symptoms
  • hearing loss is usually unilateral (90%)
  • Weber test lateralizes to the unaffected ear
• gradual onset of symptoms generally progressive rather than episodic
• symptoms are often unilateral
• vestibular symptoms (unsteadiness, balance issues)
• acoustic & vestibular symptoms are not reliable indicators of tumor growth
• cranial nerves 5, 7, 9, 10, 11 may be affected with tumor progression
• even large schwannomas generally do not affect facial-nerve, trigeminal motor, or lower cranial-nerve dysfunction
• abnormal finger to nose test suggests compression of cerebellum

Diagnostic procedures

• audiometry 6 months after diagnostic MRI, then annually
• confirmatory biopsy rarely needed

Radiology

• magnetic resonance imaging (MRI) of the posterior fossa & internal auditory canal with gadolinium contrast
• yield of MRI for vestibular schwannoma diagnosis < 3%
• once diagnosed, serial imaging should be obtained at annually, regardless of symptoms

Complications

• compression of cochlear nerve or labyrinthine artery
• impaired circulation of CSF
• inflammation mediated by schwannoma
• as the tumor enlarges, it compresses cranial nerves & the cerebellum

Differential diagnosis

• facial-nerve schwannoma
• meningioma
• malignant peripheral-nerve sheath tumors
• metastases from primary tumors at other sites
• otosclerosis: associated with conductive hearing loss*
• cholesteoma: associated with conductive hearing loss*
• central vertigo due to stroke - sudden onset, vertical nystagmus

* Weber test lateralizes to affected ear

Management

• referral to otorhinolaryngologist
• stereotactic radiosurgery - gamma-knife radiosurgery
  • maximal neoplasm diameter < 3.0 cm in the cerebellopontine angle
  • complications include: brain-stem edema, trigeminal neuralgia, hydrocephalus
  • upfront radiosurgery for small & medium size tumors results in greater tumor reduction at 4 years than treatment with tumor growth
• microsurgical resection
  • treatment of choice for large neoplasm associated with:
    • symptomatic brain-stem compression, hydrocephalus, trigeminal neuralgia
  • general anesthesia, operating microscope, intraoperative neural monitoring
• sensorineural hearing loss & vestibular dysfunction are not reversed with treatment
• conservative management
  • prioritizing preservation of neurologic function vs cure
  • potential for overtreatment resulting in unnecessary complications & health care expenses
  • untreated vestibular schwannoma in patients >= 70 years not associated with shorter lifespan
• investigational drug treatment includes aspirin & monoclonal antibodies
  • no strong evidence any treatment is superior to others
• some patients may require rehabilitation

More general terms

• schwannoma (neurilemoma, neurinoma)
• benign cranial nerve neoplasm
• neuroma

Patient information

vestibular schwannoma (acoustic neuroma) patient information