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Acoustic neuroma
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Acoustic neuroma

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Contributors: Madeleine Strohl MD, Paul C. Bryson MD
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Synopsis

Acoustic neuromas, also known as vestibular schwannomas, are intracranial tumors that arise from the Schwann cell sheath of the eighth cranial (vestibulocochlear) nerve. The incidence of acoustic neuromas in the United States is 10-20 per 1 000 000 people. Acoustic neuromas account for approximately 8% of intracranial tumors in adults and represent 80% of all tumors of the cerebellopontine angle. Ninety percent of tumors are unilateral, affecting the left and right sides equally. The median age at diagnosis is 50 years. The tumors are rare in children, except for patients with neurofibromatosis type II. There is a 3:2 female to male ratio. All races and ethnicities are equally affected.

The most common presenting symptoms are one-sided hearing loss and/or tinnitus. Vertigo and disequilibrium are relatively uncommon presentations. As the tumor expands, it may compress the facial or trigeminal nerves, resulting in decreased facial sensation or facial muscle weakness. Late complications include cerebellar and brainstem dysfunction as a result of compression. Obstructive hydrocephalus is also possible due to effacement of the fourth ventricle.

On physical exam, the Weber and Rinne tests and formal audiogram may be used to uncover unilateral sensorineural hearing impairment. Neurologic examination may reveal defects of the fifth and seventh cranial nerves, such as a decreased or absent corneal reflex or hypoesthesia. Romberg and Hall-Pike tests are typically normal.

Patients with neurofibromatosis type II classically develop bilateral acoustic neuromas at a young age. Other risk factors associated with the development of acoustic neuromas include childhood exposure to low dose radiation and a history of parathyroid adenoma.

Acoustic neuromas are typically slow-growing tumors. They usually grow at a rate of 2-4 mm/year, but can occasionally grow as rapidly as 2 cm/year. If treated with current techniques, patients have a very good prognosis with minimal complications. However, if left untreated, these tumors eventually lead to lethal brain stem compression or intracranial hypertension.

For more information on neurofibromatosis type II, see OMIM.

Codes

ICD10CM:
D33.3 – Benign neoplasm of cranial nerves

SNOMEDCT:
126949007 – Acoustic neuroma

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Differential Diagnosis & Pitfalls

Other causes of unilateral hearing loss and/or tinnitus should be considered, although the demonstration of a cerebellopontine angle lesion on a contrast-enhanced MRI in the setting of unilateral hearing loss or tinnitus virtually rules out other causes of hearing loss, tinnitus, or vertigo. Laboratory testing can also help exclude these causes.
  • Cerebrovascular accident
  • Vertebrobasilar insufficiency
  • Meniere disease – Constellation of clinical symptoms including episodic vertigo, sensorineural hearing loss, and tinnitus; requires all other causes ruled out
  • Benign positional vertigo – Vertigo experienced in specific positions, no hearing loss
  • Multiple sclerosis – Demonstration of plaques on MRI
  • Perilymphatic fistula – History of head injury, barotrauma, or heavy lifting; imaging may show fluid collection in region of round window recess
  • Viral cochleitis (see sensorineural deafness) – History of viral disease
  • Ototoxic drugs – Review medication history (aminoglycosides, some diuretics)
  • Thyrotoxicosis – Order TSH/T4 levels
  • Sudden sensorineural hearing loss (see sensorineural deafness) – Evaluation will reveal no underlying condition by history, examination, or imaging
Approximately 20% of tumors at the cerebellopontine angle are not acoustic neuromas. These conditions can be differentiated by their main presenting symptoms and differences on imaging.
  • Meningioma – Hearing loss is a less prominent symptom; often has a dural tail on MRI
  • Primary cholesteatoma – Presence of chronic drainage and granulation tissue in the ear canal and middle ear; CT is diagnostic modality of choice to evaluate bony defects
  • Epidermoid – Hearing loss is less prominent symptom; no enhancing component on MRI
  • Facial nerve schwannoma – Clinically associated with more prominent and earlier facial weakness; enhancement on MRI extends into the geniculate ganglion of the facial nerve and facial canal
  • Trigeminal schwannoma – Clinically associated with more prominent facial numbness; enhancement on MRI does not extend into the internal acoustic meatus

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Last Updated: 05/02/2019
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Acoustic neuroma
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Acoustic neuroma : Gait disturbance, Hearing loss, Tinnitus, Vertigo, Facial paresthesias
Clinical image of Acoustic neuroma
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