Vestibular schwannomas, also known as acoustic neuromas, are intracranial tumors that arise from the Schwann cell sheath of the eighth cranial (vestibulocochlear) nerve. The incidence of vestibular schwannomas in the United States is 10-20 per 1 000 000 people. Vestibular schwannomas 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 2. 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 examination, 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 2 classically develop bilateral vestibular schwannomas at a young age. Other risk factors associated with the development of vestibular schwannomas include childhood exposure to low dose radiation and a history of parathyroid adenoma.
Vestibular schwannomas 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.
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.
Meniere disease – Constellation of clinical symptoms including episodic vertigo, sensorineural hearing loss, and tinnitus; requires all other causes ruled out.
Approximately 20% of tumors at the cerebellopontine angle are not vestibular schwannomas. 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.
