Acoustic neuroma: What the evidence says about evaluation and treatment

When a patient presents with unilateral hearing loss—especially with a report of gradual onset— that is accompanied by tinnitus, consider an acoustic neuroma (AN). Also known as vestibular schwannoma, ANs represent just 9% of all intracranial tumors. But its relatively slow growth rate can insidiously lead to impaired quality of life and even complete hearing loss.¹ Vestibular symptoms, such as vertigo, may be present. And in some instances, tinnitus may be absent. Even without hearing loss or other symptoms, ANs may be detected incidentally on magnetic resonance imaging (MRI) performed for other reasons. In this article, I describe the diagnostic work-up for AN and 3 options for treatment.

How acoustic neuroma arises

ANs evolve from the abnormal growth and proliferation of Schwann cells, or neurolemmocytes, at their junction with glial cells surrounding the vestibular nerve. ANs represent 80% of all cerebellopontine angle tumors.¹ The incidence in the general population is about 1 in 100,000 people per year, with equal distribution between men and women.¹ Among adults with sensorineural hearing loss, about 1% have ANs.² Tumor growth within the internal auditory canal and resultant compression of cranial nerves VII and VIII causes associated symptoms. Unabated growth can lead to prolapse into the cerebellopontine angle with compression of the brainstem and cerebellum.¹

There are 2 major types of AN. The sporadic type, which will be the focus of this discussion, occurs in 95% of all cases, is unilateral, and usually affects individuals 40 to 60 years old. AN associated with neurofibromatosis type 2 is typically bilateral, autosomal dominant, and usually affects teens and young adults.¹

The only known possible risk factor for the development of AN is the use of cell phones, but data are conflicting. Although 2 meta-analyses did find a correlation between AN and ipsilateral cell phone use >10 years, these studies were limited by possible recall bias and misclassification.^3,4

How acoustic neuroma can present

Slowly progressive, high-frequency, sensori-neural hearing loss is typical for AN. In most cases, hearing loss is unilateral. Nerve compression and stretching from the growing neuroma cause hearing loss of gradual onset.¹ However, up to 25% of patients may present with sudden onset hearing loss due to total occlusion of the internal auditory canal and the artery supplying the cochlea.¹ Tinnitus is reported in up to 70% of patients with AN.¹ The mechanism of injury is the same as for hearing loss.

A feeling of imbalance or unsteadiness occurs in more than 50% of patients with AN.¹ One research group found that vertigo was the more common symptom in patients with smaller tumors, whereas patients with larger tumors complained more of dysequilibrium.¹

Other physical findings can include trigeminal nerve dysfunction (found in 50% of patients with AN, but patients rarely note the absent corneal reflex), facial nerve motor dysfunction (2%), increased intracranial pressure (rare in tumors <3 cm), and brainstem and cerebellar symptoms (rare).¹

Asymptomatic AN. Small tumors may be detected by MRI incidentally before the onset of hearing loss. Such a finding accounts for about 12% of all patients diagnosed with AN.⁵ A 2005 study by Lin et al found the prevalence of incidental AN to be about 2 per 10,000 people.⁶ This is higher than the 1 in 100,000 suggested by epidemiologic studies,⁶ but Lin’s study was performed at a large tertiary center.

Diagnostic evaluation

Contrast MRI is the gold standard for diagnosing AN.² One study did find that a heavily T2-weighted noncontrast scan in the hands of an experienced radiologist reduced the procedural cost and was as effective as contrast MRI in evaluating the VII and VIII cranial nerves within the cerebellopontine angle and internal auditory canal.⁷

Although not as sensitive for small tumors, the auditory brainstem response can be used in certain circumstances. During the initial evaluation, other diagnoses to consider are facial neuroma and jugular foramen tumors.¹

Three options for treatment

The goal of treatment is to slow or eliminate both tumor growth and deterioration in hearing and neurological function. Lin’s study found that 43% of patients with incidental AN had abnormal audiometry findings.⁶ A hearing evaluation may therefore be helpful in guiding patients through a meaningful discussion about prognosis, further testing and consultations, and the 3 therapeutic options—watchful waiting, microsurgery, and stereotactic radiosurgery.⁸