Review articleAcoustic neuroma: Assessment and management
Section snippets
Classification
In the past, acoustic neuroma was thought to be mainly a disease of the superior vestibular nerve; however, a recent study shows that they arise with nearly equal frequency on both the superior and inferior vestibular nerves [2].
Acoustic neuroma can be classified into two categories. One type is associated with neurofibromatosis type 2 (NF-2). In this rare, autosomal dominant disorder, the acoustic neuromas are bilateral. In addition to the bilateral acoustic neuromas, NF-2 is associated with
Epidemiology
Acoustic neuroma occurs in all parts of the world without ethnic predilection [3]. No specific risk factor has been identified. The true incidence of this disease is unclear. The best estimate according to the NIH consensus places the incidence at 1 per 100,000 individuals per year in the United States [5], [6], [7], which translates to 2000 to 3000 new cases diagnosed per year in the United States; however, three large autopsy series have identified these tumors in 0.8% to 1.7% of patients [8]
Presentation and physical findings
Hearing loss is the most common finding, occurring in more than 95% of patients over the course of this disease [10], [11]. The typical presentation is a slowly progressive, high-frequency sensorineural hearing loss (SNHL) on the affected side. More importantly, the reduced speech discrimination occurs out of proportion to the pure tone loss. Episodic and sometimes permanent, sudden hearing loss also has been reported as the presenting symptoms in as many as 25% of patients, as reported by the
Audiometric assessment
Audiometric assessment is usually the first diagnostic test performed. In a review of 500 audiograms, Johnson [20] reported that 66% of patients with acoustic neuromas demonstrated high-frequency loss; 10%, low-frequency loss; and 10%, flat audiograms. In all of these patients, the loss was unilateral and, therefore, asymmetric.
Loss of speech discrimination, an indicator of retrocochlear hearing loss, is also associated with acoustic neuroma. In the same study, Johnson [20] reported that 72% of
Imaging assessment
Plain radiography is no longer used for detecting acoustic neuroma. The deep recess in which the acoustic neuroma originates makes plain radiography difficult and confusing to interpret.
Computed tomography has a limited role in detecting acoustic neuroma. This technique clearly delineates the bony architecture of the petrous bone and labyrinth. Soft tissue differentiation and resolution are usually insufficient on CT to clearly delineate a small acoustic tumor. Calcification is rarely seen in
Diagnostic assessment
With a wide variety of clinical presentations, acoustic neuroma may be difficult to diagnose. During evaluation of the patient, certain clinical symptoms and findings should raise a clinician's suspicion of the presence of acoustic neuroma. The Otology Group has categorized the patients into three distinct risk groups based on the symptomatic presentation and audiogram findings.
Group 1 patients have limited symptoms, including isolated vertigo, historically explained unilateral hearing loss and
Natural history of acoustic neuroma
The natural history of untreated acoustic neuroma remains unpredictable. No factors predictive of tumor growth have been identified [29]. Small tumor size and advanced age are not predictors of slow tumor growth. Most of the recent studies demonstrate slow growth of acoustic neuroma ranging from 0.1 to 0.23 cm/y [30], [31], [32]. Less than 30% of untreated acoustic neuromas demonstrate growth greater than 0.2 cm/y on MR imaging; however, tumors larger than 2.0 cm are statistically more likely
Observation
With the slow growth of this tumor, close observation is an acceptable treatment option in a select group of patients. For elderly and infirm patients with small tumors, observation definitely is a preferred choice until the tumor has demonstrated significant growth. In young patients, this option is controversial. Even in the absence of obvious tumor growth, the risk for useful hearing loss is significant with noninvasive management [33]. Furthermore, the enlarged tumor increases the risks
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