Acoustic neuroma other diagnostic studies
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Simrat Sarai, M.D. [2]
Overview
Other diagnostic studies
Hearing test (audiometry)
- Audiometry as the best initial screening laboratory test for the diagnosis of acoutic neuroma, can detect asymmetric sensorineural hearing impairment in about ninety five percent of patients.
- Pure tone (audiogram) and speech audiometry should be performed. However test results does not essentially correlate with tumor size.
- Speech audiometry include two parts: the speech reception threshold (SRT) and the word discrimination score. The speech discrimination score is noticeably decreased in the affected ear and out of proportion to the measured hearing loss.
Auditory brainstem response test
- Brainstem-evoked response audiometry (ABR, BAER, or BSER) may be done in some cases with unexplained asymmetries in standard audiometric testing as a further screening measure.
- This test provides information on the passage of an electrical impulse along the circuit from the inner ear to the brainstem pathways. An acoustic neuroma can interfere with the passage of this electrical impulse through the cochlear nerve at the site of tumor growth in the internal auditory canal, even when the hearing is not necessarily impaired.
- This implies the possible diagnosis of an acoustic neuroma when the test result is abnormal. 20-35% of acoustic neuroma tumors smaller than 1 cm are missed by ABR screening techniques. the false negative rate can be as high as 30 percent with small vestibular schwannomas, and there is a 10 percent false positive rate.
- An abnormal auditory brain stem response test should be followed by an MRI.
- If an MRI is not available or cannot be performed, a computerized tomography scan (CT scan) with contrast is suggested for patients in whom an acoustic neuroma is suspected.
- The combination of CT scan and audiogram approach the reliability of MRI in making the diagnosis of acoustic neuroma.