Acoustic neuroma other diagnostic studies

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Simrat Sarai, M.D. [2] Mohsen Basiri M.D.

Overview

Audiometry as the best initial screening test for the diagnosis of acoustic neuroma. It can detect asymmetric sensorineural hearing impairment in about 95% of the patients. Brain stem-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 and an abnormal auditory brain stem response test should be followed by an MRI.

Audiometry as the best initial screening test for the diagnosis of acoustic neuroma.
It can detect asymmetric sensorineural hearing impairment in about 95% of the patients.
Speech audiometry includes speech reception threshold (SRT) and the word discrimination score. The word discrimination score is noticeably decreased in the affected ear and out of proportion to the measured hearing loss.

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% with small vestibular schwannomas, and there is a 10% 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 suspected of having the tumor.
The combination of CT scan and audiogram can approach the reliability of MRI in making the diagnosis of acoustic neuroma.