Weber and Rinne Tests Assess Cranial Nerve VIII (Vestibulocochlear Nerve)
The Weber and Rinne tuning fork tests are used to assess cranial nerve VIII (the vestibulocochlear nerve), specifically evaluating its cochlear component to differentiate between conductive and sensorineural hearing loss. 1, 2
Anatomical Basis
- CN VIII is a purely special sensory nerve with two functional components: the vestibular nerve (detecting head and body motion) and the cochlear nerve (detecting sound). 2
- The Weber and Rinne tests specifically evaluate the auditory function mediated by the cochlear portion of CN VIII. 1
- CN VIII nuclei are located in the brainstem, anatomically separate from the spinal cord. 3
Clinical Application of These Tests
The Weber and Rinne tuning fork tests differentiate conductive hearing loss (CHL) from sensorineural hearing loss (SNHL), which is essential for determining the anatomical location of pathology. 1
Weber Test Interpretation:
- Normal finding: Sound heard at midline or "everywhere" 1
- Lateralization to one ear indicates either:
- Conductive hearing loss in that ear, OR
- Sensorineural hearing loss in the opposite ear 1
- The test lateralizes at approximately 2.5 dB difference between ears 4
Rinne Test Interpretation:
- Normal finding: Air conduction louder than bone conduction 1
- Abnormal finding: Bone conduction louder than air conduction indicates conductive hearing loss in that ear 1
- The test changes from positive to negative at approximately 13 dB air-bone gap 4
- Sensitivity is 97% for normal hearing or SNHL, and 72% for detecting CHL 4
Technical Performance
- Use a 256 Hz or 512 Hz tuning fork for both tests 1
- Weber: Place vibrating fork at midline of forehead or on maxillary teeth (not dentures) 1
- Rinne: Place vibrating fork over mastoid bone, then move to ear canal entrance without touching the ear 1
Important Caveats
- These tests have limited sensitivity for mild conductive hearing loss (air-bone gap 5-35 dB), with accuracy dropping significantly in this range 4
- Patients with SNHL typically have normal otoscopic examination, while CHL patients often show visible abnormalities 1
- Impacted cerumen must be removed before establishing a diagnosis, as it can cause false-positive CHL findings 1