Audiologic Changes in Vestibular Schwannoma
Vestibular schwannomas typically present with progressive unilateral sensorineural hearing loss, with approximately 50% of patients losing functional hearing within 3-4 years of diagnosis. 1
Primary Audiologic Findings
- Unilateral or asymmetric sensorineural hearing loss is the most common initial symptom of vestibular schwannoma 2
- Approximately 50% of patients with vestibular schwannoma will lose functional hearing during a 3-4 year observation period 1
- Full speech discrimination score at initial diagnosis is considered a good predictor for preservation of functional hearing 1
- All types of audiometric patterns can be found in patients with vestibular schwannoma, although low-frequency hearing loss patterns are less commonly associated with tumors 1
Diagnostic Audiologic Testing
- Serial audiometry is an important component of monitoring for vestibular schwannoma, though less sensitive than MRI 1
- Progressive hearing loss of greater than 10 dB (HL) in 2 or more frequencies or a drop in word recognition scores of greater than 10% should trigger evaluation with ABR or MRI 1
- Auditory Brainstem Response (ABR) testing may be used for initial evaluation but has limitations:
- ABR may miss 8-42% of intracanalicular vestibular schwannoma tumors 1
- ABR is highly sensitive for tumors >1 cm in size but less reliable for smaller tumors 1
- ABR testing is not possible when hearing loss exceeds 80 dB in the 2000-4000 Hz range 1
- The sensitivity of ABR is proportional to the degree of hearing loss; milder losses are more likely to yield false-negative results 1
Tumor Location and Hearing Impact
- Vestibular schwannomas arise from Schwann cells along the eighth cranial nerve, with approximately 80% found in the vestibular portion and 20% in the cochlear portion 1
- Small intracanalicular tumors (<5mm) most commonly originate near the fundus (61%), followed by the midpoint (34%), and least commonly near the porus acusticus (5%) 3
- Tumor location within the internal auditory canal does not appear to correlate with hearing outcomes 3
Monitoring Recommendations
- Audiological monitoring is recommended as part of the observational management of vestibular schwannoma 1
- Annual follow-up with audiometry is recommended for conservatively treated, radiated, and incompletely resected vestibular schwannoma for 5 years 1
- If tumor size remains stable for 5 years, follow-up intervals can be doubled thereafter 1
- MRI with gadolinium enhancement remains the gold standard for diagnosis and monitoring of vestibular schwannoma, with audiometry serving as a complementary assessment 1
Clinical Pitfalls and Caveats
- No clinical features can reliably distinguish sudden sensorineural hearing loss caused by vestibular schwannoma from idiopathic varieties 1
- Hearing recovery does not predict whether a patient's sudden hearing loss is the result of a tumor 1
- Associated events or diseases (e.g., barotrauma or recent viral infection) that were presumed to cause sudden hearing loss are present in approximately one-third of patients with vestibular schwannoma 1
- While vestibular schwannomas typically present with chronic progressive symptoms, they can occasionally manifest as acute vestibular syndrome mimicking vestibular neuritis 4
- Tinnitus in the affected ear prior to hearing loss onset, associated otalgia, or paresthesias are more common in patients with vestibular schwannoma but are too rare for their absence to reliably rule out a retrocochlear lesion 1