Diagnostic Investigation for Acoustic Neuroma
Magnetic resonance imaging (MRI) with gadolinium enhancement is the gold standard investigation for suspected acoustic neuroma, with specific protocols including thin-slice T1-weighted sequences before and after gadolinium administration and high-resolution T2-weighted sequences. 1
Initial Audiologic Assessment
- Pure tone audiometry should be performed as the first-line screening test for patients with suspected acoustic neuroma 2, 3
- MRI screening is recommended for patients with ≥10 dB of interaural difference at 2 or more contiguous frequencies or ≥15 dB at 1 frequency 1
- Selectively screening patients with ≥15 dB of interaural difference at 3000 Hz alone may optimize diagnostic yield while minimizing unnecessary MRIs 1
- Speech discrimination testing often reveals disproportionately poor word recognition compared to pure tone thresholds in acoustic neuroma patients 4
- Acoustic reflex testing can be used as a supplementary screening tool, with absence of reflex, elevated threshold, and reflex decay being suggestive findings 5, 4
MRI Protocol Recommendations
- Axial submillimetric heavily T2-weighted sequences (FIESTA, CISS, or DRIVE) are essential to evaluate the vestibulocochlear nerve and its branches 1
- Contrast-enhanced 3D T1 MPRAGE or high-resolution T2 sequences are recommended for preoperative surveillance 1
- Post-gadolinium T1-weighted MRI remains the gold standard in diagnostic workup despite debates about potentially omitting contrast 1
Additional Diagnostic Tests
- Auditory brainstem response (ABR) testing can be used when MRI is contraindicated or unavailable, with IT5 being the most useful parameter 5, 3
- Electronystagmography (ENG) and vestibular testing may reveal decreased or absent caloric responses in approximately 90% of patients 4, 3
- For patients with asymmetric tinnitus without hearing loss, MRI is still recommended though the diagnostic yield is lower (<1%) 1
- For patients with sudden sensorineural hearing loss, MRI is recommended despite a relatively low yield (<3%) for acoustic neuroma detection 1
Follow-up Imaging Recommendations
- For patients under observation ("watch and wait" approach), MRIs should be obtained annually for 5 years, with interval lengthening thereafter if the tumor remains stable 1
- Post-treatment imaging frequency depends on the extent of resection - annual MRI scans for 5 years are reasonable for subtotal resections, while a single postoperative MRI at 1 year may be sufficient after gross total resection 1
Special Considerations
- Cystic vestibular schwannomas may behave more aggressively with more rapid growth and should be monitored accordingly 1
- The degree of lateral internal auditory canal involvement should be carefully assessed as it adversely affects facial nerve and hearing outcomes 1
- Patients with neurofibromatosis type 2 may require more frequent imaging due to more variable tumor growth rates 1