Should all patients referred for magnetic resonance imaging scans of their internal auditory meatus be followed up in ENT clinics?

Incidental findings on magnetic resonance imaging of the internal auditory meatus for vestibular schwannoma: a systematic review

OBJECTIVE

Magnetic resonance imaging of the internal auditory meatus is a highly sensitive and specific way to diagnose vestibular schwannoma. However, the rate of incidental findings with this method is believed to be high and can lead to increased patient anxiety and health interventions with unclear benefit.

METHOD

A systematic review of the literature was performed using the Preferred Reporting Items for Systematic Review and Meta-Analyses guidelines to identify incidental findings from magnetic resonance imaging of the internal auditory meatus; 12 studies were identified for inclusion within this review.

RESULTS

A total of 10 666 patients were included within the review. The overall rate of diagnosis of vestibular schwannoma was 0.87 per cent; 21 per cent of the study population had incidental findings on magnetic resonance imaging of the internal auditory meatus, and 9.56 per cent had clinically significant incidental findings.

CONCLUSION

Standardised pre-scan counselling may mitigate the risks of overdiagnosis, but future work should be undertaken to assess the benefits of such a strategy as well as the exact significance of some incidental findings.

Hearing disorders in brainstem lesions

Auditory processing can be disrupted by brainstem lesions. It is estimated that approximately 57% of brainstem lesions are associated with auditory disorders. However diseases of the brainstem usually involve many structures, producing a plethora of other neurologic deficits, often relegating "auditory symptoms in the background." Lesions below or within the cochlear nuclei result in ipsilateral auditory-processing abnormalities detected in routine testing; disorders rostral to the cochlear nuclei may result in bilateral abnormalities or may be silent. Lesions in the superior olivary complex and trapezoid body show a mixture of ipsilateral, contralateral, and bilateral abnormalities, whereas lesions of the lateral lemniscus, inferior colliculus, and medial geniculate body do not affect peripheral auditory processing and result in predominantly subtle contralateral abnormalities that may be missed by routine auditory testing. In these cases psychophysical methods developed for the evaluation of central auditory function should be employed (e.g., dichotic listening, interaural time perception, sound localization). The extensive connections of the auditory brainstem nuclei not only are responsible for binaural interaction but also assure redundancy in the system. This redundancy may explain why small brainstem lesions are sometimes clinically silent. Any disorder of the brainstem (e.g., neoplasms, vascular disorders, infections, trauma, demyelinating disorders, neurodegenerative diseases, malformations) that involves the auditory pathways and/or centers may produce hearing abnormalities.