Magnetic resonance imaging for acoustic neuromas

OBJECTIVE: The aim of this retrospective study was to evaluate the use of magnetic resonance imaging (MRI) of the internal auditory meatus (IAM) in identifying acoustic neuromas. MATERIALS AND METHODS: Retrospective case review involving 335 patients who presented to the Department of Otolaryngology in Leighton Hospital, United Kingdom for the treatment of various otologic symptoms. RESULTS: In 3 of the 335 patients evaluated, an MRI scan revealed an acoustic neuroma in the cerebellopontine (CP) angle. MRI scans of 326 patients did not show a pathologic condition in the CP angle. Six patients did not undergo MRI because of various contraindications, 2 patients presented with both a progressive asymmetrical sensorineural hearing loss of > 15 dB and tinnitus, and 1 patient presented with a unilateral hearing loss, tinnitus, and vertigo (all of which were sudden in onset). None of the patients with NIHL (10 dB at 4 kHz) or with vertigo alone had a pathologic condition of the CP angle. Most of study subjects had been exposed to loud noise in the past. CONCLUSIONS: Magnetic resonance imaging of the internal auditory meatus should be considered for patients in whom clinical examination does not reveal the cause of a unilateral or asymmetrical hearing loss of > 15 dB and concomitant tinnitus. We found that hearing loss was more significant if it was progressive or of sudden onset. Patients with noise-induced hearing loss (10 dB at 4 kHz), vertigo without hearing loss (a disorder unlikely to result from an acoustic neuroma), or asymmetrical hearing loss due to Eustachian tube dysfunction were unlikely to have an acoustic neuroma and therefore did not require magnetic resonance imaging. Evaluation with pure tone audiometry should always be considered before magnetic resonance imaging of the internal auditory meatus is performed. The results of magnetic resonance imaging should be compared with those of previous pure tone audiometric studies, and any change in frequency thresholds should be noted. This approach prevents the unnecessary imaging of healthy patients and decreases both the radiology staff workload and the cost of patient care.