Unilateral hearing loss: To MR or not to MR?

The occasional case of unilateral hearing loss sometimes poses a dilemma. Should we order MRIs to rule out acoustic neuroma for every case of unexplained unilateral SNHL when the incidence is only 1 in 100,000?

Perhaps our suspicion index can be guided by the symptom profile of acoustic neuroma where there is:
93.4% hearing impairment
75.5% tinnitus
40.6% vertigo
38.8% unsteadiness

Hearing loss can be sudden (12-47%) or insidious

Ho & Kveton, 2002, recommended a protocol for investigation:
- for patients with limited symptoms (isolated vertigo, historically explained unilateral hearing loss or tinnitus, or symmetrical hearing loss; estimated risk of acoustic neuroma < 5%): ABR as initial test and MRI if abnormal ABR
- for patients with intermediate symptoms (sudden sensorineural hearing loss or unexplained persistent unilateral tinnitus; estimated risk of acoustic neuroma 5-30%): MRI as initial test
- for high-risk patients with combination of unilateral asymmetric sensorineural hearing loss, tinnitus and decreased speech discrimination (estimated risk of acoustic neuroma > 30%): MRI with gadolinium initially and periodic ABR testing if negative MRI


On the other hand, it is worth remembering that tumor growth is on average 1-2.3 mm/year and less than 30% grow > 2 mm/year so that serial MRIs are hardly helpful and may not require any intervention in the elderly.

References
Arch Otolaryngol Head Neck Surg 2004 Feb;130(2):216
Neurosurgery 2006 Jul;59(1):67
J Laryngol Otol 1994 Feb;108(2):116
Am J Otolaryngol 1999 May-Jun;20(3):157
Neurosurgery 1997 Jan;40(1):1
Otolaryngol Clin North Am. 2002 Apr;35(2):393-404, viii