Design: Systematic review and random-effects meta-analysis of 11 studies
Population: 4014 adults having microvascular decompression for hemifacial spasm
Primary outcome: Permanent postoperative hearing loss
Effect: 2.60% (95% CI 1.13% to 5.87%), I² = 87.4%

A systematic review of 11 studies (4014 adults) with objective hearing tests before and after microvascular decompression for hemifacial spasm estimated permanent hearing loss at 2.60% (95% CI 1.13% to 5.87%), with high heterogeneity (I² = 87.4%). Prospective studies reported more (5.29%) than retrospective ones (1.97%), a difference that was not significant.

Changes in brainstem auditory evoked responses, especially wave V latency or amplitude, consistently predicted hearing loss, and more cerebellar retraction — deeper, further or longer — was associated with higher risk.

For ENT surgeons, the figure is useful for consent and for interpreting a new post-operative hearing complaint. Higher rates in prospective studies suggest some loss is missed without formal audiometry.

Obtain a pure-tone audiogram before and after microvascular decompression for hemifacial spasm.
Quote a risk of about 1 in 40 for permanent hearing loss when counselling, noting the uncertainty.
Support intraoperative brainstem auditory evoked response monitoring where it is available.
Investigate any new post-operative hearing complaint promptly with audiometry.

Why it matters

Prospective studies with formal testing found more hearing loss, so it is likely under-recognised without audiometry.

The statistics, in plain English

A pooled 2.6% with an interval of 1.1% to 5.9% means between about 1 in 90 and 1 in 17. The high I² means the estimate is unstable, largely because studies tested hearing differently.