Vascular loops causing otological symptoms: a systematic review and meta-analysis

Objective of review: To determine evidence for a relationship between vascular loops in contact with the vestibulocochlear nerve (CN VIII) and otological symptoms. Type of review: Systematic review and meta-analysis of observational studies. Search strategy: Comprehensive search of MEDLINE, EMBASE, CINAHL, Cochrane Library, Clinical Evidence and Cochrane Central Register of Trials. Reference lists cross-referenced and authors contacted for missing data. No language restrictions. Evaluation methods: Included studies: (1) compared symptoms in subjects with a vascular loop contacting CN VIII to subjects without (inter-subject control); (2) compared the prevalence of vascular loop in contact with CN VIII in symptomatic ears to contra-lateral asymptomatic ears (intra-subject control). Study quality systematically appraised. Results: Five case-control studies included. A statistically significant association was demonstrated for the prevalence of vascular loops in contact with CN VIII, with unilateral sensorineural hearing loss: pooled odds ratio (OR) 2.0 [95% confidence interval (CI): 1.5-2.6]. No association was demonstrated for non-pulsatile tinnitus. A highly significant association with vascular loops was shown in subjects having pulsatile tinnitus, with pooled OR: 78.8 (95% CI: 10.9-821.8). Conclusions: Vascular loops in contact with CN VIII are a normal variant. Subjects with unilateral hearing loss were twice as likely to have these vascular loops in the symptomatic ear, than in the asymptomatic ear. Subjects with pulsatile tinnitus were 80 times more likely to have a contacting vascular loop than patients with non-pulsatile tinnitus, suggesting in some cases a causal relationship exists for pulsatile tinnitus, where surgical intervention may be occasionally indicated.