BACKGROUNDSome studies indicated that cases of idiopathic oculomotor nerve palsy can be explained by vascular compression of the oculomotor nerve. Vascular contact with or compression to the cisternal segment of the oculomotor nerve has been reported frequently in asymptomatic individuals. In this study, we retrospectively analyzed the relationship between the oculomotor nerve's cisternal segment and adjacent arteries in asymptomatic patients and the prevalence of this occurrence via magnetic resonance imaging (MRI).

METHODMRI of bilateral oculomotor nerves in 93 asymptomatic patients were reviewed. The oculomotor nerve-artery relationship was evaluated and classified from levels 1 to 3, representing the degrees of contact on oblique transverse and oblique sagittal reconstructed MRI. Prevalence of the nerve-artery relationship at each level was described. The correlation between the nerve-vessel relationship (levels) and the age was analyzed by Spearman's rank correlation analysis.

RESULTSCisternal segment of the oculomotor nerve did not have contact with any artery (level 1) in 27.4% (51/186) nerves. One hundred nerves made contact with at least one artery (level 2), but their shapes or configurations were not changed; 35 nerves (18.8%) were displaced or distorted due to artery compression (level 3). The posterior cerebral artery had the greatest incidence of making contact with or compressing the cisternal segment of the oculomotor nerve (58.1%). No significant correlation between nerve-vessel relationship (levels) and the age was found in this study.

CONCLUSIONSWhether oculomotor nerve contact with or compression by one or more arteries is of high prevalence in asymptomatic individuals as evidenced by MRI examination. There is no correlation with individual age. Discretion should be used when making an etiological diagnosis of vascular compression for patients with oculomotor nerve palsy. Further investigation of other causes is warranted.