A case-controlled MRI/MRA study of neurovascular contact in hemifacial spasm

Background: Neurovascular contact (NVC) with the root exit zone (REZ) of th e ipsilateral facial nerve is associated with hemifacial spasm (HFS), but u nresolved issues remain. Objectives: To 1) determine the frequency of sympt omatic and nonsymptomatic NVC, 2) determine the features of NVC associated with HFS, and 3) correlate severity of HFS to these features. Methods: Two independent, blinded, prospective assessments of high-resolution MR and MR angiography (MRA) images were performed on Chinese cases (HFS: n = 44; age- matched control subjects: n = 20). Results: Over 88% of 44 symptomatic side s in patients with HFS had NVC of the ipsilateral facial nerve. At least 80 % of symptomatic sides involved NVC at the anterior aspect of the REZ [REZ( ant.)]. Although NVC was observed in approximately half of nonsymptomatic s ides, at least 70% of them mere not at REZ(ant.). NVC at the cisternal and intracanalicular portions of the facial nerve were not associated with HFS. Half of our patients with HFS had bilateral NVC, but none had bilateral sy mptoms. Most of our MR/MRA images showed that the size and position of the arterial branches of the vertebrobasilar system were markedly asymmetric. O f patients with bilateral NVC, over 83% had asymmetric NVC sites. The anter ior inferior cerebellar artery was the most common vessel involved in NVC, but was not significantly associated with HFS. Most of the NVC involved one vessel at one contact point with no indentation. The development of HFS wa s significantly associated with nerve indentation in NVC. The development a nd severity of HFS were not associated with multiple contact points in NVC. No significant interobserver variability existed between the blinded asses sments. Conclusions: MRI/MR angiography are accurate, fast, and safe in cha racterizing neurovascular contact (NVC) at the brainstem. The site of NVC a nd ipsilateral facial nerve indentation in NVC are significant determinants for the development of hemifacial spasm (HFS). The lack of bilateral NVC a t the anterior aspect of the root exit zone of the facial nerve could expla in in part the lack of bilateral symptoms. The development and severity of HFS are not associated with a specific blood vessel or multiple contact poi nts in NVC.