title: A case-controlled MRI/MRA study of neurovascular contact in hemifacial spasm.
abstract: BACKGROUND
  Neurovascular contact (NVC) with the root exit zone (REZ) of the ipsilateral facial nerve is associated with hemifacial spasm (HFS), but unresolved issues remain.
  
  
  OBJECTIVE
  To 1) determine the frequency of symptomatic 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 sides 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 sides, at least 70% of them were 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 symptoms. Most of our MR/MRA images showed that the size and position of the arterial branches of the vertebrobasilar system were markedly asymmetric. Of patients with bilateral NVC, over 83% had asymmetric NVC sites. The anterior 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 was significantly associated with nerve indentation in NVC. The development and severity of HFS were not associated with multiple contact points in NVC. No significant interobserver variability existed between the blinded assessments.
  
  
  CONCLUSIONS
  MRI/MR angiography are accurate, fast, and safe in characterizing neurovascular contact (NVC) at the brainstem. The site of NVC and ipsilateral facial nerve indentation in NVC are significant determinants for the development of hemifacial spasm (HFS). The lack of bilateral NVC at the anterior aspect of the root exit zone of the facial nerve could explain in part the lack of bilateral symptoms. The development and severity of HFS are not associated with a specific blood vessel or multiple contact points in NVC.
authors.affiliation: University Department of Medicine, University of Hong Kong, Hong Kong.
authors.forename: S L
authors.initials: SL
authors.lastname: Ho
authors.forename: P W
authors.initials: PW
authors.lastname: Cheng
authors.forename: W C
authors.initials: WC
authors.lastname: Wong
authors.forename: F L
authors.initials: FL
authors.lastname: Chan
authors.forename: S K
authors.initials: SK
authors.lastname: Lo
authors.forename: L S
authors.initials: LS
authors.lastname: Li
authors.forename: K L
authors.initials: KL
authors.lastname: Tsang
authors.forename: L L
authors.initials: LL
authors.lastname: Leong
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001488:Basilar Artery / Q000473:pathology; D001933:Brain Stem / Q000098:blood supply; D002531:Cerebellum / Q000098:blood supply; D004292:Dominance, Cerebral / Q000502:physiology; D005154:Facial Nerve / Q000473:pathology / Q000503:physiopathology; D005155:Facial Nerve Diseases / Q000175:diagnosis* / Q000503:physiopathology; D005260:Female; D019569:Hemifacial Spasm / Q000175:diagnosis* / Q000503:physiopathology; D006801:Humans; D007089:Image Enhancement; D007091:Image Processing, Computer-Assisted; D018810:Magnetic Resonance Angiography; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009408:Nerve Compression Syndromes / Q000175:diagnosis* / Q000503:physiopathology; D011446:Prospective Studies; D013126:Spinal Nerve Roots / Q000473:pathology / Q000503:physiopathology; D014711:Vertebral Artery / Q000473:pathology