As in the two other aforementioned conditions, irritation of the nerve at the root exit zone by an aberrant vascular structure is usually a cause. Up to 100% of cases had a vessel contacting the nerve in symptomatic patients, whereas up to 30% of asymptomatic patients had a similar finding. This matches day to day experience, where an elongated and ectatic vertebrobasilar system is commonly seen incidentally. The vessels most commonly implicated are the AICA, PICA and vertebral artery (decreasing order of frequency).
Other causes of HFS have been reported including:
- vascular compression as discussed above: most common
- intracranial lipoma
- arteriovenous malformation (AVM)
- multiple sclerosis (MS): very rarely implicated
Often the condition begins insidiously with spasm of the orbicularis oculi gradually spreading in extent and severity to involve the majority of the face, although often sparing the frontalis muscle. It is not a painful condition (after all it is a motor nerve!).
Hemifacial spasm should be distinguished from myokymia a fine undulating fascicular tremor of facial musculature. The two conditions may co-exist.
Microvascular decompression is a useful treatment, with up to 80% complete and immediate resolution of symptoms.
- 1. R Tash et al "Hemifacial spasm: MR imaging features" American Journal of Neuroradiology, Vol 12, Issue 5 839-842
- 2. JD Swatrz, HR Harnsberger "Imaging of the Temporal Bone" Thieme