Case 20 - Facial twitching
What is the lesion?
Hemifacial spasm is often idiopathic, but is worth investigating as there may be a structural cause, including dangerous ones.
Most commonly the lesion is a blood vessel contacting the root at the exit zone from the pons – termed neurovascular conflict. The main culprits are the vertebral artery (VA) and the anterior inferior cerebellar artery (AICA). It may be an artery which is entirely normal, just contacting the nerve – but also can be an abnormal vessel, for example dilated due to an aneurysm or dolichoectasia.
Other structural lesions can be seen, including pontine infarctions, pontine tumours, demyelination, and masses at the cerebellopontine angle (CPA) such as vestibular schwannoma or arachnoid cyst. In some cases, secondary causes such as this might include addition features such as facial muscle weakness or additional deficits - for example sensorineural hearing loss (VIII) or facial numbness (V) with a CPA mass, or long tract damage or other cranial nerve deficits from a pontine lesion.
Imaging, including angiography, is worthwhile. Finding one of the various structural causes above could influence management in numerous ways, including surgery. Finding neurovascular conflict can support the diagnosis, but the diagnosis is clinical - not based on scan changes. It should be borne in mind that in some patients the contacting vessel is on the wrong side, or there is bilateral conflict despite unilateral symptoms. A vessel contacting VII can also be seen in otherwise healthy people who do not have HFS!
Clinical formulation