it is commonly caused by vascular compression of the facial nerve at its Root Exit Zone (REZ) from the brainstem.
There is now considerable evidence that primary HFS is, in almost all cases related to a vascular compression of the facial nerve at its Root Exit Zone (REZ) from the brainstem 4,5 .
Though no apparent cause may be found in some cases, the most common finding is a focal compression of the root exit zone of the facial nerve by an aberrant, atherosclerotic or ectatic vessel, commonly the posterior inferior cerebellar artery or anterior inferior cerebellar artery, or a combination of anterior inferior cerebellar artery and posterior inferior cerbellar artery, or the 20 vertebral artery .
1) Magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) are sensitive studies that often show vascular compression of the root exit zone of the ipsilateral facial nerve.
The most common cause of hemifacial spasm is neurovascular compression of the facial nerve at its root exit zone.