Head and Neck ImagingHemifacial spasm
unilateral involuntary contractions of the facial muscles. The condition is slowly progressive and usually painless. The most common aetiology is pressure of a vessel on the cisternal component of the facial nerve, at the level of the root exit zone (neurovascular conflict). The vessel most commonly responsible for this conflict is the posterior inferior cerebellar
artery, followed in frequency by the vertebral
artery and the anterior inferior cerebellar
artery. In a minority of cases, a
vein is found to cause the neurovascular conflict.
MRI has been reported to have a high diagnostic efficiency in identifying neurovascular conflicts in the cerebellopontine angle.
Other lesions on the path of the facial nerve may also cause hemifacial spasm; the facial nerve should therefore be imaged over its entire course in patients with hemifacial spasm to exclude other lesions (Fig.1) (Fig.2).
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Axial gradient-echo MR image of cerebellopontine angles. The left vertebral artery (arrow) is displaced posteriorly, deforming the brainstem and cerebellar peduncle at the level of the root exit zone of the facial nerve (courtesy by Danielle Baleriaux, Brussels, Belgium).
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Hemifacial spasm, Fig.1 | | Hemifacial spasm, Fig.2 | |