Hypoplasia of the internal carotid artery associated with spasmodic torticollis: the possible role of altered vertebrobasilar haemodynamics.

We describe an unusual case of hypoplasia of the left internal carotid artery associated with an anomalous origin of the ipsilateral middle cerebral artery in a patient with spasmodic torticollis. Collateral circulation to the territory of the middle cerebral artery was through the vertebrobasilar circulation, and the left vertebral artery was dilated and compressing the ventrolateral aspect of the cervicomedullary junction, as evidenced by MRI. We believe this to be the first report of unilateral hypoplasia of the internal carotid artery associated with spasmodic torticollis. Compression of the left accesory nerve by the dilated vertebral artery as a result of altered haemodynamics was thought to cause spasmodic torticollis.