Mechanical occlusion of the vertebral artery.

Acute insufficiency of the basilar artery, in the absence of organic disease, has been encountered in 20 patients. Attacks are transient and are precipitated by turning the head laterally and upwards. Two conditions are extant: (1) obliteration of vertebral artery flow by the contraction of the longus colli muscle and the scalene muscle at the level of the vertebral foramen of the sixth cervical vertebra and (2) a hypoplastic contralateral artery which does not adequately supply the basilar circulation. Vertebral angiography confirms the diagnosis by demonstrating one hypoplastic artery and a large contralateral artery that occludes upon forced lateral rotation of the head. The treatment consists of clearing the sixth vertebral foramen of all tendonous attachments and interposing a fat pedicle amongst the severed tendons to obviate their reattachment.