Occipitoatlantal instability and vertebrobasilar ischemia: case report.

A 37-year-old woman had occipitoatlantal instability due to hypoplasia of the occipital condyles. Neck pain and transient ischemic attacks in the vertebrobasilar territory occurred with extension of the neck, which also caused convergence spasm. Angiography demonstrated that these manifestations were due to compression of the vertebral arteries during neck extension. Immobilization of the neck in a Minerva cast resulted in complete relief of symptoms.