Rotational occlusion of the vertebral artery caused by transverse process hyperrotation and unilateral apophyseal joint subluxation. Case report.

The authors describe transverse process hyperrotation and unilateral apophyseal joint subluxation as a novel mechanism of rotational vertebral artery (VA) occlusion. The patient, a 56-year-old man, complained of episodic bilateral blindness when rotating his head more than 90 degrees to the right. Plain cervical x-ray films showed spondylotic osteophytes of the right C4-5 uncovertebral portion. Dynamic angiography revealed right VA occlusion at C4-5 and left VA occlusion at C1-2 with head rotation to the right. It was demonstrated on three-dimensional images constructed from computerized tomography scans that C-4 transverse process hyperrotation compressed the right VA against the apex of the C-5 subluxating superior articular process via the inner surface of the transverse process anterior root (processus costarius) rather than the osteophytes. It is also proposed that the true site of occlusion is different from that observed in angiographic studies.