[Vertebral artery dissection due to a bone anomaly of the superior facet of C6: a rare cause of embolic stroke].

We report a rare case of repeated vertebral artery (VA) occlusion. The VA occlusion was due to a distal embolism originating from traumatic VA dissection resulting from mechanical compression due to excessive bone formation of the superior facet of C6. A 39-year-old male suffered from two embolic events in the right VA with a 4-month intervals. Three-dimensional computed tomography (3D-CT) revealed abnormal bone of the superior facet at the level of C6 and the verterbral artery compression. Angiography demonstrated the irregularity and the late clearance of the contrast material at the stenosis of VA, which was diagnosed as the dissection. Dynamic angiography showed right VA occlusion when rotating the patients head to the left and extending it backwards. External orthosis using a cervical collar for 1 month was undertaken, but the dissection remained, so coil embolization of the right VA was performed using an intravascular procedure. Because of the age of the patient, location, radiological features and clinical course, the authors considered the excessive bone formation was a bone anomaly rather than a cervical spondylotic change.