Teaching NeuroImages: Vertebral artery compression by head tilt around the roll axis diagnosed by transcranial Doppler

A 59-year-old man reported transient vertigo and diplopia during leftward head tilt around the roll axis. Neurologic examination was unremarkable with the head erect or tilted. Magnetic resonance angiography of the head and neck showed hypoplasia of the right vertebral artery (figure 1). Transcranial Doppler waveform was monitored during leftward head tilt. The left vertebral artery flow velocity decreased with tilt, and abruptly increased after returning to erect posture (figure 2). Vertebral artery can be stretched or kinked by head rotation or tilt,1,2 typically at the C1-2 level.1 Transcranial Doppler could be helpful in diagnosis of such cases.