Fig. 1

A The nystagmus at her second visit in the sitting position; the leftward nystagmus according to the leftward neck rotation transited to the rightward nystagmus via downbeat nystagmus after the head returned to the center position. The nystagmus was analyzed by the infrared CCD camera using a macro program in Image J (National Institutes of Health, USA), which was provided by the Department of Otolaryngology, Yamaguchi University, Japan. B MR angiography showed the hypoplasia of the right vertebral artery in intracranial and extracranial portions. C 3D-CT also showed the hypoplasia of the right vertebral artery (white arrows). D Carotid ultrasonography in supine position: The blood flow of the right vertebral artery (Fig. 1D-a) was less than the left (Fig. 1D-b) even in the supine position. Then, when the neck was rotated leftward, further reduction of blood flow was seen in the doppler waveform of the right vertebral artery (Fig. 1C-c) (white arrows)