[Angles between left and right vertical semicircular canals]

To clarify anatomical relationships between the left and right vertical semicircular canal (SCC), we measured angles between the left and right posterior SCCs, and angles between left and right anterior SCCs. Subjects were T2 images of axial magnetic resonance imaging (MRI) in 50 patients reporting headaches. The mean angle between the left and right posterior SCC was 92.6 degrees (S.D. = 11.7) and that between the left and right anterior SCC was 76.1 degrees (S.D. = 10.4). These results suggest that angles between the left and right vertical semicircular canals are not always 90 degrees, and interindividual differences in the relationship between canal planes are great, indicating a need for discretion in analyzing peripheral nystagmus.