Abstract
Five patients with craniovertebral junction anomalies were examined neuro-otologically.
Three patients had Chiari I malformation and cervicobasilar bone anomalies. Magnetic resonance imaging (MRI) showed cervicomedullary kinking, in addition to peg-like tonsils below the level of the foramen magnum (Group A). Two patients had Chiari I malformation without any cervicobasilar bone anomalies (Group B). We noted the differences in neuro-otological findings between the two groups and the changes after operation.
1. Differences in neuro-otological findings
(1) Group A patients had downbeat nystagmus in the dark with the eyes open on forward and lateral gaze. Horizontal OKN abnormalities were as follows : at a stripe speed of 0-50°/s, pursuit of stripe movement showed stair-like swaying. When the stripe speed was increased further, pursuit of stripe movement became virtually impossible, and the number of nystagmus beats decreased markedly.
(2) Group B patients had no nystagmus in the dark with the eyes open. Horizontal OKN abnormalities showed saccadic pursuit during stripe movement, and a decrease in the number of nystagmus beats at a high stripe speed (more than 100-110°/s).
2. Changes in neuro-otological findings
(1) In group A, surgery improved the areas of sway in stabilometry tests, the frequency of nystagmus and the visual suppression rate of the slow phase velocity of caloric nystagmus. Horizontal OKN abnormalities were unchanged.
(2) In group B, surgery improved the areas of sway, visual suppression rate and horizontal OKN. These results provide evidence that Chiari I malformations should be divided into those with and those without cervicomedullary kinking.
