Convergence nystagmus associated with Arnold-Chiari malformation
S. S. Mossman, A. M. Bronstein, M. A. Gresty, B. Kendall and P. Rudge
Medical Research Council Neuro-Otology Unit, National Hospital, London, England.
A case of convergence nystagmus associated with an Arnold-Chiari type I
malformation is presented. The nystagmus appeared in the absence of
fixation, was provoked during Valsalva's maneuver and neck flexion and
extension, and attenuated on deep inspiration. Sagittal magnetic resonance
images showed that the diameter of the cerebral aqueduct increased with the
neck in full flexion and in full extension. Surgical foramen magnum
decompression considerably reduced the nystagmus and abolished the postural
variation of aqueduct diameter. It is postulated that this nystagmus was
due to a combination of mechanical distortion and abnormal transmission of
cerebrospinal fluid pressure to the aqueductal region.
