Posterior vermal split syndrome.

We have studied a battery of movements in 5 children (age, 6-15 years) after transection of the posterior inferior cerebellar vermis. In each case, the surgery destroyed the midline vermis only (ranging from lobules VI-X). Tandem gait was badly impaired in all subjects. No subjects had impairments of kicking, reaching, pinching, or speech. Regular gait, standing, and hopping on one leg were relatively unimpaired. Cutting the parallel fibers that cross the midline may be the critical variable causing incoordination in tandem gait.