Surgical transection of the posterior inferior cerebellar vermis in 5 children (ages 6-15 years) treated at Washington University School of Medicine, St Louis, MO, was followed by selective impairment of tandem gait. Surgery performed for removal of tumors in the fourth ventricle involved destruction of the midline parallel fibers ranging from lobules VI-X. Regular self-paced gait, Romberg posture, and hopping were only minimally impaired, and kicking, reaching, or speech were unaffected. 
COMMENT. Profound and persistent ataxia of tandem gait occurs after surgical division of midline fibers crossing the posterior inferior vermis of the cerebellum, whereas regular gait, hopping, individual limb coordination, and speech are relatively unaffected. Damage to both vestibular and visual inputs subserved by the posterior midline vermis fibers may explain the preferential impairment of tandem gait.
Vermian agenesis without posterior fossa cyst or fourth ventricle enlargement was diagnosed by MRI at 16 months to 5 years in 14 children presenting with oculo-motor apraxia, ataxia, and global developmental delay at Saint-Vincent de Paul Hospital, Paris, France , and presented at the VIII International Child Neurology Congress, Ljubljana, Slovenija, Sept 1998.