A 13-year-old girl with post-traumatic cerebellar ataxia, transient upper extremity weakness, and lower cranial nerve dysfunction was found to have a Type I Chiari malformation on MRI at the Depts of Neurosurgery and Neurology, San Francisco General Hospital, California. She lost consciousness and had a cardiopulmonary arrest after hitting her neck and head on the windshield in an automobile accident. On the 2nd day, her right upper limb was paralyzed; on day 4 she had upbeating nystagmus and was unable to swallow, phonate, or protrude her tongue; and on day 12 right vocal cord paralysis was noted which recovered by day 15. She continued to have improvement of the lower cranial nerve weakness but the ataxia persisted at the time of discharge. It was thought that the initial cardiopulmonary arrest after trauma and the brain stem dysfunction and ataxia were causally related to the Type I Chiari malformation. The continued improvement argued against surgical decompression. 
COMMENT. This sudden manifestation of symptoms and signs of Chiari I malformation after head and neck trauma is unusual. Previously reported cases include a 3-year-old child who died 48 hours after a mild head injury, a 2 1/2 year-old boy who developed acute paraparesis after a fall, a 17-year-old girl who developed hemianesthesia, nystagmus, dysarthria, and tongue deviation 1 week after chiropractic manipulations, and acquired torticollis after endotracheal anesthesia for tonsillectomy. All cases were found to have Chiari I malformation; only one had an associated syringomyelia. The diagnosis of Chiari I malformation has been facilitated by the use of MRI and asymptomatic cases are being uncovered by this imaging technique.