Recurrent syncope and Chiari malformation.

Downward herniation of the cerebellar tonsils through the foramen magnum (C hiari I malformation) is usually revealed by head and neck pain, often asso ciated with brain-stem or spinal cord disturbances. Syncopes are rarely rep orted and may be difficult to link to their cause when they occur alone. We report two cases with brief and repetitive syncopes revealing a Chiari I m alformation. These manifestations may be attributed to transient compressio n of brain stem or vascular structures at the craniocervical junction, trig gered by intracranial pressure increase, as they disappear after posterior fossa decompression.