The adult Chiari malformation.

The adult or type 1 Chiari malformation is a hindbrain anomaly in which the cerebellar tonsils, but not the vermis, are chronically dispalced into the foramen magnum (1). Syringomyelia or syringobulbia are frequently associated with the anomaly (2-4). Seventeen cases of surgically verified adult Chiari malformations with or without a syrinx were recently diagnosed at the Neuropsychiatric Institute. University of California at Los Angeles. A review of these patients confirmed this anomaly has protean manifestations. Recognition of paroxysmal complaints induced by a variation of the Valslava maneuver, especially in the presence of nystagmus, might lead to early neurodiagnostic procedures and surgical intervention, with reduced morbidity.