The mechanism of hydromyelia in Chiari type 1 malformations

Abstract

Experimental and clinical findings are presented to show that the magnitude of displacement of cerebro-spinal fluid from the basal cisterns during systole is an adequate force to cause hydromyelia in the presence of a Chiari malformation. The abnormal mechanism is discussed in detail and involves obstruction of the foramen magnum by the cone of depressed cerebellum adherent to the spinal cord, systolic deflection of the cerebro-spinal fluid from the basal cisterns into the 4th ventricle, and a milking action of the adherent cerebellum on the brainstem. These factors force cerebro-spinal fluid into the central canal of the spinal cord, tending to form a syrinx. Changes in epidural pressure associated with coughing and straining may cause extension of such a syrinx once it has formed.