Reflux of metrizamide into the lateral ventricles in vomiting

Two cases are presented in which metrizamide refluxed into the lateral ventricles after vomiting, the contrast having been brought in intrathecally by lumbar route for CT-scanning of the basal cisterns. It is suggested the intrathoracic and intraabdominal pressures transority achieved in vomiting are transmitted to the spinal canal through the vertebral venous plexus. This results in a pressure which is transmitted through the C.S.F. to the posterior fossa, and from there, for anatomical reasons, to the ventricular system. Transitory dilatation of the ventricles results in aspiration fluid from the fourth ventricle, and hence reversal of normal flow in the aqueduct of Sylvius.