Experimental brain stem displacement. Its implications in the upward and downward herniation syndromes

6 dogs were anesthetized and a silver clip attached to a cotton plug as surgically placed in the aqueduct of Sylvius. An immediate postoperative lateral skull film was obtained to demonstrate the position of the clip. The animals developed signs of hydrocephalus within hours after the procedure. 2 weeks after placement of the aqueduct plug, the animals recieved a permanent ventriculostomy. Immediate pre- and postoperative ventriculostomy lateral skull films were taken again to indicate position of the silver clip. Finally, a lateral skull film was taken 2 weeks after ventriculostomy and just prior to sacrifice. Radiological techniques were standardized. In this experimental setting downward brain stem herniation predominated and upward herniation of the brain stem was an infrequent occurrence.