X-ray manifestations of the Holter valve in hydrocephalus.

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The exact mechanism of production and absorption of cerebrospinal fluid remains in question. Also lacking is a clear understanding of the alternate pathways that can develop when the normal flow of cerebrospinal fluid is obstructed. When there is obstruction to the ventricles, overproduction or poor absorption of cerebrospinal fluid, the resulting high-pressure hydrocephalus destroys brain tissue. A number of operative shunting procedures have been developed to allow egress of the fluid from the ventricular system and thus limit the extent of brain damage. Radiologic control during the procedure and postoperative follow-up studies are important in the proper management of the patient. It is the radiologist's responsibility to detect malplace-ment, mechanical breakdown, and other causes of shunt failures. Davidoff in 1929 (3) reviewed the approaches to the therapy of hydrocephalus. He traced the treatment back to Hippocrates who is given credit for forming trephine holes in the skull and then puncturing the ventricles. Payr in 1908 used a vascular graft, connecting the longitudinal sinus to the lateral ventricles by an autogenous or homologous vein. Postoperative follow-up is not well documented. Melnic in 1909 used a F-shape vessel and transplanted it to the jugular vein in the neck. His single patient died after the operation (8). Since these early attempts, numerous shunting procedures have been tried. The present-day method for treatment had its origin with Ingraham and his associates in 1948 (5). They studied dogs having obstructed hydrocephalus with shunts to the venous system both in the anesthetized state and while awake. The cerebrospinal fluid flow was away from the ventricles when the animals were anesthetized. Upon awakening, however, the dogs became active and the reversal of flow from increased venous pressure caused the shunts to clot. It was concluded that a unidirection valve system was needed to prevent clotting in the tubing. The three basic shunting systems utilized today are the ventricular-atrial shunts, ventricular-pleural shunts, and ventricular-peritoneal shunts. The peritoneal and pleural shunts are used as temporary measures when intracranial hemorrhage or infection is present. They are later replaced by the more efficient ventricular-atrial shunt (9). The shunting device has a valve that opens at a determined pressure and thus permits drainage of cerebrospinal fluid from the ventricles of the brain to another body compartment. The two popular valve mechanisms used are the Holter valve and the Hakim valve (4). Although they are basically similar in construction, our experience has been chiefly with the Holter valve and its use in ventricular auriculostomies. The Holter valve is composed of a double fish-mouth valve that opens at variable intracranial pressures. At one end of the valve is a catheter that extends into the ventricular system.