Ventriculo-peritoneal Shunt Malfunction with Anti-siphon Device in Normal-pressure Hydrocephalus

Three patients with normal-pressure hydrocephalus, treated by installation of a low-pressure ventriculo-peritoneal shunt system equipped with an anti-siphon device, did not improve in clinical signs and ventricular size on computed tomography (CT). However, the lumbar infusion manometric test in the horizontal position showed that the shunt systems were functioning and cerebrospinal fluid absorption was good in all patients. The clinical signs and ventricular dilatation on CT were remarkably improved by replacing the shunt system to one without an anti-siphon device. The shunt malfunction seemed to be caused by the anti-siphon function itself, especially when the patients were in sitting and/or standing position.