Clinical experience with the Dual-Switch-Valve in patients with normal pressure hydrocephalus

In patients with normal pressure hydrocephalus in the late stage conventional differential valves have the disadvantage that they open abruptly while changing the body position to the vertical line and that they can therefore induce a suction on the ventricles of the atrophic brain. Can these disadvantages and over- drainage complications be minimized by hydrostatic valves? In 117 patients diagnosed for normal pressure hydrocephalus we have implanted 47 Cordis Standard Valves (CSV), 20 Cordis Orbis Sigma Valves Type I (OSV) and 50 Miethke Dual Switch Valves (DSV). 95 patients (36/19/40) could be re-evaluated by means of a control examination. Normal pressure hydrocephalus was graduated according to the results of the intrathecal infusion test in an early and late stage. According to our NPH-Recovery-Rate and to the clinical grading of normal pressure hydrocephalus by Kiefer and Steudel we compared the postoperative results of each group of patients. There were no statistical differences in mechanical and infectious complications between the different valve types. We found significant differences in overdrainage and subdural hematomas. 4 patients (11%) with a CSV, 5 patients (26%) with an OSV and 2 patients (5%) with a DSV had a decrease of the ventricular width visualised in the CT. Of those patients 2 (16%) with a CSV, 3 patients (16%) with an OSV and 1 patient (3%) with a DSV developed clinical symptoms. The course of the disease in patients with normal pressure hydrocephalus is influenced by the stage of the disease degree of cerebral atrophy - and also by the implanted valve type. The high amount of overdrainage complications and subdural hematomas in the Cordis Orbis Sigma Valve Type I group is an argument: against: its use. Our clinical experiences with the Miethke Dual Switch Valve show that this hydrostatic valve is of advantage for patients with a normal pressure hydrocephalus.