The importance of the dual-switch valve for the treatment of adult normotensive or hypertensive hydrocephalus.

Since the beginning of 1995 the new hydrostatic dual-switch valve (DSV) was implanted in 35 adult patients with hydrocephalus of different etiology. 26 patients suffered from normotensive hydrocephalus (10 idiopathic and 16 symptomatic), and 9 patients from hypertensive hydrocephalus of various origin. The first 21 cases of this cohort were compared in a randomized study with a comparable group of 21 hydrocephalic patients who received a conventional differential-pressure (DP-) valve. The clinical status and CT were assessed prior to shunting, 14 days and 3 and 6 months after the operation. The reduction of ventricular size was evaluated by the measurement of the Evans Index. The CT follow-up in the DSV group was characterized by an only minimal (14) or only slight (16) reduction of ventricular size in the vast majority of cases. A comparison of 21 patients with a DSV and the patients with DP valves, evaluated by measuring the reduction of the Evans Index, revealed a distinctly higher percentage of significant regressions in the DP valve collective, without doubt due to chronic overdrainage. The overall clinical result of our 35 patients with a DSV was excellent and good in 31 patients, but the outcome seems to be more dependent on the preshunt damage of the brain than on hydrocephalic aspects. A neglegible incidence of subdural effusions in the DSV group compared to 11 cases in the DP valve collective reflects the ability of the DSV to prevent overdrainage. The capability of the DSV to maintain the IVP within physiological limits after shunting, especially in the upright position, is documented by a comparison with possible unphysiological IVP variations in other valve constructions, which depend on the level of implantation, subcutaneous pressure or CSF flow through the valve.