Is there a correlation between operative results and change in ventricular volume after shunt placement? A study of 60 cases of idiopathic normal-pressure hydrocephalus.

In patients with communicating or normal-pressure hydrocephalus, ventricular volume decreases following implantation of differential pressure valves. We implanted hydrostatic (Miethke dual-switch) valves in 60 patients with normal-pressure hydrocephalus (NPH) between September 1997 and December 2001. The patients underwent CT 1 year after operation, and we measured the Evans index. Although 83% of the patients showed no change in ventricular volume as assessed by this index, 72% nevertheless showed good to excellent and 16% satisfactory clinical improvement, while 12% showed no improvement. Moderate or marked reduction in ventricular size was observed in 17%, of whom 40% of these patients showed good to excellent and 20% satisfactory clinical improvement; 40% showed unsatisfactory improvement. The favourable outcome following implantation of a hydrostatic shunt thus did not correlate with decreased ventricular volume 1 year after operation, better outcomes being observed in patients with little or no alteration in ventricular size than in those with a marked decrease. Postoperative change in ventricular volume in NPH thus does not have the same significance as in patients with high-pressure hydrocephalus.