Computed tomography and pneumoencephalography compared to conductance to outflow of CSF in normal pressure hydrocephalus.

The conductance to outflow of CSF (Cout) was measured in 66 patients with normal pressure hydrocephalus (NPH). All patients were investigated with computed tomography (CT); 34 of the patients also had pneumoencephalography (PEG). Periventricular hypodensity on CT indicates a low Cout. Cortical sulci smaller than 1.9 mm on CT indicate a low Cout, while wide cortical sulci do not exclude a low Cout. There was a good correlation between ventricular size on CT and PEG, but the ventricular size is unrelated to Cout. No findings on PEG indicate a low Cout.