Isotope cisternography and conductance to outflow of CSF in normal pressure hydrocephalus

In 50 patients with normal pressure hydrocephalus (NPH) the findings on lumbar isotope cisternography (IGG) were compared to the conductance to outflow of CSF (Cout) as measured by lumbo-ventricular perfusion. The purpose was to identify those ICG-characteristics that imply a low Cout and thus may indicate CSF shunting therapy. Normal ICG was found only in three patients, where Cout was not, or only moderately, decreased. There was a significant correlation between a low Cout and occurrence of ventricular retention and absent parasagittal accumulation at 24 hours or later, following injection. These findings may, however, also be present in patients with no, or only moderate, decreased Cout, where CSF shunting may seen unjustified. It is concluded, that the indication for CSF shunting cannot be based on the results of ICG alone.