Cerebral oxygen metabolism in idiopathic-normal pressure hydrocephalus.

Objective: To distinguish idiopathic-normal pressure hydrocephalus (i-NPH) from the elder with brain atrophy is difficult. This investigation was undertaken to determine the cerebral oxygen metabolism and the cerebral blood flow using positron emission tomography (PET) in patients with i-NPH. Comparison of the variables between i-NPH patients and the age-comparable control with asymptomatic ventricular dilatation were performed.

Methods: Nineteen patients were studied. Nine i-NPH patients with a mean age of 74.8 +/- 1.8 years (mean +/- SD) were examined using PET. The subjects who underwent a ventriculoperitoneal shunt (VPS) had the triad of NPH and ventricular dilatation on computed tomography (CT) and/or magnetic resonance imaging (MRI). The results of the PET study were compared with those for ten age-comparable controls (74.8 +/- 5.5 years) with asymptomatic ventricular dilatation and no severe cerebrovascular disease on MRI and magnetic resonance angiography (MRA). The PET study included analyses of regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV), regional oxygen extraction fraction (rOEF) and regional cerebral metabolic rate of oxygen (rCMRO(2)).

Results: In i-NPH, rCBF tended to decrease in the frontal lobe and the basal ganglia. rCMRO(2) in the frontal lobe of i-NPH was significantly higher than that in the controls (p<0.05 by Student's t-test), although rCMRO(2) in the basal ganglia of i-NPH was reduced. rCBV and rOEF showed no significant differences.

Conclusion: Reduction of oxygen metabolism in the basal ganglia might be one of the factors causing symptoms in i-NPH. Particular pattern of cerebral oxygen metabolism in i-NPH was not obvious in the present study.