Impaired wakefulness is associated with reduced anterior cingulate CBF in patients with normal pressure hydrocephalus.

Objective: To evaluate if impaired wakefulness (IW) in normal pressure hydrocephalus (NPH) is associated with reduced blood flow in regions associated with the brain arousal system.

Method: NPH (n = 28) patients were studied before and after surgery. Wakefulness was assessed using a new developed scale. Relative regional cerebral blood flow (rrCBF) was quantified using SPECT and rectangular regions of interest analysis.

Results: Sixteen patients presented with IW at baseline and in 14 of these, IW vanished after surgery. Patients presenting with IW had reduced rrCBF in the anterior cingulate cortex compared with those without. After surgery, rrCBF increased significantly in thalamic, frontal and hippocampal grey matter regions. Increased hippocampal rrCBF correlated with increased basal frontal rrCBF (r = 0.64). In patients where IW vanished after surgery, rrCBF increased in the mesencephalon, hippocampus and the frontal association cortex. The postoperative increase in wakefulness correlated with increased rrCBF in frontal (r = 0.74) and parietal (r = 0.65) association cortex areas.

Conclusion: IW in NPH is associated with reduced rrCBF in the anterior cingulate cortex. Improved wakefulness following surgery corresponds to rrCBF increments in the frontal association cortex. This study provides support for a functional coupling between frontal, hippocampal, thalamic and mesencephalic rrCBF in NPH at large.