Idiopathic normal pressure hydrocephalus: cerebral perfusion measured with pCASL before and repeatedly after CSF removal

Abstract

Pseudo-continuous arterial spin labeling (pCASL) measurements were performed in 20 patients with idiopathic normal pressure hydrocephalus (iNPH) to investigate whether cerebral blood flow (CBF) increases during the first 24 hours after a cerebrospinal fluid tap test (CSF TT). Five pCASL magnetic resonance imaging (MRI) scans were performed. Two scans were performed before removal of 40 mL CSF, and the other three at 30 minutes, 4 hours, and 24 hours, respectively after the CSF TT. Thirteen different regions of interest (ROIs) were manually drawn on coregistered MR images. In patients with increased CBF in lateral and frontal white matter after the CSF TT, gait function improved more than it did in patients with decreased CBF in these regions. However, in the whole sample, there was no significant increase in CBF after CSF removal compared with baseline investigations. The repeatability of CBF measurements at baseline was high, with intraclass correlation coefficients of 0.60 to 0.90 for different ROIs, but the median regional variability was in the range of 5% to 17%. Our results indicate that CBF in white matter close to the lateral ventricles plays a role in the reversibility of symptoms after CSF removal in patients with iNPH.

Figure 1

Example of two ROIs in two different patients. Upper row is an example of the right lentiform nucleus ROI in patient 1 and lower row shows the medial frontal cortex ROI in patient 2. (A and D) FLAIR images that were used to draw the ROIs. (B and E) pCASL perfusion images. (C and F) Smoothed pCASL images that were used to calculate CBF. CBF, cerebral blood flow; FLAIR, fluid-attenuated inversion recovery; pCASL, pseudo-continuous arterial spin labeling; ROIs, regions of interests.

Figure 2

Segmentation of the lateral ventricles in two different slices (using SyMRI), used for CSF volume estimates pre and post CSF TT. CSF, cerebrospinal fluid; CSF TT, CSF tap test; SyMRI, synthetic magnetic resonance imaging.

Figure 3

Differences in proportional gait improvement between patients with an increased versus reduced CBF at different investigation times. The whiskers in the box-and-whiskers graph represent maximum/minimum. (A) Frontal white matter. (B) Lateral white matter. CSF TT, cerebrospinal fluid tap test; 10 m, 10 m walking test at maximum pace; TUG, timed ‘up and go'. Significant difference: *P<0.05; **P<0.01.

Figure 4

The mean value of the measured volumes at MRI 1 and MRI 2 was taken as reference volume. This was subtracted from the volumes at all five investigation times to obtain the volume difference per subject. The error bars indicate the 95% CI of the volume difference, obtained from the complete group. Cerebrospinal fluid tap test (CSF TT) was performed after MRI 2. The boxes: 30 minutes, 4 hours, and 24 hours, refer to time after the CSF TT. A significant difference was found between baseline (average of MRI 1 and MRI 2) and 30 minutes (P<0.001); baseline and 4 hours (P<0.01); 30 minutes and 4 hours (P<0.001); and 30 minutes and 24 hours (P<0.01), using the Wilcoxon signed-rank test.