Intracranial cerebrospinal fluid distribution and its postoperative changes in normal pressure hydrocephalus.

Background: This study was conducted to investigate the usefulness of intracranial cerebrospinal fluid (CSF) volume measurement using MR-based methods in the management of patients with normal pressure hydrocephalus (NPH).

Methods: The study group comprised 19 patients with NPH who showed a favorable outcome after ventricular shunting, 15 normal volunteers (NV), and 15 patients with cerebrovascular disease (CVD). A 3D-fast asymmetric spin echo MR imaging sequence and the region-growing method were used to extract the CSF space from MR images. Ventricular volume (VV) and intracranial CSF volume (ICV) were measured and the VV/ICV ratio was calculated in each case. In NPH patients, the CSF volume was measured again after shunting.

Findings: The mean VV and VV/ICV ratio in the NPH group (91.1 mL and 45.2%, respectively) were significantly (p < 0.01) higher than those in the NV group (26.5 mL and 13.7%) and in the CVD group (44.5 mL and 17.8%). On the other hand, mean ICV values were not significantly different among the three groups. The VV was markedly decreased postoperatively (mean -40.7%), whereas the ICV was unchanged, resulting in a marked reduction in the VV/ICV ratio (mean -39.3%).

Interpretation: These results suggest that patients with NPH have a unique intracranial CSF distribution, with an enlarged VV and a slightly increased ICV, resulting in a high VV/ICV ratio. Shunting led to dramatic improvement in our patients. It is likely that CSF measurement can provide valuable information in the management of patients with NPH.