• Mitsuhito Mase, Toshiaki Miyati, Harumasa Kasai, Koichiro Demura, Tomoshi Osawa, Masaki Hara, Yuta Shibamoto, and Kazuo Yamada.
• Department of Neurosurgery and Restorative Neuroscience, Graduate School of Medical Sciences, Nagoya City University, 1-Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya 467-8602, Japan. mitmase@med.nagoya-cu.ac.jp
• Acta Neurochir. Suppl. 2008 Jan 1; 102: 115-8.

BackgroundThe pathophysiology of idiopathic normal pressure hydrocephalus (I-NPH) is still unclear and the diagnosis is sometimes difficult. The aim of this study was to assess the biophysics of I-NPH by measuring intracranial compliance using cine MRI.MethodsThe study included patients with I-NPH (I-NPH group, n = 13), brain atrophy or asymptomatic ventricular dilation (VD group, n = 10), and healthy volunteers (control group, n = 13). Net blood flow (bilateral internal carotid and vertebral arteries and jugular veins) and cerebrospinal fluid (CSF) flow in the subarachnoid space at the C2 cervical vertebral level were measured using phase-contrast cine MRI. CSF pressure gradient (PG(p-p)) and intracranial volume changes (VC(p-p)) during a cardiac cycle were calculated.FindingsThe compliance index (CI=VC(p-p)/PG(p-p)) in the I-NPH group was significantly lower than in the control and VD groups, whereas no difference was found between the control and VD groups. CI values of I-NPH patients after the tap test were larger than those before. These results clearly show that the intracranial compliance of I-NPH is relatively low compared to that of brain atrophy or normal subject. The increase of CI after a tap test also supports this finding.ConclusionsIt is possible to estimate intracranial compliance as CI non-invasively using cine MRI. CI could become a useful method for the diagnosis of I-NPH.

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