Magnetic Resonance Imaging Findings of Idiopathic Normal Pressure Hydrocephalus and Cognitive Function Before and After Ventriculoatrial Shunt

BACKGROUND: The idiopathic normal pressure hydrocephalus (iNPH) is characterized by the triad of gait impairment, incontinence, and dementia. Cases that do not comply with the diagnostic criteria of ventriculomegaly have increased. It has led to the questions about the current criteria of guidelines. As the number of patients with dementia increases with aging, iNPH is importantly placed as a treatable dementia. The purpose of this study was to verify the validity of radiological diagnostic criteria of ventriculomegaly in iNPH. MATERIALS AND METHODS: A board-certified neuroradiologist retrospectively examined 80 patients with definite iNPH about magnetic resonance imaging (MRI) findings of Evans index (EI) and disproportionately enlarged subarachnoid space hydrocephalus (DESH). The score of mini-mental state examination (MMSE) was measured to represent the cognitive function. The presurgical score of MMSE (pre-MMSE) and postsurgical best score of MMSE (best-MMSE) were compared statistically between patients dichotomized by either EI >0.3 or DESH. RESULTS: The pre-MMSE was not different regardless of dichotomization by EI >0.3 or DESH. The MMSE score (median) increased significantly (P < 0.0001) by shunt from 20.0 to 26.0 in patients with EI >0.3 and from 21.5 to 25.5 with EI ≤0.3. No difference in the best-MMSE was observed between EI >0.3 and EI ≤0.3. The MMSE score increased significantly (P < 0.0001) by shunt from 21 to 27.5 with DESH and from 20 to 24.5 with non-DESH. Regardless of fulfilling or notfulfilling Japanese radiological diagnostic criteria (combination of EI >0.3 and DESH), cognitive function was significantly (P < 0.0001) improved to the same level. Only 24 cases (30%) fulfilled Japanese radiological diagnostic criteria. CONCLUSION: Cognitive function of iNPH patients was significantly improved by shunt regardless of MRI-findings. Radiological diagnostic criteria of iNPH may need careful reconsideration.