特発性正常圧水頭症の画像診断

Neuroimaging of the Idiopathic Normal Pressure Hydrocephalus―Current Concepts

はじめに

　特発性正常圧水頭症（idiopathic normal pressure hydrocephalus: iNPH）の診断や治療方針決定に画像診断は重要な役割を果たしているが，検査戦略に関するコンセンサスや画像所見に対する理解は十分とはいえない。本稿ではiNPHに関する形態画像診断，機能画像診断の最近の動向について解説し，診療ガイドラインにおける位置づけについても言及する。

Abstract

　Neuroimaging plays an important role in the diagnosis and management of the idiopathic normal pressure hydrocephalus (iNPH).　In addition to a ventricular dilatation with an Evans index of 0.3 or more, a tightness of the subarachnoid space in the high convexity/midline areas with a concurrent dilatation of the sylvian fissure and basal cistern is characteristic in iNPH.　Voxel-based morphometry techniques can readily determine the validity of these findings.　Periventricular hyperintensity, marked flow void in the aqueduct, and ventricular reflux and stasis of contrast agents are believed to have limited advantages in differential diagnosis and patient management.　Cerebral blood flow measurement may help in discriminating iNPH from other disorders; however, partial volume effects due to disproportionate narrowing and dilatation of the subarachnoid space can cause substantial errors during post-processing and interpretation.