3D-CTAによる内頸動脈-後交通動脈分岐部の動脈瘤とInfundibular Dilatationの鑑別診断

Differential Diagnosis between Aneurysm and Infundibular Dilatation in the IC-PC Region with 3D-CTA

I．はじめに

　近年magnetic resonance angiography（以下MRAと略）での脳血管スクリーニング検査の普及などに伴い，無症候性の血管隆起を発見する機会が増えている．なかでも内頸動脈-後．交通動脈分岐部（以下IC-PCと略）はinfundibular dilata-tion（以下IDと略）の好発部位であり，動脈瘤との鑑別が必要となる．digital subtraction angio-graphy（以下DSAと略）でも動脈瘤かIDかの鑑別が困難なIC-PCの血管隆起を，three-dimen-sional CT angiography（以下3D-CTAと略）の撮影方法を工夫して鑑別したので報告する．

In cases of asymptomatic internal carotid-posterior communicating artery (IC-PC) protrusions, it issometimes difficult to differentiate infundibular dilatation (ID) from aneurysm by digital subtraction angio-graphy. We applied three-dimensional CT angiography (3D-CTA) in 32 cases of these IC-PC protrusions.SOMATOM PLUS 4 was used under such conditions as to provide images with high spatial resolution.The shaded surface display (SSD) method was adopted to reconstruct the 3D images because of its advan-tage in separating overlapped vasculature. We also made reference to source images and maximum intensi-ty projection (MIP) to make sure of our diagnoses. In all cases including 4 aneurysms and 28 Ws, wewere able to distinguish between ID and aneurysm. The accuracy of 3D-CTA was confirmed by 9 surgicalcases.

Our technique was as follows : 1) To inject a high dose of diluted contrast medium rapidly to smallerarteries for opacification of contrast medium. 2) To exclude neighboring useless structures except for thevery close structures such as posterior clinoid process from the target image focusing on the IC-PC region.3) To observe the reconstructed image of MW and SSD from various angles. The contralateral and cra-niocaudal view were valuable. 4) To change the threshold level gradually and observe the configurationalchanges of the apex of protrusion. Poorly developed PcomA was mostly delineated at the optimumthreshold level. Otherwise, the apex of protrusion remained spherical in an aneurysm and became pyramid-al in shape in an ID when the threshold level was gradually decreased.

In conclusion, 3D-CTA was a useful modality for IC-PC protrusions to distinguish between ID andaneurysm.