Incidental asymptomatic aneurysmの診断におけるCTの果す役割

DIRECT DETECTION OF INCIDENTAL ASYMPTOMATIC ANEURYSM BY COMPUTED TOMOGRAPHY

I．はじめに

　Computed Tomography （以下CT）は，今日，脳神経外科領域において，各種疾患に対し広く応用され，その有用性についてはもはや論を待たないところであり，最も重要な補助診断法の1つとしてその座を揺ぎないものとしている。

　脳動脈瘤の診断においても，CTを応用することにより，動脈瘤の破裂に続発する血腫，脳腫脹，脳室拡大，血管攣縮にもとづく梗塞などの二次的変化を詳細かつ容易に把握する事が可能となり，破裂脳動脈瘤の診断および治療に対するCTの有用性は益々高まつてきている。

Incidental asymptomatic aneurysms were found in 9 of 52 patients with intracranial aneurysms from February, 1978 to March, 1980.

They had only mild initial symptoms, namely, headache, dysarthria, aphasia, light hemiparesis and others. No patients had severe neurological deficits.

In eight of 9 patients with asymptomatic aneu-rysm, except one case of hypertensive intracerebral hematoma, 9 aneurysms (8 patients) were directly detected by high resolution CT (GE CT/T 8800) and confirmed by angiography.

Location of these aneurysms as follows: three at the MCA trifurcation, two at the IC-PC junction, one at anterior communication artery, one at the basilar top, one at the BA-SCA junction and one at the posterior cerebral artery.

The smallest aneurysm detected by CT was 5×4×4 mm in size on angiography.

The aneurysm may be suggested by small round or oval defect in the Sylvian fissure or suprasellar cistern, defect of the edge of the so called"pen-tagon"in the plain CT and then if its density is highly and homogeneously increased alter contrast-enhanced (CE) scan. As the circle of Willis and other major cerebral arteries can often be demon-strated on CE･CT images, the aneurysm is fre-quently seen on these cerebral arteries.

Limiting factors to direct CT detection of intra-cranial aneurysms are seemed to be size and location of aneurysm, anatomic location of circle of Willis and motion of patients etc.

It may be considered, in our experiences, that the CT is useful in diagnosis of asymptomatic aneurysm and the higher direct CT detection rate to aneurysms, small or medium sized as well as giant aneurysms, will be obtained by devising scan-ning method, namely, multiprojection scans, multiple overlapping method and improvement of enhanced method.