[Evaluation of changes in brain tissues surrounding cerebral arteriovenous malformations using NMR-CT]

Patients with cerebral arteriovenous malformation (AVM) show various clinical symptoms, but they can be divided into two groups; one resulting from rupture of AVM and another derived from chronic ischemia in surrounding tissues of AVM. Intracerebral or subarachnoid hemorrhages due to rupture of AVM can be detected by X-ray CT scan, however, it is difficult to obtain three dimensional image of changes in the surrounding area of AVM that has never experienced hemorrhagic attacks. We are using 0.15 Tesla NMR-CT (resistive type) produced by Bruker Company in West Germany and its pulse sequence is Carr-Purcell-Meiboom-Gill (CPMG) method which is best reformed type of spin echo. With this machine, we observed images of AVM and its surrounding tissue, made calculated images of T1 and T2 relaxation time and measured T1 and T2 values of ROI. On images of NMR, nidus and many dilated vessels were distinctly revealed as low or no signal intensity area in all cases without contrast media. And it is noteworthy that surrounding areas of AVM on calculated T1 and T2 images were observed as tissues showing elongated relaxation time in all cases. These tendencies were confirmed by measurement of T1 and T2 in ROI compared with contralateral side. We think elongations of T1 and T2 in surrounding tissues mean ischemic or necrotic changes in these areas induced by steal phenomena due to arteriovenous shunting.