MR imaging of middle cerebral artery stenosis and occlusion: value of MR angiography

To investigate the effectiveness of MR angiography in conjunction with spin-echo imaging for evaluating vascular patency in patients with middle cerebral artery (MCA) stenosis or occlusion.

Seven patients with MCA stenosis or occlusion, verified with contrast angiography in five and correlated with transcranial Doppler sonography in two, were examined using two-dimensional and/or three-dimensional time-of-flight MR angiographic techniques as well as conventional spin-echo imaging.

Of the seven patients, six demonstrated basal ganglionic and/or cortical infarct in the MCA territory. Except one case with minimal stenosis immediately distal to the MCA origin, all six cases with either severe stenosis or occlusion of the main trunk of the MCA showed the absence of normal flow voids using spin-echo imaging in the sylvian fissure on the affected side. However, it was not possible to discriminate between stenosis and occlusion. Although different mechanisms (ie, flow-induced spin dephasing for the 2-D technique and progressive spin saturation for the 3-D technique) were predominantly responsible for the loss of signal through the area of stenosis, both the 2-D and 3-D MR angiograms clearly depicted the compromised flow of the MCA: a focal discontinuity with decreased vessel caliber corresponded to stenosis, and nonvisualization of distal MCA branches represented occlusion.

Either 2-D or 3-D time-of-flight MR angiography is a useful adjunct to conventional parenchymal spin-echo imaging for evaluating vascular patency in patients with MCA stenosis or occlusion, although it is important to recognize that each technique has a different basis for the loss of signal through the area of stenosis.