Relationship between vascular enhancement, cerebral hemodynamics, and MR angiography in cases of acute stroke

Abstract

Background and purpose: The use of MR angiography and contrast-enhanced T1-weighted MR imaging in cases of acute cerebral ischemia may be helpful in the evaluation of middle cerebral artery (MCA) occlusion and leptomeningeal collaterals, respectively. The aim of our work was to investigate the relationship between MCA occlusion, T1-weighted vascular contrast enhancement, hemodynamic alterations, and tissue damage in cases of acute ischemic stroke.

Methods: We studied the MCA territory in 15 patients with acute ischemic stroke within 8 hr of symptom onset. The first MR imaging study (<8 hr after onset) comprised diffusion-weighted imaging, MR angiography, perfusion-weighted imaging, and contrast-enhanced T1-weighted MR imaging sequences. Follow-up MR imaging, performed 1 week later, consisted of MR angiography and T2-weighted fluid-attenuated inversion recovery MR imaging.

Results: Early MR angiography showed MCA stem occlusion in nine of 15 patients. Patients with MCA occlusion had significantly larger areas of abnormality on early diffusion-weighted images, significantly larger areas of altered hemodynamics, larger final lesion volumes, and poorer clinical outcome. Among the nine patients with MCA stem occlusion, vascular enhancement was marked in seven and absent in two who had complete MCA infarcts and poor clinical outcome. Among patients with MCA patency, vascular enhancement was marked in only one, mild in four, and absent in one. Patients with marked vascular enhancement had significantly larger regions of altered hemodynamics and significantly higher asymmetries in both regional cerebral blood volume and mean transit time because of increased values in the affected hemisphere.

Conclusion: Among patients with stroke with MCA occlusion, marked vascular enhancement and increased blood volume indicate efficient leptomeningeal collaterals and compensatory hemodynamic mechanisms.

fig 1.

MR images of patient 12, who was studied 1 hr after the onset of stroke. A, MR angiogram (43/2.3/1 [TR/TE/excitations]) shows left MCA occlusion, mild caliber reduction of the supraclinoid tract of the left internal carotid artery with respect to the contralateral one, asymmetry in the A1 segments (right > left) with good filling of both the anterior cerebral arteries (A2 tracts), and left posterior cerebral artery filling out farther than the contralateral one. B, Contrast-enhanced T1-weighted images (560/14/2) show marked vascular enhancement of the thin vessels in the left superficial frontotemporal region. C, Diffusion-weighted image (left) (6000/64/1) shows early damage in the left deep MCA territory. The lesion extent is substantially unchanged on the follow-up MR image (right) (FLAIR image obtained 1 week later [6000/100/2]). D, Perfusion-weighted maps show an increase of both rCBV (left) and MTT (right) in the left superficial MCA territory, outside the area of altered diffusion-weighted imaging (outlined). The rCBV and MTT asymmetries were 105% and 54%, respectively.