Mechanisms of bihemispheric brain infarctions in the anterior circulation on diffusion-weighted images

Abstract

Background and purpose: Multiple acute brain infarctions in both cerebral hemispheres usually suggest an embolic mechanism, particularly one of aortic or cardiac origin. The purpose of this study was to clarify the etiologic mechanisms and topographic features of bihemispheric infarctions depicted on diffusion-weighted imaging (DWI).

Methods: Among 411 consecutive patients with ischemic stroke who underwent MR imaging in the acute phase, DWI showed bilateral infarctions in 19 (4.6%). In these patients, we analyzed the presence of carotid, aortic or cardiac embolic sources by using ultrasonography, cerebral angiography, and/or transesophageal echocardiography and evaluated the size and topographic distribution of the lesions. We assessed intracranial cross-flow through the anterior communicating artery, mainly on the basis of the anatomic information obtained from angiography or MR angiography.

Results: Bilateral lesions were derived from cardiac and/or aortic embolic sources in 16 (84%) of 19 patients and appeared to originate from unilateral carotid diseases in three (16%). In nine (82%) of 11 patients with cardiac embolic sources, at least one large territorial or subcortical lesion was found in either hemisphere, whereas in all eight patients without a cardiac embolic source, the lesions were small and disseminated bilaterally.

Conclusion: Unilateral carotid lesions can cause bihemispheric infarctions through cross-flow in the anterior communicating artery. On DWI, small bihemispheric, disseminated lesions strongly suggest an artery-to-artery embolism. In such cases, aortic and carotid lesions should be assessed as potential embolic sources.

Fig 1.

Classification of infarction. A, Right-sided infarction was defined as territorial; left sided, subcortical. Total volume of the infarcts was smaller on the left than right, which was defined as the predominantly affected hemisphere. B, DWI shows small disseminated lesions. The predominantly affected hemisphere is the left side, and infarcts on the contralateral side are localized in the ACA area.

Fig 2.

Angiographic and DWI findings in four patients in group CA. A/M = watershed area between the ACA and MCA, Lt. = left, Rt. = right, gray circle = carotid stenotic lesion or complicated lesion in the arch; black circle = culprit lesion; asterisk = cross-flow, intracranial cross-flow through the AcoA from the predominantly affected side to the contralateral side; double asterisk = right MCA area, which was supplied by the left ICA through the AcoA because the right ICA was completely occluded at the origin; and triple asterisk = aortic lesion, which remains unknown because of the lack of transesophageal echocardiography.