Specific Imaging Findings

Embolic infarcts may be isolated or multiple and vary in size depending on the size of the dislodged thrombus. Small acute embolic infarcts are extremely difficult to detect prospectively on CT or conventional MR sequences, particularly in patients with pre-existing chronic ischemic lesions. The infarcts are hypodense on CT and T2 hyperintense, with little or no mass effect when small. Diffusion MRI is the most sensitive technique for early detection of infarcts, which are bright on trace DWI and dark on ADC maps, consistent with reduced diffusion. The infarcts are typically located peripherally in the cortex or subcortical white matter of the cerebral hemispheres, but involvement of deep structures such as the basal ganglia and centrum semiovale is not uncommon, as well as location along “watershed” areas between vascular territories. Most embolic infarcts occur in the middle cerebral artery territory due to preferential blood flow through the MCA. The presence of multiple infarctions involving more than one major arterial territory is highly suggestive of embolic etiology. Bilaterality and/or involvement of anterior and posterior circulations suggests a cardiac or aortic source, while multiple infarcts of differing ages suggest ongoing embolization. Like with other infarcts, enhancement may occur in the subacute period.