Specific Imaging Findings

On non-enhanced CT scan acute infarction will be recognized as a hypoattenuating area of the brain parenchyma in a typical vascular distribution, involving both the gray and white matter with loss of contrast between the two and effacement of the cortical sulci. In larger infarcts a more prominent mass effect such as compression of the ventricular system or even herniations may be observed. Increased T2 signal intensity with cortical swelling and mild mass effect is observed on MRI, along with gyral effacement and T1 hypointensity. FLAIR images may show hyperintensity along the occluded vessels (comparable to the CT “hyperdense vessel” sign). Acute ischemic lesions are characterized by a very bright signal on DWI and low ADC values. ADC gradually normalizes over time, but remains decreased for the first 5–10 days. Contrast enhancement may be present in the acute phase, which is usually gyriform along the cortex. However, smaller infarcts (especially in the brainstem and basal ganglia) may show ring-like or patchy enhancement, mimicking neoplasms. T2* MR images are highly susceptible to the paramagnetic effect of the blood products, and thus highly specific for identifying areas of microscopic and macroscopic hemorrhage. Extremely low rCBV and rCBF values are present in infarcted areas on perfusion imaging.