Figure 13a. Cortical gyral enhancement in embolic cerebral infarction in a 65-year-old woman. (a) On an axial nonenhanced CT scan, the sulci in the right hemisphere are normally prominent; on the left, the parietal sulci are effaced within a wedge-shaped region of abnormal hypoattenuation. The gyral surface is actually slightly hyperattenuating due to reperfusion injury with secondary petechial hemorrhage in the infarcted cortex. (b) Axial contrast-enhanced CT scan shows cortical gyral enhancement. The same endothelial damage that allows red cells to extravasate also permits contrast material to escape the vascular lumen and enter the brain parenchyma.