Imaging description

Anoxic–ischemic injury to the brain as a result of cardiorespiratory insufficiency, such as seen in cardiac arrest, respiratory arrest, prolonged hypotension, and asphyxia, is difficult to diagnose because of the subtlety and symmetry of abnormalities seen on MRI and CT scans. These scans are frequently misinterpreted, particularly when radiologists are not aware of the clinical circumstances. CT scans show diffuse decrease in gray/white differentiation and mild edema in the early stages. On MRI, diffuse increase in the cortical signal is seen on FLAIR/T2-weighted images as well as diffusion-weighted images (DWI) in most cases (Figs. 2.1, 2.2), although different patterns are occasionally encountered, including signal changes in the deep gray matter structures only, in both gray and white matter, and in the white matter only [1].

The underlying pathophysiologic processes leading to differences in pattern are not clearly understood, although essentially all types of global anoxic–ischemic injury portend a very poor prognosis. DWI sequence is the most sensitive imaging modality. DWI shows a much increased contrast difference between the diffusely abnormal cortex and relatively preserved white matter, creating a more “eye-pleasing” appearance compared to a normal DWI scan, which shows only a mild difference between gray and white matter (Fig. 2.3). However, there are differences in the normal contrast present between the cortex and white matter in different MRI scanners and different DWI sequences, and radiologists should become familiar with the normal appearance of the DWI images in their practice settings. High-b-value DWI may increase sensitivity [2].