Early Signs of Ischemic Brain Injury on Noncontrast CT

Axial noncontrast CT images of the brain of two different patients presenting with acute stroke within 3 hours of symptom onset. The top row is images in a "brain" window, while the bottom row shows images in an "acute stroke" window. Early ischemic changes (cortical ribbon sign) of the right posterior inferior cerebral artery (left images) and right middle cerebral artery (right images) are much better appreciated on the acute stroke window.  

Loss of gray-white differentiation

• Lenticular obscuration: loss of distinction among basal ganglia nuclei
• Insular ribbon sign: blending of densities of cortex and white matter of insula
• Cortical ribbon sign:  blending of densities of cortex and white matter of other lobes

Swelling of gyri producing sulcal effacement

Detectability

• Seen on less than 1/3 of patients imaged within 3 hours of symptom onset
• Detection influenced by infarct size, severity and time between symptom onset and imaging
• Large interobserver variability, which may be improved by the use of a structured scoring system such as Alberta Stroke Program Early CT Score (ASPECTS) or the CT Summit Criteria, as well as the use of better CT windowing and leveling (use of "acute stroke" window)

Implications of these signs to management

• More rapid these signs become evident, the more profound the degree of ischemia
• Presence, clarity and extent of these signs on noncontrast CT correlates with higher risk of hemorrhagic transformation after Rx with fibrinolytic agents
• Involvement of greater than 1/3 of MCA territory increases risk of intracranial hemorrhage, shown in a European trial in patients of less than 6-hour symptom onset. This criterion has been used as an exclusion from entry in several trials evaluating the benefit of IV fibrinolytic therapy in the 3- to 4.5-hour window

Reference:
Jauch EC, et al. Guidelines for the early management of patients with acute ischemic stroke: a guideline for healthcare professionals from the American Heart Association/American Stroke Association. Stroke 2013 (January)