On MRI, what imaging finding is most diagnostic of an acute ischemic stroke?

On MRI, what imaging finding is most diagnostic of an acute ischemic stroke?

• A. Diffusion-weighted imaging showing restricted diffusion in the affected brain tissue.
• B. T1-weighted hyperintensity.
• C. T2 hyperintensity in cortex only.
• D. Perfusion MRI mismatch.

Answer: (A)

Restricted diffusion on diffusion-weighted MRI is the hallmark of acute ischemic stroke because it reflects cytotoxic edema from energy failure in ischemic tissue. When neurons lose their ability to maintain ion gradients, water moves into cells and diffusion becomes severely restricted, which appears as bright signal on diffusion-weighted images and dark signal on ADC maps. This change happens within minutes of onset and remains highly sensitive and specific for acute infarction, making it the most diagnostic finding for an acute stroke. T1 hyperintensity is not typical in the hyperacute phase and usually appears later or with other processes; T2 hyperintensity in cortex alone can occur with various types of edema and is not specific to acute ischemia, especially early on when changes may be subtle or absent. Perfusion MRI mismatch can indicate tissue at risk and guide treatment decisions, but it is not by itself a definitive sign of infarction; some patients have perfusion abnormalities without established infarction, and vice versa.

Restricted diffusion on diffusion-weighted MRI is the hallmark of acute ischemic stroke because it reflects cytotoxic edema from energy failure in ischemic tissue. When neurons lose their ability to maintain ion gradients, water moves into cells and diffusion becomes severely restricted, which appears as bright signal on diffusion-weighted images and dark signal on ADC maps. This change happens within minutes of onset and remains highly sensitive and specific for acute infarction, making it the most diagnostic finding for an acute stroke.

T1 hyperintensity is not typical in the hyperacute phase and usually appears later or with other processes; T2 hyperintensity in cortex alone can occur with various types of edema and is not specific to acute ischemia, especially early on when changes may be subtle or absent. Perfusion MRI mismatch can indicate tissue at risk and guide treatment decisions, but it is not by itself a definitive sign of infarction; some patients have perfusion abnormalities without established infarction, and vice versa.