MRI or CT: Which to choose in stroke?
The choice of imaging modality in acute cerebrovascular accident depends on the time factor. Non-contrast CT remains the baseline study for rapidly ruling out hemorrhage, which is essential before initiating anticoagulant therapy. Adding CT angiography and CT perfusion helps identify the thrombus and estimate the volume of the ischemic penumbra (penumbra).
However, CT has distinct disadvantages: it poorly visualizes the deep brain nuclei and posterior cranial fossa structures. In these cases, MRI demonstrates absolute superiority. Tomography accurately differentiates acute from old lesions and has high sensitivity regardless of the affected zone. The main reason why MRI is not the first-line method for all patients lies in logistics: the method requires lengthy preparation (ruling out metallic implants), the scanning process itself is time-consuming, and round-the-clock machine availability is often limited.
Key sequences and "wake-up stroke"
For maximum accuracy, radiologists use a combination of pulse sequences:
- DWI (diffusion-weighted imaging) is exceptionally sensitive to acute parenchymal infarction, demonstrating cytotoxic edema.
- T2 gradient echo (T2*) and FLAIR—combined with DWI, allow for the detection of the smallest foci of hemorrhage.
MRI becomes indispensable in the so-called "wake-up stroke" (wake-up stroke), when the time of symptom onset is unknown. Physicians look for a radiological mismatch between the infarction core (already irreversible changes) on DWI scans and the area of the ischemic penumbra on FLAIR. Careful selection of such patients allows for expanding the therapeutic window for thrombectomy up to 24 hours.
Specific causes of ischemia in children
In pediatric practice, involvement of the large intracranial vessels of the anterior circulation (middle and anterior cerebral arteries, terminal internal carotid artery) predominates.
The most common cause of childhood strokes worldwide is sickle cell anemia (SCA). Abnormal hemoglobin deforms red blood cells, causing capillary occlusion. SCA is characterized by infarction in watershed infarction zones. These patients develop progressive cerebral vasculopathy (moyamoya disease / moyamoya disease), in which large arteries narrow and a network of small proximal collaterals compensatorily expands. Skull radiographs in SCA also show diffuse thickening of the diploic space due to enhanced erythropoiesis.
Another atypical pattern occurs in mitochondrial cytopathy MELAS. In this condition, the area of extensive infarction crosses the boundaries of classical cerebral arterial blood supply basins, while CT reveals symmetrical calcification of the caudate and lentiform nuclei.
Toxic and vasculitic lesions
Strokes can occur against the background of intoxications and blood vessel inflammation:
- Cocaine: more frequently triggers hemorrhagic rather than ischemic strokes. Hemorrhages occur either due to the rupture of concomitant aneurysms following a sharp blood pressure surge or (without background pathology) directly into the basal ganglia and thalamus. Ischemia results from toxic vasoconstriction.
- Alcohol: chronic use can lead to Marchiafava–Bignami disease (Marchiafava–Bignami disease). This is necrosis of the corpus callosum, which in the acute phase yields a high-intensity signal on T2, restricted diffusion, and peripheral contrast enhancement.
- Primary angiitis of the CNS (PACNS): a rare disease of middle-aged individuals. FLAIR shows diffuse signal hyperintensity in the white and gray matter. MR angiography may demonstrate inflammation of the walls of small and medium-sized arteries, but a definitive diagnosis is established solely by biopsy (furthermore, a single negative result does not exclude the disease due to the patchy nature of the lesions).
To remember the role of sequences in "wake-up stroke": DWI shows what has already "died" (the infarction core), while FLAIR shows what has not yet managed to change. The mismatch between them is a chance to salvage the tissue.
Class and exam questions
Why is CT performed first rather than MRI when stroke is suspected?
CT is performed faster and allows for the instant exclusion of intracerebral hemorrhage. This is the primary condition for safely initiating anticoagulant therapy (thrombolysis) within the first 6 hours.
What imaging predictors of a good outcome exist?
The best predictors are a small infarction size according to CT perfusion data and a well-developed collateral vessel network assessed on multiphase CT angiography.
Why is MR angiography (MRA) superior to CT angiography (CTA) when examining neck arteries?
MRA better detects acute arterial dissection and is not subject to artifacts from calcified atherosclerotic plaques, which create major interference on CTA.
What else to study on this topic
- Acute hemorrhagic leukoencephalomyelitis: screening for microbleeds on T2*
- Dysembryoplastic neuroepithelial tumor (DNT) and the "FLAIR rim" sign
- Marchiafava–Bignami disease: stages of corpus callosum destruction
- Reversible toxic encephalopathy following gadolinium administration in acute kidney injury
- Comparison of CTA and MRA in pulmonary vessel imaging (thromboembolism and malformations)
Master the entire topic in the "Diagnostic Radiology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Stroke on MRI" and 2,199 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 10 video lessons on the subject
Other topics in the Neuroimaging section
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.