Presentation: 

33 y/o male with aphasia. Stroke evaluation.

Key findings:

• Patchy left multifocal MCA distribution foci of diffusion restriction (e.g., here and here) indicating acute ischemia/infarction. There is associated FLAIR siabnormality and correlative ADC mapping hypointensity (here and here).
• Left frontal component contains small quantity petechial hemorrhage.
• An ovoid focus of encephalomalacia within the right posterior striatum is favored to represent a remote infarct given peripheral hemosiderin.

Diagnosis: 

1. Acute left multifocal MCA distribution foci of ischemia/infarction.

2. Additional bilateral frontal and right basal ganglia encephalomalacia, likely sequela of remote infarction.

Highest-yield Sequences:

• FLAIR – Parenchymal hyperintensity appears before other sequences become abnormal. Major vessel occlusion can be seen as an intravascular hyperintensity.
• DWI – Cytotoxic edema shows up as hyperintensity. 95% hyperacute stroke detection rate. Gives a pretty accurate idea of the infarct core size, but some diffusion abnormalities are reversible (e.g., TIA or migraine). Restriction typically lasts 7-10 days.
• Confirm that the ADC map shows corresponding hypointensity in the same locations.
• SWI – Highly sensitive for microscopic hemorrhage.

Discussion: 

Patients present to the ED at various times after stroke symptom onset, and since the timeframe matters for treatment planning, MRI can come in very handy for providing relative stroke dating. Also, MRI is more sensitive for strokes than CT is. Here’s a Radiographics chart that beautifully lays out the MRI sequence criteria for dating a stroke (https://pubs.rsna.org/cms/10.1148/rg.325115760/asset/images/large/115760t01.jpeg). Since IV tPA is typically only given within 4.5 hours of stroke symptoms onset, it can be helpful to differentiate early hyperacute (0-6 hours) from late hyperacute (6-24 hours) strokes. Ischemic foci show DWI hyperintensity and ADC hypointensity for at least the first week, so that won’t help you. However, while FLAIR can show a variable signal during the first 6 hours, it’s usually hyperintense after the 6 hour mark. While DWI is highly sensitive, it’s important to note it can rarely be falsely negative in patients with hyperacute (6-24 hours) or acute posterior circulation, or lacunar strokes. Differentiating between late hyperacute (6-24 hours) and acute (24 hours-1 week) strokes also has indications for determining whether mechanical disruption/ embolectomy might be indicated. You get the point – try to date the stroke(s) using that chart. SWI can show hypointense hemorrhagic transformation, which can show up in small packages as petechial hemorrhages (which occurs in over half of ischemic stroke patients by around 48 hours, and may just be part of the expected evolution of a stroke), or large packages (non-subtle parenchymal hematoma). Notably, hemorrhagic transformation rarely happens within the first 12 hours of a stroke, particularly during the first 6 hours.

Management: 

Neurology runs the show.

Resources:

“Sequence-specific MR Imaging Findings That Are Useful in Dating Ischemic Stroke.”

Radiographics. https://pubs.rsna.org/doi/10.1148/rg.325115760.

Acute Cerebral Ischemia/Infarction. StatDx. https://app.statdx.com/document/acute-cerebral-ischemiainfarction/a405285f-aaea-43ca-8dc4-6f8120eaabc1?searchTerm=acute%20stroke

AHA/ASA 2018 Guidelines for the Early Management of Patients With Acute Ischemic Stroke. https://www.ahajournals.org/doi/pdf/10.1161/STR.0000000000000158

Helpful Quick Videos:

“Magnetic Resonance Imaging in Stroke.” https://www.youtube.com/watch?v=L-k0oJ7rQ4k.

Pretty good brain MRI sequence review. https://www.youtube.com/watch?v=wVWtXZQcMyM&feature=emb_title