A 68-year-old with atrial fibrillation presents with sudden right-sided weakness and aphasia. CT scan shows no hemorrhage. Which intervention is most appropriate within 4.5 hours of symptom onset?
AAdminister IV tPA to dissolve the likely cardioembolic thrombus
BAdminister IV heparin to prevent further clot extension
CWithhold treatment until MRI DWI confirms ischemia — CT alone is insufficient for diagnosis
DAdminister reversal agents for anticoagulation to prevent hemorrhagic transformation
This presentation is classic cardioembolic ischemic stroke (atrial fibrillation is the most common cardiac source). CT serves its purpose by excluding hemorrhage — tPA can then be administered. Waiting for MRI is not indicated in the acute window; CT negative for hemorrhage is sufficient to proceed. Heparin is not the acute thrombolytic agent. Reversal agents are for hemorrhagic stroke, which the CT has ruled out.
Question 2 Multiple Choice
Why does 'time is brain' have a precise biological basis in ischemic stroke?
ABrain cells die instantly at occlusion, so every second of delay adds irreversible infarct
BThe penumbra — hypoperfused but still viable tissue surrounding the ischemic core — converts to irreversible infarct at approximately 1.9 million neurons per minute without restored perfusion
CEdema forms progressively and compresses healthy tissue, causing secondary death within the first hour
DThrombus extension occurs rapidly, enlarging the occluded territory within minutes of onset
The penumbra is the key concept. The ischemic core (directly deprived of perfusion) dies quickly, but surrounding tissue with some collateral flow — the penumbra — remains viable for a time-limited window. It is not dead yet but is dying. The penumbra converts to core at ~1.9 million neurons per minute if perfusion is not restored. Thrombolysis and thrombectomy are attempts to rescue this tissue before that window closes.
Question 3 True / False
The distinction between hemorrhagic and ischemic stroke cannot be reliably made on clinical presentation alone — brain imaging is mandatory before any treatment decision.
TTrue
FFalse
Answer: True
Both stroke types can present with sudden focal neurological deficits and are clinically indistinguishable in many cases. Hemorrhagic stroke must be excluded by CT before administering tPA, because tPA given to a hemorrhagic stroke could be catastrophic. The treatments are mechanistically opposite: restore perfusion for ischemic stroke, control the bleed and manage ICP for hemorrhagic stroke.
Question 4 True / False
In hemorrhagic stroke, neuronal injury is confined to the immediate vicinity of the bleed, with no ischemia occurring in distant brain regions.
TTrue
FFalse
Answer: False
Hemorrhagic stroke causes mass effect: the hematoma raises intracranial pressure, which reduces cerebral perfusion pressure globally and can shift brain structures (herniation). This creates secondary ischemia in tissue distant from the hematoma. Additionally, blood products trigger inflammatory cascades that compound injury over days, extending the zone of damage well beyond the bleed itself.
Question 5 Short Answer
Explain the therapeutic significance of the ischemic penumbra — what it is, why it exists, and why its existence justifies the urgency of stroke treatment.
Think about your answer, then reveal below.
Model answer: The penumbra is tissue surrounding the ischemic core that receives reduced but not zero perfusion — metabolically stressed but still viable. It exists because arterial occlusion creates a perfusion gradient: the core supplied only by the blocked vessel dies quickly, while surrounding tissue supplied by collateral vessels retains some flow. This viable tissue is the therapeutic target: restoring perfusion through tPA or mechanical thrombectomy can rescue it. Without treatment, the penumbra converts to infarct at ~1.9 million neurons per minute — the biological basis for the narrow treatment window and the maxim 'time is brain.'
The penumbra concept transforms stroke from a single catastrophic event into a race against time. Treatment isn't simply useful — it has a mechanistic basis for why earlier intervention saves more neurons. The shrinking penumbra also explains why thrombectomy eligibility (up to 24h) requires imaging confirmation of salvageable tissue: if the penumbra has already converted to core, intervention no longer helps.