Neuroradiology Multiple Choice Questions - Acute Ischemic Stroke Imaging
Question 1: Initial Imaging for Acute Stroke
A 65-year-old patient presents to the emergency department 2 hours after sudden onset of right-sided weakness and aphasia. What is the MOST appropriate initial imaging modality?
A) MRI with diffusion-weighted imaging (DWI)
B) Non-contrast CT (NCCT) of the head
C) CT angiography (CTA) of the head and neck
D) CT perfusion (CTP)
E) Either NCCT or MRI, whichever is immediately available
Correct Answer: E
Explanation: For patients within the 4.5-hour window who are IV tPA candidates, either NCCT or MRI is recommended to exclude intracranial hemorrhage before treatment administration 1, 2. The primary goal is to distinguish hemorrhagic from ischemic stroke rapidly 2. While NCCT remains most widely used due to rapid acquisition (seconds) and excellent hemorrhage detection 2, MRI with DWI is more sensitive for early ischemic changes 2, 3. However, the key principle is that imaging should not delay treatment - whichever modality is immediately available should be used 3. The complete multimodal MRI can be performed in approximately 10 minutes if available 24/7 1, 3.
Question 2: Sensitivity of DWI for Acute Ischemia
What is the sensitivity of diffusion-weighted imaging (DWI) for detecting acute ischemic stroke within 6 hours of symptom onset?
A) 61%
B) 75%
C) 85%
D) 91%
E) 97%
Correct Answer: D
Explanation: DWI has a sensitivity of 91% and specificity of 95% for detecting acute ischemia within 6 hours, compared to CT's sensitivity of only 61% and specificity of 65% 3. DWI is the single most sensitive and specific imaging technique for detecting acute ischemia 3. When combined with perfusion-weighted imaging (PWI), the sensitivity increases to 97.5% for diagnosing acute ischemic stroke 4. DWI detects ischemic changes within minutes of symptom onset and is considered the gold standard for ischemic core assessment 3. In head-to-head comparison with CT performed at the same time delay, DWI demonstrated significantly better diagnostic accuracy (91% vs 61%) and superior interrater reliability 5.
Question 3: Vascular Imaging in Acute Stroke
A 58-year-old patient presents 1.5 hours after stroke onset with NIHSS score of 18. NCCT shows no hemorrhage. An endovascular team is available at your institution. What is the MOST appropriate next step in imaging?
A) Proceed directly to IV tPA without further imaging
B) Obtain vascular imaging (CTA/MRA) during initial evaluation
C) Wait until after IV tPA administration to obtain vascular imaging
D) Obtain CT perfusion first, then vascular imaging
E) Vascular imaging is not indicated within 3 hours
Correct Answer: B
Explanation: For acute stroke patients who are candidates for endovascular therapy, vascular imaging (CTA, MRA, or conventional angiography) is strongly recommended during the initial imaging evaluation 1, 2. Even within the 3-hour window, vascular imaging is indicated if an endovascular team is available and it does not unduly delay IV tPA administration 1, 3. Acute large-vessel intracranial thrombus is very accurately detected by CTA, DSA, and MRA (Class I, Level of Evidence A) 1. The presence of large vessel occlusion significantly influences treatment decisions and prognosis 1. CTA, DSA, and MRA far surpass the sensitivity of non-vascular studies like NCCT, FLAIR, or gradient-echo MRI for detecting intravascular thrombus 1. The key caveat is that vascular imaging cannot unduly delay IV tPA administration 1, 3.
Question 4: Gradient-Echo (GRE) Sequence
What is the PRIMARY advantage of gradient-echo (GRE) or susceptibility-weighted imaging (SWI) sequences in acute stroke evaluation?
A) Detection of early ischemic changes
B) Detection of hemorrhage and microhemorrhages
C) Assessment of perfusion deficits
D) Visualization of large vessel occlusions
E) Differentiation of acute from chronic infarcts
Correct Answer: B
Explanation: GRE sequence detects acute, subacute, and chronic hemorrhage with superior sensitivity compared to CT 3. GRE can detect microhemorrhages, both old and new, better than CT, indicating the presence of amyloid angiopathy, hypertension, small vascular malformations, and other vascular diseases 1, 3. This is critical for risk stratification before thrombolysis. Small numbers of microbleeds (<5) do not contraindicate intravenous thrombolysis, though the risk with multiple microbleeds (>5) remains uncertain 3. GRE exceeds the sensitivity of NCCT for detecting thrombus within the vasculature 1. MRI is superior to CT for demonstration of subacute and chronic hemorrhage and hemorrhagic transformation of acute ischemic stroke 1.
Question 5: Imaging Beyond 6 Hours
A 72-year-old patient presents 8 hours after last known normal with left hemiparesis. NCCT shows no hemorrhage or early ischemic changes. What imaging is MOST essential for treatment selection?
A) Repeat NCCT in 2 hours
B) MRI with DWI only
C) Multimodal imaging with perfusion assessment (CTP or PWI)
D) Carotid ultrasound
E) No further imaging needed
Correct Answer: C
Explanation: For patients beyond 6 hours from symptom onset, multimodal imaging with perfusion assessment is essential for treatment selection 2. A vascular study is strongly recommended during initial imaging evaluation of acute stroke patients who present >3 hours after ictus, especially if intra-arterial thrombolysis or mechanical thrombectomy is contemplated (Class I, Level of Evidence A) 1. Perfusion imaging identifies the ischemic penumbra (salvageable tissue) and helps distinguish it from the irreversibly infarcted core 1. CT perfusion differentiates between infarcted core and salvageable penumbra and is essential for selecting patients beyond 6 hours from symptom onset 2. The diffusion-perfusion mismatch pattern on MRI identifies salvageable tissue 3. This approach allows for patient selection with an acceptable risk-benefit ratio for late-window interventions 1.
Question 6: DWI-Negative Stroke
What percentage of acute ischemic stroke patients may have a negative DWI despite true ischemic stroke?
A) <1%
B) 2-3%
C) 8%
D) 15%
E) 25%
Correct Answer: C
Explanation: Approximately 8% of all ischemic stroke patients may be DWI-negative 4. However, when PWI is added to DWI, the combined sensitivity reaches 97.5% for diagnosing acute ischemic stroke 4. DWI negativity is associated with less severe strokes, location in the posterior circulation, longer time from onset to scan, and improved 90-day outcome 4. Small-vessel disease strokes are more likely to be DWI-negative 4. This highlights the importance of combining DWI with PWI for comprehensive stroke diagnosis, particularly in patients with milder symptoms or posterior circulation involvement. The combination of DWI and PWI provides the highest diagnostic accuracy for acute ischemic stroke 4.
Question 7: Common Pitfall in Acute Stroke Imaging
What is a MAJOR pitfall that can lead to suboptimal patient outcomes in acute stroke imaging?
A) Using MRI instead of CT as initial imaging
B) Focusing solely on NCCT without vascular imaging when large vessel occlusion is suspected
C) Obtaining GRE sequences
D) Using contrast for CTA
E) Performing imaging before clinical examination
Correct Answer: B
Explanation: Focusing solely on NCCT without vascular imaging may miss large vessel occlusions requiring endovascular therapy 2. This represents a critical missed opportunity for potentially life-saving intervention. For patients who are endovascular therapy candidates, vascular imaging is strongly recommended during initial evaluation 1, 2. The detection of large vessel occlusion significantly influences treatment decisions, as these patients may benefit from mechanical thrombectomy even beyond the IV tPA window 1. However, the key caveat is that obtaining advanced imaging must be balanced against the time-sensitive nature of reperfusion therapies 2. A standardized imaging approach should be selected upfront, with all studies performed in as few sessions as possible to avoid treatment delays 1.