Cerebrovascular disease / Stroke

Objectives: You will learn

Q1: What are the common causes of stroke?
Q2: Which imaging procedure should be ordered to evaluate stroke?
Q3: What are the advantages and disadvantages of CT?



Q4: What are the advantages and disadvantages of MRI?



Q5: Does a normal CT rule out stroke?
Q6A: What are the imaging findings of acute infarction (<24 hours) ?

Non-contrast CT:



Q6B: What are the imaging findings of subacute stroke (24 hours to 1 week) ?


Q6C: What are the imaging findings of subacute to chronic infarction (1 week to 2 months) ?


Q6D: What are the imaging findings of chronic old infarct (>2 months) ?


Figure 1: Non-contrast axial CT brain


Acute to Subacute Infarct

Case 1:

Imaging findings: Figure 1

  • Large area of low CT attenuation (hypodense) is seen involving the left middle cerebral artery distribution (yellow arrows), with involvement of both gray and white matter.
  • White arrows points to involvement of basal ganglia region with infarction also.
  • Gyri and sulci are effaced on the left side (compare to normal right side).


Figure 2: Non-contrast axial CT head



Hypertensive Hemorrhagic Infarct

Case 2:

Imaging findings: Figure 2

  • Hemorrhage (hyperdense area) involving left basal ganglia/thalamic regions (yellow arrow) is noted.
  • Extension of hemorrhage into left frontal horn (red arrow).
  • Black arrow points to normal calcification of choroid plexus.

Hemorrhage secondary to hypertension is more common in basal ganglia / thalamic regions.

Not a candidate for thrombolytic therapy or anticoagulation.

Figure 3: MR Images


One Day Old Acute Infarction Involving the Right Middle Cerebral Artery (MCA) Territory

Case 3:

Imaging findings: Figure 3

  1. Diffusion weighted image identifies an area of acute infarct as bright signal (white arrow).
  2. Pre-contrast axial T1 wtd.. MRI shows gyral thickening (arrows) compared to contralateral side. Findings of acute infarct are not as readily visible as in DW pulse sequence.
  3. Post-contrast coronal T1 wtd. MRI shows delayed vascular enhancement (white arrow) in the area of infarct due to distal arterial occlusion.
  4. MR angiography shows right middle cerebral artery branches to be narrower in caliber (white arrow), as compared to left side, likely from embolic occlusion.

Figure 4: MR Images (DWI)

Left Middle Cerebral Artery Territory Acute Stroke

Case 4:

Imaging findings: Figure 4

  • A and B: Diffusion weighted images shows areas of acute infarction as bright signal due to intracellular cytotoxic edema, restricting movement of water molecule in and out of the cell.
  • In figure A, left temporal lobe acute infarction (yellow arrow) and left lateral basal ganglia-thalamic regions (red arrow) are noted.
  • Left frontal lobe infarct (arrow) is shown in Fig. B.


Figure 5 A-C: MR Images


Posterior cerebral artery territory Acute Stroke

Case 5:

Imaging findings: Figure 5 A-C

  1. Pre-contrast axial T1 wtd. MRI
  2. Axial flair image
  3. Post-contrast axial T1 wtd. MRI

Acute infarction is seen involving the left occipital lobe (yellow arrow) and adjacent left temporal lobe (white arrow). The left posterior cerebral artery territory infarction is better seen on flair sequence (Fig. B) than on T1 wtd. pulse sequence (Figs. A, C).


Figure 5 D-E: MR Images



Imaging findings: Figure 5 D-E (DW images)

Acute infarction involving the left occipital lobe (yellow arrow in Fig. A), adjacent left temporal lobe (white arrow in Fig. D) and infarction within the left thalamus (red arrow in Fig. E) is best appreciated on diffusion wtd. pulse sequences.

Figure 6: MR Images


Left Anterior Cerebral Artery Territory Acute Infarction (5 days old)

Case 6:

Imaging findings: Figure 6

  1. Post-contrast axial T1 wtd. image demonstrates gyral enhancement (yellow arrows) involving the territory of left anterior cerebral artery.
  2. Flair image shows an area of increased signal (yellow arrows) related to acute infarct.


Q7: Describe possible subsequent changes following acute infarction (See answers to Q6B, 6C, 6D).

When an embolus blocking a major vessel migrates, lyses, or disperses, recirculation into the infarcted area can cause a hemorrhagic infarction and may aggravate edema formation due to disruption of the blood-brain barrier.

Subacute to chronic infarct: (1-8 weeks)

Old Infarct:

Figure 7: MR Images

Three Week Old Subacute to Chronic Infarction Involving the Right Middle Cerebral Artery Territory with Reperfusion Hemorrhage

Case 7:

Imaging findings: Figure 7

  1. Diffusion weighted image reveals bright signal involving the cortex (white arrows). This is from restricted diffusion secondary to acute infarction.
  2. Axial flair shows increased signal involving the posterior temporoparietal cortex with gyral thickening (white arrows).
  3. Pre-contrast axial T1 wtd. MRI shows increased signal (white arrows) in the same area from subacute blood in the distribution of infarct.

Q8: How does information gathered from imaging influence clinical management?

The goal of imaging in a patient with acute stroke is to determine:

  1. Is there an infarct?
  2. If there is an infarct, is it associated with hemorrhage? Thrombolytic therapy is then contraindicated.
  3. If there is an infarct, is there reversibly impaired brain tissue that could benefit from thrombolytic therapy?
  4. Nature of vascular abnormality? Is the abnormality in extracranial arteries or intracranial arteries?


Is there an infarct?


If there is an infarct, is it associated with hemorrhage?


If there is an ischemic infarct, is there reversibly impaired brain tissue?


Nature of vascular abnormality? Options to investigate?

US of carotids

No radiation

Normal digital subtraction contrast angiogram

Arterial puncture required.

Selective intra arterial contrast injection into right internal carotid artery.

Normal CT arterial angiography

Contrast administered intravenously.


Normal MR arterial angiography

No radiation.

Contraindicated when there are metallic objects in the critical sites.


When you interpret imaging studies during your clerkship, I want you to make the following statements:

  1. Is it hemorrhagic infarct or non-hemorrhagic infarct? Obviously anticoagulation or thrombolytic therapy is contraindicated in hemorrhagic infarct. If it is hemorrhagic, assess extension into ventricles.
  2. Decide on which vascular territory: anterior, middle, posterior cerebral artery?
  3. Is it acute, subacute or chronic? DWI is most valuable for this purpose.
  4. Is there reversibly impaired brain tissue? At this stage of learning, you need not worry about this. For this you need to understand perfusion and diffusion imaging. Thrombolytic therapy is not useful if there is no reversibly impaired brain tissue.
  5. Are there signs of mass effect due to edema and hemorrhage? Look for effacement of gyri and sulci, compression of ventricles, etc.
  6. Is the stroke due to intracranial vascular disease or due to extracranial vascular disease? You will need history and other clinical information to make this assessment. This will help guide in further work-up.