Cerebrovascular Disease (Stroke)

Q1: What are the common causes of stroke?

Cerebrovascular disease can be

• Ischemic
  • due to arterial thrombosis
    • large vessel disease
    • small vessel disease
  • from an embolus from the heart, aorta or larger artery upstream
  • from inadequate cerebral blood flow due to decreased perfusion pressure
• Hemorrhagic
  • from rupture of a vessel.

Q2: Which imaging procedure should be ordered to evaluate stroke?

• CT is ordered to rule out hemorrhage or other mass lesions in unstable, deteriorating patients with or without head injury.
  • evidence of hemorrhage will be a contraindication to the use of thrombolytic or anticoagulant agents.

Q3: What are the advantages and disadvantages of CT?

• Advantages of CT are widespread access, noninvasiveness, and shorter scanning time.
• CT, however, does have several disadvantages:
  • it may not detect an acute infarct
  • it has limited capacity to show smaller infarcts in the brain stem, cerebellum and deep within the cerebral hemispheres.

Q4: What are the advantages and disadvantages of MRI?

• Advantages
  • MRI can help define intra cerebral hemorrhages, old and new.
  • MRI is more sensitive than CT for the early diagnosis of brain infarction.
  • Lacunar infarcts and small cortical infarcts are seen with higher sensitivity.
  • MRI scanners with the ability to perform FLAIR images (fluid-attenuated inversion recovery) and DWI (diffusion-weighted images) are very useful in showing infarcts early, soon after onset of symptoms.
  • DWI images are useful in distinguishing acute from chronic ischemic changes.
    
    
• Disadvantage
  • Cannot scan patients who are unstable, claustrophobic or have pacemakers.

Q5: Does a normal CT or MRI rule out stroke?

• No.
• It is important to remember that in patients with very acute ischemia, both CT and MRI may be normal (except for DWI images).
• Repeating a CT in 48 hours will most likely demonstrate an infarct of moderate size.

Q6: What are the imaging findings of acute infarction?

Acute Infarct:

• DW imaging is the most sensitive MRI sequence to demonstrate acute infarction. This sequence is sensitive to restricted water diffusion within the cell from stroke-induced cytotoxic edema and the region of acute infarction is seen as an area of bright signal on DWI immediately after the insult.
• Sulcal effacement, gyral edema and loss of gray-white matter interface can be seen within hours on CT or MRI.
  
• Old Infarct (> 1 month):
  • Sharply outlined area of infarct without edema
  • Compensatory dilatation (ex vacuo) of adjacent ventricle

Acute One Day Old Infarction Involving the Right Middle Cerebral Artery (MCA) Territory A. Diffusion weighted image shows area of infarct as bright signal. B. T1 image shows no evidence of blood in the area of infarct (blood would appear as white). C. Post contrast coronal image shows vascular enhancement in the area of infarct. D. MR angiography shows right middle cerebral artery branches to be narrower in calibre, as compared to left.

Q7: Describe possible subsequent changes on CT following a cortical infarction.

• When an embolus blocking a major vessel soon 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.
  • After 24 hours, a cerebral or cerebellar infarct is usually a hypo dense area involving both the gray and white matter in a typical vascular distribution.
  • Whether or not hemorrhagic transformation occurs, a mass effect may develop due to edema and is at its maximum 3-5 days post infarct.
• Acute infarction
• Subacute hemorrhagic infarction

Three Week Old Subacute Infarct Involving The Right Middle Cerebral Artery (MCA) Territory A. Diffusion weighted image reveals bright signal involving the cortex. This is from restricted diffusion secondary to acute stroke. B. Flair image shows bright signal in the posterior parietal cortex with gyral thickening. C. T1 weighted image shows bright signal in the same area from blood. D. Post contrast study shows bright signal in the same areas. Enhancement is obscured by the presence of blood. E. Post contrast study shows bright signal in the same areas. Enhancement is obscured by the presence of blood.

Q8: What are the CT findings of intracerebral hemorrhage (ICH)?

• Hypertensive ICH commonly occurs in the basal ganglia or thalamus. Traumatic hemorrhages (contusions) tend to occur at the frontal, temporal or occipital poles or at the inferior orbitofrontal lobe, which overrides the roughened surface of the frontal bone.
• Acute intraparenchymal bleeding is readily seen as a white density located within the brain tissue.
• Occasionally, intraparenchymal hemorrhage will extend into the subarachnoid space and ventricles.
• Intraparenchymal bleeding (especially if supratentorial) will cause a shifting of the adjacent structures away from the area of hemorrhage.

Intracerebral Hemorrhage Non contrast CT Left parietal hemorrhage with break through into left lateral ventricle. Arrowheads point to hemorrhagic infarct with extension of blood into lateral ventricle (arrow).