Various modalities used to image collateral blood flow in the brain during stroke

1. NBIC REVIEW PAPER
PRESENTATION
COLLATERAL BLOOD FLOW
DYNAMICS IN STROKE
Shrut Kirti Saksena
8th Semester

2. CONTENTS
• Introduction
• Anatomy Of Collateral Circulation
• Imaging Of Collateral Vessels
• Digital Subtraction Angiography (DSA)
• CT Angiography
• Magnetic Resonance Angiography (MRA)
• Trans-cranial Doppler (TCD)
• Augmentation Of Cerebral Blood Flow In Acute Stroke
• Conclusion

3. INTRODUCTION
Stroke continues to impose an overwhelming burden on global health.
It is the second most common cause of death.
Main causes of stroke are: -
• Ischemia, or restricted blood flow; typically due to occlusion of a cerebral arteries
• hypertension
• diabetes
Collateral flow i.e. perfusion via alternative, indirect pathways, might off set potential
injury to the brain.
Imaging of the brain and vessels has shown that collateral flow can sustain brain tissue
for hours after the occlusion of major arteries to the brain, and the augmentation or
maintenance of collateral flow is therefore a potential therapeutic target.

4. ANATOMY OF COLLATERAL CIRCULATION
Three principal anatomical features underlie collateral perfusion to the
brain:-
• The first consists of large-artery communications between the extra-
cranial and intra-cranial circulations
• Second, four major arteries coalesce to form an equalising distributor, the
circle of Willis, which can redistribute blood flow in the event of a sudden
occlusion of a parent vessel i.e. the anterior and posterior communicating
arteries of the Circle of Willis -PRIMARY COLLATERAL PATHWAY.
• Third, leptomeningeal anastomoses potentially provide arterial blood to
the cortical surface i.e. SECONDARY COLLATERAL PATHWAY

6. Factors that stimulate collateral recruitment : -
• Systemic Blood Pressure
• Systolic Hypertension
• Atherosclerosis, an intracranial disease, also results
in vessel stiffening and could inhibit blood flow.
• The Pace of Occlusion - Gradual Chronic Occlusion
e.g. progressive atherosclerotic internal carotid
artery stenosis at the bulb, or neovascularisation.

7. IMAGING OF COLLATERAL VESSELS
Although no ideal or specific imaging modality is available
for demonstration and accurate measurement of the
collateral circulation, several techniques can provide insight
into collateral flow in patients with ischemic stroke .
These are:-
• Digital Substraction Angiography (DSA)
• CT Angiography
• Magnetic Resonance Angiography (MRA)
• Trans-Cranial Doppler(TCS)

8. DIGITAL SUBTRACTION ANGIOGRAPHY(DSA)
Conventional digital subtraction angiography is
referred to as the gold standard against which all other
methods are compared.
It allows assessment of all three major collateral
routes:
• Extracranial–Intracranial Anastomoses
• Willisian
• Leptomeningeal collaterals.

10. • Retrograde filling of three or more branches of the
Middle Cerebral Artery (MCA) up to the M2 segment is
said to be evidence of good collaterals, whereas
anything less was rated as poor.
• A five-point scale is also used to study collaterals that
was based on a score endorsed by the American
Society of Interventional and Therapeutic
Neuroradiology and the Society of Interventional
Radiology.
• The drawback of DSA is that it is an invasive technique.

11. CT ANGIOGRAPHY
•The non-invasive nature of CT angiography and its rapid
availability for patients with acute stroke makes it ideal for study
of collateral status.
•Three categories for collateral status: Good, Moderate and Poor
collaterals.
•The National Institutes of Health Stroke Scale (NIHSS) score was
significantly lower in patients with good collaterals than in
patients in the other two groups.
•More routinely used than DSA but has less spatial resolution.

14. MAGNETIC RESONANCE ANGIOGRAPHY (MRA)
•This has been used to grade collateral status and its relation to
outcome.
•Hyper-intense proximal intracranial vessels on MRI obtained with
fluid-attenuated inversion recovery (FLAIR) in patients with acute
stroke are indicative of intraluminal thrombus.
•Distal hyper-intense vessels have a serpentine appearance, and
might be an indicator of slow retrograde collateral flow.
•Drawback-The high sensitivity of MRA restrict it to detect
leptomeningeal collaterals.

16. TRANS-CRANIAL DOPPLER (TCD)
•The researchers used TCD to judge collateral status within
24 h of a stroke secondary to carotid dissection and
showed how this non-invasive technique could help to
establish the long-term prognosis in such patients.
•Flow velocity was systematically measured within the
ophthalmic, anterior, and posterior communicating arteries.
•TCD’s drawback is that it provides very little information
about collaterals and only Circle of Willis.

18. AUGMENTATION OF CEREBRAL
BLOOD FLOW IN ACUTE STROKE
The therapeutic modalities used to increase blood flow to the brain are:
•Plasma Expanders: Dextran and Hydroxyethyl Starch were used as
plasma expanders.
•No improvement in neurological outcome or reduction in mortality
was recorded
•Vasodilators: Drugs (methylxanthine derivatives) that cause
cerebral arterial vasodilation could potentially increase blood flow
to ischemic tissue through collateral channels
•Induced hypertension: A rise in systemic blood pressure could
improve blood flow to the brain, possibly through increased
collateral flow.

19. CONCLUSION
In acute stroke, the severity of ischemia determines how fast
brain tissue might sustain irreversible damage.
• Pial collaterals, if well developed, might allow protracted
tissue survival in the event of a proximal occlusion of a large
intracranial blood vessel.
• Imaging of collateral blood flow is challenging, but
multimodal CT and MRI techniques (perfusion combined
with vessel imaging) seem to be the most promising
methods for the routine assessment.

20. REFERENCES

21. THANK YOU
Questions?