Recommended
Recommended
More Related Content
Similar to CTA Collateral Scoring system- RADIOLOGY 2
Similar to CTA Collateral Scoring system- RADIOLOGY 2 (20)
Recently uploaded
Recently uploaded (20)
CTA Collateral Scoring system- RADIOLOGY 2
- 1. CTA COLLATERAL GRADING SYSTEMS JIM LAPNITEN, MD, FPCR US FELLOW-IN-TRAINING
- 2. CTA COLLATERAL GRADING SYSTEMS ▪ ANATOMY ▪ SIGNIFICANCE OF GRADING THE COLLATERALS ▪ COLLATERAL SCORING SYSTEMS ▪ ANGIOGRAPHY ▪ sCTA ▪ mCTA
- 3. ANATOMY OF THE CEREBRAL COLLATERAL SYSTEM
- 4. Cerebral Collateral Circulation - alternative or indirect arterial pathways that provide blood flow when an artery that normally supplies an area of brain tissue is occluded Structural Classification ▪ Circle of Willis ▪ Microvascular intracranial collaterals (arterioles) ▪ Leptomeningeal (pial) ▪ Subcortical collaterals ▪ Extracranial sources of collateral circulation Functional Classification ▪ Primary- permanently functioning - immediately reroute flow ▪ Secondary- pre-existing conduits that can be recruited - recruitment takes 12 sec in rats ▪ Tertiary- formation of new blood vessels or the maturation of pre-existent vessels Collateral Circulation in Ischemic Stroke: An Updated Review, Maguida and Shuaib, 2022
- 6. INTRA-CRANIAL COLLATERAL CIRCULATION Collateral Circulation, Liebeskind, 2003
- 7. EXTRA-CRANIAL COLLATERAL CIRCULATION Collateral Circulation, Liebeskind, 2003
- 8. LEPTOMENINGEAL (PIAL) COLLATERAL SYSTEM ▪ Arteriolo-arteriolar connections (50-400 microns) ▪ Seen at the distalmost branches of large cerebral and cerebellar vessels ▪ Variable configurations: end-to-end and end-to-side anastomoses ▪ Bidirectional flow governed by hemodynamic and metabolic needs of the territories they connect ▪ Formation during the embryonic period (collaterogenesis) Collateral Circulation in Ischemic Stroke: An Updated Review, Maguida and Shuaib, 2022
- 9. LEPTOMENINGEAL (PIAL) COLLATERAL SYSTEM Collateral Circulation in Ischemic Stroke: An Updated Review, Maguida and Shuaib, 2022 PIAL COLLATERAL RECRUITMENT PRESSURE GRADIENT > NITRIC OXIDE > DILATATION NEURAL REGULATION EXTRINSIC INNVERVATIONS VIA PNS > VESSELS ON THE BRAIN SURFACE NEURAL REGULATION INTRINSIC INNERVATIONS VIA THE CNS (MAINLY VIA THE BRAINSTEM) > PARENCHYMAL VESSELS
- 10. OTHER FACTORS THAT MODIFY THE COLLATERAL SYSTEM ▪ Aging – decrease in number and diameter ▪ Vascular risk factors – HPN, CCA occlusion, DM > impaired recruitment ▪ Smoking – Positive correlation in CAD(?) due to ischemic preconditioning; Positive correlation in ischemic stroke ▪ Physical exercise – increased blood flow stimulates endothelial mechanisms for maintenance, defense and repair > improved collateral circulation and capacity to vasodilate ▪ Statin use – enhancement of arteriogenesis and eNOS-mediated vasodilatation ▪ Extracranial ICA stenosis - >75% stenosis=good collaterals Collateral Circulation in Ischemic Stroke: An Updated Review, Maguida and Shuaib, 2022
- 11. SIGNIFICANCE OF GRADING THE PIAL COLLATERAL SYSTEM
- 13. Better collaterals Increased distribution of thrombolytics to clot surface Increased susceptibility to thrombolysis = recanalization
- 14. ▪ Collaterals are the key element setting the pace of the ischemic process ▪ Temporal growth of ischemic core is modulated by collateral blood flow ▪ Fast progressors – failing collaterals, rapid infarct growth; large ischemic core despite presenting early (6 hrs of stroke onset) ▪ Slow progressors - good collaterals, small ischemic core and large penumbra beyond 6 hrs and up to several days after stroke onset - raises possibility for EVT beyond conventional time windows (<6hrs) for acute reperfusion therapies
- 17. SIGNIFICANCE OF GRADING THE COLLATERALS Collateral Scoring may be used as a tool to: ▪ Distinguish fast and slow progressors – identify patients that may benefit from EVT beyond the conventional time window ▪ Predict infarct size – NECT + CTA vs NECT + CTA + CTP/MRP ▪ Help neurologic outcome prognosis ▪ Predict recanalization and reperfusion after IV rTPA and EVT – incorporation to guidelines for AIS treatment beyond the conventional time window?
- 20. IMAGING THE PIAL COLLATERAL SYSTEM Structural studies ▪ Digital subtraction angiography ▪ Methods based on CT ▪ Single phase CTA ▪ Multiphase CTA ▪ Methods based on MR ▪ Time-of-flight MRA ▪ Contrast-enhanced MRA ▪ FLAIR ▪ Transcranial Doppler Collateral Circulation in Ischemic Stroke: An Updated Review, Maguida and Shuaib, 2022 Functional studies ▪ CT Perfusion ▪ MR perfusion ▪ Positron emission tomography CT and single- photon emission CT
- 21. IMAGING THE PIAL COLLATERAL SYSTEM DSA sCTA mCTA Gold standard Most commonly used Increased utilization in specialized centers Advantages Dynamic evaluation Excellent spatial and temporal resolution Widely available Rapid image acquisition Technically easier to perform and interpret Dynamic study that allows assessment of delay in contrast arrival and washout Better interrater reliability in detecting LVO Better association with final infarct volume and clinical outcomes Disadvantag es Invasive Procedural risks Contrast administration Static evaluation Suboptimal in diminished ejection fraction or extracranial carotid stenosis sCTA in the early arterial phase – underestimates Slightly higher radiation dose and takes longer to perform than sCTA
- 22. • 2002 • Diagnostic angiogram of 162 patients enrolled in the PROACT II study • Collateral score correlation with clinical presentation and outcome Roberts et al., 2002 Conventional angiogram (n162) 1 None (n:50) 2 Partial - Collateral flow to parts of the vascular territory at risk (n:100) 3 Full - Collateral flow to the entire vascular territory at risk, with the clot visible from the distal side (n: 11)
- 23. ASITN/SIR 2003 - Conventional angiogram 0 No collaterals visible to the ischemic site 1 Slow collaterals to the periphery of the ischemic site with some persistence of some of the defect 2 Rapid collateral to the periphery of ischemic site with persistence of some of the defect and to only a portion of the ischemic territory 3 Collaterals with slow but complete angiographic blood flow of the ischemic bed by the late venous phase 4 Complete and rapid collateral blood flow to the vascular bed in the entire ischemic territory by retrograde perfusion ▪ 2003 ▪ American Society of Interventional and Therapeutic Neuroradiology/Society of Interventional Radiology ▪ Time of collateral filling is subjective >determined by counting the number of frames from opacification of petrous carotid artery and proximal basilar artery ▪ Slow flow – filling that is 2 sec slower than the normal contralateral side ▪ Rapid flow – filling within 2 sec
- 25. ▪ 2004 ▪ Roberts et al., 2002 – global scoring system; ASITN/SIR 2003 - subjective ▪ Study assessed collateral score per region similar to ASPECTS Kim et al., 2004- Conventional angiogram 0 No collaterals visible to the ischemic site (absence of any capillary blush 1 Collaterals to the periphery of the ischemic site 2 Complete irrigation of the ischemic bed via collateral flow 3 Normal antegrade flow
- 27. Christoforidis et al., 2005- Conventional angiogram 1 Collaterals reconstituted the distal portion of the occluded segment (in M1 segment occlusion the M1 segment distal to the occlusion reconstituted) 2 Collaterals reconstituted vessels in the proximal portion of the segment adjacent to the occluded vessel (in M1 occlusion, reconstitution to the proximal M2 segments) 3 Collaterals reconstituted vessels in the distal portion of the segment adjacent to the occluded vessel (in M1 occlusion, reconstitution to the distal portion of the M2 segments) 4 Collaterals reconstituted vessels two segments distal to the occluded vessel (in M1 occlusion, reconstitution up to the M3 segment) 5 Little or no significant reconstitution of the territory of the occluded vessel
- 28. Tan et al., 2007 - sCTA 0 Absent collaterals 1 Collaterals filling ≤ 50% of the occluded territory 2 Collaterals filling >50%, but <100% of the occluded territory 3 Collaterals filling 100% of the occluded territory ▪ 2007 ▪ 113 patients ▪ NCT, PCT and CTA was compared with follow-up CT or MRI for final infarct location and volume
- 29. • CTA MIPs are the most appropriate way to assess the collateral circulation • CTA MIPs is a predictor of the final infarct volume both in patients with persistent arterial occlusion and in patients with recanalization
- 30. ▪ 2009 ▪ Graded in comparison with normal hemisphere Maas et al., 2009 - sCTA 1 Absent 2 Probably present 3 Hairline 4 Definitely present 5 Robust
- 31. Miteff et al., 2009- sCTA 3 Vessels are reconstituted distal to the occlusion 2 Vessels can be seen at the Sylvian fissure 1 Contrast opacification is merely seen in the distal superficial branches ▪ 2009 ▪ Collateral status simply divided into good, moderate or poor
- 32. ▪ 2011 ▪ Previous studies either compare with contralateral side (Maas and Miteff), or assess retrograde filling without considering regional variability (Tan) ▪ Regional ASPECT-based CS (rASPECTS-CS) ▪ High interrater reliability ▪ Less subjective ▪ Stronger correlation with clinical outcomes Sylvian sulcus: 0 – not seen; 2 – less; 4 – same or more prominent
- 33. Souza et al., 2012 - sCTA 0 Absent collaterals in >50% of an M2 branch territory 1 Diminished collaterals in >50% of an M2 branch territory 2 Diminished collaterals in <50% of an M2 branch territory 3 Collaterals equal to the contralateral hemisphere 4 Increased collaterals ▪ 2012 ▪ Modification from Tan et al., 2007 ▪ Study only included terminal ICA and MCA stem occlusion
- 34. ▪ 2013 ▪ One of the first to assess leptomeningeal collaterals using mCTA ▪ Divided pial collaterals based on origin – either from ANTERIOR (ACA to MCA) or POSTERIOR (PCA to MCA) circulation. Then the following three properties were graded: ▪ Anatomic extent (graded 0 – 2) ▪ Pial prominence (0 – 2) ▪ Retrograde filling time
- 35. ▪ 2015 ▪ Data are from the IMS III study ▪ Of 656 patients enrolled in the study, 306 patients had CTA at baseline
- 36. Menon et al., 2015 - sCTA Description ACA-MCA region PCA-MCA region Compared with asymptomatic contralateral hemisphere, increased or normal prominence and extent of pial vessels beyond the occluded artery within the symptomatic hemisphere 5 5 Compared with asymptomatic contralateral hemisphere, slightly reduced prominence and extent of pial vessels beyond the occluded artery within the symptomatic hemisphere 4 4 Compared with asymptomatic contralateral hemisphere, there is moderately reduced prominence and extent of pial vessels beyond the occluded artery within the symptomatic hemisphere 3 3 Compared with asymptomatic contralateral hemisphere, there is decreased reduced prominence and extent and regions with no vessels in some part of the territory occluded 2 2 Compared with asymptomatic contralateral hemisphere, there is just a few vessels visible in the occluded vascular territory 1 1 Compared with asymptomatic contralateral hemisphere, there is no vessels visible in the occluded vascular territory 0 0
- 37. ▪ Menon et al., 2015 ▪ University of Calgary scoring system ▪ 147 patients with NECT, sCTA, mCTA and CTP ▪ Multiphase CTA ▪ Aortic arch to vertex (arterial phase) ▪ Skull base to vertex (peak venous phase and late venous phase)
- 40. mCTA CTP First phase (sCTA) - <7sec; DLP: 700- 800mGy*cm 8cm section of the brain scanned Second scan – 3.4 sec 24 passes over 66 seconds (total scan time) Third scan – 3.4 sec (total exposure time: 14sec) Total exposure time 19.2 sec 80 mL of contrast at 5ml/sec followed by 50 ml saline chase at 6ml/sec 45 mL of contrast at 4.5ml/sec followed by 40 ml of saline chase at 6ml/sec Total of 60 mGy radiation dose to the eye 200 mGy radiation dose to the eye • mCTA and perfusion CT imaging are CONGRUENT for treatment decision-making
- 41. ▪ Advantages of mCTA based on the study ▪ Minimal addition radiation (NECT + mCTA vs NECT + CTP) ▪ No additional contrast material (sCTA vs mCTA) ▪ Whole brain coverage (vs CTP) ▪ No post-processing (vs CTP) ▪ Slightly better in the prediction of clinical outcomes than NECT, sCTA and CTP
- 42. Collateral scoring systems DSA sCTA mCTA Roberts et al., 2002 Tan et al., 2007 Menon et al., 2013 ASITN/SIR 2003 Maas et al., 2009 Menon et al., rCS, University of Calgary scoring system, 2015 Kim et al., 2004 Miteff at al., 2009 Christoforidis et al., 2005 Menon et al., r-ASPECTS 2011 Souza et al., 2012
- 43. ▪ 2022, Trial investigators of ESCAPE, EXTEND-IA, SWIFT-PRIME, REVASCAT, MR-CLEAN, PISTE, and THRACE established the HERMES collaboration ▪ Highly Effective Reperfusion Using Multiple Endovascular Devices (HERMES) – endovascular thrombectomy is superior to standard medical care in AIS with proximal anterior circulation occlusion ▪ Pooled analysis of individual patient-level data - total of 1709 patients with baseline images (CTA or MRA) were available. ▪ Only patients with intracranial internal carotid artery and/or M1 MCA segment were included.
- 46. Association of each Collateral Score with mRS at 3 mo ▪ Primary outcome – functional independence at 3mo defined by a mRS of 0-2 ▪ Secondary outcome – ordinal mRS score (0-6) at 3 mo
- 47. ▪ RESULTS ▪ rCS – most strongly associated with mRS at 3mo (primary and secondary outcome) ▪ On sCTA, the rCS and the rASPECT-CS performed significantly better in predicting 3-month functional (primary) outcome than the Tan CS ▪ On mCTA or dCTA, no statistically significant differences were noted in predicting 3-month functional (primary) outcome between the 3 CSs ▪ In practice, the choice of CS type might be of greater relevance when using sCTA compared with mCTA
- 48. Status of the COLLATERAL SCORE at present Collateral Circulation in Ischemic Stroke: An Updated Review, Maguida and Shuaib, 2022 ▪ No concensus on the more accurate non-invasive imaging technique or scoring system for collateral circulation assessment ▪ Role of collateral circulation status in the selection of patient for endovascular treatment or the role of potential modifying therapies to enhance collateral flow in AIS is unknown
- 49. Sources ▪ http://aspectsinstroke.com/collateral-scoring ▪ https://www.youtube.com/watch?v=9T0bxrDjSUE ▪ Collateral Circulation in Ischemic Stroke: An Updated Review, Maguida and Shuaib, 2022 ▪ Collateral Circulation, Liebeskind, 2003 ▪ Collaterals at Angiography and Outcomes in the Interventional Management of Stroke (IMS) III Trial, Liebeskind et al., 2014 ▪ Collateral Circulation in Thrombectomy for Stroke After 6 to 24 Hours in the DAWN Trial, Liebeskind et al., 2022 ▪ Computed Tomographic Findings in Patients Undergoing Intra-arterial Thrombolysis for Acute Ischemic Stroke due to Middle Cerebral Artery Occlusion Results From the PROACT II Trial, Roberts et al., 2002 ▪ Trial Design and Reporting Standards for Intra-Arterial Cerebral Thrombolysis for Acute Ischemic Stroke, Higashida et al., 2003 ▪ Regional Angiographic Grading System for Collateral Flow Correlation With Cerebral Infarction in Patients With Middle Cerebral Artery Occlusion, Kim et al., 2004
- 50. Sources ▪ Angiographic Assessment of Pial Collaterals as a Prognostic Indicator Following Intra-arterial Thrombolysis for Acute Ischemic Stroke, Christoforidis et al., 2005 ▪ Systematic Comparison of Perfusion-CT and CT-Angiography in Acute Stroke Patients, Tan et al., 2007 ▪ The independent predictive utility of computed tomography angiographic collateral status in acute ischaemic stroke, Miteff et al., 2009 ▪ Collateral Vessels on CTA Predict Outcome in Acute Ischemic Stroke, Maas et al., 2009 ▪ Regional Leptomeningeal Score on CT Angiography Predicts Clinical and Imaging Outcomes in Patients with Acute Anterior Circulation Occlusions, Menon et al., 2011 ▪ Malignant CTA Collateral Profile Is Highly Specific for Large Admission DWI Infarct Core and Poor Outcome in Acute Stroke, Souza et al., 2012 ▪ Multiphase CT Angiography: A New Tool for the Imaging Triage of Patients with Acute Ischemic Stroke, Menon et al., 2015 ▪ Comparison of Three Scores of Collateral Status for Their Association With Clinical Outcome: The HERMES Collaboration, Gensicke et al., 2022
- 51. ▪THANK YOU
- 52. MODIFIED ASITN/SIR FOR mCTA 0 Non-existent or barely visible pial collateral on the ischemic site during any point of time 1 Partial collateralization of the ischemic site until the late venous phase 2 Partial collateralization of the ischemic site before the venous phase 3 Complete collateralization of the ischemic site by the late venous phase 4 Complete collateralization of the ischemic site before the venous phase
- 53. ▪ Interterritorial leptomeningeal collaterals between the posterior circulation and the MCA territory are functionally better than those between the ACA and MCA territories ▪ Variability in size and retrograde filling time of pial arteries probably related to blood flow regulation – may relate to functional status
- 54. ▪ Relative advantages of rCS ▪ Assessing difference between ACA-MCA and PCA-MCA collateral status ▪ Capturing hemodynamic aspects of collateral filling (prominence of vessels)
Editor's Notes
- The collateral circulation of the brain refers to alternative or indirect arterial pathways that can provide blood flow when an artery that normally supplies an area of brain tissue is occluded. Subdivided using a structural classification and a functional classification. Under the structural classification, the collaterals are categorized into… Under the functional classification, the collaterals are categorized into… The primary collateral circulation corresponds to permanently functioning pathways that can immediately reroute blood flow when a blood vessel occlusion occurs. This term refers mainly to the CoW. The secondary collateral circulation refers to pre-existing arterial conduits that can instantaneously be recruited to provide an alternative pathway for blood flow. This refers mainly to the leptomeningeal collaterals. recruitment of leptomeningeal collaterals is extremely fast. For example, in rat models of ICA occlusion, it takes only 12 seconds for leptomeningeal collaterals to reach their maximal vasodilatation. The tertiary collaterals is used to refer to the formation of new blood vessels or the maturation of pre-existent vessels in ischemic areas. Two main processes are involved. Angiogenesis is the physiologic process in which new blood vessels arise from pre-existent onesThe main stimuli for angiogenesis are ischemia and hypoxia. In contrast, arteriogenesis refers to the maturation of pre-existent arterioles into arteries. It is an important process of adaptation of blood vessels to new demands from tissue at risk after an arterial occlusion. The main stimulus for arteriogenesis is the shear stress on the endothelium, which is generated by pressure gradients
- Diagram of the COW which has 10 components, namely.. Middle image is a CTA showing a complete COW, seen only in 20-25% Left image is another CTA showing an absent left PCOM, which is the most common anatomic variant seen in ~30% hypoplastic/absent A1 segment of ACA ~15% (range 10-15%) absent or fenestrated ACOM ~12.5% (range 10-15%) origin of PCA from the ICA with absent/hypoplastic P1 segment (fetal PCA) ~20% (range 17-25%) infundibular dilatation of the PCOM origin ~10% (range 5-15%)
- Diagram of the intracranial collateral circulation connecting the anterior circulation (black) and posterior circulation (gray) Focus on the leptomeningeal anastomosis POSTERIOR COMMUNICATING ARTERY LEPTOMENINGEAL ANASTOMOSIS BETWEEN THE ACA AND MCA LEPTOMENINGEAL ANASTOMOSIS BETWEEN THE MCA AND PCA TECTAL PLEXUS BETWEEN THE PCA AND SUPERIOR CEREBELLAR ARTERIES ANASTOMOSES OF DISTAL CEREBELLAR ARTERIES aCOMM
- Diagram of the extra-cranial collaterals that originate from the branches of the ECA Shown are anastomoses from the facial (a), maxillary (b), and middle meningeal (c) arteries to the ophthalmic artery and dural arteriolar anastomoses from the middle meningeal artery (d) and occipital artery through the mastoid foramen (e) and parietal foramen (f). several possible extra-intracranial anastomoses, which can provide blood flow in the case of a blood vessel occlusion. These extracranial sources originate from branches of the external carotid artery or from ascending and deep cervi occlusion of the internal carotid artery (ICA) before the emergence of the ophthalmic artery. If there is a complete and functional CoW, the terminal ICA may receive retrograde flow through the circle and immediately restore the anterograde flow through the ophthalmic artery. e external carotid artery, which can anastomose with branches of the ophthalmic artery and provide retrograde flow, which will ultimately reach the terminal ICA
- Several neurohumoral mechanisms involved in the process of leptomeningeal collateral recruitment. The main driver of the functionality of these pathways is pressure gradients. Where increased pressure and shear stress activates nitric oxide (NO)- dependent mechanisms that lead to their dilation and improved blood flow. There is also a neural regulation of the cerebrovascular tone through intrinsic and extrinsic innervations. The intrinsic nerves originate mainly in the brainstem and are distributed predominantly in the parenchymal vessels. Whereas the extrinsic nerves supply the vessels on the surface of the brain. The extrinsic parasympathetic nerves, which arise from the superior salivatory nucleus and pass along cranial nerve VII to the sphenopalatine and otic ganglia, are involved in vasodilation and their stimulation has been studied as a therapeutic target
- 1. Aging causes a decrease in number and diameter and an increase in tortuosity of leptomeningeal collaterals, which lead to increased vascular resistance. These changes are associated with impaired endothelial NO synthase (eNOS) signaling and increased oxidative stress. 2. In animal models of chronic hypertension, induction of collateral flow during acute ischemic stroke is impaired. Similarly, murine models of common carotid artery occlusion have shown impaired collateral flow in diabetic mice. 3. On patients with coronary artery disease, previous studies showed that smoking may be associated with better collaterals. The proposed mechanism is ischemic preconditioning; However, a 2021 meta-analysis of 18 studies and more than 4,000 patients did not demonstrate a positive association. In the case of ischemic stroke patients, a retrospective analysis of embolic LVO in more than 600 patients found a positive correlation between smoking (current or previous) and good collaterals. 4. Regular exercise has been shown to improve collateral circulation in patients with coronary artery disease and in animal models of stroke. Physical exercise increases blood flow and the shear stress stimulates different mechanisms in the endothelium, which lead to maintenance, defense, and repair of the vasculature. It also enhances the capacity of the vessels to vasodilate. Another more indirect effect of physical exercise is the reduction of vascular risk factors 5. Statin use and better collaterals in ischemic stroke patients. Proposed mechanisms for this effect are enhancement of arteriogenesis and eNOS-mediated vasodilation. 6. observational study of 385 patients who underwent mechanical thrombectomy for LVO, patients with an ipsilateral stenosis of the extracranial ICA of more than 75% had good collaterals
- 2014 331 SUBJECTS using angiography Study aimed to establish an association between the degree of collaterals before endovascular therapy (intra-arterial t-PA and ) and the likelihood of recanalization, reperfusion, and good clinical outcome at 90 defined as mRS of 2 or less. Their results showed that for these primary outcomes, there is positive correlation between good collaterals of grades 3 and 4, with increased likelihood of recanalization and reperfusion seen in more than 80% of cases. Positive correlation is also noted between good collaterals and better clinical outcome at 90 days.
- Other than its correlation to EVT outcome…. As discussed before, there is a concept of infarct core and ischemic penumbra, where the penumbra grows gradually if perfusion is not re-established.
- A large study of 161 patients shows the correlation of collaterals with infarct size at baseline and 24 hours of onset. Collateral scores were stratified into good, fair and poor. The study showed that good collaterals were associated with smaller core infarcts at presentation and 24 hours post-ictus. Comparing the change of infarct size with baseline and 24 hrs, there is notable slower infarct evolution in those with good collaterals
- Same study also shows good correlations between clinical outcome and good collaterals
- Class of recommendation Iib – weak Level of evidence – limited data No recommendation for any imaging study to be used for collateral circulation assessement No recommendation on which CS system to be used
- Since no recommendation was given, we will briefly discuss all CS systems, focusing on their merits and demerits
- The methods to assess the collateral circulation can be broadly divided into structural and functional types Focus on DSA and CTA, both sCTA and mCTA e not as readily available and they are usually slower to perform. Time-of-flight MR angiography (TOF-MRA) is a T1-based sequence that does not require gadolinium injection and is used to assess the proximal intracranial vasculature. ontrast-enhanced MR angiography (CE-MRA) is also a T1- based sequence and it requires the injection of a bolus of gadolinium. Its advantages are a high signal-to-noise ratio and a relative insensitivity to slow flow.42 hyperintensities represent a more indirect marker of leptomeningeal collaterals, but they are non-specific and their usefulness is limited. T This non-invasive method provides real-time information about intracranial blood flow. It only allows the assessment of proximal blood vessels at the level of the CoW there is no consensus about the more accurate noninvasive technique or scale for CC assessment. Furthermore, the role of the CC status in the selection of patient for endovascular treatment or the role of the potential modifying therapies to enhance collateral flow in acute ischemic stroke is unknown
- Digital subtraction angiography (DSA) is considered the gold standard for structural assessment of the collateral circulation. It allows dynamic evaluation of blood flow with excellent spatial and temporal resolution. Its main disadvantages are its invasive nature, its associated procedural risks, the need for contrast agent administration, and its limited availability. sCTA is the most frequently used study in the assessment of the collateral circulation because of their widespread availability and rapid image acquisition. Single-phase CT angiography (sCTA), which is performed at a single time point in relation to the contrast bolus injection, has the limitation of being a static evaluation. It will provide an inexact measurement of the state of collaterals if the acquisition is not performed at the optimal time point. For example, in patients with a diminished cardiac ejection fraction or an extracranial carotid stenosis, the collaterals may be underestimated because the image acquisition will tend to be performed before the contrast agent can reach the leptomeningeal vessels. studies have suggested that collateral assessment in sCTA in the early arterial and late venous phases underestimate and overestimate the collateral status, respectively. Multiphase CTA (mCTA) is performed in different time points and provides a better characterization of the collateral circulation than sCTA because it allows the assessment of the delay in contrast arrival and washout. This technique also has a better interrater reliability for the detection of LVO, it allows for a more precise assessment of the thrombus length, and it has a better association with final infarct volume and clinical outcomes
- The first few CS systems were derived from conventional angiogram Simplistic – more pt will be categorized under partial (2) Collateral circulation was assessed from the baseline diagnostic angiogram in blinded fashion by the core laboratory neuroradiologist. The presence of collateral vessels was categorized as (1) none, (2) partial (collateral flow to parts of the vascular territory at risk), or (3) full (collateral flow to the entire vascular territory at risk, with the clot visible from the distal side) present report describes the CT findings in PROACT II and their correlation with clinical presentation, angiographic findings, and outcome 2002 Of 162 patients (108 r-ProUK patients and 54 control patients) who actually received the treatment to which they were randomized, 50 patients had no angiographic collaterals, 100 had partial collaterals, and 11 had full collaterals (1 patient could not be assessed for collaterals).
- Note that descriptors such as slow and rapid collateral is now incorporated, which makes this scoring system subjective However, time of collateral filling might be determined by counting the number of frames from contrast-agent filling of the petrous carotid artery (from the anterior circulation) and the proximal basilar artery (in the posterior circulation) to complete collateral filling (provided that the number of frames per second is known, so that the time for collateral filling can be calculated.) This is then compared with time to normal filling of the nonoccluded hemisphere in the parenchymal phase of the angiogram. Slow collateral flow is defined, arbitrarily, as filling that is 2 seconds slower than the contralateral side. Rapid collateral flow is defined as filling that is within 2 seconds of the contralateral side.
- 2013
- Notably the first to perform a regional scoring system Image on the left shows ASPECTS regions, with decreased collaterals in the M1, M2 and M6 regions, correlating well with infarctions in these regions as shown in the CT scan. Notice that there is variability in collaterals per region, which cannot be properly addressed using a global scoring system
- Anteroposterior (A and C) and lateral (B and C) images from a left internal carotid artery angiogram obtained during the early (A and B) and delayed angiographic phases (C and D) in a patient with acute ischemic stroke due to occlusion at the M1 segment (arrow). Note the retrograde opacification of the MCA branches via pial collateral vessels extending from the ACA (arrowheads). Because there is reverse opacification of the MCA extending to the distal M1 segment, a pial collateral formation score of 1 was assigne
- Global scoring that use >50 but <100% descriptor for grade 2 collaterals. This collateral filling of more than 50% may still denote a large infarct core in cases of ICA or proximal M1 occlusion, which may reach 150ml of infarcted brain tissue which is the threshold for not performing EVT due to high chances of hemorrhagic conversion. So a grade of 2 which is supposed to be a good collateral score, is to be taken with caution using this scoring system.
- As one of the first studies to use CTA in collateral assessment
- Global and simplistic with vague descriptors
- Global and simplistic
- Arteries in the Sylvian sulcus are given a higher score, ie, 0, 2, or 4 (0, not seen; 2; less; 4, same or prominent compared with the opposite Sylvian sulcus) because opacification of these vessels is a strong indicator of good retrograde flow via these collateral networks
- Menon et al again!
- ACA-MCA and PCA-MCA pial arterial backfilling are each scored from 0 to 5 (0-absent, 1-minimal, 2-significantly decreased prominence and extent of pial arteries with regions of no vessels, 3-moderately decreased prominence and extent, 4-mildly decreased prominence and extent, 5-normal or increased prominence and extent) when compared with the opposite normal hemisphere; the total score combines scores from these 2 regions to give an ordinal score ranging from 0 to 10.14
- Same scoring system as the previous study Compared sCTA and mCTA Aortic arch vertex CT athe peak arterial phase - <7sec skull base to the vertex in the equilibrium/peak venous and late venous phases a 0.625-mm section thickness. 8 secs apart 80 ml of contrast 50 ml saline chase @ 6ml/sec All patients underwent standard unenhanced CT with 5-mm section thickness followed by head and neck CT angiography, including multiphase CT angiography and perfusion CT.
- Tables show the sCTA and mCTA scoring systems in this study. The difference is that sCTA is only able to compare for the prominence and extent of collaterals, while the mCTA scoring also detects for delay in contrast filling.
- Graph shows the incongruence between scores between sCTA and mCTA. We can see that more patients are labelled as having good collaterals with scores of 4 and 5 using mCTA, which means that there is mislabeling of many patients as having a poor score if we use sCTA.
- Study also compared mCTA with CTP B, A proximal right M1 MCA occlusion is seen (i). Multiphase CT angiography (three phases) maximum intensity projection images are shown (ii, iii, iv). Pial arterial filling is modest, with delay of two phases and some regions indicating minimal filling when compared with the contralateral side, thus indicating that no treatment be performed. C, Perfusion CT Tmax and cerebral blood flow (CBF) maps (i, ii ). Tissue with Tmax greater than 6 seconds (pink) is superimposed onto the CT perfusion average maps for both gray and white matter (iii and iv, respectively). CBF less than 10 mL·min21 ·100 g21 and less than 7 mL·min21 ·100 g21 for gray and white, respectively, is flooded in blue on the CT perfusion average maps (iii, iv). CBF-defined infarct core is 100 mL. A mismatch ratio (total Tmax hypoperfusion volume/ total CBF infarct volume) of 1.7 and a large infarct core indicates that no treatment should be performed. Multiphase CT angiography and perfusion CT imaging are congruent for treatment decision
- association of each CS with mRS at 3 months Primary outcome – functional independence at 3mo defined by a mRS of 0-2 Secondary outcome – ordinal mRS score at 3 mo
- We hypothesize that differences in sympathetic innervation and autoregulatory capacity between the two circulations could be a potential explanation for the observed differences Many previous CTA-based leptomeningeal collateral scores have used relative size of back-filling pial arteries as a marker of leptomeningeal collateral status.1,3,4,13,15,27,28 We note significant variability in size of these pial arteries when compared with anatomically similar vessels in the contralateral hemisphere. This temporal variability could be an indicator of the functional status of leptomeningeal collaterals and/or autoregulatory capacity of pial arteries. Further studies are needed to understand the relationship between leptomeningeal collateral status and the rate of backfilling in pial arteries
- Relative advantages of the rCS include (1) assessing differences between anterior cerebral artery-MCA- and posterior cerebral arteryMCA-collateral status and (2) capturing hemodynamic aspects of collateral filling (prominence of vessels).