ISCHEMIC STROKE / ACUTE THERAPY

Angiographic grading of cerebral revascularization

Created 03/03/2022, last revision 06/11/2023

revascularization is a broader term and includes:
- recanalization (the removal of a clot from the target vessel)
- anterograde reperfusion (restoration of blood flow to the peripheral circulation)
recanalization does not automatically mean reperfusion (if peripheral embolization persists, recanalization will have minimal or no clinical effect)
reperfusion is a better marker of revascularization because it considers the state of the tissue and is, therefore, more closely related to the clinical outcome
on the other hand, the quantification of recanalization is an essential parameter for evaluating the direct effects of an intervention
upon the completion of each endovascular intervention, both recanalization (via AOL scale) and reperfusion (via mTICI scale) should be documented
- criteria of successful intervention: mTICI 2b-3 and AOL 2-3
other scales have been introduced but are rarely used
- The Qureshi scale
- The Recanalization in Brain Ischemia (RBI) scale
- the Mori scale

Revascularization
Recanalization	restoration of flow in the occluded arterial segment (primary arterial occlusive lesion)	AOL
Reperfusion	restoration of flow in the territory of an occluded vessel (distal vascular bed)	mTICI

Reperfusion assessment

the modified Treatment In Cerebral Infarction (mTICI) score specifies the extent of tissue perfusion; it was derived from the original TICI classification (Thrombolysis In Cerebral Infarction)
- the original name was changed to reflect the current endovascular practice better
- TICI 2 category was subdivided to distinguish between reperfusion in < 1/2 of the target vascular territory (mTICI 2a) and > 1/2 of it (mTICI 2b) [Zaidat, 2013]
- score has good interrater reliability and is a strong predictor of clinical outcomes
- mTICI has superior reproducibility and predictive value compared to the original TICI [Yoo, 2013]

Modified Treatment In Cerebral Infarction (mTICI)
Grade	Definitions
0	no perfusion
1	antegrade reperfusion past the initial occlusion, with limited distal branch filling and minimal or slow distal reperfusion
2a	antegrade reperfusion of less than half of the previously occluded target artery´s ischemic territory (e.g., in 1 major division of the MCA and its corresponding territory)
2b	antegrade reperfusion of more than half of the previously occluded target artery´s ischemic territory (e.g., in 2 major divisions of the MCA and their corresponding territories)
3	complete antegrade reperfusion of the previously occluded target artery´s ischemic territory, with no visualized occlusion in all distal branches
Some authors have proposed a further modification: grade 2c – near-complete perfusion except for slow flow or distal emboli in a few distal cortical vessels

recanalization scales evaluate the direct impact of therapeutic intervention on the Target Arterial Lesion (TAL)
these scales do not directly assess downstream perfusion but may still provide additional prognostic information (residual stenosis increases the risk of reocclusion or distal embolization)

the Arterial Occlusive Lesion (AOL) scale is designed to measure the degree of recanalization at the TAL
- it is preferred for its ease of use and accurate assessment of device effectiveness at the occlusion site
- AOL categorizes arterial patency based on the degree of luminal opening (none, partial, or complete)
- further qualification is made based on the presence (grades 2 or 3) or absence (grades 0 or 1) of downstream flow
there is a good correlation between AOL and mTICI, as well as an excellent ability to predict the outcome
however, assessing target arterial lesion (TAL) may be problematic (see below)
- for example, in a tandem lesion involving the ICA+M1, recanalization of the siphon with persistent M1 occlusion may yield conflicting assessments – AOL 3 / mTICI 0
- it would be better to evaluate the whole thrombus, although determining its distal end poses a problem.
differentiating between partial recanalization with residual intraluminal thrombus and underlying intracranial atherosclerotic stenosis presents another challenge

TAL = most proximal part of the intracranial occlusion
- except for isolated extracranial artery occlusion (e.g., ICA occlusion with distal hypoperfusion)
in cases of combined occlusion involving the cervical segment of ICA+ M1, the target artery is the MCA

ICA	MCA
T-occlusion (terminal ICA+M1+A1) L-occlusion (terminální ICA+M1) isolated terminal ICA occlusion	M1 proximal lesion with occlusion of the lenticulostriate arteries distal lesion without occlusion of the lenticulostriate arteries M2