ISCHEMIC STROKE / ACUTE THERAPY

Angiographic grading of cerebral revascularization

Created 03/03/2022, last revision 04/05/2023

revascularization is a broader term and includes:
- recanalization (clot removal from the target vessel)
- anterograde reperfusion of the peripheral circulation
recanalization does not automatically mean reperfusion (if peripheral embolization persists, recanalization will have little 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 of the direct effect of the intervention
at the end of each endovascular intervention, both recanalization (AOL scale) and reperfusion (mTICI scale) should be assessed and reported
- criteria of successful intervention: mTICI 2b-3 and AOL 2-3
other scales have been presented 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

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
- TICI 2 was divided – reperfusion in < 1/2 of the target vascular territory (mTICI 2a) and > 1/2 of it (mTICI 2b) [Zaidat, 2013]
- it has good interrater reliability and strongly predicts clinical outcome
- the mTICI has better reproducibility and predictive value than the original TICI [Yoo, 2013]

Modified Treatment In Cerebral Infarction (mTICI)
Grade	Definitions
0	no perfusion
1	antegrade reperfusion past the initial occlusion, but limited distal branch filling with little or slow distal reperfusion
2a	antegrade reperfusion of less than half of the occluded target artery previously ischemic territory (e.g., in 1 major division of the MCA and its territory)
2b	antegrade reperfusion of more than half of the previously occluded target artery ischemic territory (e.g., in 2 major divisions of the MCA and their territories)
3	complete antegrade reperfusion of the previously occluded target artery 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 effect of therapeutic intervention on the Target Arterial Lesion (TAL)
they 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 the grading scale intended 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 site of occlusion
- AOL describes arterial patency at the site of occlusion based on the degree of luminal opening (none, partial, or complete) with further qualification based simply on the presence (grades 2 or 3) or absence (grades 0 or 1) of downstream flow
there is good agreement between AOL and mTICI and an excellent ability to predict the outcome
target arterial lesion (TAL) assessment may be problematic (see below)
- for example, in a tandem lesion of ICA+M1 – recanalization of the siphon with persistent M1 occlusion may result in conflicting assessment – AOL 3 / mTICI 0
- it would be better to evaluate the whole thrombus (⇒ problem with determining its distal end)
differentiating partial recanalization with residual intraluminal thrombus from underlying intracranial atherosclerotic stenosis is another challenge

The Arterial Occlusive Lesion (AOL) scale
0	Complete occlusion of the target artery
1	Incomplete occlusion or partial local recanalization at the target artery with no distal flow
2	Incomplete occlusion or partial local recanalization at the target artery with any distal flow
3	Complete recanalization and restoration of the target artery with any distal flow

TAL = most proximal part of the intracranial occlusion
- except for isolated extracranial artery occlusion (e.g., ICA occlusion with distal hypoperfusion)
for combined occlusion of 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