ISCHEMIC STROKE / CLASSIFICATION

SSS-TOAST CLASSIFICATION OF ISCHEMIC STROKE

Created 26/09/2022, last revision 22/02/2023

The SSS-TOAST classification is an evidence-based classification algorithm that reflects advances in stroke imaging and epidemiology [Ay, 2005]
based on certain clinical and imaging criteria, each TOAST subtype is divided into 3 subcategories “certain”, “probable”, or “possible”
the new algorithm refines the determination of the most likely etiology in the presence of multiple competing mechanisms
an automated web-based version of the SSS-TOAST, the Causative Classification System (CCS), was developed to facilitate its utility in multicenter settings (Ay, 2007)
- CCS allows rapid analysis of patient data with excellent intra- and inter-examiner reliability when accurate subtyping is critical (trials)
- the purple text was not present in the original SSS-TOAST publication in 2005

Evident

occlusion or stenosis ≥50% (according to NASCET) or <50 % diameter reduction with plaque ulceration or thrombosis caused by atherosclerosis in the clinically relevant extra-/intracranial arteries

AND

the absence of acute infarction in vascular territories other than the stenotic or occluded artery

Probable

occlusion or stenosis ≥50% (according to NASCET) caused by atherosclerosis in the clinically relevant extra-/intracranial arteries
history of ≥ 1 TIA/stroke from the territory of the index artery affected by atherosclerosis within the last month

evidence of near-occlusive stenosis or non-chronic complete occlusion judged to be due to atherosclerosis in the clinically relevant extra-/intracranial arteries (except for the vertebral arteries)

the presence of ipsilateral border-zone infarctions (BZI) or multiple, temporally separate infarctions only within the territory of the affected artery

Possible

atherosclerotic plaque causing stenosis <50% in the absence of any detectable plaque ulceration or thrombosis in a clinically relevant extra-/intracranial artery
history of ≥ 2 TIAs/strokes from the territory of index artery affected by atherosclerosis; at least 1 event within the last month

evidence of extensive artery atherosclerosis in the absence of complete diagnostic investigation for other mechanisms

Evident

The presence of a high-risk cardiac source of cerebral embolism

Probable

presence of multiple acute infarctions that have occurred closely related in time within both right and left anterior or both anterior and posterior circulations in the absence of occlusion or near-occlusive stenosis of all relevant vessels; other diseases that can cause multifocal ischemic brain injury such as vasculitides, vasculopathies, and hemostatic or hemodynamic disturbances must not be present

Possible

evidence of obvious cardio-aortic embolism in the absence of complete diagnostic investigation for other mechanisms

Evident

imaging evidence of a single, clinically relevant acute infarction < 2 cm in greatest diameter within the territory of penetrating arteries
absence of significant pathology in the parent artery at the site of the origin of the penetrating artery (most commonly junction focal atheroma, less frequently parent vessel dissection, vasculitis, vasospasm, etc.); parent artery pathology is also referred to as branch artery disease (BAD) / branch occlusive disease (BOD) and is classified as TOAST 1
- diagnosis based on high-resolution MRI [Petrone, 2016]
- more likely in younger patients
- infarct is usually larger than a typical arteriolopathic stroke and is typically located in the pons [Zhou, 2018]

Probable

Possible

classical lacunar syndrome in the absence of imaging that is sensitive enough to detect small infarctions

evidence for small artery occlusion in the absence of complete diagnostic investigation for other mechanisms

Evident

presence of a specific disease process that involves clinically appropriate brain arteries

Probable

a specific disease process that has occurred in clear and close temporal relation to the onset of brain infarction, such as arterial dissection, cardiac or arterial surgery, and cardiovascular interventions

Possible

evidence for an evident other cause of stroke in the absence of complete diagnostic evaluation for mechanisms listed above

cryptogenic embolism → ESUS criteria
- vessel imaging findings suggesting embolic etiology:
  - evidence of abrupt cutoff consistent with a blood clot within otherwise angiographically normal-looking intracranial arteries
  - evidence of complete recanalization of the previously occluded artery
  - presence of multiple acute infarctions that have occurred closely related in time without detectable abnormality in the relevant vessels
other cryptogenic strokes – those not fulfilling the criteria for cryptogenic embolism
incomplete evaluation – the absence of diagnostic tests that would have been essential to uncover the underlying cause
unclassified – the presence of >1 evident mechanism; either there is probable evidence for each, or no single cause can be reliably established