ISCHEMIC STROKE / CLASSIFICATION

SSS-TOAST CLASSIFICATION OF ISCHEMIC STROKE

Created 26/09/2022, last revision 04/09/2023

the SSS-TOAST classification is an evidence-based classification algorithm that reflects advancements in stroke imaging and epidemiology [Ay, 2005]
based on specific clinical and imaging criteria, each TOAST subtype is further categorized into on of three subcategories: “certain”, “probable”, or “possible”
this new algorithm refines the determination of the most likely etiology, particularly when multiple competing mechanisms are present
an automated web-based version of the SSS-TOAST, known as the Causative Classification System (CCS), was developed to facilitate its utilization in multicenter settings (Ay, 2007)
- CCS enables swift analysis of patient data with excellent intra- and inter-examiner reliability
- particularly valuable in situations where precise classification is of critical importance (such as in clinical trials)
- the text highlighted in purple was not included 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 due to atherosclerosis in clinically relevant extra-/intracranial arteries

AND

absence of acute infarcts in vascular territories other than those corresponding to the stenotic or occluded artery

Probable

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

evidence of near-occlusive stenosis or non-chronic total occlusion, determined to result from atherosclerosis, in relevant extra-/intracranial arteries (excluding the vertebral arteries)

the presence of ipsilateral border-zone infarctions (BZI) or multiple, temporally separated infarcts occuring within within the region supplied by the affected artery

Possible

atherosclerotic plaque causing stenosis <50% in without any detectable plaque ulceration or thrombosis in a relevant extra-/intracranial artery
history of ≥ 2 TIAs/strokes in the territory of index artery affected by atherosclerosis; at least one event occurring within the past month

evidence of extensive artery atherosclerosis in the absence of a complete diagnostic workup for alternative causative mechanisms

Evident

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

Probable

presence of multiple acute infarcts occurring in close temporal relation within the 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 could potentially lead to multifocal ischemic lesions, such as vasculitides, vasculopathies, and hemostatic or hemodynamic disturbances, are not present

Possible

evidence of obvious cardio-aortic embolism in the absence of a complete diagnostic workup for other potential causes

Evident

imaging evidence of a single, clinically relevant acute infarct < 2 cm in greatest diameter within the territory of the penetrating arteries
absence of significant pathology in the parent artery at the site of the origin of the penetrating artery (most commonly ostial atheroma, less commonly 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 is 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 sensitive enough to detect small infarctions

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

Evident

presence of a specific disease process involving clinically relevant cerebral arteries (→ TOAST classification)

Probable

a specific disease process that has occurred in close temporal relation to the stroke onset (e.g., arterial dissection, cardiac or vascular surgery, and cardiovascular procedures

Possible

evidence pointing to a different identifiable cause of stroke in the absence of complete diagnostic evaluation for mechanisms mentioned above

cryptogenic embolism → ESUS criteria
- vascular imaging indicative of an embolic origin:
  - abrupt absence of contrast consistent with a blood clot within otherwise angiographically normal-appearing intracranial arteries
  - complete recanalization of the previously occluded artery
  - multiple acute infarcts occurring in a close temporal relationship, without apparent abnormalities in the relevant arteries
other cryptogenic strokes – those not meeting the criteria for cryptogenic embolism
incomplete evaluation – the absence of essential diagnostic tests required to determine 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