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Proposed methodology and classification of Infarct in New Territory (INT) after endovascular stroke treatment
  1. Mayank Goyal1,
  2. Bijoy K Menon1,
  3. Andrew Demchuk1,
  4. Jeffrey L Saver2,
  5. Muneer Eesa1,
  6. Charles Majoie3,
  7. Mahesh Jayaraman4,
  8. Michael D Hill1
  1. 1Department of Radiology and Clinical Neurosciences, University of Calgary, Calgary, Alberta, Canada
  2. 2Stroke and Vascular Neurology Program, Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, California, USA
  3. 3Department of Radiology, Academic Medical Center, Amsterdam, The Netherlands
  4. 4Departments of Diagnostic Imaging, Neurology and Neurosurgery, Warren Alpert School of Medicine at Brown University, Providence, Rhode Island, USA
  1. Correspondence to Dr Mayank Goyal, Department of Radiology, Seaman Family MR Research Center, Foothills Hospital, 1403, 29th St NW, Calgary, Alberta, Canada T2N2T9; mgoyal{at}


While the overall complication rates for endovascular treatment for acute stroke has been extremely low in recent trials, it is important to separate out and accurately document complications. One of these complications that is usually related to the endovascular intervention is Infarct in New Territory (INT). We propose a standardized methodology for documenting INT after the procedure. This new classification takes into account variations in vascular anatomy and location of the occlusion. In addition, given that after the recent trials, vascular imaging (eg, CT angiography (CTA)) is now the standard of care in the work up of acute ischemic stroke, this classification utilizes the information on the pre-procedure non-invasive vascular imaging, the angiography images from end of procedure and the location of lesions on the follow-up scan.

  • Stroke

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Based on recent evidence, endovascular treatment using stent retrievers is now the standard of care for acute anterior circulation large vessel ischemic stroke.1–5 In all recent trials there was documentation of proximal vessel occlusion using CT angiography (CTA) or MR angiography (MRA). Proximal vessel occlusion included patients with M1 middle cerebral artery (MCA) and/or intracranial internal carotid artery (ICA) occlusions. In addition, some trials allowed the inclusion of tandem occlusions (occlusion of cervical ICA with proximal intracranial occlusion). As part of the reporting of trial data and to better understand complications associated with endovascular procedures, it is important to have a standardized methodology classifying these complications.6 ,7 One such complication is an Infarct in a New Territory (INT). An INT means that the intervention resulted in a new infarct. This new infarct should be in a territory that was unaffected by the original occlusion—for example, a patient with a mid M1 occlusion who has an ipsilateral anterior cerebral artery (ACA) infarct after the procedure. An INT is invariably identified on a follow-up non-contrast CT (NCCT) scan or MRI (diffusion imaging) performed within the first 24 h. However, there is a significant difference in detection of small acute infarcts, especially in the older stroke population, between NCCT scan and diffusion MRI. This needs to be kept in mind while interpreting and reporting INT. Here we propose a methodology for defining and classifying INT.

Proposed methodology

  1. Review the pre-procedure CTA (or MRA)

    1. Understand the vascular territory at risk based on the site of occlusion, anatomy of the circle of Willis and presence of other occlusions. For M1 occlusions, this is quite straightforward: it would be the entire MCA territory. However, for L (intracranial ICA+M1) or T (intracranial ICA+M1+A1) occlusions, there are some common possibilities:

      1. Absent/hypoplastic contralateral A1 segment: both A2 territories would be considered to be involved.

      2. Fetal ipsilateral posterior cerebral artery (PCA) with involvement of its origin: PCA territory would be considered to be involved.

      3. Contralateral chronic ICA occlusion with sizeable anterior communicating artery (ACom): both contralateral ACA and MCA territories would be considered to be involved.

        Look for other rarer possibilities as well.

    2. Look for other acute occlusions—for example, a distal ACA occlusion or a distal PCA occlusion if the PCA is fetal. If these are identified, mark the territory distal to that occlusion as involved.

    3. If available, review transit time (time to maximum (Tmax), mean transit time (MTT) map) on CT perfusion (CTP) or MR perfusion images to assist with the territory involved. However, in the event of a difference in interpretation between CTA and CTP, use CTA information (eg, carotid T occlusion but no MTT defect in the ipsilateral ACA territory on CTP (because of the presence of a patent ACom)).

  2. Assess follow-up imaging (usually at 24 h). Document whether it is a non-contrast CT scan or diffusion MRI. Also document whether or not the patient received intravenous tissue plasminogen activator. Mark all infarcts not in the affected territory. Compare follow-up imaging with baseline imaging to confirm if these infarcts are new or not. Only include infarcts considered to be new as INT.

  3. Proposed classification of INT: All INTs have to be outside the affected territory as defined above. INT is classified based on two parameters: size (types I, II, and III; table 1) and catheter manipulation across territory ostium (types A and B; table 2). Thus an INT may be classified as IA, IIB, etc.

Limitations of this classification

  1. There will be significant differences in reported rates depending on whether CT or MR is used at follow-up.

  2. Type B infarcts could be procedure-related (dislodging plaque from aortic arch).

  3. The number of infarcts is not well captured and could range from one to a massive shower.

Table 1

Classification of INT based on size

Table 2

Classification of INT based on catheter manipulation across territory ostium

Advantages of this classification

We feel that this classification is simple, easy to follow, and would allow for consistent reporting of adverse events. In addition, it would allow (albeit not perfectly) separation of what are likely to be clinically significant INTs from those that are likely to be relatively inconsequential.

Stroke is a dynamic disease where there is a risk of additional ischemia in the early period, especially in patients with a cardiac source. In addition, patients receiving intravenous tissue plasminogen activator may have a higher likelihood of further emboli in patients with atrial fibrillation. This classification has the potential to identify these.

We propose to use this classification in ESCAPE, MR CLEAN and SWIFT PRIME to report INT.



  • Competing interests None declared.

  • Provenance and peer review Not commissioned; internally peer reviewed.