Stroke Triage: The Radiologist's Perspective
Patricia Desmond1

1University of Melbourne, Royal Melbourne Hospital


Acute ischemic stroke is a heterogeneous disease, with major stroke caused by proximal artery occlusions representing the stroke subtype with the most devastating outcomes. With the recent success of the endovascular clot retrieval trials for major stroke, the primary role of the radiologist to identify the patients suitable for treatment rapidly and accurately. The most common way to get this information is with non contrast CT, and CT angiography. In present clinical practice, time is dominant (<6hr) over physiology for decisions related to implementing therapy. There is evidence from the recent trials that it may be possible to extend the selection criteria to include a larger group of patients that will still benefit from IA therapy. However, this will require clinical trials to demonstrate that advanced imaging techniques to select these patients for treatment, leads to improved outcomes.


Intravenous thrombolysis is the mainstay of acute ischemic stroke management for any patient presenting with disabling deficits within 4.5 hrs of treatment onset. This is based on the results of the National Institute of Neurological Disorders (NINDS) (1) study that showed a 16% increase in favourable outcome in patients receiving IV tpa within 3 hr and a subsequent trial Haacke et al (2) that showed increase favourable outcome by 10% in the 3 - 4.5 hr window . A recent meta- analysis (3 ) showed a benefit for IV tpa, irrespective of age and stroke severity with earlier treatment (<3hrs) being associated with bigger proportional gains. However, after IV tpa alone, only 10 – 15% of internal carotid artery occlusions and 25 to 50% of middle cerebral artery occlusions recanalise. Proximal artery occlusion and thrombi greater than 8mm are relatively resistant to IV tpa alone (4,5). Proximal artery occlusion is the cause of occlusion in up to a third of cases. As such methods aiming at improving recanalization and reperfusion have been the basis of large clinical trials.

The results of the recent trials of endovascular clot retrieval in acute ischemia (6-10) have proven the effectiveness of endovascular therapy in improved outcome in patients with intracranial large vessel occlusion when compared to those that receive IV treatment only. Systematic review (11) of the recent endovascular trials show between a 10% - 33% benefit in favourable outcome for patients treated with combined IA/IV compared to IV alone. Comparison of the trials shows better outcomes are associated with use of stent retriever catheter than either intrarterial thrombolysis or earlier coil retrievers. Stent retrievers were associated with good reperfusion in between 80 – 94% of patients compared with much lower historical reperfusion rates. Comparison of trial data also suggests that both deceased time to reperfusion and better achieved reperfusion (TICI 2b (50%) or 3(100%) reperfusion) both result in more favourable outcome (11). Although the trials were all slightly different in inclusion criteria the results all endorse the recently adopted American Stroke Association guidelines for endovascular clot retrieval in the following patients: Patients >18years who were previously independent, were treated with IV tpa within 4.5hts of stroke onset, had an NIHSS score of >6, had internal carotid or middle cerebral artery M1 segment occlusion and had an ASPECTS > 6 and were treated <6hrs.

The role of the radiologist in the treatment and assessment of acute stroke is:

1. Diagnosis of acute ischemia

Non contrast CT (NCCT)is known to be unreliable for the diagnosis of acute ischemia with agreement between skilled reviewers of only (12) (50 – 70% agreement). This is improved if a systemised approach of scan review using ASPECTS is employed (13) ( 75% better for dichotomised , >6) and further if Aspects is applied to multiphase CT Angiography (CTA) data (>85%) (14). Diagnosis of ischemia is additionally improved with the use of CTPerfusion(CTP) ( 91% sensitive ,100% specific)(15). Renal disease, contrast nephropathy radiation (extra 4 mS, additional 2 – 3 minutes scan time and 5 – 15 min post processing) are no longer barriers to routine implementation of CTP. DWI MRI scanning remains the gold standard for identification of ischemic lesions in the brain.

2. Assessment for IV therapy-<4.5hrs

The exclusion of haemorrhage is easily done by NCCT or MR. The exclusion of a large infarct ( > 1/3 MCA territory (~100ml) is variably performed by NCCT, NCCT + ASPECTS ( ~<6 ~100ml, <7~70ml ,~ 75%sens, 75% sensitivity) (16), CTA source images, CTP, CTP Aspects, CBF( Aspects/vol), CBV ( Aspects /vol) or DWI vol, DWI Aspects (85%sens, 80%specificity) (16)

3. Assessment for IA therapy-<6hrs

Requires identification of a blocked vessel. Although clot may be seen well on thin slice NCCT, minimum imaging now requires CTA, MRA before proceeding to endovascular clot retrieval. There is still controversy about the place of CT or MR penumbral imaging in the selection of patients for IA therapy. The trials that used penumbral imaging for patient selection had the best patient outcomes but were also the trials that had the shortest time to reperfusion and had the highest revascularisation rates. Assessment of core (<70 ml) : NCCCT, Aspects, CTA aspects, Aspects/vol , CBV, CBF, DWI.

4. Endovascular clot retrieval.

Should be performed within 6 hr of stroke onset by a skilled operator

5. Access 24 hr availability.

This is best facilitated with dedicated stroke centres – networks, expedited access to scanners, neurointerventionalists availability 24/7 and potentially stroke ambulances

6. Research

Current research is focussed on expanding the eligibility pool of patients that can receive endovascular therapy . Trials are underway and needed to assess the benefit to the elderly, patients with mild ischemia (all in trials had NIHSS>5), wake up strokes (mismatch imaging may help), time >6hr (patient profile and mismatch imaging may help), treatment of large infarcts especially in early time window (MR Clean aspects 0 -4 no benefit) and development of better techniques to assess salvageable tissue: sodium ,amide, DTI, DKI, DSI.


No acknowledgement found.


1.Tissue plasminogen activator for acuteischemic stroke. N Engl J Med. 1995;333(24):1581-1587.

2. Hacke W, Kaste M, Bluhmki E, et al. Thrombolysis with alteplase 3 to 4.5 h after acute ischemic stroke. N Engl J Med 2008; 359:1317–1329.

3. Emberson J, Lees KR, Lyden P, Blackwell L, Albers G, Bluhmki E, Brott T, Cohen G, Davis S, Donnan G, Grotta J, Howard G, Kaste M, Koga M, von Kummer R, Lansberg M, Lindley RI, Murray G, Olivot JM, Parsons M, Tilley B, Toni D, Toyoda K, Wahlgren N, Wardlaw J, Whiteley W, del Zoppo GJ, Baigent C, Sandercock P, Hacke W; Stroke Thrombolysis Trialists' Collaborative Group. Effect of treatment delay, age, and stroke severity on the effects of intravenous thrombolysis with alteplase for acute ischaemic stroke: a meta-analysis of individual patient data from randomised trials. Lancet. 2014 Nov 29;384(9958):1929-35.

4. Broderick JP, Palesch YY, Demchuk AM, et al.Endovascular therapy after intravenous t-PA vs t-PAalone for stroke. N Engl J Med. 2013;368(10):893-903.

5. Riedel CH, Zimmermann P, Jensen-Kondering U et al .The importance of size: successful recanalization by intravenous thrombolysis in acute anterior stroke depends on thrombus length. Stroke 2011;42: 1775–7.

6. Goyal M, Demchuk AM, Menon BK, et al. Randomized assessment of rapid endovascular treatment of ischemic stroke. N Engl J Med 2015; 372:1019–1030.

7.Campbell BC, Mitchell PJ, Kleinig TJ, et al. Endovascular therapy for ischemic stroke with perfusion-imaging selection. N Engl J Med 2015; 372:1009–1018.

8. Saver JL, Goyal M, Bonafe A, et al. Stent-retriever thrombectomy after intravenous t-PA vs. t-PA alone in stroke. N Engl J Med 2015; 372:2285–2295.

9. Jovin TG, Chamorro A, Cobo E, et al. Thrombectomy within 8 h after symptom onset in ischemic stroke. N Engl J Med 2015; 372:2296–2306.

10. Berkhemer OA, Fransen PS, Beumer D, et al. A randomized trial of intraarterial treatment for acute ischemic stroke. N Engl J Med 2015; 372:11–20.

11. ShyamPrabhakaran, MD, MS; Ilana Ruff, MD; Richard A. Bernstein, MD, PhD Acute Stroke Intervention A Systematic Review JAMA 2015 Volume 313, Number 14 ;1451-1460.

12. von Kummer R, Holle R, Gizyska U, Hofmann E, Jansen O, Petersen D, Schumacher M, Sartor K. Interobserver agreement in assessing early CT signs of middle cerebral artery infarction.AJNR 1996 Oct;17(9):1743-8.

13. A.C. Gupta, P.W. Schaefer, Z.A. Chaudhry, T.M. Leslie-Mazwi, R.V. Chandra, R.G. González, J.A. Hirsch, and A.J. Yoo Interobserver Reliability of Baseline Noncontrast CT Alberta Stroke Program Early CT Score for Intra-Arterial Stroke Treatment Selection. AJNR Am J Neuroradiol 2012 33: 1046-1049.

14. Bal S, Bhatia R, Menon BK et al Time Dependence of reliability of non-contrast computed tomography in comparison to computed tomography angiography source image in acute cerebral ischemia. Int J Stroke 2015;10;55-60.

15. Campbell BC, Weir L, Desmond PM, Tu HT, Hand PJ, Yan B, Donnan GA, Parsons MW, Davis SM. CT perfusion improves diagnostic accuracy and confidence in acute ischaemic stroke.J Neurol Neurosurg Psychiatry. 2013 Jun;84(6):613-8

16. McTaggart RA, Jovin TG, Lansberg MG, Mlynash M, Jayaraman MV, Choudhri OA, Inoue M, Marks MP, Albers GW; DEFUSE 2 Investigators. Alberta stroke program early computed tomographic scoring performance in a series of patients undergoing computed tomography and MRI: reader agreement, modality agreement, and outcome prediction. Stroke. 2015 Feb;46(2):407-12.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)