Current concepts in imaging and endovascular treatment of acute ischemic stroke: implications for the clinician
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During the last decade, the management of acute ischemic stroke has changed dramatically, from an expectant bedside “wait and see” attitude towards active treatment, thanks to the continuous improvement of new therapeutic options. In addition to the use of intravenous (IV) thrombolysis in emergent large vessel occlusion (ELVO), endovascular therapy (EVT) has proven to be very efficient in selected acute stroke patients. The indications for EVT have progressed from the era of thrombolysis to individual patient profiling. Recently, several indication parameters, e.g., “treatment time window” or “more distal vessel occlusion,” are under debate for adjustment. In this article, we review the imaging strategies in acute stroke and discuss several EVT indication dogmas, which are subject to change.
KeywordsAcute stroke Patient selection Endovascular procedure Cerebrovascular accident Diagnostic imaging
American Heart Association/American Stroke Association
Alberta Stroke Program Early CT Score
Basilar artery occlusion
Basilar Artery International Cooperation registry Study
Cerebral blood flow
Cerebral blood volume
Emergent large vessel occlusion
European Society for Minimally Invasive Neurological Therapy
European Society of Neuroradiology
European Stroke Organization
Fluid-attenuated inversion recovery
Internal carotid artery
Middle cerebral artery
Mechanical Embolus Removal in Cerebral Ischemia
Maximum intensity projection
modified Rankin Scale
Mean transit time
National Institutes of Health Stroke Scale
Randomized controlled trials
recombinant tissue Plasminogen Activator
Time to peak
Endovascular recanalization treatment has become the predominant therapy of acute ischemic stroke due to large vessel occlusion.
Neuroimaging, including basic vessel-imaging, is mandatory for proper patient selection for endovascular therapy (EVT).
The use of advanced neuroimaging techniques (CT or MRI perfusion and/or DWI MRI) allows selection of patient with late-presenting (> 6 h) or wake-up stroke with large vessel occlusion for EVT.
Indication setting for EVT in acute stroke is not fixed and is subject to changes in clinical insights and development of current and new recanalization techniques and devices.
The growing role of imaging and image-guided treatment in the management of acute stroke patients
A proposed advanced CT imaging protocol for selecting acute ischemic stroke patients for EVT
Questions to be answered
• Parenchymal brain imaging
• Hemorrhage? Alternative diagnosis?
Head and neck CT angiography
• From aortic arch to vertex
• 60–80 mL, 350 mg iodide/mL
• Small or large vessel occlusion?
• Tandem lesion?
• Roadmap for EVT
Brain 4D CT angiography
• Low dose
• Multiple scans
• Collateral vascular status?
• Brain coverage, depending on available scan width
• 40–60 mL, 350 mg iodide/mL
• Infarct volume
• Mismatch penumbra/infarct
The starting point of acute stroke patient evaluation always consists of non-enhanced imaging of the brain. The way of implementation of the following imaging steps can be tailored to the specific clinical situation (e.g., time window after symptom onset, clinical stroke syndrome).
What about the time window for endovascular treatment (EVT)?
Less common clinical situations in endovascular treatment (EVT)
The ideal situation for EVT is represented by patients with a single occlusive lesion arriving at the hospital within the shortest possible time, with non-hemorrhagic stroke and high NIHSS. Unfortunately, the clinical reality is oftentimes different. In the next paragraphs, we will discuss some “less common” and also “suboptimal” situations.
Tandem lesions are defined as (sub) occlusive “double” lesions, located both proximally (at the level of the cervical internal carotid artery) and distally (at the level of the intracranial arteries). In 10–20% of acute strokes, tandem lesions are present . The most common causes of cervical lesions are dissection (especially in younger people) and atherosclerotic plaques . Contrary to popular belief, a cervical carotid artery occlusion is not a contra-indication for EVT. Although not always successful, in practice, it is often surprisingly easy to navigate a distal access catheter through the proximal lesion for treatment of the distal lesion. The primary focus for treatment should be the symptomatic lesion (the so-called culprit lesion), which is almost invariably the distal lesion. There is an ongoing debate among interventional neuroradiologists whether or not to treat the proximal lesion first in order to get proper access to the distal lesion [33, 34]. Stenting of the cervical lesion in the acute phase can be useful in order to prevent recurrent stroke , especially in atherosclerotic disease. We are not aware of any large patient series concerning the safety and effectiveness of stenting of tandem lesions in the acute phase of stroke. In one publication of the RECOST study, it was stated that a conservative approach (without stenting) in case of adequate primary collateral circulation by the circle of Willis may be reliable and safe . It is important to note that early treatment with anti-aggregants, after intravenous thrombolysis, might increase the risk of (symptomatic) hemorrhagic transformation during or after stenting of stroke patients . A potential complication after treatment of a chronic cervical carotid artery subocclusion is the occurrence of cerebral hyperperfusion syndrome . It is believed that this syndrome is caused by impairment of the cerebrovascular autoregulation. Clinical symptoms include headache, seizures, and focal neurological symptoms. If not adequately detected and treated, brain edema and hemorrhage can develop, potentially leading to death . In our practice, we limit carotid stenting and/or balloon angioplasty to patients with persisting hemodynamic insufficiency in the acute phase.
Patients with low NIHSS
A significant proportion of patients with large vessel occlusions present initially in relatively good clinical condition, i.e., with a low NIHSS. However, the natural course of the disease can lead to a secondary worsening of clinical symptoms. In these situations, the neurovascular team is confronted with a dilemma, because, in case of persisting occlusion, the risk of secondary clinical worsening in the acute or subacute phase increases [40, 41]. A recent, retrospective multicenter cohort study, which included 214 patients, showed no improvement in independent functional outcomes in mild strokes (NIHSS < 6) in patients receiving EVT compared to medical treatment, irrespective of occlusion location, with increased symptomatic intracerebral hemorrhage rates . Therefore, it needs to be determined if it is justifiable to expose patients with modest symptomatology to the potential risks of a recanalization procedure. Furthermore, the occurrence of spontaneous recanalization of large vessel occlusions has been described . Two other studies, however, demonstrated the effectiveness of mechanical thrombectomy with excellent clinical outcome for patients with low NIHSS score (< 5) undergoing endovascular recanalization for large vessel occlusion in the anterior circulation [44, 45]. Until now, there are no clear guidelines on EVT in ELVO patients with low NIHSS. In such cases, it is advisable to assess the collateral vascular status of the patient . The risk of treatment should always be carefully weighed against the expected potential benefits, in order to make the best possible decision for the individual patient.
Endovascular treatment in distal occlusions
The benefit of EVT in acute ischemic stroke patients was established in RCTs for proximal large vessel occlusions, focusing exclusively on the internal carotid artery and proximal middle cerebral artery (M1 segment) [7, 8, 9, 47]. However, the effectiveness of mechanical thrombectomy in more distally located lesions, e.g., at the level of distal M2 segment or proximal M3 segment of the middle cerebral artery, has not been determined yet. After intravenous (IV) thrombolytic therapy alone, patients with distal lesions tend to show a more favorable clinical outcome when compared to patients with more proximally located lesions . Since IV thrombolysis has proven to be more efficient in smaller clots , IV treatment might offer a relative advantage over EVT for smaller vessel occlusions. In practice, EVT at the level of more distally located smaller vessels with thinner vessel walls can be technically more challenging, with potentially a higher risk of complications. Nevertheless, it is proven that EVT of more distal occlusions, i.e., isolated M2 occlusions, is just as safe and effective as EVT performed in proximal large vessel occlusions [50, 51]. Therefore, in specific cases presenting with a significant neurological deficit due to a strategic small vessel occlusion (e.g., patients with aphasia as a single symptom), EVT should be considered as a valuable treatment tool. In such cases, the decision whether or not to treat the patient with EVT should be made based on symptoms, age, and clinical status of the patient, pre-existent vascular disease, and the precise location of the distal vessel occlusion.
Acute basilar artery occlusion
The current guidelines indicate that the use of mechanical thrombectomy with stent retrievers is considered as “reasonable” to treat carefully selected patients who have “causative occlusion of the basilar artery” [10, 11]. In our practice, advanced imaging with DWI plays an important role in selecting candidates with vertebrobasilar artery occlusion for EVT by providing information about the extent and location of the infarcted areas.
When dealing with ELVO patients who might be eligible for EVT, knowledge about the occlusion site and infarct volume are of paramount importance. Adequate and fast pre-endovascular stroke treatment vessel imaging is vital in selecting suitable patients. A good impression of the potential benefit of EVT can be achieved by the assessment of collateral vascular networks in ELVO patients, and this can be done in a robust and fast way by the use of (multiphasic) CT angiography. In more doubtful cases, it is advisable to apply more advanced neuroimaging techniques, such as CT perfusion or MR DWI and/or perfusion imaging. The policy concerning indication setting for EVT in ELVO is rapidly changing; treatment paradigms, e.g., time windows and sites of occlusion, are constantly being questioned and adjusted, based on evidence from RCTs. In addition to the clinical decision-making process, patient profiling on the basis of advanced neuroimaging is becoming increasingly important. Individual assessment is taking precedence over patient group profiling, and this highlights the increasing role of the neuroradiologist in the management of acute stroke patients.
We would like to thank Dr. Luc van den Hauwe (Antwerp University Hospital, Wilrijkstraat 10, 2650 Edegem and AZ Klina, Augustijnslei 100, 2930 Brasschaat, Belgium) for providing us the post-EVT follow-up axial FLAIR MRI image in Fig. 5.
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TVDZ and AM were the major contributors in writing the manuscript. All the authors (TVDZ, AM, LY, MV, and PP) revised the manuscript. All authors read and approved the final manuscript.
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