Introduction

Acute ischemic stroke from large vessel occlusion (LVO) is associated with high morbidity and mortality, especially when internal carotid artery (ICA) terminus or basilar artery occlusion is involved. The clinical benefit of intravenous (IV) thrombolysis with tissue plasminogen activator (tPA) was demonstrated in the landmark 1995 National Institute of Neurological Disorders and Stroke (NINDS) study, and this therapy received Food and Drug Administration approval for the treatment of acute ischemic stroke in 1996. However, its efficacy for the treatment of stroke due to LVO is limited.

Intra-arterial (IA) pharmacological thrombolysis with tPA and its analogs, clot destruction with microwire manipulation, and mechanical thrombectomy using the Merci retriever device are examples of initial attempts to design catheter-guided therapies as alternatives to IV tPA. In a series of randomized trials published in 2013, such therapies failed to demonstrate significant benefit over medical therapy alone. It should be mentioned that many neurointerventionists believe that other critical factors, such as poor selection of patients for randomization (e.g., lack of LVO) and delays to initiation of the procedure, also might have contributed to the lack of success from IA revascularization.

In 2015, five trials of endovascular therapy were published (MR CLEAN, Multicenter Randomized Clinical Trial of Endovascular Treatment of Acute Ischemic Stroke in the Netherlands; ESCAPE, Endovascular Treatment for Small Core and Anterior Circulation Proximal Occlusion with Emphasis on Minimizing CT to Recanalization Times; SWIFT PRIME, Solitaire With the Intention For Thrombectomy as PRIMary Endovascular treatment; EXTEND-IA, Extending the Time for Thrombolysis in Emergency Neurological Deficits–Intra-arterial; and REVASCAT, Randomized Trial of Revascularization with Solitaire FR Device vs Best Medical Therapy in the Treatment of Acute Stroke Due to Anterior Circulation Large Vessel Occlusion Presenting within Eight Hours of Symptom Onset), all demonstrating safety and efficacy of modern IA thrombectomy in achieving favorable clinical outcomes in patients with anterior circulation LVO, in comparison to medical therapy, including the use of IV tPA. The trials provided strong evidence for the treatment of patients with anterior circulation LVO using IA thrombectomy with retrievable stents (called stent retrievers), when this therapy is combined with prior administration of IV tPA and the thrombectomy is initiated within the first 6 hours of stroke symptom onset. However, subgroup analyses also showed evidence of benefit from IA thrombectomy in patients who were not eligible to receive IV tPA or in whom thrombectomy was initiated as long as 12 hours after stroke onset ( 1 in algorithm ).

Major controversies in decision making addressed in this chapter include:

1. 
   

   Safety and efficacy of intracranial endovascular mechanical thrombectomy.

   
   
2. 
   

   Indications for intracranial endovascular mechanical thrombectomy.

   
   
3. 
   

   Role of endovascular mechanical thrombectomy in patients with more than 6 hours of time from onset (unknown or wake-up stroke).

   
   
4. 
   

   Different mechanical thrombectomy techniques.

Whether to Treat

Several studies have shown that the efficacy of IA thrombectomy is time dependent. Therefore, acute stroke should be considered a true neurological emergency; and in qualified patients, such treatment should be initiated without delay. The decision to treat is based on many factors. Stroke severity, which is typically based on the level of the National Institutes of Health Stroke Scale (NIHSS) score, can be used to estimate the likelihood of LVO but should be confirmed with a noninvasive study, such as computed tomographic angiography (CTA) or magnetic resonance angiography (MRA).

On the basis of the American Health Association (AHA)/America Stroke Association (ASA) guidelines on the acute management of ischemic stroke that were updated in 2015 to reflect the findings of the 2015 endovascular trials, patients with an NIHSS score of 6 and above should be considered candidates for stroke thrombectomy ( 2 in algorithm ). Among the 2015 trials, subgroup analyses showed that patients with advanced age do show benefit from endovascular therapy. Also, previous administration of IV tPA does not increase the risk of adverse events, such as intracranial hemorrhage (ICH).

It is still unknown at which time point endovascular interventions for acute stroke become futile or harmful—in other words, when it is too late to perform IA revascularization. As mentioned, the 2015 trials provided strong evidence for thrombectomy when that treatment was initiated within the first 6 hours from the onset of stroke symptoms. The ESCAPE trial included patients in whom thrombectomy was initiated in up to 12 hours, and there was a trend toward benefit from thrombectomy, although it did not reach statistical significance, possibly due to the limited sample size (n = 49) of this subgroup of patients. Currently, many endovascular centers utilize CT- or MR-based perfusion imaging as a tool to determine the extent of irreversible ischemic damage versus salvageable tissue (penumbra) when selecting patients for interventions beyond the 6-hour therapeutic window or in patients with unknown time of stroke onset. Studies from these centers demonstrate that such a selection approach achieves clinical results that are comparable to those achieved in the 2015 trials, supporting the use of endovascular therapy at later time points in carefully selected patients ( 3 in algorithm ).

Anatomical Considerations

Anterior circulation strokes account for the majority of all strokes from LVO, with the M1 middle cerebral artery (MCA) segment being the most common location affected (▶ Fig. 2.1a–c ). Stent retrievers were considered the first-line treatment strategy; nowadays high recanalization rates are achieved with aspiration thrombectomy alone.

Severe carotid artery stenosis or acute occlusion makes endovascular stroke intervention more challenging, as these conditions require the performance of an angioplasty or a stenting procedure before access to the intracranial circulation can be established (▶ Fig. 2.1a–e ). Transfemoral access is most commonly utilized for stroke intervention. However, rarely, alternative access such as via a transradial or a transbrachial approach or even via a direct carotid artery puncture is required, such as in cases of type III arch, extreme tortuosity, severe angulation, or loops of the common carotid artery, and ostial stenosis of the common carotid artery where the classic transfemoral approach is likely to cause significant delay or such access cannot be established.

Cases of posterior circulation strokes can be complicated by the presence of severe vertebral artery origin stenosis, which can also be treated via balloon angioplasty or stenting.