Fig. 12.1
Schematic illustrations of (a) embolic occlusion and (b) in situ thrombo-occlusion due to intracranial atherosclerotic stenosis
Fig. 12.2
A 56-year-old man presenting with NIHSS score of 15. (a) Left carotid angiogram showing occlusion of the left middle cerebral artery M1 segment. (b) Frontal and (c) lateral angiogram immediately after stentriever deployment showing complete recanalization with a focal stenosis in the M1 trunk. Note that the bifurcation of the middle cerebral artery is preserved without stenosis or clots. (d) Immediately after stentriever retrieval, angiogram revealing complete recanalization with a focal stenosis in the M1 trunk. (e) Reocclusion is noted in a 5-min delayed angiogram. (f) Angiogram immediately after four passes showing complete recanalization. (g) Rotational angiogram disclosing a focal stenosis (arrowheads) in the M1 trunk without involving the bifurcation site after multiple passes of the stentriever followed by repeated reocclusion. (h) A 20-min delayed angiogram after glycoprotein IIb/IIIa inhibitor showing complete recanalization yet a slowed flow due to remnant stenosis in the M1 trunk
12.3 Suggested Solutions for Refractory ILAO Based on Pathomechanism
12.3.1 Solution for Refractory Occlusion Due to Underlying ICAS
In Asian populations, ICAS is one of the major causes of acute stroke, with recent studies showing that ICAS is responsible for 15–20% of acute ILAO strokes [7, 8, 10, 11]. The majority of non-embolic occlusions are truncal type, as revealed in angiograms during intra-arterial recanalization treatment, and most are due to ICAS thrombo-occlusion, especially in Asian patients [8]. This type (TTO) of occlusion shows refractoriness to a stentriever due to repeated reocclusion [7, 8, 10, 11]. While there are no reports of intimal damage from the use of a stentriever for acute ischemic stroke treatment of Western patients, in whom ICAS is rare as the cause of an ILAO [12], the application of a stentriever can damage the atheromatous surface if an acute ILAO is due to an ICAS thrombo-occlusion. In this case, the use of a stentriever can result in increased platelet activation, leading to repeated reocclusion and even dissection [8, 13].
To prevent repeated reocclusion in the case of an ILAO due to ICAS, inhibiting the platelet function can play a key role. Therefore, the first option is to administer a glycoprotein IIb/IIIa inhibitor, which inactivates platelets and thereby prevents repeated reocclusion (Fig. 12.3) [7]. However, ICAS occlusions are occasionally refractory to glycoprotein IIb/IIIa inhibitors. For recanalization in such a case, permanent stenting with or without balloon angioplasty may be effective [8, 10, 14].
Fig. 12.3
A 60-year-old man presenting with NIHSS score of 17. (a) Initial angiogram showing left middle cerebral artery M1 segment occlusion. (b) Angiogram immediately after stentriever deployment at the focal stenosis without involving the bifurcation. (c) Angiogram after multiple passes of the stentriever followed by repeated reocclusion showing irregular stenosis in the M1 trunk getting toward reocclusion. (d) A 5-min delayed angiogram showing reocclusion. (e) Angiogram after fifth pass of stentriever showing recanalization. (f) A 20-min delayed angiogram after glycoprotein IIb/IIIa inhibitor showing persistent recanalization with irregular stenosis in the M1 trunk. The flow speed is also improved
12.3.2 Solution for Refractory Occlusion Due to Embolic Organized (Hard) Clot
An organized (hard) clot is resilient and less sticky in character, making it less engaged with a stentriever and leading to clot loss during stentriever retrieval, especially in the case of a tortuous and large proximal artery. Plus, since an organized clot causes more tension in the stentriever-deployed segment of the parent artery, this can also cause an arterial spasm. Such effects then increase the probability of stentriever failure.
For successful recanalization of an ILAO due to an organized clot, the first option is to apply a vasodilator, which releases the tension of the stentriever-deployed arterial segment, thereby increasing the chance of successful clot retrieval. The second option is to switch to an aspiration thrombectomy or the simultaneous utilization of a stentriever and an aspiration thrombectomy. After deploying the stentriever, an aspiration catheter (Penumbra) or intermediate catheter is advanced as close to the clot as possible. A stentriever and suction thrombectomy can be performed simultaneously, as described in Chap. 11 (Figs. 11.4 and 11.5).
If the organized clot is still refractory after switching to aspiration and the simultaneous utilization of a stentriever and aspiration thrombectomy, permanent stenting can be considered as the final resort [14]. The organized clot may be refractory due to less engagement with the stentriever [9]. In contrast, if permanent stenting is conducted, the stented artery becomes more patent as the organized clot is less engaged inside the stent struts (Fig. 12.4) [14].
Fig. 12.4
Schematic drawing of the interaction between a stentriever and a clot according to the clot characteristics
12.4 Permanent Stenting for Acute ILAO
In a meta-analysis of five recent randomized clinical trials, 25–30% of ILAO cases failed to achieve recanalization with a stentriever thrombectomy [2]. Irrespective of the etiology of the refractoriness of an ILAO, a rescue modality is needed for such refractory cases, as successful recanalization is the most powerful factor for a good outcome. One possible modality is the intra-arterial infusion of thrombolytics (tissue plasminogen activator or urokinase) and/or antiplatelets (glycoprotein IIb/IIIa inhibitor), which can promote mTICI 2b-3 recanalization in some refractory ILAOs due to ICAS [7, 8, 14]. However, the final rescue modality is permanent stenting, which has also been suggested as a primary approach or rescue tool for the recanalization of an acute ILAO [8, 10, 14–20]. A stentriever-failed ILAO is likely due to either ICAS, intracranial artery dissection, or an organized (hard) clot, as previously described [8, 9, 14, 22]. In the case of an ICAS occlusion, the refractoriness is mainly due to repeated reocclusion [7, 8, 11]. As mentioned above, a glycoprotein IIb/IIIa inhibitor can help to prevent such reocclusion [7, 8]. Notwithstanding, ICAS occlusions are often refractory to glycoprotein IIb/IIIa inhibitors, probably because of underlying severe stenosis. In such cases, permanent stenting combined with a glycoprotein IIb/IIIa inhibitor can be very effective (Fig. 12.5) [14]. Permanent stenting can also be the last resort after the failure of a stentriever and aspiration thrombectomy due to an organized (hard) clot (Fig. 12.6). In a recently published study on the safety and efficacy of permanent stenting following a failed mechanical thrombectomy, 83.3% of the stented patients showed thrombolysis with a cerebral ischemia 2b-3 recanalization rate. Among 17 stented cases, only 40% underwent balloon angioplasty [14]. A Wingspan stent was used in seven cases, while a Solitaire stent, which is also used for thrombectomies, was used in ten cases. These results suggest that most of the refractory occlusions were due to a soft plaque ICAS or organized embolus, rather than a hard plaque ICAS. In other words, the radial force of the Solitaire stent was enough to open the occlusion, and angioplasty was not always required in the case of a soft plaque or hard embolus occlusion [14]. Meanwhile, platelet inactivation by a glycoprotein IIb/IIIa inhibitor was found to be essential to prevent reocclusion due to acute in-stent thrombosis [14]. The stented patients had significantly more favorable outcomes (modified Rankin Scale score [mRS] of 0–2, 35.5%) and less cerebral herniation (11.8%) than the non-stented patients (mRS, 0–2, 7.1%; cerebral herniation, 42.9%), while there were no differences in the symptomatic intracranial hemorrhage and mortality rates between the patient groups (symptomatic hemorrhage and mortality, 11.8 and 23.9% in stented group versus 14.3 and 39.4% in non-stented group) [14]. While the major concern with permanent stenting is that it requires antiplatelet medication, thereby increasing the risk of intracranial hemorrhage in an acute stroke setting, the results of previous studies suggest that the benefit of recanalization’s success by permanent stenting outweighs this drawback in patients with a stentriever-failed ILAO that is otherwise left non-recanalized [8, 10, 15–21].
