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INTRODUCTION
Mechanical thrombectomy (MT) is a standard treatment for ischemic stroke with large vessel occlusion. Recent clinical studies have led to an expansion of time windows for MT [1], demonstrating its efficacy even in patients with large ischemic cores [2]. Moreover, the application of MT has extended to distal medium vessel occlusions [3], suggesting an anticipated increase in the number of thrombectomy procedures in the future.
MT techniques are primarily categorized into those utilizing aspiration catheters, stent retrievers, or a combination of both, such as in the Solumbra technique or a direct aspiration first pass technique [4]. Since the introduction of the Solitaire stent (Medtronic) for MT, there have been advancements in stent design, enhancing thrombus capture and improving procedural success.
Despite its efficacy, MT is associated with various vascular complications, including vasospasm, arterial dissection, and vessel perforation [5]. During stent retrieval, small perforating arteries may be inadvertently damaged, potentially leading to subarachnoid hemorrhage. Furthermore, it is known that unintended detachment during the stent retrieval process can occur very rarely, with a rate of less than 1% [6,7]. This complication was notably reported with the Solitaire AB (Medtronic), a detachable stent used previously; however, such reports are scarce with newer designs of stents [6]. Herein, we present 2 cases of inadvertent stent retriever detachment during MT utilizing the pRESET stent (Phenox).
CASE REPORT
Case 1
An elderly patient presented with left hemiplegia and extinction 60 minutes after symptom onset. His medical history included diabetes mellitus, dyslipidemia, coronary artery disease, and paroxysmal atrial fibrillation managed with clopidogrel. On presentation, his National Institutes of Health stroke scale (NIHSS) score was 11. Brain computed tomography (CT) angiography revealed occlusion of the M2 inferior division of the middle cerebral artery (MCA), with perfusion CT indicating involvement of the ischemic core of 8.2 mL and penumbra of 129.9 mL in the basal ganglia. Intravenous recombinant tissue plasminogen activator (tPA) was administered.
Under local anesthesia, access to the right common femoral artery was obtained, and an 8F sheath was introduced. Digital subtraction angiography (DSA) confirmed an occlusion in the proximal M2 inferior division of the right MCA (Fig. 1A). Utilizing a 0.035-inch×260 cm exchange-length guidewire, the diagnostic catheter was exchanged for a 6F aspiration catheter (Esperance; Wallaby Medical), which was navigated within an 8F balloon guide catheter (Optimo; Tokai Medical Products). A combination of a Synchro-14 microwire (Stryker) and a Phenom-21 microcatheter (Medtronic) was advanced through the aspiration catheter, with the microcatheter successfully traversing the occlusion and reaching the distal M2 division of the MCA. A stent retriever (pRESET, 5 mm×40 mm) was deployed through the microcatheter and unsheathed within the M1/M2 segments (Fig. 1B). The stent retriever was subsequently withdrawn into the aspiration catheter, and both devices were removed. Despite partial thrombus removal, the first pass failed to achieve recanalization of the M2 segment of the MCA. A second thrombectomy was attempted, but an unintended stent detachment occurred during retrieval, resulting in loss of antegrade blood flow in the proximal M1 segment (Fig. 1C, D). An attempt to retrieve the detached stent using a microsnare (4 mm; Medtronic) was unsuccessful. Instead, the aspiration catheter was advanced into the occluded M1 segment within the stent, and contact aspiration thrombectomy was performed 3 times, though recanalization of the MCA remained unsuccessful (Fig. 1E). Subsequently, 1 mg of tirofiban was administered intra-arterially (Fig. 1F). A microwire was navigated through the detached stent, followed by advancement of the 3×15 mm Gateway balloon catheter (Stryker) over the wire, positioning the balloon from the distal to mid segment of the MCA (Fig. 1G). Following balloon angioplasty using a balloon catheter, final angiography revealed recanalization of the right MCA with an expanded thrombolysis in cerebral infarction (eTICI) score of 2b67 (Fig. 1H). The patient improved, scoring 6 points on the NIHSS and modified Rankin scale (mRS) of 3 at 8 days post-procedure.
Case 2
An elderly patient with chronic kidney disease stage 4, diabetes mellitus, hypertension, and anticoagulation for atrial fibrillation was referred to the neurology department with sudden left hemiplegia and mental status change 3 days after discontinuing apixaban due to hematuria. The NIHSS score was 17. Brain CT perfusion angiography confirmed right distal M1 occlusion with a core infarct of 64 mL and penumbra of 104.8 mL. Intravenous recombinant tPA administration was precluded due to recent hematuria.
Under local anesthesia, the right common femoral artery was accessed, and an 8F sheath was inserted. DSA confirmed an occlusion in the distal M1 segment of the MCA (Fig. 2A, B). A 6F aspiration catheter (Sofia Plus; MicroVention) was advanced through an 8F balloon guide catheter (Cello; Medtronic) after exchanging the diagnostic catheter. A 0.021- inch microcatheter (Phenom-21; Medtronic) was navigated through the occlusion to the distal M2 division of the MCA, and a stent retriever (pRESET, 5 mm×40 mm) was deployed (Fig. 2C, D). The stent was retracted into the aspiration catheter, which was subsequently removed. Despite 2 retrievals of stent, no recanalization was achieved. During the third attempt, the stent detached unintentionally (Fig. 2E–H). During the stent retrieval process, significant resistance was encountered, indicating a potential risk of vessel injury. Considering the presence of hematuria, tirofiban, which poses a risk of bleeding, was not administered. The procedure was terminated as the microcatheter could not traverse the detached stent. The final eTICI score was 1. The patient was transferred to the rehabilitation department 1 month later with an NIHSS score of 12 and mRS of 5.
DISCUSSION
In our cases, unintentional stent detachment occurred during thrombectomy, with poor prognosis observed in cases where flow restoration was not achieved. This finding is consistent with previous studies [8]. Stent detachment is a very rare event, and there is no established method for managing it when it occurs. Previous case reports have attempted various methods, such as deploying another stent retriever to simultaneously retrieve the detached stent, or using microwires and snares for retrieval [9]. Balloon angioplasty and intra-arterial tirofiban injection have also been tried [8]. In some cases, when these methods failed, surgical removal was attempted [10]. We also attempted to grasp the proximal marker of the detached stent with a snare for retrieval, but this was unsuccessful. We advanced an aspiration catheter to the distal portion of the stent in an attempt to capture and retrieve it. However, as the catheter could not advance beyond the mid-portion of the stent, only suction thrombectomy was performed. After intra-arterial tirofiban injection, slight flow restoration was observed, but the stent was deformed during retrieval, and it was judged that the lumen was insufficient to allow adequate blood flow. Therefore, balloon angioplasty was performed to secure the lumen, ultimately resulting in successful flow restoration.
If the detached stent cannot be retrieved and remains in the vessel, dual antiplatelet therapy (DAPT) must be administered to prevent re-occlusion. In patients with large vessel occlusion, maintaining DAPT raises concerns about hemorrhagic transformation [11]. Therefore, stent retrieval should be attempted whenever possible. However, as no devices are specifically designed for this purpose, the deployment of another stent for simultaneous retrieval should be considered, and a phantom study has reported the feasibility of this approach [12]. In clinical practice, however, in vessels with severe tortuosity, there is a risk of dissection or perforation. To minimize this risk, as previous reports suggest, minimizing the overlap between the 2 stents would be appropriate [9].
The structure of the stent retriever connects the stent to the delivery/push wire via a ball-and-socket joint, an area known to be vulnerable to tensile forces, potentially leading to detachment [13]. Multiple retrieval attempts can lead to device fatigue, increasing the risk of breakage between the push wire and the stent, particularly when the stent is oversized relative to the vessel, or when significant resistance is encountered due to vessel tortuosity [6]. However, recent stent retrievers, including both the Solitaire and pRESET stents, feature an integrated structure connecting the wire and stent.
In our cases, the placement of the distal marker of the stent in the distal portion of the MCA M2 may have contributed to detachment, as the stent size was disproportionally larger relative to the vessel diameter. In tortuous vessels, twisting forces may act on the wire in addition to the pulling force during retrieval, further increasing the likelihood of detachment. In our first case, the distal part of the fractured push wire exhibited twisting, and detachment occurred at the connection with the stent. In the tension load test, the pRESET stent exhibited the second lowest detachment force [12]. The inadvertent detachment of the stent may have been influenced using a relatively oversized stent in a tortuous vessel, multiple retrieval attempts, and the stent’s susceptibility to tension forces.
Although inadvertent stent detachment is rarely reported in recent stent retrievers, it should be recognized that it can still occur during multiple retrieval attempt, depending on the patient’s vascular tortuosity. Therefore, it is important to be aware of the available rescue therapy options. In cases where the patient’s vascular anatomy raises concerns about vessel damage, balloon angioplasty may serve as a suitable alternative.
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