Incidental aneurysm rupture during endovascular thrombectomy for acute ischaemic stroke

Summary

Acute ischaemic stroke remains a leading cause of disability and mortality worldwide. Treatments include systemic fibrinolysis and more recently, endovascular thrombectomy (EVT). The presence of incidental intracranial aneurysms may increase procedural risk during EVT, particularly given their potential higher prevalence in patients with stroke due to shared risk factors such as smoking and hypertension.

We present the case of an elderly woman who experienced rupture of an unrecognised intracranial aneurysm during EVT. This case underscores the importance of meticulous preprocedural imaging review, awareness of high-risk anatomical locations and cautious selection of EVT techniques. We also provide a brief review of the literature regarding the incidence, mechanisms and management of intraprocedural aneurysm rupture.

Background

Acute ischaemic stroke is a major global health burden, driving the rapid advancement of treatment strategies such as systemic fibrinolysis and endovascular thrombectomy (EVT). While systemic fibrinolysis can improve outcomes, it is limited by a narrow therapeutic window and contraindications related to age, anticoagulant use, prior stroke or trauma and pre-existing intracranial pathology.^{1 2} EVT offers an effective alternative for patients with large vessel occlusion and has demonstrated a favourable number needed to treat (2.6).³,⁷

Although generally well tolerated, EVT carries procedural risks. Subarachnoid haemorrhage secondary to arterial perforation occurs in approximately 2.8% of cases and is associated with failed revascularisation and poor clinical outcomes.⁸ Other complications include arterial dissection and distal embolisation. Importantly, these complications are often multifactorial, with patient-specific factors, such as arterial stiffness, contributing to haemorrhage risk.^{9 10}

Incidental intracranial aneurysms may be one such factor. Although rare, there are documented cases of aneurysm identification and rupture during EVT.^{11 12} Despite limited data, these cases highlight a significant concern: the risk of iatrogenic aneurysm rupture during thrombus manipulation.

Case presentation

A woman in her early 80s presented with acute left-sided hemiplegia and neglect. She was found collapsed on the bathroom floor by her husband. The witnessed loss of consciousness was unclear. Time last known well was approximately 3 hours prior to assessment. Neurological evaluation revealed a National Institutes of Health Stroke Scale (NIHSS) score of 20.

Investigations

Initial non-contrast CT demonstrated a hyperdense right distal middle cerebral artery (MCA) consistent with the thrombus. No haemorrhage or loss of grey–white matter differentiation was seen (figure 1).

Figure 1. Axial non-contrast CT images (A, B and C) demonstrate a hyperdense artery sign in the distal right M1 segment (white arrow), appearing slightly lobulated. No grey–white matter differentiation loss is observed in panels B and C.

CT angiogram (CTA) confirmed a distal right M1 MCA occlusion extending into the M2 branches, particularly the superior division (figure 2). No significant carotid stenosis was noted despite bilateral calcified plaques (figure 2).

Figure 2. Axial (A) and coronal (B) CT angiography maximum intensity projection images show an occlusion of the distal right M1 segment (white arrow).

Multiphase CTA revealed subtle, millimetric, blind-ending contrast filling at the distal M1, suspicious for a small MCA bifurcation aneurysm (figure 3). This was only recognised on retrospective review after the intervention.

Figure 3. Multiphase axial CT angiography images in the early arterial (A), late arterial (8 s, (B)), and early venous (16 s, (C)) phases reveal subtle, millimetric, blind-ending contrast filling at the level of the distal M1 occlusion, suspicious for anmiddle cerebral artery bifurcation aneurysm.

CT perfusion demonstrated a large perfusion mismatch in the right MCA territory, with suspected infarction in the right frontal lobe (figure 4).

Figure 4. Axial CT perfusion maps—cerebral blood flow (CBF, (A)), cerebral blood volume (CBV, (B)), and time to peak (TTP, (C))—demonstrate a perfusion deficit in the right middle cerebral artery territory due to a distal right M1 occlusion, with a notable mismatch between CBV and CBF.

Treatment

The patient underwent urgent EVT under conscious sedation. Intraprocedural angiography confirmed a distal right M1 MCA occlusion with extension into the superior and partially into the inferior divisions (figure 5).

Figure 5. Anteroposterior (A) and lateral (B) right ICA angiograms show a filling defect in the distal right M1 segment (white arrow) and a corresponding perfusion deficit during the capillary phase (white ovoid circle).

Capillary-phase angiography demonstrated rounded contrast stasis at the MCA bifurcation (white arrow), raising concern for an underlying aneurysm. This was only recognised on retrospective review after the intervention (figure 6).

Figure 6. Anteroposterior right ICA angiograms in the late arterial (A), capillary (B), and early venous (C) phases demonstrate rounded contrast stasis at the MCA bifurcation (white arrow), raising concern for an underlying aneurysm.

A direct aspiration first pass technique (ADAPT) was employed as the primary recanalisation strategy. Following the first pass, angiography demonstrated brisk contrast extravasation from the distal M1, consistent with vessel rupture (figure 7). Temporary haemostasis was achieved with balloon tamponade.

Figure 7. Anteroposterior (A) and lateral (B) right ICA angiograms reveal extensive active contrast extravasation (*) originating from a small aneurysm at the distal middle cerebral artery bifurcation (white arrow).

Given the patient’s severe neurological deficit and the belief that the haemorrhage resulted from a small wire perforation rather than an aneurysm rupture, a second thrombectomy attempt was pursued. However, repeat angiography after microwire passage again showed active contrast extravasation. Balloon tamponade was unsuccessful, and the patient’s pupils became fixed and dilated.

Due to the poor neurological prognosis, embolisation of the distal M1 was not pursued. Non-contrast Dyna-CT confirmed diffuse contrast extravasation, consistent with subarachnoid and intracerebral haemorrhage (figure 8).

Figure 8. Coronal reconstruction from a non-contrast Dyna-CT shows extensive diffuse contrast extravasation, consistent with ongoing intracranial haemorrhage.

Retrospective review of the multiphase CTA and pre-ADAPT angiograms revealed a likely ruptured small, partially thrombosed aneurysm at the MCA bifurcation (figures3 6).

Outcome and follow-up

Given the patient’s grave neurological status, neurosurgery declined external ventricular drain insertion. The patient was palliated and transferred to the intensive care unit.

Discussion

Unruptured intracranial aneurysms have an estimated prevalence of approximately 3.2% in the general population.¹³ The prevalence is potentially higher in stroke patients due to shared risk factors, such as smoking and hypertension.¹²,¹⁵ Further, the relationship has been postulated to be causative when there are intra-aneurysmal thrombi present.¹⁶ Potential mechanisms include intra-aneurysmal thrombi extension into the parent vessel, thrombus embolisation with distal occlusion, and mass effect causing parent vessel occlusion. Intra-aneurysmal thrombosis is more common in giant aneurysms, but there are reported cases of non-giant aneurysm thrombosis as the proposed cause for acute ischaemic stroke.¹¹¹⁶,¹⁹

Given the relationship between intracranial aneurysms and acute ischaemic stroke, it is pertinent to explore the risks that incidental aneurysms introduce to EVT. Of the reported cases that identified incidental aneurysms during EVT, only a few reported aneurysms rupture resulting in poor clinical outcomes.^{11 12 20 21} Zibold et al highlighted three critical, high-risk steps during EVT with stent retrievers.¹² First, aneurysm perforation may occur when a microwire and microcatheter are passed through the thrombus prior to deployment. Second, shearing stress during withdrawal increases aneurysm rupture risk. Specifically, the mechanical stretch associated with stent retrievers has been shown to cause vessel wall weakening secondary to angiographically occult ruptures.²² Finally, sudden reperfusion after clot retrieval introduces increased vessel wall pressure, further exacerbating rupture risk of the weak aneurysm vessel wall.

Aneurysm location plays a crucial role in rupture risk. Aneurysms located at or distal to an occlusion may not be visualised prethrombectomy and are vulnerable to procedural manipulation. Further, aneurysms at bifurcations have been shown to have a higher rupture risk in comparison to sidewall aneurysms.²³ As such, occluded segments near vessel bifurcations should be treated with increased caution. Indeed, the case presented herein demonstrates an aneurysm located beyond the occluded segment and at the MCA bifurcation, both high-risk factors. On the other hand, aneurysms within the contralateral hemisphere or distant from the occluded segment likely have a low risk of rupture as they are generally undisturbed during EVT.

Use of alternative EVT techniques may reduce the risk of aneurysm rupture. ADAPT is associated with lower intracranial haemorrhage complications compared with stent retrievers and achieves comparable recanalisation rates.²⁴,²⁷ In cases of incidental aneurysms, direct aspiration would avoid much of the technique-specific risks described above.

Nevertheless, our case presented demonstrates that aneurysm rupture can still occur with ADAPT. Despite careful technique, unawareness of the aneurysm contributed to rupture. Careful review of multiphase CTA and pre-intervention angiography—particularly capillary-phase images—may help identify high-risk vascular anatomy prior to EVT. In this case, the aneurysm was retrospectively visible (figures3 6).

Once haemorrhage has occurred, further attempts at recanalisation must be approached with caution. The imaging review should be thorough and not be compromised by the urgency of endovascular treatment. If the source of the bleeding is unknown, a less aggressive approach is justified. If aneurysmal rupture is confirmed, endovascular treatment of the aneurysm is indicated.

Learning points.

• Incidental intracranial aneurysms may be identified during endovascular thrombectomy (EVT) and carry a risk of iatrogenic rupture.

• Thorough preprocedure imaging review—especially multiphase CT angiography and capillary-phase angiography—may help detect aneurysms. The imaging review should be thorough and not be compromised by the urgency of endovascular treatment.

• High-risk EVT manoeuvres, such as microwire passage and stent retriever withdrawal, should be undertaken with caution, especially at vessel bifurcations.

• In the setting of intraprocedural haemorrhage, reassessment of the imaging and procedural strategy is essential.