Endovascular strategies for management of intradural vertebral artery dissecting aneurysms
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.222811
Source of Support: None, Conflict of Interest: None
Objective: Endovascular treatment of vertebral intradural dissecting aneurysms is complex and requires different strategies for each case. The current study aims to classify these aneurysms for an easy selection of optimal strategies for endovascular therapy.
Keywords: Dissecting, vertebral aneurysm, subarachnoid hemorrhage
Vertebral artery (VA) is the most commonly involved artery in spontaneous posterior circulation dissections. The annual incidence of spontaneous vertebral arterial dissections has been estimated at 1 to 1.5 per 100000., The dissection typically arises from a tear in the intimal layer of the artery, which permits subsequent hemorrhage into the vessel wall. The clinical presentation, natural history, and subsequent management of dissections in the extradural and intradural VA segments are different and are based on the anatomy of the vasculature and histology of the aneurysm. Depending upon the depth of arterial dissection into the vessel wall, pseudoaneurysms may develop; or, if the dissection communicates with the vessel lumen, the vessel may occlude or narrow. Intramural hematomas, caused by extravasation of luminal blood or by hemorrhage from a vasa vasorum within the media, are most commonly located between the internal elastic lamina and the media. As the intradural VA has a thicker internal elastic lamina but no external elastic lamina, a thinner adventitia, and fewer elastic fibers in the media, the intradural VA is more susceptible to developing a pseudoaneurysm and rupturing into the adjoining subarachnoid space than the extradural VA., The extradural VA dissection has a subintimal extravasation, which is usually limited by the thick external elastic lamina inside the media (as the dissection extend inwards). It tends to project inside the vessel lumen leading to luminal narrowing/occlusion.,, In contrast to the intradural VA, an extradural VA dissection is less likely to extend into the subadventitial layer, and hence, is less likely to lead to dilatation of the outer wall of the vessel, (i.e., to form a pseudoaneurysm). The typical clinical course of an extradural VA dissection is reported to be a single neurological event followed by recovery over a few weeks or months. Progression is thought to result from propagation of a thrombus or its distal embolization, and hence, antiplatelet and antithrombotic treatments are recommended in the case of an extradural VA dissection. Intradural VA dissections can result in both the ischemic phenomenon and subarachnoid hemorrhage (SAH). In contrast to the benign natural course of an extradural VA dissection, an intradural VA dissection is associated with a high mortality and morbidity due to the risk of recurrent bleed., Prompt surgical or endovascular treatment is indicated in the case of an intradural VA dissection.
Surgical treatment of vertebral dissecting aneurysms (VADAs) include surgical clipping, trapping, wrapping, and especially when the dissection involves the posterior inferior cerebellar artery (PICA) origin, PICA revascularization may have to be considered., As the surgical approach is associated with a high incidence of treatment associated mortality and morbidity (lower nerve palsy and brain stem infarction), endovascular procedures are favored in the treatment of intradural VA dissecting aneurysms.,, Different endovascular interventional therapy strategies are described in literature, which are confusing and complex. We have tried to classify the intradural VADAs based on their location and the status of contralateral VA. This classification also helps in optimizing the strategy for endovascular technique.
Between May 2014 and June 2016, 10 patients with intradural VADA underwent endovascular treatment. We retrospectively evaluated clinical, imaging, as well as angiographic and endovascular treatment data for these patients [Table 1]. All patients were admitted to the Neurosurgery critical care unit. After a complete clinical evaluation, the patients underwent a cerebral digital subtraction angiogram in a biplanar digital subtraction angiography unit (Philips AlluraXper FD20).
Among the 10 patients, 6 were females and 4 were males. Their mean age was 54 years. Nine patients presented with acute subarachnoid hemorrhage, and one with acute-onset headache with no cerebrospinal fluid (CSF) evidence of xanthochromia. The clinical status of the patients was documented according to the modified Hunt and Hess (H and H) grading system. Two patients were in H and H grade I, 4 patients in grade II, and 4 patients in grade III.
Angiographic results and classification
The aneurysms were classified into two types, as dominant (A) or hypoplastic (B), depending upon the developmental state of the contralateral VA. Type A included a dominant contralateral VA that would provide adequate posterior circulation blood supply following the ipsilateral VA occlusion. Type A aneurysms were further divided into three subtypes depending upon the location of the aneurysm in relation to the PICA: aneurysm proximal to the PICA (Type I), involving the PICA (Type II), and distal to the PICA (Type III).
Type B included a contralateral VA that was hypoplastic and was, therefore, less likely to provide adequate posterior circulation blood supply following an ipsilateral VA occlusion.
All procedures were performed under general anesthesia. The treatment approach was chosen according to the classification [based on the flow chart, [Table 1]. If reconstructive endovascular management with stent was planned, a loading dose of double antiplatelets [300 mg aspirin +300 mg clopidogrel/40 mg prasugrel] was given through the Ryle's tube in the catheterization labarotatory (Cath Lab), after administering general anesthesia, before the stent deployment. If external ventricular drainage (EVD) was required, it was done before giving these medications, and a postprocedural computed tomography (CT) scan was done to document the appropriate position of the drainage catheter and for any possible intracranial bleed.
When internal trapping was planned, we used 2–3 mm oversized coils so that the coil stayed in the position they were planned to be in. Coiling was continued till the aneurysm as well as the adjoining proximal and distal few millimeters of the parent artery had been occluded.
Results and clinical outcome
Among the 10 patients, 4 patients underwent stent-assisted coiling, 4 patients underwent aneurysm coiling plus parent artery occlusion (internal trapping), and 2 patients underwent proximal coil occlusion. Among the 4 patients who underwent stent-assisted coiling, 3 had a poor contralateral VA flow, for which a reconstructive approach was offered. In 1 patient, the contralateral VA was codominant, so an internal trapping procedure was offered as the first option, but because the patient refused the option of VA occlusion, stent-assisted coiling was done to preserve the VA [Table 2].
No intraoperative aneurysmal rupture was encountered in any of the 10 cases. One patient in whom stent-assisted coiling was performed, developed small clots on the stent struts, which were treated with immediate heparinization and intra-arterial tirofiban. Postprocedural CT scan in this case did not show any infarct. Two patients on dual antiplatelet agents developed hemorrhagic foci along the external ventricular drainage track. One patient who underwent proximal coil occlusion for a dissecting aneurysm involving the PICA showed a clinically asymptomatic small infarct in the left inferior cerebellar hemisphere–PICA territory. Two patients developed visual deficits secondary to vitreous hemorrhage. No mortality was reported among the 10 patients. At follow-up visit, one patient developed severe cognitive impairment after the SAH but was independent in activities of daily living.
The location of the dissection determines the clinical presentation of vertebral artery dissecting aneurysms and also determines their subsequent management. Patients with dissection in the extradural segment of VA are likely to present with stroke/transient ischemic attacks (TIA) while those with an intradural dissection involving the VA usually present with SAH and sometimes with symptoms of brainstem or cerebellar ischemia. A very high incidence of recurrent hemorrhage has been reported in such cases of intradural VA dissection., Mizutani et al., retrospectively analyzed the clinical manifestations in 42 patients with recurrent hemorrhage caused by the rupture of VA intradural dissecting aneurysms and revealed that 40.5% of recurrent hemorrhages occurred within 24 hours, and 57.1% occurred within one week following the first hemorrhage. Thus, institution of an early treatment is strongly recommended. The dissecting aneurysm does not have a real neck and has an irregular fusi-saccular morphology that may often be evident on angiography. The conventional surgical clipping is often not effective in obliterating these aneurysm successfully. Moreover, surgery is associated with a high surgical morbidity due to the high incidence of lower cranial nerve involvement. Endovascular interventional therapy is, therefore, becoming the primary option for treating VA intradural dissections.,,,
Both deconstructive and reconstructive strategies can be achieved with novel endovascular interventions. The deconstructive approach by parent artery sacrifice and internal trapping was considered after evaluation of the status of the contralateral VA and was offered only when the contralateral VA was codominant/dominant and was able to supply the posterior circulation independently. We relied on the angiographic appearance of the VA and the selective angiographic image. We did not perform a balloon test occlusion (BTO) as it is often time consuming and increases the technical complexity as well as the cost of the procedure. BTO is not always recommended during an acute SAH. Zoarskia and Seth  studied the safety of unilateral occlusion of the VA without prior test balloon occlusion. They showed that, as long as both vertebral arteries were patent and converged at the vertebrobasilar junction, there is anatomical potential for retrograde filling of the distal intracranial VA upto to the level of the PICA origin. Thus, the mere angiographic appearance of both intracranial arteries and their selective injections are adequate to take a decision regarding the feasibility of parent artery occlusion. Reconstructive techniques that maintain the blood flow through the parent artery are indicated if important vessels such as PICA take off from the diseased segment, or if the contralateral VA is insufficient to supply the posterior circulation independently.
In this study, the treatment approach was chosen according to the classification [flow chart, [Table 1]. For all patients in group A (with a contralateral dominant VA), we advised internal trapping of the parent vessel [Figure 1] and [Figure 2] except when the aneurysm involved the PICA origin (subtype II). PICA occlusion can result in a clinically symptomatic lateral medullary infarct; hence, we advocated proximal arterial occlusion in these cases so that retrograde flow from the contralateral dominant VA could provide enough blood to the ipsilateral PICA. Proximal coil occlusion carries the risk of posttreatment rebleeding because of the retrograde blood flow into the aneurysm from the contralateral VA with outflow into the ipsilateral PICA., Rabinov et al., reported 35 patients with an intradural dissecting VA aneurysm, out of which 14 patients underwent proximal occlusion. However, the indications for proximal vessel occlusion in this study were diverse. The authors had used proximal coil occlusion as a safer alternative to trapping in the cases in whom important side branches were involved, in the cases harbouring an aneurysm located at the vertebrobasilar junction, and also in the cases in whom they felt that it was risky to traverse the extremely narrow segment of the parent blood vessel. They reported two cases of rebleed after proximal occlusion of the parent VA. In our study, two patients underwent proximal coil occlusion [Figure 3] and 1 patient developed a small clinically asymptomatic infarct in the distal PICA territory. No patient suffered from an episode of rebleeding. The follow-up contrast enhanced magnetic resonance (MR) angiography in both the patients showed complete aneurysmal occlusion and a patent ipsilateral PICA through a retrograde flow [Figure 3]. All the patients in group B (with a contralateral hypoplastic VA) underwent a reconstructive approach since the contralateral hypoplastic VA was inadequate for maintaining the posterior circulation blood supply following the ipsilateral VA occlusion [Figure 4].
We conducted a comprehensive literature review on the status of endovascular treatment for managing VADA [Table 3].,, Recently, Lim et al., published their study of 23 patients and proposed the therapeutic approaches in ruptured VADA. The authors suggested stent-assisted coiling or internal trapping followed by surgical bypass in patients with a poor contralateral VA. For dissecting aneurysms involving a hypoplastic VA (that is either proximal or distal to the origin of PICA), the authors proposed trapping, and for lesions involving the VA segment harbouring the origin of PICA, they suggested stent-assisted coiling or internal trapping followed by surgical bypass. In our series, we proposed proximal coil occlusion for this group. In our experience, proximal coil occlusion is a safer and cheaper option with lower postoperative complications and is a technically simple procedure. Moreover, it must be considered that the combination of open bypass surgery and endovascular procedure, as an integrated multimodal approach, is not available in most of the centers in India.
Based on our experience, we propose that patients with a VA intradural dissecting aneurysm be treated with an endovascular interventional strategy, based on the status of the contralateral VA and the relation of the aneurysm to the ipsilateral PICA [Table 1]. However, further studies consisting of larger patient cohorts and a longer follow-up data are required to confirm the results.
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Conflicts of interest
There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3]