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NI FEATURE: THE EDITORIAL DEBATE I-- PROS AND CONS
Year : 2018  |  Volume : 66  |  Issue : 3  |  Page : 657-660

Parent vessel occlusion and revascularization: A dying art?


Department of Neurosurgery, Manipal Hospital, Bengaluru, Karnataka, India

Date of Web Publication15-May-2018

Correspondence Address:
Dr. Paritosh Pandey
Department of Neurosurgery, Manipal Hospital, Bengaluru, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0028-3886.232315

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How to cite this article:
Pandey P. Parent vessel occlusion and revascularization: A dying art?. Neurol India 2018;66:657-60

How to cite this URL:
Pandey P. Parent vessel occlusion and revascularization: A dying art?. Neurol India [serial online] 2018 [cited 2018 May 20];66:657-60. Available from: http://www.neurologyindia.com/text.asp?2018/66/3/657/232315




Parent vessel occlusion is the oldest treatment for intracranial aneurysms, with Hunterian ligation being used for aneurysms since more than a century now.[1],[2] Decades of technological progress later, Hunterian ligation of the parent vessel still remains the standard of treatment for many types of intracranial aneurysms, such as giant and fusiform aneurysms, dissecting aneurysms, and in many instances, blood blister-like aneurysms. Parent vessel occlusion has been supplemented with a bypass in situ ations where the collateral circulation is deemed inadequate. This strategy was further refined with the addition of procedures like balloon test occlusion, where the vessel to be sacrificed was temporarily occluded, and the flow was replaced with a bypass.[3] With the advent of endovascular techniques, many of the aneurysms which were hitherto candidates for surgical clipping had another treatment option in the form of coiling, either with or without the use of adjuncts such as stents and balloons. However, the results of conventional endovascular treatment in these select groups of patients (giant/fusiform aneurysms, dissecting aneurysms, blood blister like aneurysms [BBA]) was poor.[4],[5] With the advent of flow diverters (FDs), more and more of these aneurysms are being treated with this technology. However, there are challenges in the use of FDs in the setting of acutely ruptured aneurysms, such as the risk of rebleeding, the need to use dual anti-platelets in this setting, and the risk of thrombo-embolic complications.[6],[7] In this background, the authors perform a systematic review of patients treated with parent artery occlusion (with or without revascularization) for patients with ruptured aneurysms.[1]

In an age where the majority of patients with ruptured aneurysms can be treated using conventional techniques like clipping, coiling or other surgical and endovascular methods, only a selected group of patients with ruptured aneurysms will require more complex treatments like revascularization and vessel sacrifice. Although there are many reports of surgical results with revascularization and parent vessel occlusion, the reports that deal with outcomes of this paradigm for ruptured aneurysms exclusively, are very few. In the setting of subarachnoid haemorrhage (SAH), treatments like revascularization, parent artery occlusion and FDs become risky, because of other variables like risk of increased intracranial pressure, vasospasm and reduced tolerance to temporary occlusion. Hence, it is commendable that the authors have done a systematic review of patients undergoing parent artery occlusion (PAO) with or without revascularization in patients with ruptured aneurysms.[1]

Blood blister like aneurysms (BBA) are rare aneurysms that arise from non-branching points of the vessels, and are a challenge to treat. Their walls are very fragile, and they have a poorly defined neck. They have a tendency to rupture during attempted clipping or coiling, and hence, they have poor outcomes as compared to saccular aneurysms.[8] Most of the ruptured BBAs tend to present with large volume SAH, and hence, there is a high risk of developing vasospasm. Conventional clipping strategies are associated with a high risk of developing complications since there is a risk of intraoperative rupture of the aneurysm. The surgical strategies that have been tried with some success are direct clipping, encircling clip placement, vascular closure clip placement, wrapping with clipping, and trapping.[9] While the direct clipping approaches have a high risk of intraoperative rupture, trapping without bypass almost invariably leads to infarcts and poor outcomes, as reported by Meling et al.[10] In their series, internal carotid artery (ICA) sacrifice led to poor outcomes in all the 7 patients, while a vessel preserving strategy led to a good outcome in 6 out of 7 patients. The endovascular strategies that have been tried include coiling, stenting and coiling, balloon assisted coiling, multiple overlapping stents, and recently, FDs.

PAO without revascularization is a poor treatment for BBAs, as there is a very high risk of infarcts, even when there is evidence of excellent collaterals from anterior or posterior communicating arteries. For the ICA, collaterals from the anterior communicating artery are the most important, as there is a chance of sacrifice of posterior communicating artery during trapping of the aneurysm due to proximity of the aneurysm to the vessel. Despite excellent collaterals, there is a high risk of ischemia owing to vasospasm and increased intracranial pressure secondary to subarachnoid haemorrhage (SAH). In a meta-analysis of BBAs by Peschillo et al.,[11] only 68.1% patients who underwent direct attempts to clip the aneurysm, without any bypass, had a good outcome (modified Rankin's scale score [mRS] 0-2). In contrast, 17 out of 19 patients (89.5%) who underwent revascularization had excellent outcomes. Similar results have been reported by other authors, who have reported good outcomes in 81-90% of their patients with this approach.[12],[13],[14],[15],[16],[17],[18],[19],[20],[21],[22],[23] The reported rates of good outcomes with direct clipping procedures are 30-60%. Kazumata et al., changed their strategy from direct clipping to radial artery bypass and ICA sacrifice in 20 patients, and achieved a favorable outcome in 90% of the patients.[14] Hence, it is clear from the literature that PAO with bypass procedure is preferable to direct attempts at clipping.[15] Currently, FD is the preferred endovascular method of treatment of BBAs. Though there are many issues with FD in BBAs, including the need to use dual anti-platelet agents, delayed occlusion of the aneurysm with resultant risk of bleeding in the immediate postoperative period, and thrombo-embolic complications, many authors have reported their experiences with FD in BBAs. The largest series was published recently, in a multicenter experience of 49 patients with 51 BBAs, out of which 43 patients with 45 BBAs treated with PED were analyzed.[16] Long term good outcomes were seen in 68% of the patients as compared to 81-90% in the series with bypass surgery as the strategy. One patient had a fatal delayed re-rupture after initial treatment, and a total of 9 patients (20%) had peri-procedural complications. In their review, they found that 80.5% patients had a good outcome out of 36 patients with an ICA blister aneurysm. Hence, although FD is a promising treatment for BBAs, its inherent shortcomings makes PAO with high flow bypass an excellent alternative treatment for the same.

Intracranial dissections (ICDs) are another group of aneurysms for which parent vessel occlusion is the standard of treatment. Ruptured intracranial dissections are extremely unstable lesions, and have a very high risk of re-bleeding. ICDs are commonest in the posterior circulation, with most occurring along the course of the vertebral arteries or at the vertebrobasilar junction (VBJ), while the rest occur in basilar artery, or its branches like posterior inferior cerebellar artery (PICA), anterior inferior cerebellar artery (AICA), superior cerebellar artery (SCA) or posterior cerebral artery (PCA). PAO plays a very important role in the treatment of these aneurysms as well, as the aneurysms do not have a neck, and they basically are part of a disease involving the entire wall of the vessel. For the VBJ dissections, the treatment options need to factor in the location of the aneurysm, the cross circulation, dominance of the affected vertebral artery, location of branches and dominance of PICA or AICA.[17] The simplest of the scenarios is when PICA is either proximal or distal to the dissection, and not involved by the dissection. In that scenario, a simple parent artery occlusion suffices, if the other vertebral artery is either dominant or co-dominant. It is prudent to do a balloon test occlusion before occluding the artery. In patients who have single vertebral artery with dissection, a flow diversion strategy is probably warranted, though there is a significant risk of re-bleeding and thrombo-embolic complications associated with this strategy. In patients where a major branch like the PICA or SCA is involved, the choice is between deliberate occlusion of the involved artery, parent artery occlusion with bypass, or flow diversion. There is a high risk of infarction in the PICA territory or the medulla, if deliberate occlusion of the artery is performed. Lee et al., reported a 44% risk of ischemia, with 36% mortality in patients treated with occlusion of the vertebral artery in vertebrobasilar dissection (VBD).[18] Aihara et al., found a 30% incidence of medullary infarcts after PAO in patients with VBD.[19] They recommended reconstructive therapies in patients with VBD in close relation to the PICA or the anterior spinal artery.

In patients with VBD with vessel involvement, there are several options for revascularization. In a review article by Balik et al.,[17] various options of surgery for dissecting aneurysms of the posterior circulation were discussed. For PICA dissections, the revascularization can be with either the occipital artery, or using the contralateral PICA via a PICA-PICA bypass. Re-implantation of the PICA has also been reported by some authors. For SCA and PCA, either a STA-SCA bypass, or a radial artery graft from the proximal vertebral artery to the PCA has been reported. Hence, for VBD with major artery involvement, revascularization procedures are recommended, in view of the very high risk of ischemia with deliberate occlusion of the involved vessels.

FD is another treatment technique for those dissecting aneurysms, that have important side branches arising from the dissected segment. Many authors have reported their experience with FD in patients with dissecting aneurysms. However, as with BBAs, there are issues with the use of FD in patients with dissecting aneurysms. Fang et al., compared their experience with FD and PAO in dissecting aneurysms, and found that complete occlusion of the aneurysm was seen in 81.8% of patients undergoing PAO versus 55.6% in the FD group.[20] Procedure related complication rates were similar in both the groups, at 24% and 28%, respectively. Other authors have reported better outcomes. In a meta-analysis comparing reconstructive versus deconstructive strategies in VBD, PAO achieved higher occlusion rates as compared to reconstructive techniques (95% vs 83%), while the perioperative mortality was 13% in the deconstructive group as compared to 7% in the reconstructive group. Good long-term outcomes were seen in 88% of the reconstructive group as compared to 83% of the deconstructive group.[21],[22] Hence, for dissecting aneurysms, all the three treatments, PAO, PAO with revascularization and FD have a role in management, and the appropriate procedure should be chosen after considering various factors like dominance of the artery, cross flow, involvement of branch vessels and the age of the patient.

Recently, FD has emerged as an excellent treatment for large or giant aneurysms, complex or fusiform aneurysms and other aneurysms for which conventional endovascular methods have been unsuccessful. Most of the large and giant aneurysms had very high recurrence rates with the conventional methods of treatment. However, most of the aneurysms treated with FD have been unruptured aneurysms. In the setting of ruptured aneurysms, treatment with flow diverters has familiar challenges including the risk of immediate re-bleeding, risks associated with dual anti-platelets on a background of subarachnoid hemorrhage, risk of thrombo-embolism, and branch occlusion. However, as discussed above, flow diverters have been used in selected situations in the acute period, like BBAs, dissections and ruptured giant or fusiform aneurysms. Treatment with flow diverters in the acute phase has a higher complication rate than in patients with unruptured aneurysms. Lozupone et al.,[23] reported their experience with the use of FD in 17 patients with ruptured aneurysms, out of which 8 were BBAs and 9 had dissecting aneurysms. The mortality and morbidity were 12% each (with a combined morbidity and mortality of 24%). The angiographic complete occlusion rate was 80%, while the other 20% patients had either remnant of aneurysms or enlargement of the aneurysms. Madaelil et al., reported a meta-analysis of patients treated with FD in the acute phase.[24] They reported complete occlusion of the aneurysm in 90% of the patients, with good clinical outcomes in 81%. There was a 9% risk of composite post-procedure intracranial hemorrhagic complications; however, this was higher in patients with aneurysms sized more than 2 cm. Maus et al., reported their experience of FD in VBD, and found that although there was no rebleeding in the acute period, favorable outcome could be achieved only in 27% of the patients, while 47% of the patients died because of the morbidity associated with SAH.[25]

Murakami et al., noted that balloon test occlusion (BTO) did not decrease the complication rate in patients with a ruptured aneurysm.[26] BTO is widely used for patients of giant/fusiform aneurysm to check if they will tolerate parent artery occlusion. However, the effectiveness of BTO in patients with ruptured aneurysms may be limited, because of non-cooperation of patients, depressed levels of consciousness related to SAH, and a poor cerebrovascular reserve in patients with SAH-associated vasospasm. In such a scenario, an angiographic BTO may be performed, in which the venous phase delay is a reliable marker of the cross flow. Even when the cross flow is adequate, there may be a poor outcome following PAO with revascularization, as reported by Murakami et al.[26] In their series, though the revascularization was guided by BTO, there were acute ischemic complications in 10 out of 24 aneurysms, owing to perforator occlusion and thrombo-embolism. Other authors have also experienced higher incidences of ischemic complications in patients with ruptured aneurysms. Hence, it is important to consider this issue in patients with ruptured aneurysms. Patients at a high risk for vasospasm (poor clinical grade, higher Fisher grade) should be treated with alternative methods or a high-flow bypass if required, even when the cross-flow seems adequate.

The authors of the present study in focus have noted that the morbidity associated with distal vessel occlusion was similar to that associated with occlusion of larger aneurysms.[1] The morbidity associated with occlusion of PICA and SCA is quite high, as has been discussed before, and hence, there should be an attempt at revascularization or flow preservation, whenever there is a risk of deliberate occlusion of the end arteries. However, patients with distal PCA aneurysm have been reported to tolerate the occlusion very well. Chang et al.,[27] evaluated the role of bypass in 34 distal PCA aneurysms, and found that patients who underwent a bypass had worse outcomes as compared to those that did not. Their recommendation is to reserve revascularization in patients who fail BTO, and in those who cannot undergo procedures like stenting and coiling. Cotroneo et al.,[28] presented their experience with 4 patients who underwent PCA occlusion, and reported visual field deficits in 2 (50%) of them. Other authors have reported a lower incidence of visual field deficits. On angiography, it is better to do a BTO and ascertain if there are adequate collaterals from the pial branches of the MCA. A reconstructive approach may be better if there are inadequate collaterals. Andreou et al.,[29] presented their series of PAO in 27 patients with peripheral intracranial aneurysms, out of which 20 patients had SAH/intracranial hemorrhage. Ischemia in the involved territory was seen in 27.7% of the patients who underwent PAO. However, only 11.1% of the patients with PCA occlusion developed visual field deficits.

In summary, PAO, bypass and reconstructive surgery with flow diversion and vessel preservation are appropriate treatments for patients with ruptured aneurysms who are not good candidates for conventional surgical or endovascular treatment. All these treatments have worse results in patients with ruptured aneurysms, as compared to the those with unruptured aneurysms. A judicious treatment must be chosen, and the treatment should be individualized. Parent artery occlusion with revascularization remains an important treatment of complex intracranial aneurysms.



 
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