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|THE EDITORIAL DEBATE
|Year : 2015 | Volume
| Issue : 2 | Page : 138-141
Treatment of giant intracranial aneurysms: What is the best option?
Basant Kumar Misra
Department of Neurosurgery and Gamma Knife Surgery, P.D. Hinduja National Hospital and Medical Research Centre, V.S. Marg, Mahim, Mumbai, Maharashtra, India
|Date of Web Publication||5-May-2015|
Basant Kumar Misra
Department of Neurosurgery and Gamma Knife Surgery, P.D. Hinduja National Hospital and Medical Research Centre, V.S. Marg, Mahim, Mumbai, Maharashtra
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Misra BK. Treatment of giant intracranial aneurysms: What is the best option?. Neurol India 2015;63:138-41
Giant intracranial aneurysms (GIA) have been defined as those that are greater than 25 mm. Aneurysms (including the GIA) may be of congenital or acquired origin.  Either way, these are treacherous lesions with a grave prognosis. Their management is problematic because of the presence of a wide atheromatous neck, the involved branches, a thrombus within, a calcified wall and a complex anatomy. Yet, patients with GIAs need treatment as their natural history is terrible. Left alone, the mortality rate at 2 and 5 years after their diagnosis is 68% and 85%, respectively. 
Over the years, there have been refinements in both the endovascular treatment (EVT) and microsurgical techniques in tackling intracranial aneurysms. While majority of the small saccular aneurysms are optimally excluded from the circulation by the EVT, there is a high failure rate after EVT of GIA due to the unique aneurysm morphology that includes a broad neck, giant size, outflow arteries arising from the aneurysm, and often, a fusiform shape. Coiling of a broad-necked aneurysm may result in herniation of coils into the parent artery lumen. Adjuncts like balloon and stent-assisted coiling techniques increase the feasibility of treatment but at a high price; the additional risk of parent artery ischemia, perforation, distal thromboembolism and occlusion of adjacent perforators and branch arteries by the lattice of the stent.  There is also an unacceptably high risk of recurrence of GIAs after an EVT because of the complex hemodynamics at the inflow zone, incomplete initial obliteration, thrombus within the lumen, poor radiographic visualization of the aneurysmal anatomy and its adjacent branches, and tortuosity of the feeding vessels making catheterization difficult.  Flow diverters have a lot of potential but it is still too early for the procedure to occupy the "prime time" slot.
In their article "Endovascular management of giant aneurysms: An introspection" in the current issue, Zhang et al. have reported a retrospective analysis of their experience with giant GIAs. Out of 39 cases seen by them, 30 were managed by EVT and 9 did not undergo any intervention. As expected, within a short follow up of two and a half years, 67% patients left untreated had died or deteriorated. While the mortality and morbidity in the EVT group was better, yet at only a 28-month follow up, 30% patients had either died or become disabled. In fact, when only the patients managed by EVT other than parent vessel occlusion (PVO) were analyzed, the mortality and treatment morbidity rate was a high 37%! The outcome with a longer follow up is bound to be higher as the post-procedural complete occlusion achieved by the authors was only 50%. Two of their patients who had a presumed complete occlusion experienced re-hemorrhage. The article "Endovascular management of giant aneurysm: An introspection" is indeed very appropriately titled. Introspection is definitely the need of the hour!
The poor results of EVT are not surprising. Jahromi et al. found a cumulative morbidity and mortality of 55% over 24.8 months of clinical follow up following an EVT for GIAs.  Darsant et al. also reported a higher morbidity and mortality rate of 23% and 20% respectively, after an EVT as compared to a peri-procedural morbidity and mortality rate of 15% and 14%, respectively, following microsurgery of very large and giant aneurysms. Moreover, they also found the EVT to be a contributory factor for a higher incomplete occlusion rate of a large-to-giant aneurysm. ,
Limaye et al. reported their results with the EVT in 22 cases of giant posterior circulation aneurysms treated over 13 years. Complications occurred in 41 percent of patients. The mortality and morbidity in their series was 18 and 22%, respectively. On a closer analysis of their data, it was again obvious that the patients treated with parent vessel sacrifice did better than when any other modality of EVT was used.  Gao et al. reported their experience with 71 consecutive patients with a large or a giant aneurysm managed using a neuroform stent.  Immediate angiographic occlusion was achieved in only 59.7% patients and the overall recanalization rate was 28.8%. Gonzalez et al. also reflected on the inadequacy of endovascular management of GIAs in their article. They concluded, "Although there is a wide variety of endovascular therapeutic options for the treatment of GIAs, none of the current techniques is completely successful and free of complications in the management of these complex lesions." 
The initial promising reports with flow diverting stents (FDS) in the treatment of aneurysms have led many centers to attempt the treatment of GIAs with flow diverters like the pipeline embolization device (PED). , Cherian et al., reported the first Indian experience with PED in 5 cases of intracranial aneurysms with excellent results. However, the follow up was very short (only 6 months). Moreover, there were no GIAs in their series.  PED have been particularly suitable for ICA aneurysms proximal to the ophthalmic artery. In fact, in USA, PED has FDA approval since April 2011, for large and giant wide-necked aneurysms in the internal carotid artery (ICA) arising from the petrous to superior hypophyseal segments. While the procedure is promising, the fact that a flow diverter is not a panacea is evident from the recent reports of many complications associated with treatment with FDS. Siddiqui et al. reported their experience with 7 patients treated with FDS for large or giant fusiform vertebrobasilar aneurysms. During the follow up, 4 patients had died and one was seriously disabled.  The authors cautioned against its wide spread use for vertebrobasilar fusiform aneurysms. Ertl et al. reported their experience with 6 patients having a fusiform vertebrobasilar giant aneurysm who had been treated with FDS. Within a mean follow up of 13 months, 4 patients had died and the other 2 were severely disabled. The authors concluded that they do not intend to treat fusiform vertebrobasilar giant aneurysms with FDS until further understanding of the situation evolves.  Another issue in the endovascular treatment of GIAs is the inability to relieve the mass effect. The combined mass of the thrombosed aneurysm and the coils or other embolized mass may further worsen the patient and risk his/her life.  To salvage this situation is extremely difficult. 
Thus, while FDS represent a significant advancement in the EVT of GIAs, it is not a panacea. Microsurgery of GIAs is neither easy nor can all GIAs be treated this way. Yet, there are many advances and novel microsurgical approaches that can provide solutions to many GIAs. Moreover, the mass effect of GIAs is better relieved by microsurgery. The neurosurgical solution is often simple, economical and avoids the use of long-term antiplatelet medication. The various technical advances that have helped us in tackling many of the GIAs microsurgically are the utilization of skull base approaches, the use of little or no brain retraction, introducing novel clipping techniques, endoscopic assistance to visualize perforators and completeness of aneurysm occlusion, utilization of various revascularization techniques for vessel replacement, use of adenosine asystole to soften the aneurysm before its clipping or in the case of its premature rupture, and very rarely, a hypothermic cardiac arrest. , Concurrent technological advances, a preoperative three-dimensional digital subtraction angiography, and an intraoperative microvascular Doppler and indocyanine green (ICG) angiography, have also helped. 
A summary of the various neurosurgical options that have helped us to manage GIAs are as follows:
- Proximal ligation/trapping without revascularization: Symptomatic GIAs of proximal ICA that need treatment may be managed with simple ICA ligation in the neck without revascularization. This is especially appropriate for elderly patients having an excellent collateral circulation and those who tolerate balloon test occlusion (BTO). The procedure is simple, having a low risk and is economical.
- Proximal ligation/trapping of the parent artery with external carotid-to-internal carotid artery (ECIC) bypass. Parent artery sacrifice and an ECIC bypass is a particularly useful option for GIAs on the ICA proximal to the ophthalmic artery and is a low risk, economical and time-tested procedure as compared to the FDS. Young patients, patients with bilateral aneurysms, patients with a recent-onset subarachnoid hemorrhage, and elderly patients not tolerating a BTO are appropriate candidates for this procedure. This is well exemplified by the following successfully performed procedure. A 45-year-old lady presented with a right-sided painful ophthalmoplegia. The digital subtraction angiogram and the computed tomographic angiogram (CTA) of the brain demonstrated bilateral carotico-cavernous aneurysms. The left one was small and asymptomatic. The right aneurysm was giant and was the symptomatic one. Since she had bilateral aneurysms, BTO was not performed. A right ICA ligation in the neck was carried out following an external carotid artery (ECA) - M2 segment of the middle cerebral artery radial artery graft (RAG) bypass. The patient recovered uneventfully and was relieved of her painful ophthalmoplegia. The postoperative CTA confirmed the patency of the RAG, occlusion of the right ICA and non-filling of the aneurysm. [Figure 1]
|Figure 1: (a) Preoperative computed tomography angiogram (CTA) demonstrating bilateral carotid cavernous aneurysms; and (b) postoperative CTA showing occlusion of the right internal carotid artery as well as non-filling of aneurysm and a patent radial artery graft bypass graft|
Click here to view
- Excision/decompression of the aneurysm, trapping of the parent artery and an ECIC bypass: Occasionally, the GIA may be acting as a big mass and may need to be decompressed before revascularization can be carried out, as was done in the following patient. A 27-year-old man had presented at another center in a comatose state due to the development of an acute subdural hematoma from a huge (8cm) right ICA (from petrous to supraclinoid segment) aneurysm. He survived a decompressive craniectomy and was referred to us for the definitive management of his aneurysm. He also had another asymptomatic basilar top aneurysm. He had almost completely recovered and refused any intervention only to return back after a few months with intractable headache and progressive hemiparesis. The right ICA was trapped by occluding it in the neck and in the supraclinoid segment, the aneurysm was decompressed in the middle cranial fossa (MCF), and an ECA-M2 RAG graft was successfully performed without any morbidity. Subsequently the basilar top aneurysm was also clipped in a subsequent sitting.
- Direct clipping: Most of the intradural GIAs in our practice have been managed by direct clipping. Novel clipping techniques like the tandem clipping, aneurysmorrhaphy with various combination of clips, such as the fenestrated clips and booster clips, permit successfully occlusion of many aneurysms. Adenosine asystole has been an excellent adjunct to soften the aneurysm before its definitive clipping. It is important not to compromise the parent artery when occluding these thick-walled GIAs. Intraoperative ICG angiography as well as endoscopic assistance have significantly helped in confirming the patency of parent and branch arteries as well as in documenting complete occlusion of the aneurysm. 
Occasionally, we have performed a protective bypass to maintain circulation when prolonged temporary clipping was anticipated so as to avoid ischemic injury to the patient.
- Combined microsurgery and EVT: Some GIAs are best managed by a combination of planned microsurgery and an EVT. An early EVT with partial coiling in a sick patient to protect the aneurysm with partial occlusion, followed by a definitive microsurgical clipping is an option that results in complete occlusion and reduced morbidity. Occasionally a small residual aneurysm, left behind to prevent compromise of a branch or perforators after microsurgical clipping or EVT, can be safely coiled or clipped later on resulting in a satisfactory outcome.
- Microsurgical clipping under deep hypothermic circulatory arrest: The technique of deep hypothermic circulatory arrest has evolved but still results in a significant mortality and morbidity in a third of the patients. Hence, it has been infrequently utilized in the author's practice and has been limited to a few giant basilar trunk or basilar top aneurysms.
In summary, it is necessary to be proficient in utilizing the various options as the treatment of GIAs is a formidable task. Any decision to treat these aneurysms should weigh the various options like microsurgery, EVT and observation. The treatment should be patient-oriented after taking into consideration the particular aspects of an individual case and the expertise available locally. Any intervention is expected to be better than the natural history of the disease. Most GIAs need treatment except for the asymptomatic or minimally symptomatic ICA cavernous aneurysms and some fusiform aneurysms. Many advances in the EVT and its continuing evolution make it an attractive option for the treatment of GIAs. Unfortunately, the high incidence of incomplete treatment, delayed complications, recurrence, and inadequate long-term follow-up data after the instillation of the flow diverters still makes microsurgery the treatment of choice in the majority of GIAs. There have been many advances in recent years in microsurgery. Skull base approaches, neuro-protective measures, adjuncts like adenosine-induced cardiac standstill, rapid ventricular pacing, extracorporeal circulation, intraoperative ICG angiography, endoscopic assistance, and the innovative use of clips and various bypass techniques, have made it possible to achieve satisfactory results in the majority of GIAs showing an improved outcome that is better than the natural history of the disease. However, the treatment of GIA is a major endeavor and should not be taken up by the occasional aneurysm surgeon or endovascular therapist. Committed groups in specialized centers having access to all available resources are best suited to tackle these life-threatening GIAs.
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