|Year : 2021 | Volume
| Issue : 2 | Page : 61-67
Microsurgery of complex intracranial aneurysms
Basant K Misra1, Harshad R Purandare2
1 Department of Neurosurgery and Gamma Knife Surgery, P D Hinduja National Hospital and Medical Research Centre, Mumbai, Maharashtra, India
2 Department of Neurosurgery, Jupiter Hospital, Thane, Maharashtra, India
|Date of Submission||14-Jan-2022|
|Date of Decision||20-Jan-2022|
|Date of Acceptance||21-Jan-2022|
|Date of Web Publication||5-Apr-2022|
Prof. Basant K Misra
Department of Neurosurgery and Gamma Knife Surgery, P D Hinduja National Hospital and Medical Research Centre, Mumbai, Maharashtra
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Misra BK, Purandare HR. Microsurgery of complex intracranial aneurysms. J Cerebrovasc Sci 2021;9:61-7
| Introduction|| |
Aneurysms with a complex configuration are typically aneurysms that are not amenable to current endovascular therapy (EVT). EVT is ideally suited for those aneurysms that are most readily treated by microsurgery. Post-ISAT, as EVT has become the treatment of choice for a large number of simple and straightforward aneurysms, microsurgery will be required for the treatment of an increasingly complex population of aneurysms, either independently or in combination with EVT., Neurosurgeons, hence, need to be trained to optimize their surgical skills and innovative capacities to device strategies to treat these lesions.
[TAG:2]Definition of Complex Aneurysms,,[/TAG:2]
Giant and complex aneurysms are not synonymous. There are numerous factors other than size that make a given intracranial aneurysm “complex.” These factors include:
- Location: Difficult access
- Configuration: Complicated wall structure, blister aneurysms, involving arterial trunks and branches, pseudoaneurysms, intraluminal thrombus, wall calcification, presence of intraluminal thrombus, mural or parent vessels calcification
- Size: Very large and giant aneurysms
- Failed surgical or failed endovascular treatment (acute, recent, or past).
[TAG:2]Preoperative Tests and Evaluation,[/TAG:2]
Three-dimensional (3D) computed tomography (CT) scan with CT angiography as well as magnetic resonance (MR) imaging scan with MR angiography gives vital information. A 4 vessel 3D DSA (with cross compression study and Allcock's test) of giant and complex aneurysms provides dynamic information about the direction and extent of blood flow, amount of collateral flow, hypoplastic or aplastic segments, and filling component of the aneurysmal sac. Balloon Occlusion Test (BOT):, BOT determines the tolerance of patients to the sacrifice of the internal carotid artery (ICA). To increase its sensitivity, it is combined with adjuncts: HMPAO single-photon emission computed tomography, Stable Xenon-enhanced CT cerebral blood flow measurement (Xe CT-CBF), transcranial Doppler study and induced hypotension to help patient selection. The test has a 2%–8% complication rate and a 1.5%–4.8% risk of stroke following ICA sacrifice despite a well-tolerated BOT. If BOT evokes neurological deficits, a high-flow bypass (extracranial-to-intracranial [EC-IC]) is recommended. The senior author prefers performing bypass before surgical occlusion of any major intracranial artery regardless of the nature of collateral flow in younger patients, and patients presenting with SAH.
| Perioperative Management and Adjuncts|| |
Perioperative monitoring often includes physiological studies such as electroencephalogram (EEG), somato-sensory evoked potential (SSEP) and brainstem auditory evoked response (BAER). Flow studies include intraoperative DSA, indocyanine green videoangiography (ICGVA), fluorescein angiography, and microvascular Doppler.,, Mild (ambient) hypothermia to a core temperature of 33°C–34°C is achieved by cooling blanket and reduction of the overall operating room temperature. The use of intravenous barbiturates or propofol titrated to electroencephalographic burst suppression enhances cerebral protection. Induced hypertension (20% over the baseline systolic pressure) with pharmacological cerebral protection, when administered before periods of temporary clipping is most effective to prevent focal ischemic injury. Occasionally, treatment of these lesions needs adjunct techniques such as deep hypothermia and circulatory arrest. But with safer techniques often used in combination, such as induced hypotension, mild hypothermia, barbiturate or propofol-induced burst suppression, adenosine-induced asystole, and rapid ventricular pacing, deep hypothermic arrest is considered only in rare case scenarios when the above techniques are deemed inadequate.,,
[TAG:2]Treatment of Complex Aneurysms [1,4-6,11][/TAG:2]
The surgical strategy for complex aneurysms is decided on the basis of preoperative neuroradiological and intra-operative determinants.
The main goals of surgery are:
- Exclusion of the aneurysm from the circulation
- Preservation of distal blood flow, and
- Decompression of neural structures.
The possible options are:
- Direct aneurysm clipping with/without vessels reconstruction by clips (with “protective” bypass in case of prolonged temporary occlusion)
- Complete trapping with flow “replacement” bypass. It can be of two types:
- Classic: The aneurysm and all the branches originating from the aneurysmal segment are excluded.
- Variant: The aneurysm is completely occluded with sacrifice of one or more, but not all, of the branches arising from the aneurysmal segment.
Complete trapping without bypassPartial trapping– proximal or distal with flow diversion. The aneurysm is not completely excluded from the circulation.
Skull base approach, wide opening of the sylvian fissure and cisterns, minimal or no retraction, and preservation of veins are some of the basic principles for safe microsurgery of complex aneurysms.
The authors currently utilize dedicated skull base approaches more often in aneurysm surgery than in surgery of skull base tumors. Skin incision should be well planned and carefully taken in an attempt to preserve the STA trunk and its branches (or the OA in far lateral approach) for potential anastomosis, as a supply pedicle for an interposition graft, or as a contingency measure for any unexpected requirement during surgery.
[TAG:2]Surgical Clipping Techniques of Giant and Complex Aneurysms,,,[/TAG:2]
Once vascular control has been achieved, attention is directed toward reducing the mass of the aneurysm in giant aneurysms [Figure 1] and [Figure 2]. This provides more working space and enhances visualization of neck of the aneurysm, branches, and perforators. For soft aneurysm with the absence of thrombus or calcification and a favorable anatomy, temporary clipping provides adequate softening for direct clip occlusion. Reconstruction of complex aneurysms by clips can be possible after thrombectomy in case of partially thrombosed aneurysm. Sometimes even direct vessel reconstruction is a valid option. These treatment modalities need a “protective” bypass when prolonged temporary occlusion time is needed., Occasionally, parent vessel reconstruction with obliteration of aneurysm may be possible by multiple tandem clipping technique with fenestrated clips applied in series to create a vascular channel through the fenestration. In the presence of significant thrombus or calcification, the aneurysm may require an aneurysmotomy after temporary clipping to evacuate the clot using suction, sharp dissection, or CUSA.
|Figure 1: (a and b) Clipping of a complex right middle cerebral artery bifurcation aneurysm using multiple clips|
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|Figure 2: (a) Complex giant aneurysm of the left vertebral artery. (b) Isolation of aneurysm between temporary clips followed by aneurysmotomy and excision. (c) Reconstruction of the vertebral artery using multiple tandem clips|
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Sometimes, the aneurysm may require excision to relieve mass effect and in such cases, complex reconstruction of the parent artery from the cut ends of the aneurysm wall with clip application or microvascular suturing may be needed. Even when everything seems satisfactory, use of microvascular Doppler, ICGVA, and if needed intraoperative angiography is mandatory to confirm the same.
| Blister Aneurysms|| |
The term “blister aneurysm” has been used to describe aneurysms arising from nonbranching sites of the wall of the supraclinoid ICA. Compared with saccular aneurysms, these lesions tend to have a more precipitous clinical course, enlarging rapidly and rebleeding frequently. Surgical treatments have included encircling clip grafts, aneurysm wrapping, clip wrapping, trapping with or without an EC-IC bypass, and primary suturing.
| Residual and Recurrent Aneurysm– Post-microsurgery|| |
Residual aneurysms are treated aneurysms with incomplete obliteration or persistent aneurysm filling angiographically immediately after treatment. On the other hand, those with incomplete obliteration or persistent filling angiographically at later follow-up (3 months or more) are referred to as recurrent aneurysms. These are due to a regrowth of a new aneurysm lobe or sac from a dysplastic or incomplete excluded neck.,, Microsurgical re-intervention is usually advocated but can be technically difficult due to scarring around the clip or an unstable medical condition secondary to a rebleed. Endovascular embolization may represent a good alternative for these special situations.
|Figure 3: (a) Residual coiled left internal carotid artery bifurcation aneurysm with coil mass in the neck. (b) Clipping of the aneurysm after manipulation of the coil mass|
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The lower risk of death and dependence in endovascular procedures at 1 year, as demonstrated by ISAT and BRAT trials, does not eliminate the fact that endovascular treatment inherently has lower rates of complete aneurysm occlusion and higher rates of aneurysm recurrence during long-term follow-up. This results in an increased rate of rebleeding and increased incidence of a technically challenging recurrent coiled aneurysm-needing treatment.,,
The difficulty in managing patients with aneurysm recurrences lies in distinguishing unstable aneurysm residuals, potentially prone to hemorrhage, from benign nonprogressing neck remnants, and thus to identify those patients who will need further treatment. The rebleeding rate is 0.4% for stable nonprogressing aneurysmal remnants after endovascular treatment versus 7.9% for angiographically unstable aneurysm residuals.
The decision to treat such a lesion with repeat coiling or open surgery is often difficult. Surgery is challenging due to the unyielding coil mass, fibrosis, and poor visualization. Numerous studies observed low complications during endovascular re-treatment of previously embolized aneurysms and suggested that the procedural morbidity for re-treatment may be even lower than for initial coiling. Hence Gurian, Dorfer, Kang, and others recommended attempting endovascular options in possible cases before considering surgery.,, On the contrary, the CARAT study identified life-threatening complications in 11% cases undergoing recoiling procedures.,
Dorfer et al. noted that in aneurysms with coil compaction, in the absence of aneurysmal growth or intra-aneurysmal thrombus, recoiling resulted in angiographically stable results in 78.7%. On the contrary, lesions with detectable growth of the aneurysmal sac failed or had suboptimal reembolization in 87.5% of cases. Hence, many neurosurgeons consider surgical options as more appropriate unless there is a high risk of surgical morbidity and mortality.,,,,,,,
The surgical options include (a) direct clip occlusion without coil manipulation; (b) aneurysmotomy with thrombectomy and coil extraction followed by clipping; and (c) parent artery occlusion with bypass. The first option is the preferred line of treatment and is usually possible in more than three fourth of the cases, wherein adequate coil compaction can be achieved to create a soft clippable aneurysm neck. The clip can be applied across the neck or across a few redundant loops of the coil or even a small portion of a pliable coil mass. A perfect and exacting clip placement is not mandatory. The clip blades must close parallel to the long axis of the parent vessel. Any other clip application technique will place the neck of the aneurysm at risk of injury.,,
Extreme types of such aneurysms or those of the posterior circulation may need indirect methods to include trapping or proximal occlusion with/without bypass and on rare occasions, wrapping as a last resort when other methods of aneurysm exclusion fail.,,,
Surgery is the primary treatment of most thrombotic aneurysms, considering the high recurrence rates after coiling. According to Lawton et al., the thrombus morphology determines neck compliance and thus decides the operative technique. Only the eccentric thrombotic aneurysm has a compliant neck and can be clipped primarily. Results of Lawton's series indicate that while direct clipping has the best surgical results, for the majority of thrombotic aneurysms that cannot be clipped directly, bypass and occlusion of the artery may be the preferred alternative strategy. Hence, preparedness to perform an EC-IC bypass, if patency of the parent vessel and its branches cannot be maintained or if there is inadequate collateral circulation is essential when such cases are taken for surgery.
[TAG:2]Trapping of Complex Aneurysms,,,,[/TAG:2]
Trapping strategies are combined with flow replacement bypass. The choice of “complete” or “partial” trapping depends on the aneurysmal and peri-aneurysmal anatomy. Complete trapping immediately excludes the aneurysm from circulation and is the preferred whenever feasible. However, complete trapping can be sometime hazardous when perforating vessels arise from the aneurysm sac. In these cases, partial trapping strategies are the preferred option – these can be proximal “inflow” occlusion or distal “outflow” occlusion. Either of the options stagnate the flow within the aneurysm, decreasing the hemodynamic stress. Unfortunately, prediction and control of the amount and the speed of the thrombosis are not possible. Rapid and complete thrombosis may occlude the perforators which were to be preserved. Moreover, a partially thrombosed aneurysm still carries the risk of rupture.
A shown in [Figure 4], [Figure 5], [Figure 6], the selection of the ideal bypass procedure (EC-IC vs. IC-IC; occlusive versus non-occlusive, etc.) depends on several factors such as the amount of flow to the occluded (temporary or permanently) arterial territory, the intracranial vascular angioarchitecture (collaterals, hypoplastic or dominant vessels), and the availability and anatomy of donor and recipient vessels.,,,,,,,,,,,,,,
|Figure 4: (a and b) Extracranial-to-intracranial bypass using radial artery graft|
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|Figure 5: Occipital to posterior inferior cerebellar artery (P4 segment) bypass for a fusiform aneurysm of the left P2 and P3 segment of the posterior inferior cerebellar artery|
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|Figure 6: (a and b) Trapping of left A2-A3 segment complex aneurysm followed by in situ DACA-DACA bypass|
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[TAG:2]Intraoperative Rupture - A Simple Aneurysm Made Complex,,,,,,[/TAG:2]
The main factors that contribute to intraoperative rupture are (1) brain retraction in early phase with adherent aneurysms; (2) inadequate and blunt dissection of the aneurysmal neck; and (3) poor application or transposition of the clip. In general, the incidence is significantly higher in anterior circulation aneurysms and occurs either during aneurysm dissection or clip application/clip manipulation. A rupture is better avoided than managed. Adequate exposure by skull base approaches along with wide splitting of the arachnoid planes, sharp dissection around the aneurysm, and avoidance of unessential retraction minimizes the risk of premature rupture. The use of temporary clipping liberally reduces the risk of rupture in the final stages of dissection. It is imperative to expose the feeding vessels for vascular control before approaching the aneurysm neck.
When an intraoperative rupture occurs, deliberate, precise, and decisive steps and decisions will achieve optimum patient outcome.
| Summary and Conclusion|| |
Advances in EVT have made EVT an attractive option in the treatment of aneurysms. With more and more common garden aneurysms going the EVT way, microsurgery is more often employed for complex aneurysms. Their management is problematic because of the wide atheromatous neck, involved branches, thrombus within, calcified wall, large size, complex anatomy, and previous failed treatment. Yet, these need treatment because of their disastrous natural history. Any decision to intervene should carefully consider the various options such as microsurgery, EVT, and observation. The treatment should be patient-centric taking all the patient factors, pathological factors, and expertise available and any intervention should be expected to better the natural history. There have been many advances in recent years in microsurgery. Skull base approaches, neuroprotection measures, adjuncts such as adenosine-induced cardiac standstill, rapid ventricular pacing, extracorporeal circulation, intraoperative ICG angiography, innovative use of clips, and various bypass techniques have made it possible to achieve satisfactory results in majority of complex aneurysms bettering the natural history and other options. However, their treatment is a major endeavor and should not be taken up by the occasional aneurysm surgeon. Experienced groups in specialized centers with all available resources are best suited to tackle these life-threatening pathologies.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]