Intracranial aneurysm clipping

Intracranial aneurysm clipping

Evolution in the surgical treatment of intracranial aneurysms is driven by the need to refine and innovate. From an early application of the Hunterian carotid ligation to modern-day sophisticated aneurysm clip designs, progress was made through dedication and technical maturation of the cerebrovascular neurosurgeons to overcome challenges in their practices. The global expansion of endovascular services has challenged the existence of aneurysm surgery, changing the complexity of aneurysm case mix and volume that are presently referred for surgical repair. Concepts of how to best treat intracranial aneurysms have evolved over generations, and will continue to do so with further technological innovations. As with the evolution of any type of surgery, innovations frequently arise from the criticism of currently available techniques 1).


Intracranial Aneurysm treatment with surgery remains the recommended form of treatment in high-grade SAH patients with intracerebral space occupying hematomas, where the surgical decompression of the mass effect may be warranted, and along with it the clipping of the bleeding aneurysm.

Less invasive surgical approaches for intracranial aneurysm clipping may reduce length of hospital stay, surgical morbidity, treatment cost, and improve patient outcomes.

In the US, a number of training programs are including endovascular exposure to residents during their training, assuming the endovascular suite as a regular OR room.

The training of surgeons in both techniques seems promising and the right way to go, regardless of whether a dually trained neurosurgeon will end up opting for the use of one technique over the other. The important is that we guarantee the ability to deliver our patients the best possible care by providing them with a choice that is not born out of a turf war but based on evidence both on a general, but similarly important, local one 2).

Time from rupture to treatment is a crucial factor in determining outcome.

Practice of delayed surgery to avoid edematous brain has been replaced by early surgery to minimize risk from rebleeding and vasospasm. Mahaney et al. in their analysis of intraoperative hypothermia for aneurysm surgery trial (IHAST) data observed that patients operated early (day 0-2) or late (day 7-14) fared significantly better than those operated during intermediate phase (day 3-6). Change in surgical strategy has posed challenge to the anesthesiologists as increasing number of patients are operated during off-work hours in inadequately optimized state with less expert help.


Nieuwkamp et al., performed a retrospective observational study on the timing of intracranial aneurysm surgery in The Netherlands over a two-year period.

In eight hospitals they identified 1,500 patients with an aneurysmal subarachnoid hemorrhage. They were subjected to predefined inclusion criteria. They included all patients who were admitted and were conscious at any one time between admission and the end of the third day after the haemorrhage. We categorised the clinical condition on admission according the World Federation of Neurological Surgeons (WFNS) grading scale. Early aneurysm surgery was defined as operation performed within three days after onset of subarachnoid haemorrhage; intermediate surgery as performed on days four to seven, and late surgery as performed after day seven. Outcome was classified as the proportion of patients with poor outcome (death or dependent) two to four months after onset of subarachnoid haemorrhage. We calculated crude odds ratios with late surgery as reference. We distinguished between management results (reconstructed intention to treat analysis) and surgical results (on treatment analysis). The results were adjusted for the major prognosticators for outcome after subarachnoid haemorrhage.

They included 411 patients. There were 276 patients in the early surgery group, 36 in the intermediate surgery group and 99 in the late surgery group. On admission 78% were in good neurological condition (WFNS I-III). MANAGEMENT

Overall, 93 patients (34%) operated on early had a poor outcome, 13 (36%) of those with intermediate surgery and 37 (37%) in the late surgery group had a poor outcome. For patients in good clinical condition on admission and planned for early surgery the adjusted odds ratio (OR) was 1.3 (95% CI 0.5 to 3.0). The adjusted OR for patients admitted in poor neurologicalcondition (WFNS IV-V) and planned for early surgery was 0.1 (95% CI 0.0 to 0.6). SURGICAL RESULTS: For patients in good clinical condition on admission who underwent early operation the adjusted OR was 1.1 (95% CI 0.4 to 3.2); it was 0.2 (95% CI 0.0 to 0.9) for patients admitted in poor clinical condition.

In this observational study they found no significant difference in outcome between early and late operation for patients in good clinical condition on admission. For patients in poor clinical condition on admission outcome was significantly better after early surgery. The optimal timing of surgery is not yet settled. Ideally, evidence on this issue should come from a randomised clinical trial. However, such a trial or even a prospective study are unlikely to be ever performed because of the rapid development of endovascular coiling 3).

The guidelines relevant to the anesthesiologists in the day-to-day perioperative management of patients with ruptured intracranial aneurysm given by various societies are:

Diringer MN, Bleck TP, Claude Hemphill J, 3rd, Menon D, Shutter L, Vespa P, et al. Critical care management of patients following aneurysmal subarachnoid hemorrhage: Recommendations from the Neurocritical Care Society’s Multidisciplinary Consensus Conference. Neurocrit Care. 2011;15:211–40.

Bederson JB, Connolly ES, Jr, Batjer HH, Dacey RG, Dion JE, Diringer MN, et al. Guidelines for the management of aneurysmal subarachnoid hemorrhage: A statement for healthcare professionals from a special writing group of the Stroke Council, American Heart Association. Stroke. 2009;40:994–1025.

Steiner T, Juvela S, Unterberg A, Jung C, Forsting M, Rinkel G, et al. European Stroke Organization guidelines for the management of intracranial aneurysms and subarachnoid haemorrhage. Cerebrovasc Dis. 2013;35:93–112.


Both intravenous and inhalational anesthetic technique may be used for maintenance keeping in mind the objectives of stable intraoperative hemodynamics, early smooth recovery and effect on special monitoring techniques. Cerebral perfusion increases with isoflurane when compared with propofol without increase in ICP in aSAH.

Hypocapnia is not essential in good grade patients as it can reduce ICP and increase transmural pressure within aneurysmal sac predisposing it to rupture. In poor grade patients, hyperventilation however is beneficial to reduce ICP and provide lax brain.

Brain laxity is crucial to obtain good surgical access to the aneurysm without causing IOAR or compromising underlying brain from excessive retractor pressure. This is important as early surgery risks a tense/full brain and dissection without adequate exposure can result in IOAR. Both 20% mannitol and 3% hypertonic saline are suitable osmotic agents for intraoperative brain relaxation in the dose of 2-4 ml/kg. Head end elevation, avoiding jugular venous compression, avoiding high concentration of inhalational agents and nitrous-oxide and mild hyperventilation are other measures to achieve a lax brain. If full brain persists, additional measures like moderate hyperventilation, switching to intravenous anesthetic maintenance and release of cerebrospinal fluid might be helpful. 4).

Intracranial aneurysm surgery by clipping requires meticulous technique and is usually performed through open approaches. Endoscopic endonasal clipping of intracranial aneurysms may use the same techniques through an alternative corridor.

To enhance visual confirmation of regional anatomy, endoscopy was introduced.

see Endoscopic endonasal approach for intracranial aneurysm

see Surgical clipping versus endovascular coiling for intracranial aneurysm

Clipping is an important technique for intracranial aneurysm surgery. Although clip mechanisms and features have been refined, little attention has been paid to clip appliers. Clip closure is traditionally achieved by opening the grip of the clip applier. Sato et al.. reconsidered this motion and identified an important drawback, namely that the standard applier holding power decreased at the moment of clip release, which could lead to unstable clip application develop a forceps to address this clip applier design flaw.The new clip applier has a non–cross-type fulcrum that is closed at the time of clip release, with an action similar to that of a bipolar forceps or scissors. Thus, a surgeon can steadily apply the clip from various angles. They successfully used the clip applier to treat 103 aneurysms. Although training was required to ensure smooth applier use, no difficulties associated with applier use were noted. This clip applier can improve clipping surgery safety because it offers additional stability during clip release. 5).

Pterional approach via standard frontotemporal craniotomy and interhemispheric approach via bifrontal craniotomy is the gold standard for clipping of cerebral aneurysms in the anterior circulationEndovascular treatment is now widely used, but subsets of aneurysms are still indicated for surgical clipping. Modern technological advances allow less invasive clipping techniques such as the keyhole approach. Mori and Watanabe discussed the surgical indications, preoperative simulation, surgical techniques, and pros and cons of keyhole (supraorbital) clipping. Selection of standard craniotomy or keyhole craniotomy should be uncontroversial, but keyhole clipping requires definite surgical indications based on the characteristics of the target aneurysm for safe clipping 6).

see Intracranial aneurysm clipping complications.

A challenge is to ensure noninclusion of normal vessel/perforators within the clip and perform complete aneurysmal isolation. This is done with either intraoperative microvascular Doppler sonography (IMD) or Indocyanine green videoangiography (ICG-VA) as they are simple and safe. Anesthesiologists administer ICG and also help perform IMD. ICG-VA appropriately assessed vessel patency and aneurysm obliteration in 93.5% of 109 aneurysms clipped 7) However, ICG can cause transient oxygen desaturation 8). IMD use confirms aneurysm isolation and patency of parent vessel and branching arteries. Hui et al. observed that clip repositioning was required based on IMD findings in 24% of aneurysms clipped in 91 patients and concluded that IMD could reduce the rate of residual aneurysm and unanticipated vessel stenosis 9).

The complete clipping of a cerebral aneurysm usually warrants its sustained occlusion, while clip remnants may have far-reaching consequences. The aim of this study is to identify the risk factors for clip remnants requiring retreatment and/or exhibiting growth. METHODS All consecutive patients with primary aneurysm clipping performed at University Hospital of Essen between January 1, 2003, and December 31, 2013, were eligible for this study. Aneurysm occlusion was judged on obligatory postoperative digital subtraction angiography and the need for repeated vascular control. The identified clip remnants were correlated with various demographic and clinical characteristics of the patients, aneurysm features, and surgery-related aspects. RESULTS Of 616 primarily clipped aneurysms, postoperative angiography revealed 112 aneurysms (18%) with clip remnants requiring further control (n = 91) or direct retreatment (n = 21). Seven remnants exhibited growth during follow-up, whereas 2 cases were associated with aneurysmal bleeding. Therefore, a total of 28 aneurysms (4.5%) were retreated as clip remnants (range 1 day to 67 months after clipping). In the multivariate analysis, the need for retreatment of clip remnant was correlated with the aneurysm’s initial size (> 12 mm; OR 3.22; p = 0.035) and location (anterior cerebral artery > internal carotid artery > posterior circulation > middle cerebral artery; OR 1.85; p = 0.003). Younger age with a cutoff at 45 years (OR 33.31; p = 0.004) was the only independent predictor for remnant growth. CONCLUSIONS The size and location of the aneurysm are the main risk factors for clip remnants requiring retreatment. Because of the risk for growth, younger individuals (< 45 years old) with clip remnants require a long-term (> 5 years) vascular follow-up. Clinical trial registration no: DRKS00008749 (Deutsches Register Klinischer Studien) 10).

Total index hospitalization costs for clipping are lower than for coiling. Costs of clipping and coiling are driven by different clinical variables. The cost of coils and devices is the predominant contributor to the higher total costs of coiling 11).

The mechanisms underlying neurocognitive changes after surgical clipping of unruptured intracranial aneurysms (UIAs) are poorly understood.

Minimal structural damage visualized on T2-weighted images at 6 months as a result of factors such as pial/microvascular injury and excessive retraction during surgical manipulation could cause subtle but significant negative effects on postoperative neurocognitive function after surgical clipping of a UIA. However, this detrimental effect was small, and based on the group-rate analysis

Successful and meticulous surgical clipping of a UIA does not adversely affect postoperative cognitive function 12).

Results of treatment after clipping and coiling do not differ in total for all patients, but differ depending on the presence of bleeding. Patients with bleeding aneurysms achieve better outcomes after coiling, and patients with non-bleeding aneurysms achieve better outcomes after clipping 13).

Risk of ischemia during intracranial aneurysm surgery is significantly related to temporary clipping time and final clipping that might incorporate a perforator.

Abdulrauf et al. attempted to assess the potential added benefit to patient outcomes of “awake” neurological testing when compared with standard neurophysiological testing performed under general anesthesia. The procedure is performed after the induction of conscious sedation, and for the neurological testing, the patient is fully awake.

They conducted an institutional review board-approved prospective study of clipping unruptured intracranial aneurysms (UIAs) in 30 consecutive adult patients who underwent awake clipping. The end points were the incidence of stroke/cerebrovascular accident (CVA), death, discharge to a long-term facility, length of stay, and 30-day modified Rankin Scale score. All clinical and neurophysiological intraoperative monitoring data were recorded.

The median patient age was 52 years (range 27-63 years); 19 (63%) female and 11 (37%) male patients were included. Twenty-seven (90%) aneurysms were anterior, and 3 (10%) were posterior circulation aneurysms. Five (17%) had been coiled previously, 3 (10%) had been clipped previously, 2 (7%) were partially calcified, and 2 (7%) were fusiform aneurysms. Three patients developed synchronous clinical neurological and neurophysiological changes during temporary clipping with consequent removal of the temporary clip and reversal of those clinical and neurophysiological changes. Three patients developed asynchronous clinical neurological and neurophysiological changes. These 3 patients developed hemiparesis without changes in neurophysiological monitoring results. One patient developed linked clinical neurological and neurophysiological changes during final clipping that were not reversed by reapplication of the clip, and the patient had a CVA. Four patients with internal carotid artery ophthalmic segment aneurysms underwent visual testing with final clipping, and 1 of these patients required repositioning of the clip. Three patients who required permanent occlusion of a vessel as part of their aneurysm treatment underwent a 10-minute intraoperative clinical respective-vessel test occlusion. The median length of stay was 3 days (range 1-5 days). The median modified Rankin Scale score was 1 (range 0-3). All of the patients were discharged to home from the hospital except for 1 who developed a CVA and was discharged to a rehabilitation facility. There were no deaths in this series.

The 3 patients who developed neurological deterioration without a concomitant neurophysiological finding during temporary clipping revealed a potential advantage of awake aneurysm surgery (i.e., in decreasing the risk of ischemic injury) 14).

see Virtual reality simulator for aneurysmal clipping surgery.

A total of 53 patients from Phoenix and San Francisco, who initially presented with a subarachnoid hemorrhage and underwent surgical clipping of a previously coiled intracranial aneurysm between December 1997 and December 2014 were studied. Clinical features, hospital course, and preoperative and most recent functional status (Glasgow Outcome Scale score) were reviewed retrospectively.

The mean time interval from coiling to clipping was 2.6 years, and mean follow-up was 5.5 years (range, 0.1-14.7 years). Five patients (9.8%) presented with rebleed prior to clipping. Most patients (79.3%, 42/53) experienced good neurologic outcomes. Most showed no change (81%, 43/53) or improvement (13%, 7/53) in functional status after microsurgical clipping. One patient (2%) deteriorated clinically, and there were 2 mortalities (4%).

Microsurgical clipping of previously ruptured, coiled aneurysms is a promising treatment method with favorable clinical outcomes 15).


Retrospective review of the medical records of 320 patients with 416 aneurysms treated with microsurgical clipping from 2008 to 2016 in a single neurosurgical center in Brazil. This study evaluated postoperative outcome, using the modified Rankin Scale (mRS) on hospital discharge, treatment efficacy, assessed by digital subtraction angiography (DSA) performed postoperatively, and mortality.

Among 320 patients with aneurysms, 228 patients presented with ruptured aneurysms and 92 patients with unruptured aneurysms. Overall, 81 (26,3%) presented poor outcome (mRs>2) while 227 (73,4%) showed good outcome. The presence of a ruptured aneurysm was a statistically significant factor for poor outcome (p<0,001) and mortality (p<0,015). Giant and large aneurysms were also associated with poor outcome (p=0,004). When we analyze separately, unruptured aneurysms with poor outcome were only associated with aneurysms size. Among the patients with ruptured aneurysms, those with Hunt Hess (HH) > 2 on hospital admission showed unfavorable outcomes (p<0,0001). Among patients submitted to postoperative DSA, 207 (89,8%) had complete occlusion of the aneurysms and 24 (10,2%) presented residual aneurysms, with reoperation required in eight cases.

Microsurgical treatment of intracranial aneurysms is an effective and safe method 16).


1)

Lai LT, O’Neill AH. History, Evolution and Continuing Innovations of Intracranial Aneurysm Surgery. World Neurosurg. 2017 Feb 9. pii: S1878-8750(17)30166-3. doi: 10.1016/j.wneu.2017.02.006. [Epub ahead of print] Review. PubMed PMID: 28189863.
2)

Santiago BM, Cunha E Sá M. How do we maintain competence in aneurysm surgery. Acta Neurochir (Wien). 2015 Jan;157(1):9-11. doi: 10.1007/s00701-014-2265-8. Epub 2014 Nov 14. PubMed PMID: 25391972.
3)

Nieuwkamp DJ, de Gans K, Algra A, Albrecht KW, Boomstra S, Brouwers PJ, Groen RJ, Metzemaekers JD, Nijssen PC, Roos YB, Tulleken CA, Vandertop WP, van Gijn J, Vos PE, Rinkel GJ. Timing of aneurysm surgery in subarachnoid haemorrhage–an observational study in The Netherlands. Acta Neurochir (Wien). 2005 Aug;147(8):815-21. PubMed PMID: 15944811.
4)

Sriganesh K, Venkataramaiah S. Concerns and challenges during anesthetic management of aneurysmal subarachnoid hemorrhage. Saudi J Anaesth. 2015 Jul-Sep;9(3):306-13. doi: 10.4103/1658-354X.154733. Review. PubMed PMID: 26240552; PubMed Central PMCID: PMC4478826.
5)

Sato A, Koyama JI, Hanaoka Y, Hongo K. A Reverse-Action Clip Applier for Aneurysm Surgery. Neurosurgery. 2015 Mar 12. [Epub ahead of print] PubMed PMID: 25774701.
6)

Mori K, Watanabe S. Keyhole Approach in Cerebral Aneurysm Surgeries. Adv Tech Stand Neurosurg. 2022;44:265-275. doi: 10.1007/978-3-030-87649-4_15. PMID: 35107685.
7)

Özgiray E, Aktüre E, Patel N, Baggott C, Bozkurt M, Niemann D, et al. How reliable and accurate is indocyanine green video angiography in the evaluation of aneurysm obliteration? Clin Neurol Neurosurg. 2013;115:870–8.
8)

Sriganesh K, Vinay B, Bhadrinarayan V. Indocyanine green dye administration can cause oxygen desaturation. J Clin Monit Comput. 2013;27:371.
9)

Hui PJ, Yan YH, Zhang SM, Wang Z, Yu ZQ, Zhou YX, et al. Intraoperative microvascular Doppler monitoring in intracranial aneurysm surgery. Chin Med J (Engl) 2013;126:2424–9.
10)

Jabbarli R, Pierscianek D, Wrede K, Dammann P, Schlamann M, Forsting M, Müller O, Sure U. Aneurysm remnant after clipping: the risks and consequences. J Neurosurg. 2016 Feb 12:1-7. [Epub ahead of print] PubMed PMID: 26871206.
11)

Duan Y, Blackham K, Nelson J, Selman W, Bambakidis N. Analysis of short-term total hospital costs and current primary cost drivers of coiling versus clipping for unruptured intracranial aneurysms. J Neurointerv Surg. 2014 Jun 2. pii: neurintsurg-2014-011249. doi: 10.1136/neurintsurg-2014-011249. [Epub ahead of print] PubMed PMID: 24891453.
12)

Inoue T, Ohwaki K, Tamura A, Tsutsumi K, Saito I, Saito N. Subtle structural change demonstrated on T2-weighted images after clipping of unruptured intracranial aneurysm: negative effects on cognitive performance. J Neurosurg. 2014 Jan 31. [Epub ahead of print] PubMed PMID: 24484231.
13)

Birski M, Wałęsa C, Gaca W, Paczkowski D, Birska J, Harat A. Clipping versus coiling for intracranial aneurysms. Neurol Neurochir Pol. 2014 Mar-Apr;48(2):122-9. doi: 10.1016/j.pjnns.2014.03.002. Epub 2014 Mar 31. PubMed PMID: 24821638.
14)

Abdulrauf SI, Vuong P, Patel R, Sampath R, Ashour AM, Germany LM, Lebovitz J, Brunson C, Nijjar Y, Kyle Dryden J, Khan MQ, Stefan MG, Wiley E, Cleary RT, Reis C, Walsh J, Buchanan P. “Awake” clipping of cerebral aneurysms: report of initial series. J Neurosurg. 2016 Oct 21:1-8. [Epub ahead of print] PubMed PMID: 27767401.
15)

Nisson PL, Meybodi AT, Roussas A, James W, Berger GK, Benet A, Lawton MT. Surgical Clipping of Previously Ruptured, Coiled Aneurysms: Outcome Assessment in 53 Patients. World Neurosurg. 2018 Dec;120:e203-e211. doi: 10.1016/j.wneu.2018.07.293. Epub 2018 Aug 23. PubMed PMID: 30144619.
16)

Dellaretti M, Ronconi D, Batista DM, de Souza RF, de Almeida CER, Fontoura RR, Botelho Antunes PR, Quadros RS. Safety and Efficacy of Surgical Treatment of Intracranial Aneurysms: The Experience of a Single Brazilian Center. World Neurosurg. 2018 Jun 20. pii: S1878-8750(18)31307-X. doi: 10.1016/j.wneu.2018.06.091. [Epub ahead of print] PubMed PMID: 29935315.

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