Reduction of shunt dependency rates following aneurysmal subarachnoid hemorrhage by tandem fenestration of the lamina terminalis and membrane of Liliequist during microsurgical aneurysm repair

Independent elevation of plasma fibulin-5 proceeding chronic hydrocephalus development after aneurysmal subarachnoid hemorrhage

BACKGROUND

Aneurysmal subarachnoid hemorrhage (aSAH) causes chronic hydrocephalus (CH) due to disturbance in the reabsorption of cerebrospinal fluid following subarachnoidal fibrosis via inflammatory reactions or blood clotting products. Fibulin-5 (FBLN5) is one of matricellular proteins associated with fibrosis processes.

OBJECTIVE

The aim of this study was to assess whether FBLN5 elevation is related to CH after aSAH.

METHODS

This study prospectively enrolled consecutive aSAH patients at 9 institutions in Japan from 2013 to 2016. Plasma FBLN5 levels at days 1-3, 4-6, 7-9, and 10-12 were measured. Relationships between plasma FBLN5 levels and incidence of CH were analyzed. Multivariate logistic regression analyses were performed on clinical variables with a p value of < 0.05 on univariate analyses and plasma FBLN5 levels with the highest area under the receiver-operating characteristic (ROC) curve.

RESULTS

A total of 229 aSAH patients were analyzed, and CH occurred in 67 patients. FBLN5 levels at days 4-6 from aSAH onset elevated in patients resulting in subsequent CH occurrence. The ROC curve analyses revealed that the area under the curve (AUC) at days 4-6 post-aSAH was the highest (AUC, 0.592; 95 % confidence interval, 0.514-0.671) among the four time points. Multivariate logistic regression analyses using clinical variables related to CH on univariate analyses and plasma FBLN5 levels at days 4-6 post-aSAH revealed that FBLN5 levels at days 4-6 post-aSAH ≥ 366.4 ng/mL (adjusted odds ratio, 3.14) were an independent determinant of subsequent CH development.

CONCLUSION

The elevation of plasma FBLN5 levels in a subacute phase of aSAH may contribute to the development of CH. FBLN5 may be a molecular target to develop a new therapy against post-aSAH CH.

Can a single basal cistern urokinase bolus help to prevent subarachnoid hemorrhage consequences?

Study design

Retrospective.

Background

In the 1980s, aneurysmal subarachnoid clot lysis with urokinase or alteplase (rtPA) was proven to effectively reduce vasospasm and neurological ischemic deficits, improving survival and clinical outcomes. This therapeutic option has been less commonly used since the introduction of endovascular treatment, but renewed interest has sparked in recent years.

Aims

To investigate if single bolus cisternal urokinase subarachnoid clot lysis reduces vasospasm, neurological ischemic deficits, mortality, and permanent CSF diversion rates and improves outcomes. Additionally, we want to unveil which subgroup of patients benefit most.

Material and methods

Study period January 2007-December 2019. 415 patients with saccular aneurysms and >1-year follow-up analyzed. Six groups created according to the treatment applied: no treatment (42), only external ventricular drain (16), endovascular treatment (155), clipping (53), clipping + 100,000UI urokinase (116), and incidental brain aneurysm (33).

Results

The rates and severity of vasospasm, permanent CSF diversion, and mortality in Fisher grades ≥3 subarachnoid hemorrhages were higher with endovascular treatment than with surgical clipping with simultaneous cisternal urokinase administration. The best GOSE results on discharge and 6- and 12-month follow-ups happened in this latter group. The differences were more significant the higher the Fisher grade. We neither saw intraventricular, subarachnoid, subdural, or epidural hemorrhages nor systemic fibrinolysis or infections that could be related to the urokinase administration.

Conclusions

Single bolus cisternal 100,000UI urokinase administration during emergency aneurysm clipping reduces vasospasm, mortality, and the need for permanent CSF diversion. It is not associated with a significant increase in intracranial hemorrhages or systemic fibrinolysis.

A predictive model in patients with chronic hydrocephalus following aneurysmal subarachnoid hemorrhage: a retrospective cohort study

Objective

Our aim was to develop a nomogram that integrates clinical and radiological data obtained from computed tomography (CT) scans, enabling the prediction of chronic hydrocephalus in patients with aneurysmal subarachnoid hemorrhage (aSAH).

Method

A total of 318 patients diagnosed with subarachnoid hemorrhage (SAH) and admitted to the Department of Neurosurgery at the Affiliated People's Hospital of Jiangsu University between January 2020 and December 2022 were enrolled in our study. We collected clinical characteristics from the hospital's medical record system. To identify risk factors associated with chronic hydrocephalus, we conducted both univariate and LASSO regression models on these clinical characteristics and radiological features, accompanied with penalty parameter adjustments conducted through tenfold cross-validation. All features were then incorporated into multivariate logistic regression analyses. Based on these findings, we developed a clinical-radiological nomogram. To evaluate its discrimination performance, we conducted Receiver Operating Characteristic (ROC) curve analysis and calculated the Area Under the Curve (AUC). Additionally, we employed calibration curves, and utilized Brier scores as an indicator of concordance. Additionally, Decision Curve Analysis (DCA) was performed to determine the clinical utility of our models by estimating net benefits at various threshold probabilities for both training and testing groups.

Results

The study included 181 patients, with a determined chronic hydrocephalus prevalence of 17.7%. Univariate logistic regression analysis identified 11 potential risk factors, while LASSO regression identified 7 significant risk factors associated with chronic hydrocephalus. Multivariate logistic regression analysis revealed three independent predictors for chronic hydrocephalus following aSAH: Periventricular white matter changes, External lumbar drainage, and Modified Fisher Grade. A nomogram incorporating these factors accurately predicted the risk of chronic hydrocephalus in both the training and testing cohorts. The AUC values were calculated as 0.810 and 0.811 for each cohort respectively, indicating good discriminative ability of the nomogram model. Calibration curves along with Hosmer-Lemeshow tests demonstrated excellent agreement between predicted probabilities and observed outcomes in both cohorts. Furthermore, Brier scores (0.127 for the training and 0.09 for testing groups) further validated the predictive performance of our nomogram model. The DCA confirmed that this nomogram provides superior net benefit across various risk thresholds when predicting chronic hydrocephalus. The decision curve demonstrated that when an individual's threshold probability ranged from 5 to 62%, this model is more effective in predicting the occurrence of chronic hydrocephalus after aSAH.

Conclusion

A clinical-radiological nomogram was developed to combine clinical characteristics and radiological features from CT scans, aiming to enhance the accuracy of predicting chronic hydrocephalus in patients with aSAH. This innovative nomogram shows promising potential in assisting clinicians to create personalized and optimal treatment plans by providing precise predictions of chronic hydrocephalus among aSAH patients.

Cisternal nicardipine for prevention of delayed cerebral ischemia in aneurysmal subarachnoid hemorrhage: a comparative retrospective cohort study

PURPOSE

Intrathecal vasoactive drugs have been proposed in patients with aneurysmal subarachnoid hemorrhage (aSAH) to manage cerebral vasospasm (CV). We analyzed the efficacy of intracisternal nicardipine compared to intraventricular administration to a control group (CG) to determine its impact on delayed cerebral ischemia (DCI) and functional outcomes. Secondary outcomes included the need for intra-arterial angioplasties and the safety profile.

METHODS

We performed a retrospective analysis of prospectively collected data of all adult patients admitted for a high modified Fisher grade aSAH between January 2015 and April 2022. All patients with significant radiological CV were included. Three groups of patients were defined based on the CV management: cisternal nicardipine (CN), ventricular nicardipine (VN), and no intrathecal nicardipine (control group).

RESULTS

Seventy patients met the inclusion criteria. Eleven patients received intracisternal nicardipine, 18 intraventricular nicardipine, and 41 belonged to the control group. No cases of DCI were observed in the CN group (p = 0.02). Patients with intracisternal nicardipine had a reduced number of intra-arterial angioplasties when compared to the control group (p = 0.03). The safety profile analysis showed no difference in complications across the three groups. Intrathecal (ventricular or cisternal) nicardipine therapy improved functional outcomes at 6 months (p = 0.04) when compared to the control group.

CONCLUSION

Administration of intrathecal nicardipine for moderate to severe CV reduces the rate of DCI and improved long-term functional outcomes in patients with high modified Fisher grade aSAH. This study also showed a relative benefit of cisternal over intraventricular nicardipine, thereby reducing the number of angioplasties performed in the post-treatment phase. However, these preliminary results should be confirmed with future prospective studies.

The Role of Cisternostomy and Cisternal Drainage in the Treatment of Aneurysmal Subarachnoid Hemorrhage: A Comprehensive Review

Aneurysmal subarachnoid hemorrhage (aSAH) provokes a cascade reaction that is responsible for early and delayed brain injuries mediated by intracranial hypertension, hydrocephalus, cerebral vasospasm (CV), and delayed cerebral ischemia (DCI), which result in increased morbidity and mortality. During open microsurgical repair, cisternal access is achieved essentially to gain proximal vascular control and aneurysm exposition. Cisternostomy also allows brain relaxation, removal of cisternal clots, and restoration of the CSF dynamics through the communication between the anterior and posterior circulation cisterns and the ventricular system, with the opening of the Membrane of Liliequist and lamina terminalis, respectively. Continuous postoperative CSF drainage through a cisternal drain (CD) is a valuable option for treating acute hydrocephalus and intracranial hypertension. Moreover, it efficiently removes the blood and toxic degradation products, with a potential benefit on CV, DCI, and shunt-dependent hydrocephalus. Finally, the CD is an effective pathway to administer vasoactive, fibrinolytic, and anti-oxidant agents and shows promising results in decreasing CV and DCI rates while minimizing systemic effects. We performed a comprehensive review to establish the adjuvant role of cisternostomy and CD performed in cases of direct surgical repair for ruptured intracranial aneurysms and their role in the prevention and treatment of aSAH complications.

The positive impact of cisternostomy with cisternal drainage on delayed hydrocephalus after aneurysmal subarachnoid hemorrhage

BACKGROUND

Hydrocephalus is one of the major complications of aneurysmal subarachnoid haemorrhage (aSAH). In the acute setting, an external ventricular drain (EVD) is used for early management. A cisternal drain (CD) coupled with the micro-surgical opening of basal cisterns can be an alternative when the aneurysm is clipped. Chronic hydrocephalus after aSAH is managed with ventriculo-peritoneal (VP) shunt, a procedure associated with a wide range of complications. The aim of this study is to analyse the impact of micro-surgical opening of basal cisterns coupled with CD on the incidence of VP shunt, compared to patients treated with EVD.

METHODS

The authors conducted a retrospective review of 89 consecutive cases of patients with aSAH treated surgically and endovascularly with either EVD or CD between January 2009 and September 2021. Patients were stratified into two groups: Group 1 included patients with EVD, Group 2 included patients with CD. Subgroup analysis with only patients treated surgically was also performed. We compared their baseline characteristics, clinical outcomes and shunting rates.

RESULTS

There were no statistically significant differences between the two groups in terms of epidemiological characteristics, WFNS score, Fisher scale, presence of intraventricular hemorrhage (IVH), acute hydrocephalus, postoperative meningitis or of clinical outcomes at last follow-up. Cisternostomy with CD (Group 2) was associated with a statistically significant reduction in VP-shunt compared with the use of an EVD (Group 1) (9.09% vs 53.78%; p < 0.001). This finding was confirmed in our subgroup analysis, as among patients with a surgical clipping, the rate of VP shunt was 43.7% for the EVD group and 9.5% for the CD group (p = 0.02).

CONCLUSIONS

Cisternostomy with CD may reduce the rate of shunt-dependent hydrocephalus. Cisternostomy allows the removal of subarachnoid blood, thereby reducing arachnoid inflammation and fibrosis. CD may enhance this effect, thus resulting in lower rates of chronic hydrocephalus.

Basal Cisternostomy for Severe TBI: Surgical Technique and Cadaveric Dissection

Introduction

Cisternostomy is emerging as a novel surgical technique in the setting of severe brain trauma. Different surgical techniques have been proposed with a variable degree of epidural bone work. We present here the surgical technique as it is currently performed in our Institution.

Methods

Anatomical dissection of one adult cadaveric head, injected and non-formalin fixed was perfomed. A large right fronto-temporo-parietal craniotomy was accomplished. Extradural sphenoidal drilling till opening of the superior orbital fissure was performed. The microsurgical anatomy of basal cisternostomy was then explored.

Results

A step by step description of the surgical technique, enriched with cadaveric and intraoperative images, was made.

Conclusion

Basal cisternostomy is a promising surgical technique that does not necessarily include complex surgical maneuvers. Trained neurosurgeon can safely implement it in their clinical practice.

Keyhole Approach for Clipping Anterior Circulation Aneurysms: Clinical Outcomes and Technical Note

Purpose: Keyhole craniotomy is a minimally invasive approach for the treatment of anterior circulation aneurysm. In this study, we evaluated the benefits and value of the keyhole approach by analyzing the surgical results in 235 patients with anterior circulation aneurysm treated by the keyhole approach and identifying lessons learned from addressing various complications in this approach.

Patients and Methods: This was a retrospective study in a single institution of 235 surgical patients with 248 anterior circulation aneurysms who had the supraorbital keyhole approach (SKA) or pterional keyhole approach (PKA) between January 2016 and January 2021. The modified Rankin Scale (mRS) was used to measure long-term results during follow up.

Results: All 235 patients' aneurysms were fully clamped and have not recurred. Among them, 31 (13.2%) had intraoperative aneurysm rupture, 8 (3.4%) had cerebral vascular spasm, and 4 (1.7%) had intraoperative brain edema. There were seven (3.0%) cases of postoperative infection, eight (3.4%) cases of postoperative cerebral infarction, one (0.4%) case of postoperative hematoma, and two (0.8%) patients had some form of cognitive impairment after surgery. Follow up after surgery demonstrated that 189 out of the 235 patients (80.4%) had favorable outcomes (mRS score 0–2), and 43 (18.3%) had poor outcomes (mRS from 3–5). There were three deaths (1.28%).

Conclusions: The keyhole approach has a quick postoperative recovery, a mild postoperative response, and a good surgical outcome. Our findings indicate that the keyhole approach is a safe and effective surgical method for the treatment of anterior circulation aneurysm.

The Pathogenesis of Hydrocephalus Following Aneurysmal Subarachnoid Hemorrhage

Hydrocephalus is a common complication of aneurysmal subarachnoid hemorrhage (aSAH) and reportedly contributes to poor neurological outcomes. In this review, we summarize the molecular and cellular mechanisms involved in the pathogenesis of hydrocephalus following aSAH and summarize its treatment strategies. Various mechanisms have been implicated for the development of chronic hydrocephalus following aSAH, including alterations in cerebral spinal fluid (CSF) dynamics, obstruction of the arachnoid granulations by blood products, and adhesions within the ventricular system. Regarding molecular mechanisms that cause chronic hydrocephalus following aSAH, we carried out an extensive review of animal studies and clinical trials about the transforming growth factor-β/SMAD signaling pathway, upregulation of tenascin-C, inflammation-dependent hypersecretion of CSF, systemic inflammatory response syndrome, and immune dysregulation. To identify the ideal treatment strategy, we discuss the predictive factors of shunt-dependent hydrocephalus between surgical clipping and endovascular coiling groups. The efficacy and safety of other surgical interventions including the endoscopic removal of an intraventricular hemorrhage, placement of an external ventricular drain, the use of intraventricular or cisternal fibrinolysis, and an endoscopic third ventriculostomy on shunt dependency following aSAH were also assessed. However, the optimal treatment is still controversial, and it necessitates further investigations. A better understanding of the pathogenesis of acute and chronic hydrocephalus following aSAH would facilitate the development of treatments and improve the outcome.

Timelines and rebleeds in patients admitted into neurosurgical care for aneurysmal subarachnoid haemorrhage

Background

Mortality and morbidity of aneurysmal subarachnoid haemorrhage (aSAH) remain high, and prognosis is influenced by multiple non-modifiable factors such as aSAH severity. By analysing the chronology of aSAH management, we aim at identifying modifiable factors with emphasis on the occurrence of rebleeds in a setting with 24/7 surgical and endovascular availability of aneurysm repair and routine administration of tranexamic acid.

Methods

Retrospective analysis of institutional quality registry data of aSAH cases admitted into neurosurgical care during the time period 01 January 2013–31 December 2017. We registered time and mode of aneurysm repair, haemorrhage patterns, course of treatment, mortality and functional outcome. Rebleeding was scored along the entire timeline from ictus to discharge from the primary stay.

Results

We included 544 patients (368, 67.6% female), aged 58 ± 14 years (range 1–95 years). Aneurysm repair was performed in 486/544 (89.3%) patients at median 7.4 h after arrival and within 3, 6, 12 and 24 h in 26.8%, 44.7%, 73.0% and 96.1%, respectively. There were circadian variations in time to repair and in rebleeds. Rebleeding prior to aneurysm repair occurred in 9.7% and increased with aSAH severity and often in conjunction with patient relocations or interventions. Rebleeds occurred more often during surgical repair outside regular working hours, whereas rebleeds after repair (1.8%) were linked to endovascular repair.

Conclusions

The risk of rebleed is imminent throughout the entire timeline of aSAH management even with ultra-early aneurysm repair. Several modifiable factors can be linked to the occurrence of rebleeds and they should be identified and optimised within neurosurgical departments.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00701-020-04673-3.

Lamina terminalis fenestration: An important neurosurgical corridor

Cerebrospinal fluid (CSF) disorders are challenging conditions in neurosurgical practice. The majority of CSF is contained in the basal cisterns of the brain, which are subarachnoid compartments that communicate with each other, and contribute to the circulation of CSF. Yaşargil et al. (1976) was the first to provide the systematic classification and naming of the basal cisterns. The lamina terminalis (LT) starts from the gyrus rectus and descends to the lateral aspect of the optic chiasm. It is a thick arachnoidal membrane delineating the anterior wall of the third ventricle that borders the LT cistern. With the introduction of the operating microscope and the progressive development of modern neurosurgery, the arachnoid and basal cisterns have been used as surgical corridors in order to reach deep areas of the brain and to release CSF for brain relaxation. In this way, the LT is used as a surgical corridor for the treatment of several conditions such as obstructive hydrocephalus and diencephalic tumors. In this chapter, we will describe the anatomy of the LT, possible conditions treated by opening the LT, the different surgical approaches to opening the LT, along with their advantages and disadvantages.

Effect of Microscopic Third Ventriculostomy (Lamina Terminalis Fenestration) on Shunt-needed Hydrocephalus in Patients with Aneurysmal Subarachnoid Hemorrhage

There are reports that in patients with aSAH (aneurysmal subarachnoid hemorrhage), LTF (lamina terminalis fenestration) reduces the rate of shunt-needed hydrocephalus via facilitation of CSF (cerebrospinal fluid) dynamic, diminished leptomeningeal inflammation, and decreased subarachnoid fibrosis. Regarding the conflicting results, this study was conducted to evaluate the effects of LTF on decreased shunt-needed hydrocephalus in patients with aSAH. A cross-sectional retrospective study was carried out to survey all patients with confirmed aSAH operated from March 2011 to September 2016 in an academic vascular center (Rasool Akram Hospital in Tehran, Iran). Of a total of 151 patients, 72 patients were male and 79 were female. The mean age of the participants was 51 years. A transiently CSF diversion (EVD - external ventricular drainage) was performed (the acute hydrocephalus rate) on 21 patients (13.9%). In 36 patients (23.8%), aneurysm occlusion with LTF and in 115 patients (76.2%) only aneurysm occlusion surgery was performed. In hydrocephalus follow-up after surgery, 13 (12%) patients needed shunt insertion (the rate of shunt-needed hydrocephalus). The statistical analysis demonstrated no significant relation between LTF and shunt-needed hydrocephalus. Confirmation of the hypothesis that LTF may decrease the rate of shunt-needed hydrocephalus can significantly decrease morbidity, mortality, and treatment costs of shunting (that is a simple, but a potentially dangerous procedure). So, it is advised to plan and perform an RCT (randomized controlled trial) that can remove the confounding factors, match the groups, and illustrate the exact effect of LTF on shunt-needed hydrocephalus.

Microsurgical clipping of multiple cerebral aneurysms in the acute phase of aneurysmal subarachnoid hemorrhage through a minipterional approach: The Chilean experience

OBJECTIVE

The minipterional craniotomy (MPTc) has been widely accepted as a minimally invasive alternative to the pterional approach for the treatment of certain small non-ruptured anterior circulation aneurysms. The aim of this study was to determine the effectiveness and safety of the MPTc in the context of a complex and potentially harmful scenario: acute onset of subarachnoid hemorrhage (SAH) in patients harboring multiple intracranial aneurysms (MIA).

METHODS

Patients harboring MIA clipped through a unilateral MPTc were selected from four retrospective databases of four high-volume neurosurgical centers. Patients with a Hunt & Hess score 4 or 5 were not considered candidates for clipping through a MPTc. Medical records and radiological images were retrospectively reviewed. Epidemiological, clinical and radiological data, as well as short-term outcome (modified Rankin scale at 6 month-follow-up) were analyzed.

RESULTS

16 patients harboring 33 aneurysms (16 ruptured, 17 non ruptured) met the inclusion criteria. Each aneurysm size was 5.7 ± 2.1 mm (range 3-11). 12 out of 33 aneurysms were located in the middle cerebral artery (MCA). Anterior communicating (ACom) and MCA aneurysms were the aneurysm locations most commonly ruptured (5 each, 62 %). Complete occlusion was achieved in 32 aneurysms (97 %) and near-complete occlusion in 1 (3%). 13 patients (93 %) were independent at 6 month-follow-up. Mortality rate was 0%. Complications included 1 cerebrospinal-fluid leakage.

CONCLUSION

When indicated (Hunt Hess < 4), performing a MPTc is safe and effective in aSAH cases with multiple aneurysms.

Review of CHESS Score in SAH Patients in Local Malaysian Population

Background  Chronic hydrocephalus caused by subarachnoid hemorrhage is a reversible and treatable condition. To date, existing clinical scores for predicting the development of posthemorrhagic hydrocephalus are few and difficult to apply in the clinical settings. Chronic hydrocephalus ensuing subarachnoid hemorrhage score (CHESS) was first published in 2016. Although it showed promising results, no external validation has been done outside Europe. We designed this study to validate the accuracy and reliability of CHESS score and to also look for other factors that may cause posthemorrhagic shunt dependent hydrocephalus.

Objectives  This study is to determine the reliability of CHESS score and to look for other parameters with predictive value in patients with shunt-dependent posthemorrhagic hydrocephalus.

Results  Thirty-one percent of the studied population developed shunt-dependent hydrocephalus ( n = 41). CHESS score showed an odds ratio (OR) of 2.184 with p -value < 0.001 and two other risk factors were found to be strongly related to develop shunt-dependent hydrocephalus, that is, early infarct in computed tomography (CT) brain (OR = 0.182; p -value = 0.004) and Fisher’s grade > 3 (OR = 1.986; p -value = 0.047). The sensitivity and specificity for CHESS score in this cohort population showed a sensitivity of 73.2% and specificity of 93.3%. The area under the curve for CHESS score in our cohort is 0.922.

Conclusion  CHESS score is a reliable tool in early prediction of shunt-dependent hydrocephalus post subarachnoid hemorrhage.

Incidence, classification, and treatment of angiographically occult intracranial aneurysms found during microsurgical aneurysm clipping of known aneurysms

OBJECTIVE

During the microsurgical clipping of known aneurysms, angiographically occult (AO) aneurysms are sometimes found and treated simultaneously to prevent their growth and protect the patient from future rupture or reoperation. The authors analyzed the incidence, treatment, and outcomes associated with AO aneurysms to determine whether limited surgical exploration around the known aneurysm was safe and justified given the known limitations of diagnostic angiography.

METHODS

An AO aneurysm was defined as a saccular aneurysm detected using the operative microscope during dissection of a known aneurysm, and not detected on preoperative catheter angiography. A prospective database was retrospectively reviewed to identify patients with AO aneurysms treated microsurgically over a 20-year period.

RESULTS

One hundred fifteen AO aneurysms (4.0%) were identified during 2867 distinct craniotomies for aneurysm clipping. The most common locations for AO aneurysms were the middle cerebral artery (60 aneurysms, 54.1%) and the anterior cerebral artery (20 aneurysms, 18.0%). Fifty-six AO aneurysms (50.5%) were located on the same artery as the known saccular aneurysm. Most AO aneurysms (95.5%) were clipped and there was no attributed morbidity. The most common causes of failed angiographic detection were superimposition of a large aneurysm (type 1, 30.6%), a small aneurysm (type 2, 18.9%), or an adjacent normal artery (type 3, 36.9%). Multivariate analysis identified multiple known aneurysms (odds ratio [OR] 3.45, 95% confidence interval [CI] 2.16-5.49, p < 0.0001) and young age (OR 0.981, 95% CI 0.965-0.997, p = 0.0226) as independent predictors of AO aneurysms.

CONCLUSIONS

Meticulous inspection of common aneurysm sites within the surgical field will identify AO aneurysms during microsurgical dissection of another known aneurysm. Simultaneous identification and treatment of these additional undiagnosed aneurysms can spare patients later rupture or reoperation, particularly in those with multiple known aneurysms and a history of subarachnoid hemorrhage. Limited microsurgical exploration around a known aneurysm can be performed safely without additional morbidity.