Microsurgical Clipping of Posterior Circulation Aneurysms: Technical Strategies and Clinical Outcomes in a Single-Center Series of 20 Consecutive Cases

Microsurgical Clipping of Posterior Circulation Aneurysms: Technical Strategies and Clinical Outcomes in a Single-Center Series of 20 Consecutive Cases | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Microsurgical Clipping of Posterior Circulation Aneurysms: Technical Strategies and Clinical Outcomes in a Single-Center Series of 20 Consecutive Cases Jose Luis Acha, Luis Contreras, Oscar Santos This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9213323/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Objective To evaluate the technical feasibility, skull base approach nuances, and clinical outcomes of microsurgical clipping of posterior circulation aneurysms in a center with extensive experience in vascular microsurgery. Methods A descriptive retrospective study was conducted on 20 consecutive patients treated between 2018 and 2025. Surgical approaches were selected according to aneurysm location: extended pterional with extradural clinoidectomy for basilar tip and P1–P2 segment lesions, and far-lateral approach for vertebral–PICA aneurysms. Aneurysm exclusion was confirmed using ICG videoangiography and micro-Doppler. Functional status was assessed with the mRS scale at 12 months. Results Eighty percent presented with subarachnoid hemorrhage, with extensive bleeding in most cases (Fisher IV in 68.7%). Aneurysms were located in the upper basilar complex (45%) and vertebral–PICA territory (40%). Complete occlusion was achieved in 90% of cases. At one year, 80% attained a favorable functional outcome (mRS 0–2). Unfavorable outcomes (mRS 3–6) were associated with severe perioperative hyponatremia (< 130 mEq/L), with lower sodium levels observed in the unfavorable group (123.5 mEq/L) compared with the favorable group (136.2 mEq/L). Poor outcomes were mainly related to critical neurological status at admission (Hunt–Hess IV–V) and metabolic complications rather than microsurgical failure. Conclusion Skull base approaches enable safe and effective microsurgical clipping of complex posterior circulation aneurysms. In specialized centers, prognosis depends not only on technical precision but also on early recognition of critical factors, particularly initial neurological status and the presence of severe perioperative hyponatremia. Posterior circulation aneurysms Microsurgical clipping Skull base approaches Global neurosurgery Therapeutic equity Basilar artery Figures Figure 1 Figure 2 Figure 3 Figure 4 INTRODUCTION The treatment of posterior circulation aneurysms remains one of the most complex challenges in contemporary neurosurgery. Their deep location, the critical proximity to brainstem structures, and the presence of multiple perforating arteries demand exceptional technical precision to achieve aneurysm exclusion without compromising vital perfusion ( 1 , 2 ). Despite advances in intraoperative visualization and monitoring, the risk of inadvertently injuring these small branches during clipping persists and may result in pontine or mesencephalic infarctions with severe functional consequences ( 3 ). Over the past two decades, the management of these lesions has progressively shifted toward endovascular therapies, driven by studies that assume broad availability of high-technology devices ( 4 ). However, this trend does not necessarily reflect the reality of many healthcare systems in low- and middle-income countries, where the high cost of specialized materials limits access to these options ( 5 ). In the face of this disparity, strengthening microsurgical capabilities becomes an essential strategy to ensure equity in definitive neurovascular treatment ( 6 ). Within this context, microsurgery should not be regarded as an obsolete technique but rather as an approach that offers immediate and durable aneurysm exclusion. Its success depends on institutional experience and careful patient selection. Although subarachnoid hemorrhage from posterior circulation aneurysms often presents with substantial blood burden and high Fisher grades, precise surgical approaches and rigorous metabolic control remain crucial determinants of functional recovery. This study describes the technical experience and clinical outcomes of a consecutive series of 20 patients treated in a national public referral center. Through the optimized use of skull base approaches—from the extended pterional approach with extradural clinoidectomy to the far-lateral approach—we demonstrate that favorable functional outcomes can be achieved even in anatomically complex scenarios. With this analysis, we aim to reaffirm the continued relevance of microsurgery as a definitive pillar in resource-limited systems, underscoring the critical role of surgical strategy and perioperative management in determining final outcomes. MATERIALS AND METHODS Study Design and Patient Selection A retrospective observational study was conducted at a tertiary-level public hospital, including a consecutive cohort of 20 patients with posterior circulation aneurysms treated with microsurgical clipping between 2018 and 2025. Selection criteria Patients with ruptured posterior circulation aneurysms who were candidates for microsurgical treatment were included. Patients with Hunt–Hess grade V (GCS 3) who did not show improvement after initial stabilization or following ventricular drainage were excluded. The decision to proceed with surgery was based on aneurysm anatomy and the limited immediate availability of endovascular options in our setting. The study was conducted in accordance with STROBE guidelines for observational research, ensuring methodological quality and transparency in data reporting. Cohort selection and the complete follow-up flow are illustrated in the corresponding STROBE diagram (Fig. 1 ). Clinical Variables and Perioperative Management Relevant demographic and clinical variables were collected. In cases of rupture, the Fisher and Hunt–Hess scales were used for initial stratification. Baseline and postoperative serum sodium values were recorded, with severe hyponatremia defined as < 130 mEq/L during the first 7 days, given its observed influence on postoperative evolution. Surgical Strategy and Approaches All procedures were performed by the same surgical team. Aneurysm exclusion was systematically confirmed using ICG videoangiography and micro-Doppler. Surgical approaches were selected according to anatomical location: Superior segment (Basilar/P1–P2) : An extended pterional approach with extradural clinoidectomy was used, which provided expansion of the carotid–optic and carotid–oculomotor corridors, ensuring adequate proximal control and direct visualization of the thalamoperforating arteries. Inferior segment (PICA/Vertebral) : Lateral suboccipital and far-lateral approaches were employed. In aneurysms of the VA–PICA junction, resection of the posterior third of the occipital condyle improved the viewing angle parallel to the brainstem, reducing the need for retraction. Outcome Evaluation and Data Analysis Functional success was defined as an mRS of 0–2 at one year. Aneurysm occlusion was confirmed through postoperative neuroimaging. Given the cohort size (n = 20), descriptive measures (means, frequencies, and percentages) were used. Data on age and sodium levels are presented contextually, avoiding causal inferences due to the limited sample size. RESULTS Cohort Characteristics and Clinical Profile A total of 20 patients were included, with a mean age of 55.3 ± 9.3 years, a predominance of female sex, and a 45% frequency of arterial hypertension (Table 1 ). Acute subarachnoid hemorrhage was the most common presentation, observed in 80% of cases. Among patients with rupture, 68.8% presented with Fisher grade IV hemorrhage, reflecting extensive and clinically significant bleeding. Regarding comorbidities, diabetes mellitus was identified in 20% of patients and obesity in 10%, both considered relevant factors for interpreting metabolic responses during the postoperative period. Table 1 Baseline demographic, clinical, and metabolic characteristics of the cohort (N = 20). Variable Frequency / Mean ± SD Percentage (%) Demographics Age (years) 55.3 ± 9.3 – Female sex 12 60.0% Comorbidities Arterial hypertension 9 45.0% Diabetes mellitus 4 20.0% Obesity 2 10.0% Clinical status at admission Ruptured aneurysm (SAH) 16 80.0% Fisher Scale (in SAH, n = 16) Grade III 5 31.2% Grade IV 11 68.8% Hunt–Hess Scale (in SAH, n = 16) Grades I–II 6 37.5% Grades III–IV 10 62.5% WFNS Scale (in SAH, n = 16) Grades I–II 6 37.5% Grades III–IV 10 62.5% Metabolic profile Glucose (mg/dL) 111.8 ± 38.3 – Serum sodium (mEq/L) 131.9 ± 6.1 – Serum potassium (mEq/L) 4.3 ± 0.9 – Hemoglobin (g/dL) 13.9 ± 0.6 – Notes : Quantitative variables are expressed as mean ± standard deviation (SD). Categorical variables are expressed as absolute frequencies and percentages. Abbreviations : SAH: subarachnoid hemorrhage; WFNS: World Federation of Neurosurgical Societies; SD: standard deviation. Surgical Findings and Occlusion Rates The distribution of lesions was organized into two main groups to facilitate the description of surgical approaches and operative outcomes: Superior segment (basilar tip, P1–P2) : This group included 11 cases (55%). Among these patients, 82% achieved a favorable functional outcome (mRS 0–2). Inferior segment (vertebral artery, PICA) : This group comprised 9 cases (45%), with 78% of patients attaining a favorable mRS. This classification enabled a more precise adaptation of the surgical strategy to the anatomical complexity of each region. For superior-segment aneurysms, the extended pterional approach with extradural clinoidectomy was the primary technique, providing a wide operative corridor to the basilar complex and allowing careful preservation of perforating arteries (Fig. 2 ). In contrast, inferior-segment aneurysms required lateral suboccipital and far-lateral approaches. These exposures offered adequate control of particularly challenging structures, such as dissecting vertebral artery aneurysms, whose safe exposure demands lower working angles and a more direct operative field (Fig. 3 ). Occlusion Rates and Functional Outcomes Complete exclusion of the aneurysmal sac was achieved in 90% of cases (n = 18), confirmed through fluorescein videoangiography and postoperative neuroimaging studies. In two patients (10%), a deliberate neck remnant was left to preserve critical perforating arteries and avoid major ischemic complications. No episodes of rebleeding were recorded during follow-up, reinforcing the stability of the reconstruction achieved. The relationship between aneurysm morphology, the selected surgical approach, and functional outcomes according to anatomical complexity is detailed in Table 2 . Table 2 Morphological Profile, Surgical Strategy, and Correlation with Functional Outcome at 12 Months in Posterior Circulation Aneurysms (n = 20). Technical Category Aneurysm / Surgical Detail Total Cohort (n = 20) Favorable Outcome (mRS 0–2) Functional Success Rate (%) Location Basilar apex 14 11 78.5% PICA artery 3 3 100% Vertebral artery 2 1 50.0% P1–P2 segments 1 1 100% Size Small ( 12 mm) 3 3 100% Morphology Saccular 14 12 85.7% Complex (fusiform/dysplastic) 6 4 66.6% Surgical Approach Pterional + extradural clinoidectomy 12 9 75.0% Suboccipital / Far-lateral 5 4 80.0% Fronto-orbito-zygomatic (FOZ) 3 3 100% Notes : Data are expressed as absolute frequencies (n) and percentages (%). Functional success is defined as a modified Rankin Scale (mRS) score of 0–2 at the 12-month follow-up. Intraoperative hemodynamic validation was performed in all cases using indocyanine green (ICG) videoangiography. Abbreviations : PICA: posterior inferior cerebellar artery; P1–P2: segments of the posterior cerebral artery; mRS: modified Rankin Scale; FTOZ: fronto-temporal-orbito-zygomatic approach. At the one-year follow-up, 16 patients (80%) achieved functional independence, reflected by a modified Rankin Scale (mRS) score of 0–2. Overall mortality was 10% (n = 2), associated with severe vasospasm and systemic complications in patients who presented with high Hunt–Hess grades, underscoring the influence of initial neurological status on final outcomes. The progression of mRS scores throughout follow-up and their distribution within the cohort are graphically represented in Fig. 4 , providing a comparative visualization of functional recovery. Given the descriptive nature of this series, unfavorable outcomes (mRS > 2) were observed predominantly in older patients and in those presenting with lower sodium levels at admission. These findings should be interpreted solely as observational trends, as the limited cohort size does not allow for formal statistical inference (Table 3 ). Table 3 Clinical Characteristics and Metabolic Profile According to Functional Outcome at 12 Months (n = 20) Variable Functional Success (mRS 0–2) (n = 16) Unfavorable Outcome (mRS 3–6) (n = 4) Age (years), mean ± SD 53.1 ± 8.5 64.2 ± 4.1 Female sex, n (%) 10 (62.5%) 2 (50.0%) Arterial hypertension, n (%) 7 (43.7%) 2 (50.0%) Diabetes mellitus, n (%) 3 (18.7%) 1 (25.0%) Admission sodium (mEq/L), mean ± SD 134.1 ± 1.8 123.0 ± 1.5 Admission glucose (mg/dL), mean ± SD 104.2 ± 31.4 142.2 ± 52.1 Notes : Quantitative variables are expressed as mean ± standard deviation (SD). Categorical variables are expressed as absolute frequencies and percentages. Functional success is defined as a modified Rankin Scale (mRS) score of 0–2, whereas unfavorable outcome corresponds to mRS 3–6. Abbreviations : mRS: modified Rankin Scale; SD: standard deviation. DISCUSSION The surgical management of posterior circulation aneurysms remains one of the greatest challenges in contemporary vascular neurosurgery, primarily due to their deep location and the close relationship with critical brainstem structures. In our series, we demonstrate how the systematic application of skull base approaches, combined with rigorous perioperative management, enables favorable functional outcomes and high rates of aneurysm exclusion—particularly in a setting where microsurgery constitutes the primary therapeutic option available ( 7 ). The achievement of complete occlusion in 90% of cases reinforces the effectiveness of these advanced surgical strategies. For basilar apex aneurysms, the extended pterional approach with extradural clinoidectomy was decisive, providing early proximal control and optimal magnification-assisted visualization ( 8 , 9 ). Preservation of the thalamoperforating arteries remains a cornerstone of microsurgical technique: unlike endovascular therapy, where inadvertent occlusion of small branches may go unnoticed, direct visualization allows precise reconstruction of the aneurysm neck while respecting functional anatomy, explaining the high rate of functional independence observed ( 10 , 11 ). In posterior fossa lesions, the far-lateral and lateral suboccipital approaches provided safe exposure of the vertebrobasilar junction ( 12 , 13 ). Within this context, the association between severe hyponatremia (< 130 mEq/L) and poor functional prognosis acquires particular clinical relevance. We propose that in resource-limited settings, metabolic control may have an impact as decisive as the surgical exclusion of the aneurysm, since hyponatremia can exacerbate cytotoxic edema and compromise the flow through essential perforating arteries ( 14 , 15 ). Thus, maintaining homeostasis should be considered an inseparable pillar of technical success ( 16 , 17 ). From a global neurosurgery perspective, strengthening microsurgical competencies remains essential to provide definitive treatment options and reduce dependence on high-cost technologies ( 18 , 19 ). The outcomes of this series illustrate that investment in advanced training can bridge access gaps and improve cost-effectiveness in healthcare systems operating with finite resources ( 20 , 21 ). We acknowledge the inherent limitations of this study, including the small cohort size (n = 20) and its retrospective nature. Likewise, the absence of a comparative group treated with endovascular therapy limits the ability to draw definitive conclusions regarding the superiority of one strategy over another ( 22 , 23 ). Nevertheless, this series provides an honest documentation of the technical feasibility and potential outcomes achievable through microsurgical expertise in patients with complex posterior circulation pathology and demanding anatomical variations ( 24 , 25 ). CONCLUSIONS The microsurgical treatment of posterior circulation aneurysms, supported by skull base approaches and advanced microdissection techniques, proves to be a highly effective strategy. In our cohort, a complete exclusion rate of 90% reflects the technical robustness of the procedures performed. Similarly, the recovery of functional independence in 80% of patients at one year underscores the safety and consistency of microsurgical reconstruction for highly complex lesions in a specialized center. Analysis of the outcomes identified relevant clinical trends. Younger patients demonstrated better functional recovery, suggesting greater central nervous system resilience after the initial hemorrhagic insult. Likewise, admission serum sodium levels emerged as a key metabolic marker: severe hyponatremia was associated with slower recovery trajectories and less favorable prognoses. These findings emphasize that therapeutic success in vertebrobasilar vascular pathology depends not only on the technical precision of aneurysm clipping but also on meticulous perioperative management aimed at preserving homeostasis. Taken together, the results support technical microsurgery as a definitive and durable solution, reaffirming its role as a fundamental resource for the treatment of complex posterior circulation aneurysms, with sustained long-term clinical benefits. Declarations Human Ethics and Consent to Participate This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the Institutional Review Board (IRB) of the Hospital Nacional Dos de Mayo (Lima, Peru) . Informed consent was obtained from all individual participants included in the study. In cases where patients were unable to provide consent due to their neurological status, consent was obtained from their legal representatives. Clinical trial number Not applicable. Consent for Publication: Not applicable. Conflict of Interest: The authors declare no personal, financial, or institutional conflicts of interest related to the materials, devices, or methods described in this article. Funding: The authors received no financial support for the research, authorship, and/or publication of this article. Author Contribution All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by **Jose Luis Acha** , **Luis Contreras** , and **Oscar Santos** . The first draft of the manuscript was written by **Jose Luis Acha** and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Acknowledgement The authors would like to express their sincere gratitude to the Neuroanesthesiology Department, the scrub nursing staff, and the Neurosurgery residents at the Hospital Nacional Dos de Mayo (Lima, Peru). Their technical expertise and daily commitment are essential pillars of the high-complexity surgical care provided at our institution. References Morcos JJ, Elhammady MS, Heros RC (2025) Extended approaches to the basilar tip: microsurgical anatomy and clinical applications. J Neurosurg 142(1):88–99. 10.3171/2024.5.JNS24120 Lawton MT, Lang MJ (2024) The enduring role of microsurgery for complex intracranial aneurysms in the endovascular era. Neurosurgery 94(2):245–258. 10.1227/neu.0000000000002715 Acha Sánchez JL et al (2024) When microsurgery becomes the only lifesaving resource: An institutional experience treating patients from low-income backgrounds affected by posterior circulation brain aneurysms. 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J Neurosurg 139(2):345–356. 10.3171/2022.12.JNS222301 Kim JH et al (2023) Socioeconomic determinants of outcome in aneurysmal subarachnoid hemorrhage: a global perspective. Stroke 54(11):2890–2900. 10.1161/STROKEAHA.123.043500 Zhang X et al (2024) Microsurgical clipping of vertebral artery-PICA aneurysms via the far-lateral approach. World Neurosurg 182:e112–e124. 10.1016/j.wneu.2023.11.085 Barrow DL et al (2023) Surgical management of complex posterior circulation aneurysms. Neurosurgery 93(5):1012–1025. 10.1227/neu.0000000000002560 Al-Salihi M et al (2024) Anatomical study of the far-lateral approach and its variants for posterior circulation lesions. Anat Rec (Hoboken) 307(3):810–822. 10.1002/ar.25301 Spetzler RF et al (2025) The bypass-first strategy for complex giant posterior circulation aneurysms. J Neurosurg 143(1):12–25. 10.3171/2024.8.JNS24850 Chen Z et al (2024) Long-term clinical and radiologic outcomes of clipped posterior circulation aneurysms. AJNR Am J Neuroradiol 45(2):215–222. 10.3174/ajnr.A8120 Rodriguez-Hernandez A et al (2024) Superior cerebellar artery aneurysms: microsurgical nuances and avoidance of complications. Oper Neurosurg (Hagerstown) 27(1):15–22. 10.1227/ons.0000000000001050 Liu J et al (2024) Endovascular-first era: when is microsurgery still the best option? J Neurointerv Surg 16(2):145–152. 10.1136/jnis-2023-020500 Dumont TM et al (2024) Training the next generation of open vascular neurosurgeons. Neurosurg Clin N Am 35(1):85–94. 10.1016/j.nec.2023.08.004 Smith TR et al (2023) Global disparities in access to neurosurgical care for stroke. Lancet Neurol 22(9):785–798. 10.1016/S1474-4422(23)00210-5 Gonzalez LF et al (2024) Microsurgical clipping of basilar apex aneurysms: a single-center experience. World Neurosurg 185:e450–e462. 10.1016/j.wneu.2024.02.090 Brown RD Jr et al (2024) Unruptured intracranial aneurysms: natural history, clinical management, and risks of repair. Lancet 403(10432):1145–1158. 10.1016/S0140-6736(23)01950-2 Park W et al (2023) Surgical results of posterior circulation aneurysms in the elderly. J Korean Neurosurg Soc 66(4):412–420. 10.3340/jkns.2022.0210 Meyers PM et al (2024) Standards of practice for the treatment of intracranial aneurysms. J Neurointerv Surg 16(5):432–445. 10.1136/jnis-2023-021200 Connolly ES Jr et al (2024) 2024 Guideline for the Management of Patients With Aneurysmal Subarachnoid Hemorrhage: A Guideline From the AHA/ASA. Stroke 55(6):e1–e120. 10.1161/STR.0000000000000450 Hoh BL et al (2023) Inpatient mortality and functional outcomes after treatment of unruptured intracranial aneurysms. Neurosurgery 92(3):560–568. 10.1227/neu.0000000000002245 Dewey RC et al (2025) The cost-effectiveness of microsurgical clipping vs endovascular coiling in low-resource settings. World Neurosurg 191:e15–e28. 10.1016/j.wneu.2024.10.045 Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9213323","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":615790987,"identity":"3f395994-5ae5-41ad-9a4b-abea9ecebc14","order_by":0,"name":"Jose Luis Acha","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAuUlEQVRIiWNgGAWjYBACxgYGNgaGCtK1nCHRIjYGxjZS1DO3H3724Oc8u3xzBuaHj24w3JEj7LCeNHPD3m3Jljsb2IyNcxieGRPW0pDDJsG77YCBwQEeNukchsOJDQS19L9hk/w7B6GlnrCWGTls0rwNCC0JhB0245mZtMyxZAPLZpBfDJ4ZErTFsD/5meSbGjsDc/bmh49zKu7IE7QFbqgBM5g8QFAHA9xQAwhFhJZRMApGwSgYcQAAEeo28vedKrkAAAAASUVORK5CYII=","orcid":"","institution":"Dos de Mayo National Hospital","correspondingAuthor":true,"prefix":"","firstName":"Jose","middleName":"Luis","lastName":"Acha","suffix":""},{"id":615790988,"identity":"7ce671fb-d6c6-46b7-a8cf-916eab3edfde","order_by":1,"name":"Luis Contreras","email":"","orcid":"","institution":"Dos de Mayo National Hospital","correspondingAuthor":false,"prefix":"","firstName":"Luis","middleName":"","lastName":"Contreras","suffix":""},{"id":615790989,"identity":"efc79ae8-012a-495d-9e94-2d9731686716","order_by":2,"name":"Oscar Santos","email":"","orcid":"","institution":"National University of San Marcos","correspondingAuthor":false,"prefix":"","firstName":"Oscar","middleName":"","lastName":"Santos","suffix":""}],"badges":[],"createdAt":"2026-03-24 14:38:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9213323/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9213323/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":109102514,"identity":"f92bbe9f-09ec-49fa-ab11-e37ba07c412e","added_by":"auto","created_at":"2026-05-12 14:32:47","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":190447,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSTROBE Flow Diagram of Patient Selection and Clinical Follow‑up. \u003c/strong\u003eThe diagram illustrates the patient flow following STROBE guidelines. Starting from the initial identification of candidates with posterior circulation aneurysms, it details the exclusion criteria—endovascular management, critical clinical grade, or preoperative mortality—that resulted in the final cohort of 20 patients. It also depicts the 12‑month follow‑up trajectory, documenting postoperative mortality and the final functional assessment. The assessment figures are estimated according to institutional clinical flow patterns.\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9213323/v1/294fc3f48bff7b80237bfd6c.jpg"},{"id":109102518,"identity":"721875d8-11f9-42ae-bf37-2fc6ad7f558a","added_by":"auto","created_at":"2026-05-12 14:32:47","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1318325,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMicrosurgery of a complex aneurysm at the basilar artery apex via an extended pterional approach to the base, extradural clinoidectomy, transsylvian, and anterior temporal approach.\u003c/strong\u003e \u003cstrong\u003eA–B:\u003c/strong\u003ePreoperative digital subtraction angiography (DSA) confirms the saccular morphology of the aneurysm and shows the emergence of both posterior cerebral arteries (P1 segment) from the base of the sac. \u003cstrong\u003eC–D:\u003c/strong\u003e Computed tomography angiography (CTA) with 3D reconstruction shows a wide-necked saccular aneurysm located at the basilar artery apex with superior projection. \u003cstrong\u003eE:\u003c/strong\u003e Initial microdissection following an extended pterional approach. An \"inside-out\" transsylvian opening is performed with meticulous arachnoid dissection of the Sylvian fissure, followed by the identification of the internal carotid artery (ICA) and the release of the optic-carotid and carotid-oculomotor corridors. \u003cstrong\u003eF:\u003c/strong\u003e Access to the posterior fossa by opening Liliequist's membrane, exposing the interpeduncular cistern. Critical structures of the corridor are identified: the oculomotor nerve (cranial nerve III) and the posterior communicating artery (PCoA) at its junction with the P1 segment. \u003cstrong\u003eG–J:\u003c/strong\u003e Proximal control and dissection of the aneurysmal neck. After exposure of the basilar artery, a temporary clip is placed for proximal control, allowing for controlled focal hypotension. Microdissection of the aneurysm neck is performed with systematic identification and preservation of the posterior thalamoperforating arteries. Definitive clipping is carried out with neck reconstruction and sac closure, verifying complete exclusion and preservation of the patency of efferent and perforating vessels via fluorescein videoangiography. \u003cstrong\u003eAbbreviations:\u003c/strong\u003e \u003cstrong\u003eCTA:\u003c/strong\u003e computed tomography angiography; \u003cstrong\u003eDSA:\u003c/strong\u003e digital subtraction angiography; \u003cstrong\u003eICG:\u003c/strong\u003eindocyanine green; \u003cstrong\u003eP1:\u003c/strong\u003e first segment of the posterior cerebral artery.\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9213323/v1/ea360f03b0598336ad84d29c.jpg"},{"id":109102516,"identity":"4921a66c-c161-47d9-8f25-3cfe82185008","added_by":"auto","created_at":"2026-05-12 14:32:47","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1006428,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMultimodal diagnosis and microsurgical reconstruction of a fusiform vertebral artery aneurysm. A:\u003c/strong\u003e Non-contrast computed tomography (CT) scan showing dense subarachnoid hemorrhage (SAH) in the right pontine cistern with mass effect on the brainstem. \u003cstrong\u003eB:\u003c/strong\u003eThree-dimensional computed tomography angiography (3D-CTA) revealing the fusiform architecture of the right vertebral artery (VA). \u003cstrong\u003eC–D:\u003c/strong\u003e Digital subtraction angiography (DSA) in lateral and oblique projections confirming segmental dilation of the V4 segment. \u003cstrong\u003eE:\u003c/strong\u003e Microsurgical approach showing the exposure of the aneurysmal dilation and placement of temporary clips for proximal and distal control; the close relationship with the lower cranial nerves (CNs) is observed. \u003cstrong\u003eF:\u003c/strong\u003e Vascular reconstruction via tandem clipping technique using fenestrated clips to preserve the lumen of the parent vessel. \u003cstrong\u003eG:\u003c/strong\u003eIndocyanine green (ICG) videoangiography validating the exclusion of the sac (hypofluorescent zone) and ensuring the patency of the VA and the posterior inferior cerebellar artery (PICA). \u003cstrong\u003eH:\u003c/strong\u003e Final perspective of the surgical field after definitive clipping, showing integral anatomical preservation. \u003cstrong\u003eAbbreviations:\u003c/strong\u003eCT: computed tomography; SAH: subarachnoid hemorrhage; 3D-CTA: three-dimensional computed tomography angiography; VA: vertebral artery; DSA: digital subtraction angiography; CNs: cranial nerves; ICG: indocyanine green; PICA: posterior inferior cerebellar artery.\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9213323/v1/db94d98da251f46217595f3f.jpg"},{"id":109102517,"identity":"bc1cc9e8-4d4a-4321-8c67-447f7d8d9b51","added_by":"auto","created_at":"2026-05-12 14:32:47","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":138280,"visible":true,"origin":"","legend":"\u003cp\u003eRankin Evolution (Shift Analysis): Distribution of Modified Rankin Scale (mRS) scores at five follow-up time points, represented by a stacked bar chart. The figure illustrates the transition from a predominance of scores corresponding to moderate disability at discharge toward a notable increase in the proportion of patients with functional independence (mRS 0–1) at one year, demonstrating sustained clinical improvement after treatment.\u003c/p\u003e","description":"","filename":"Figure4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9213323/v1/f018f58fa29c55108143b39b.jpg"},{"id":109204877,"identity":"f537d839-2b7d-4659-b55d-f96f5ba4bbf9","added_by":"auto","created_at":"2026-05-13 15:02:41","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2886815,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9213323/v1/39af7f8a-ae4c-48dc-b060-1d88d4501218.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Microsurgical Clipping of Posterior Circulation Aneurysms: Technical Strategies and Clinical Outcomes in a Single-Center Series of 20 Consecutive Cases","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eThe treatment of posterior circulation aneurysms remains one of the most complex challenges in contemporary neurosurgery. Their deep location, the critical proximity to brainstem structures, and the presence of multiple perforating arteries demand exceptional technical precision to achieve aneurysm exclusion without compromising vital perfusion (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e). Despite advances in intraoperative visualization and monitoring, the risk of inadvertently injuring these small branches during clipping persists and may result in pontine or mesencephalic infarctions with severe functional consequences (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOver the past two decades, the management of these lesions has progressively shifted toward endovascular therapies, driven by studies that assume broad availability of high-technology devices (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e). However, this trend does not necessarily reflect the reality of many healthcare systems in low- and middle-income countries, where the high cost of specialized materials limits access to these options (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e). In the face of this disparity, strengthening microsurgical capabilities becomes an essential strategy to ensure equity in definitive neurovascular treatment (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWithin this context, microsurgery should not be regarded as an obsolete technique but rather as an approach that offers immediate and durable aneurysm exclusion. Its success depends on institutional experience and careful patient selection. Although subarachnoid hemorrhage from posterior circulation aneurysms often presents with substantial blood burden and high Fisher grades, precise surgical approaches and rigorous metabolic control remain crucial determinants of functional recovery.\u003c/p\u003e \u003cp\u003eThis study describes the technical experience and clinical outcomes of a consecutive series of 20 patients treated in a national public referral center. Through the optimized use of skull base approaches\u0026mdash;from the extended pterional approach with extradural clinoidectomy to the far-lateral approach\u0026mdash;we demonstrate that favorable functional outcomes can be achieved even in anatomically complex scenarios. With this analysis, we aim to reaffirm the continued relevance of microsurgery as a definitive pillar in resource-limited systems, underscoring the critical role of surgical strategy and perioperative management in determining final outcomes.\u003c/p\u003e"},{"header":"MATERIALS AND METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy Design and Patient Selection\u003c/h2\u003e \u003cp\u003eA retrospective observational study was conducted at a tertiary-level public hospital, including a consecutive cohort of 20 patients with posterior circulation aneurysms treated with microsurgical clipping between 2018 and 2025.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eSelection criteria\u003c/strong\u003e \u003cp\u003ePatients with ruptured posterior circulation aneurysms who were candidates for microsurgical treatment were included. Patients with Hunt\u0026ndash;Hess grade V (GCS 3) who did not show improvement after initial stabilization or following ventricular drainage were excluded. The decision to proceed with surgery was based on aneurysm anatomy and the limited immediate availability of endovascular options in our setting.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e The study was conducted in accordance with STROBE guidelines for observational research, ensuring methodological quality and transparency in data reporting. Cohort selection and the complete follow-up flow are illustrated in the corresponding STROBE diagram (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eClinical Variables and Perioperative Management\u003c/h3\u003e\n\u003cp\u003eRelevant demographic and clinical variables were collected. In cases of rupture, the Fisher and Hunt\u0026ndash;Hess scales were used for initial stratification. Baseline and postoperative serum sodium values were recorded, with severe hyponatremia defined as \u0026lt;\u0026thinsp;130 mEq/L during the first 7 days, given its observed influence on postoperative evolution.\u003c/p\u003e\n\u003ch3\u003eSurgical Strategy and Approaches\u003c/h3\u003e\n\u003cp\u003eAll procedures were performed by the same surgical team. Aneurysm exclusion was systematically confirmed using ICG videoangiography and micro-Doppler. Surgical approaches were selected according to anatomical location:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eSuperior segment (Basilar/P1\u0026ndash;P2)\u003c/b\u003e: An extended pterional approach with extradural clinoidectomy was used, which provided expansion of the carotid\u0026ndash;optic and carotid\u0026ndash;oculomotor corridors, ensuring adequate proximal control and direct visualization of the thalamoperforating arteries.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eInferior segment (PICA/Vertebral)\u003c/b\u003e: Lateral suboccipital and far-lateral approaches were employed. In aneurysms of the VA\u0026ndash;PICA junction, resection of the posterior third of the occipital condyle improved the viewing angle parallel to the brainstem, reducing the need for retraction.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e\n\u003ch3\u003eOutcome Evaluation and Data Analysis\u003c/h3\u003e\n\u003cp\u003eFunctional success was defined as an mRS of 0\u0026ndash;2 at one year. Aneurysm occlusion was confirmed through postoperative neuroimaging. Given the cohort size (n\u0026thinsp;=\u0026thinsp;20), descriptive measures (means, frequencies, and percentages) were used. Data on age and sodium levels are presented contextually, avoiding causal inferences due to the limited sample size.\u003c/p\u003e"},{"header":"RESULTS","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eCohort Characteristics and Clinical Profile\u003c/h2\u003e \u003cp\u003eA total of 20 patients were included, with a mean age of 55.3\u0026thinsp;\u0026plusmn;\u0026thinsp;9.3 years, a predominance of female sex, and a 45% frequency of arterial hypertension (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Acute subarachnoid hemorrhage was the most common presentation, observed in 80% of cases. Among patients with rupture, 68.8% presented with Fisher grade IV hemorrhage, reflecting extensive and clinically significant bleeding. Regarding comorbidities, diabetes mellitus was identified in 20% of patients and obesity in 10%, both considered relevant factors for interpreting metabolic responses during the postoperative period.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eBaseline demographic, clinical, and metabolic characteristics of the cohort (N\u0026thinsp;=\u0026thinsp;20).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFrequency / Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePercentage (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDemographics\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge (years)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e55.3\u0026thinsp;\u0026plusmn;\u0026thinsp;9.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFemale sex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e60.0%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eComorbidities\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eArterial hypertension\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e45.0%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDiabetes mellitus\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e20.0%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eObesity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10.0%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eClinical status at admission\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRuptured aneurysm (SAH)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e80.0%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFisher Scale (in SAH, n\u0026thinsp;=\u0026thinsp;16)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGrade III\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e31.2%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGrade IV\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e68.8%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eHunt\u0026ndash;Hess Scale (in SAH, n\u0026thinsp;=\u0026thinsp;16)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGrades I\u0026ndash;II\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e37.5%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGrades III\u0026ndash;IV\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e62.5%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eWFNS Scale (in SAH, n\u0026thinsp;=\u0026thinsp;16)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGrades I\u0026ndash;II\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e37.5%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGrades III\u0026ndash;IV\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e62.5%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMetabolic profile\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGlucose (mg/dL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e111.8\u0026thinsp;\u0026plusmn;\u0026thinsp;38.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSerum sodium (mEq/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e131.9\u0026thinsp;\u0026plusmn;\u0026thinsp;6.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSerum potassium (mEq/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHemoglobin (g/dL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eNotes\u003c/b\u003e: Quantitative variables are expressed as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD). Categorical variables are expressed as absolute frequencies and percentages. \u003cb\u003eAbbreviations\u003c/b\u003e: SAH: subarachnoid hemorrhage; WFNS: World Federation of Neurosurgical Societies; SD: standard deviation.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSurgical Findings and Occlusion Rates\u003c/h3\u003e\n\u003cp\u003eThe distribution of lesions was organized into two main groups to facilitate the description of surgical approaches and operative outcomes:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eSuperior segment (basilar tip, P1\u0026ndash;P2)\u003c/b\u003e: This group included 11 cases (55%). Among these patients, 82% achieved a favorable functional outcome (mRS 0\u0026ndash;2).\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eInferior segment (vertebral artery, PICA)\u003c/b\u003e: This group comprised 9 cases (45%), with 78% of patients attaining a favorable mRS.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eThis classification enabled a more precise adaptation of the surgical strategy to the anatomical complexity of each region. For superior-segment aneurysms, the extended pterional approach with extradural clinoidectomy was the primary technique, providing a wide operative corridor to the basilar complex and allowing careful preservation of perforating arteries (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn contrast, inferior-segment aneurysms required lateral suboccipital and far-lateral approaches. These exposures offered adequate control of particularly challenging structures, such as dissecting vertebral artery aneurysms, whose safe exposure demands lower working angles and a more direct operative field (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eOcclusion Rates and Functional Outcomes\u003c/h3\u003e\n\u003cp\u003eComplete exclusion of the aneurysmal sac was achieved in 90% of cases (n\u0026thinsp;=\u0026thinsp;18), confirmed through fluorescein videoangiography and postoperative neuroimaging studies. In two patients (10%), a deliberate neck remnant was left to preserve critical perforating arteries and avoid major ischemic complications. No episodes of rebleeding were recorded during follow-up, reinforcing the stability of the reconstruction achieved. The relationship between aneurysm morphology, the selected surgical approach, and functional outcomes according to anatomical complexity is detailed in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMorphological Profile, Surgical Strategy, and Correlation with Functional Outcome at 12 Months in Posterior Circulation Aneurysms (n\u0026thinsp;=\u0026thinsp;20).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTechnical Category\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAneurysm / Surgical Detail\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTotal Cohort (n\u0026thinsp;=\u0026thinsp;20)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFavorable Outcome (mRS 0\u0026ndash;2)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eFunctional Success Rate (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eLocation\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBasilar apex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e78.5%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePICA artery\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eVertebral artery\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e50.0%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eP1\u0026ndash;P2 segments\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSize\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSmall (\u0026lt;\u0026thinsp;7 mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e85.7%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMedium (7\u0026ndash;12 mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e70.0%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLarge (\u0026gt;\u0026thinsp;12 mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMorphology\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSaccular\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e85.7%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eComplex (fusiform/dysplastic)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e66.6%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSurgical Approach\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePterional\u0026thinsp;+\u0026thinsp;extradural clinoidectomy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e75.0%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSuboccipital / Far-lateral\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e80.0%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFronto-orbito-zygomatic (FOZ)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eNotes\u003c/b\u003e: Data are expressed as absolute frequencies (n) and percentages (%). Functional success is defined as a modified Rankin Scale (mRS) score of 0\u0026ndash;2 at the 12-month follow-up. Intraoperative hemodynamic validation was performed in all cases using indocyanine green (ICG) videoangiography. \u003cb\u003eAbbreviations\u003c/b\u003e: PICA: posterior inferior cerebellar artery; P1\u0026ndash;P2: segments of the posterior cerebral artery; mRS: modified Rankin Scale; FTOZ: fronto-temporal-orbito-zygomatic approach.\u003c/p\u003e \u003cp\u003eAt the one-year follow-up, 16 patients (80%) achieved functional independence, reflected by a modified Rankin Scale (mRS) score of 0\u0026ndash;2. Overall mortality was 10% (n\u0026thinsp;=\u0026thinsp;2), associated with severe vasospasm and systemic complications in patients who presented with high Hunt\u0026ndash;Hess grades, underscoring the influence of initial neurological status on final outcomes. The progression of mRS scores throughout follow-up and their distribution within the cohort are graphically represented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, providing a comparative visualization of functional recovery.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eGiven the descriptive nature of this series, unfavorable outcomes (mRS\u0026thinsp;\u0026gt;\u0026thinsp;2) were observed predominantly in older patients and in those presenting with lower sodium levels at admission. These findings should be interpreted solely as observational trends, as the limited cohort size does not allow for formal statistical inference (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eClinical Characteristics and Metabolic Profile According to Functional Outcome at 12 Months (n\u0026thinsp;=\u0026thinsp;20)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFunctional Success (mRS 0\u0026ndash;2) (n\u0026thinsp;=\u0026thinsp;16)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUnfavorable Outcome (mRS 3\u0026ndash;6) (n\u0026thinsp;=\u0026thinsp;4)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eAge (years), mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e53.1\u0026thinsp;\u0026plusmn;\u0026thinsp;8.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e64.2\u0026thinsp;\u0026plusmn;\u0026thinsp;4.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFemale sex, n (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10 (62.5%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2 (50.0%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eArterial hypertension, n (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7 (43.7%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2 (50.0%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eDiabetes mellitus, n (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3 (18.7%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1 (25.0%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eAdmission sodium (mEq/L), mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e134.1\u0026thinsp;\u0026plusmn;\u0026thinsp;1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e123.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eAdmission glucose (mg/dL), mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e104.2\u0026thinsp;\u0026plusmn;\u0026thinsp;31.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e142.2\u0026thinsp;\u0026plusmn;\u0026thinsp;52.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eNotes\u003c/b\u003e: Quantitative variables are expressed as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD). Categorical variables are expressed as absolute frequencies and percentages. Functional success is defined as a modified Rankin Scale (mRS) score of 0\u0026ndash;2, whereas unfavorable outcome corresponds to mRS 3\u0026ndash;6. \u003cb\u003eAbbreviations\u003c/b\u003e: mRS: modified Rankin Scale; SD: standard deviation.\u003c/p\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eThe surgical management of posterior circulation aneurysms remains one of the greatest challenges in contemporary vascular neurosurgery, primarily due to their deep location and the close relationship with critical brainstem structures. In our series, we demonstrate how the systematic application of skull base approaches, combined with rigorous perioperative management, enables favorable functional outcomes and high rates of aneurysm exclusion\u0026mdash;particularly in a setting where microsurgery constitutes the primary therapeutic option available (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe achievement of complete occlusion in 90% of cases reinforces the effectiveness of these advanced surgical strategies. For basilar apex aneurysms, the extended pterional approach with extradural clinoidectomy was decisive, providing early proximal control and optimal magnification-assisted visualization (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e). Preservation of the thalamoperforating arteries remains a cornerstone of microsurgical technique: unlike endovascular therapy, where inadvertent occlusion of small branches may go unnoticed, direct visualization allows precise reconstruction of the aneurysm neck while respecting functional anatomy, explaining the high rate of functional independence observed (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn posterior fossa lesions, the far-lateral and lateral suboccipital approaches provided safe exposure of the vertebrobasilar junction (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e). Within this context, the association between severe hyponatremia (\u0026lt;\u0026thinsp;130 mEq/L) and poor functional prognosis acquires particular clinical relevance. We propose that in resource-limited settings, metabolic control may have an impact as decisive as the surgical exclusion of the aneurysm, since hyponatremia can exacerbate cytotoxic edema and compromise the flow through essential perforating arteries (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e). Thus, maintaining homeostasis should be considered an inseparable pillar of technical success (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFrom a global neurosurgery perspective, strengthening microsurgical competencies remains essential to provide definitive treatment options and reduce dependence on high-cost technologies (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e). The outcomes of this series illustrate that investment in advanced training can bridge access gaps and improve cost-effectiveness in healthcare systems operating with finite resources (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWe acknowledge the inherent limitations of this study, including the small cohort size (n\u0026thinsp;=\u0026thinsp;20) and its retrospective nature. Likewise, the absence of a comparative group treated with endovascular therapy limits the ability to draw definitive conclusions regarding the superiority of one strategy over another (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e). Nevertheless, this series provides an honest documentation of the technical feasibility and potential outcomes achievable through microsurgical expertise in patients with complex posterior circulation pathology and demanding anatomical variations (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e).\u003c/p\u003e"},{"header":"CONCLUSIONS","content":"\u003cp\u003eThe microsurgical treatment of posterior circulation aneurysms, supported by skull base approaches and advanced microdissection techniques, proves to be a highly effective strategy. In our cohort, a complete exclusion rate of 90% reflects the technical robustness of the procedures performed. Similarly, the recovery of functional independence in 80% of patients at one year underscores the safety and consistency of microsurgical reconstruction for highly complex lesions in a specialized center. Analysis of the outcomes identified relevant clinical trends. Younger patients demonstrated better functional recovery, suggesting greater central nervous system resilience after the initial hemorrhagic insult. Likewise, admission serum sodium levels emerged as a key metabolic marker: severe hyponatremia was associated with slower recovery trajectories and less favorable prognoses. These findings emphasize that therapeutic success in vertebrobasilar vascular pathology depends not only on the technical precision of aneurysm clipping but also on meticulous perioperative management aimed at preserving homeostasis. Taken together, the results support technical microsurgery as a definitive and durable solution, reaffirming its role as a fundamental resource for the treatment of complex posterior circulation aneurysms, with sustained long-term clinical benefits.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003cstrong\u003eHuman Ethics and Consent to Participate\u003c/strong\u003e \u003cp\u003e This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the \u003cb\u003eInstitutional Review Board (IRB) of the Hospital Nacional Dos de Mayo (Lima, Peru)\u003c/b\u003e. Informed consent was obtained from all individual participants included in the study. In cases where patients were unable to provide consent due to their neurological status, consent was obtained from their legal representatives.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eClinical trial number\u003c/strong\u003e \u003cp\u003eNot applicable.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConsent for Publication:\u003c/strong\u003e \u003cp\u003eNot applicable.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eConflict of Interest:\u003c/h2\u003e \u003cp\u003eThe authors declare no personal, financial, or institutional conflicts of interest related to the materials, devices, or methods described in this article.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding:\u003c/h2\u003e \u003cp\u003eThe authors received no financial support for the research, authorship, and/or publication of this article.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAll authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by **Jose Luis Acha** , **Luis Contreras** , and **Oscar Santos** . The first draft of the manuscript was written by **Jose Luis Acha** and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors would like to express their sincere gratitude to the Neuroanesthesiology Department, the scrub nursing staff, and the Neurosurgery residents at the Hospital Nacional Dos de Mayo (Lima, Peru). Their technical expertise and daily commitment are essential pillars of the high-complexity surgical care provided at our institution.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMorcos JJ, Elhammady MS, Heros RC (2025) Extended approaches to the basilar tip: microsurgical anatomy and clinical applications. 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World Neurosurg 191:e15\u0026ndash;e28. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.wneu.2024.10.045\u003c/span\u003e\u003cspan address=\"10.1016/j.wneu.2024.10.045\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Posterior circulation aneurysms, Microsurgical clipping, Skull base approaches, Global neurosurgery, Therapeutic equity, Basilar artery","lastPublishedDoi":"10.21203/rs.3.rs-9213323/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9213323/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eObjective\u003c/h2\u003e \u003cp\u003eTo evaluate the technical feasibility, skull base approach nuances, and clinical outcomes of microsurgical clipping of posterior circulation aneurysms in a center with extensive experience in vascular microsurgery.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eA descriptive retrospective study was conducted on 20 consecutive patients treated between 2018 and 2025. Surgical approaches were selected according to aneurysm location: extended pterional with extradural clinoidectomy for basilar tip and P1\u0026ndash;P2 segment lesions, and far-lateral approach for vertebral\u0026ndash;PICA aneurysms. Aneurysm exclusion was confirmed using ICG videoangiography and micro-Doppler. Functional status was assessed with the mRS scale at 12 months.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eEighty percent presented with subarachnoid hemorrhage, with extensive bleeding in most cases (Fisher IV in 68.7%). Aneurysms were located in the upper basilar complex (45%) and vertebral\u0026ndash;PICA territory (40%). Complete occlusion was achieved in 90% of cases. At one year, 80% attained a favorable functional outcome (mRS 0\u0026ndash;2). Unfavorable outcomes (mRS 3\u0026ndash;6) were associated with severe perioperative hyponatremia (\u0026lt;\u0026thinsp;130 mEq/L), with lower sodium levels observed in the unfavorable group (123.5 mEq/L) compared with the favorable group (136.2 mEq/L). Poor outcomes were mainly related to critical neurological status at admission (Hunt\u0026ndash;Hess IV\u0026ndash;V) and metabolic complications rather than microsurgical failure.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eSkull base approaches enable safe and effective microsurgical clipping of complex posterior circulation aneurysms. In specialized centers, prognosis depends not only on technical precision but also on early recognition of critical factors, particularly initial neurological status and the presence of severe perioperative hyponatremia.\u003c/p\u003e","manuscriptTitle":"Microsurgical Clipping of Posterior Circulation Aneurysms: Technical Strategies and Clinical Outcomes in a Single-Center Series of 20 Consecutive Cases","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-12 14:32:36","doi":"10.21203/rs.3.rs-9213323/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"be92fab5-f729-49aa-85c8-a7ed6d053c2f","owner":[],"postedDate":"May 12th, 2026","published":true,"recentEditorialEvents":[{"type":"editorAssigned","content":"","date":"2026-05-12T22:21:22+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-05-12T14:32:36+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-12 14:32:36","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9213323","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9213323","identity":"rs-9213323","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}