A novel classification of the basilar artery bifurcation height and the impact of fetal-type posterior cerebral artery: a radioanatomical study with implications for neurosurgical planning

A novel classification of the basilar artery bifurcation height and the impact of fetal-type posterior cerebral artery: a radioanatomical study with implications for neurosurgical planning | 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 A novel classification of the basilar artery bifurcation height and the impact of fetal-type posterior cerebral artery: a radioanatomical study with implications for neurosurgical planning George Triantafyllou, Panagiotis Papadopoulos-Manolarakis, Maria Piagkou, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6518553/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 09 Dec, 2025 Read the published version in Surgical and Radiologic Anatomy → Version 1 posted 13 You are reading this latest preprint version Abstract Purpose The vertical location of the basilar artery bifurcation (BAB) is a crucial factor in determining the best surgical approach for basilar tip (BAT) aneurysms. Although anatomical variants, such as the fetal-type posterior cerebral artery (FPCA), have been linked to aneurysm formation, their impact on BAB height remains unclear. Methods A retrospective anatomical-imaging analysis of 250 high-resolution computed tomography angiograms (CTAs) was conducted to measure the vertical distance from the BAT to the clinoidal line (CL). A dominant posterior communicating artery and/or a hypoplastic or absent P1 segment defines the FPCA. Results BATs were classified into four types based on their BAT-CL distance, with Type 2 BATs (within ± 5 mm of the CL) being the most common. The mean BAT-CL distance was + 2.88 ± 4.8 mm. An FPCA was identified in 74 patients (29.6%). The BAT was significantly lower in all fetal-type subgroups than in patients with typical PCA anatomy (p < 0.005). Bilateral FPCA exhibited the lowest BAT-CL distance (-0.9 ± 3.2 mm). An FPCA is significantly associated with a caudally positioned BAT. Conclusions This finding can assist in surgical planning by predicting aneurysm height based on vascular configuration. In such cases, the pretemporal trans-cavernous approach through extended pterional craniotomy may offer safer and more direct access, thereby reducing surgical morbidity. These results support incorporating vascular variants in preoperative assessments to optimize personalized neurosurgical strategies. Basilar artery bifurcation Clinoidal line Fetal-type posterior cerebral artery Pretemporal trans-cavernous approach Skull base surgery Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction The microneurosurgical management of basilar artery tip (BAT) aneurysms continues to represent one of the most technically intricate challenges in vascular neurosurgery. This complexity is predominantly attributed to the deep and central positioning of the basilar artery (BA), the restricted operative pathways offered by standard skull base approaches, and the proximity of vital neurovascular structures. These considerations necessitate thorough preoperative planning and exact intraoperative execution. Intracranial aneurysms in the posterior circulation are linked to a significantly higher risk of rupture and worse clinical outcomes [ 10 , 28 , 29 , 31 , 38 , 41 ]. Among these, BAT aneurysms present significant challenges owing to their deep anatomical location, propensity for earlier rupture, and complicated clinical behavior. Emphasizing the exceptional results of microneurosurgery, numerous studies advocate for timely or proactive intervention in such cases, considering their elevated risk profile and complex treatment landscape [ 7 , 8 , 14 , 17 , 18 , 20 , 26 , 30 , 33 – 37 , 42 – 44 ]. Our research team has previously highlighted that these aneurysms often manifest at significantly large or, in some instances, giant sizes, which further complicates their management [ 11 , 12 , 21 , 26 , 27 ]. Aneurysms of such magnitude may obscure vital anatomical structures, elevate the risk of intraoperative rupture, and restrict surgical maneuverability, thereby rendering anatomical assessment essential. The choice of surgical approach for BAT aneurysms depends on multiple factors, including aneurysm size, projection, and the surrounding vascular anatomy. One crucial yet often underrecognized parameter is the vertical position of the basilar artery bifurcation (BAB) to fixed cranial landmarks, especially the clinoidal line (CL), defined by a plane connecting the anterior and posterior clinoid processes (ACPs and PCPs). The BAB height relative to the CL significantly impacts surgical exposure: high-riding BABs may require more extensive skull base approaches, while low-riding bifurcations can be challenging to access due to their depth and proximity to brainstem perforators and cranial nerves. Despite the surgical significance of BAB height, standard anatomical references fail to describe specific topographical variants of the BAB [ 11 , 12 , 39 ]. Meanwhile, several morphological variants of the posterior circulation have been associated with aneurysm formation. The fetal-type posterior cerebral artery (FPCA), defined by a dominant posterior communicating artery (PComA) and a hypoplastic or absent P1 segment [ 6 , 32 ], has been linked to altered hemodynamics and a higher risk of aneurysm development, as well as increased rates of recanalization after coil embolization of PComA aneurysms [ 5 ]. Likewise, BA duplication and fenestration have been correlated with increased aneurysm incidence due to localized flow disturbances and structural vessel wall weakness [ 4 , 40 ]. Although the relationship between vascular variants and aneurysm formation has been extensively researched, their influence on the vertical topography of the BAT—and, consequently, their ramifications for surgical access and approach planning—has garnered considerably less consideration. Specifically, the potential impact of an FPCA on BAB height remains unclear. The present anatomical-imaging study seeks to bridge the gap by assessing a novel classification for the BAT position and the FPCA influence on the BAB's elevation to the CL. The primary objective is to improve anatomical comprehension and facilitate more precise and individualized surgical planning to manage basilar tip aneurysms. Materials and Methods A retrospective radioanatomical study was conducted on 250 randomly selected computed tomography angiograms (CTAs) acquired with a slice thickness of 0.8 mm. The study cohort included 138 male and 112 female patients with a mean age of 58.54 ± 15 years. Inclusion criteria required high-quality imaging and the absence of pathological processes affecting the BA, ACPs, and PCPs. Image analysis was performed using Horos software (Horos Project, New York, NY, USA). Multiplanar reconstructions in axial, coronal, and sagittal planes and three-dimensional volume renderings were utilized to evaluate the topographical relationship between the BAT and the CL. The CL was a straight line connecting the ACPs and PCPs, visualized in sagittal reconstructions ( Fig. 1 ) . The vertical distance from the BAB point to the CL was measured on coronal slices. Positive (+) values indicated a BAB located above the CL, and negative (−) values denoted a BAB below it ( Fig. 2 ) . Based on this vertical distance, the height of the BAB was classified into four types: Type 1: Infraclinoidal bifurcation ( + 5 mm above the CL), Type 4: High-riding bifurcation ( > + 10 mm above the CL). Moreover, the presence of a FPCA was defined by a dominant PComA and a hypoplastic or absent P1 segment arising from the BA. Statistical analyses were performed using IBM SPSS Statistics for MacOS, Version 29 (IBM Corp., Armonk, NY, USA). Categorical variables were compared using the Chi-square test for unpaired data and McNemar’s test for paired observations. The Shapiro-Wilk test assessed the normality of continuous variables. For normally distributed unpaired continuous variables, the independent t-test was used; otherwise, the Mann-Whitney U test was applied. A paired t-test was employed for paired continuous data when normality was met. For comparisons involving more than two groups, one-way ANOVA or the Kruskal-Wallis test was used based on the data distribution. All results are presented as means ± standard deviations unless stated otherwise. A p-value of < 0.05 was deemed statistically significant. Results The mean distance of the BAT to the CL (BAT-CL) was + 2.88 ± 4.8 mm. Stratification by gender showed a mean BAT-CL distance of + 3.37 ± 5.0 mm in females and + 2.49 ± 4.6 mm in males, with no significant difference (p = 0.231) ( Table 1 ) . Concerning, the vertical classification of the BAB, BAB of type 2 (clinoidal level) was the most frequently configuration (55.6%), followed by type 3 (supraclinoidal, 24%), type 1 (infraclinoidal, 12.4%), and type 4 (high-riding, 8%) ( Figs. 2 and 3 ). The distribution of these types did not differ significantly between males and females (p = 0.545). Table 1 Demographic and radio-anatomic data of the current study Parameter Total Gender p -value Female Male Patients - n. 250 112 138 Patients’ age - year (±SD) 56.4 (15.2) 55.7 (15.6) 57.2 (14.7) 0.440 BAT-CL distance - mean mm (±SD) + 2.88 (4.8) + 3.37 (5) + 2.49 (4.6) 0.231 BAT Types Type 1 - n. (%) 31 (12.4%) 13 (11.6%) 18 (13%) 0.545 Type 2 - n. (%) 139 (55.6%) 59 (52.7%) 80 (57%) Type 3 - n. (%) 60 (24%) 29 (25.9%) 31 (23%) Type 4 - n. (%) 20 (8%) 11 (9.8%) 9 (7%) PCA origin Fetal-type - n. (%) 74 (29.6) 31 (27.7) 43 (31.2) 0.606 Left - n. (%) 35 (14) 15 (13.4) 20 (14.5) 0.687 Right - n. (%) 25 (10) 9 (8) 16 (11.6) Bilateral - n. (%) 14 (5.6) 7 (6.3) 7 (5.1) SD: Standard Deviation. BAT-CL: basilar artery tip-clinoidal line. An FPCA was identified in 74 patients (29.6%), including 35 cases (14%) with a left-sided FPCA, 25 cases (10%) with a right-sided variant, and 14 cases (5.6%) with a bilateral configuration (Fig. 5 ) ( Table 1 ) . Analysis of the BAT-CL distance to PCA configuration showed lower mean values in all fetal-type groups compared to the typical PCA origin ( Table 2 ) . In patients with bilateral FPCA, the mean BAT-CL distance was − 0.9 ± 3.2 mm, compared to + 3.1 ± 4.8 mm in those with a bilateral typical PCA (p = 0.002). In cases with a left FPCA, the mean distance was − 1.1 ± 4.5 mm versus + 3.3 ± 4.8 mm in typical left PCA cases (p = 0.005). For right-sided variants, the fetal-type group showed a mean distance of − 0.3 ± 3.9 mm, compared to + 3.4 ± 4.8 mm in the typical configuration (p < 0.001) ( Table 2 and Fig. 4 ) . Table 2 Effect of Fetal-Type PCA on Basilar Tip Height by Sidedness Sidedness PCA variant p -value Typical Fetal-type Bilateral - mean BAT-CL distance mm (±SD) + 3.1 (4.8) -0.9 (3.2) 0.002* Left - mean BAT-CL distance mm (±SD) + 3.3 (4.8) -1.1 (4.5) 0.005* Right - mean BAT-CL distance mm (±SD) + 3.4 (4.8) -0.3 (3.9) < 0.001* PCA: posterior cerebral artery. BAT-CL: basilar artery tip-clinoidal line. SD: Standard Deviation. Discussion Our study underscores the necessity of individualized surgical planning by quantifying variability in BAT height and, importantly, identifying a clear association between vascular configuration and vertical positioning of the BAT. First, we proposed a classification system for the BAT height ( Fig. 3 ) , followed by an analysis of the results based on sex and the potential influence of the FPCA. Among the 250 patients analyzed, we found a significant correlation between an FPCA and a caudally displaced BAT ( Tables 1 and 2 ). Specifically, patients with an FPCA consistently exhibited lower BAT-CL distances than those with a typical PCA configuration, regardless of sidedness. This finding suggests that the FPCA—characterized by a dominant PComA and hypoplastic or absent P1 segment—may be a reliable radiological predictor of low bifurcation height. These anatomical findings are novel and should properly correlate with their neurosurgical significance; therefore, it is further discussed. Surgical management of BAT aneurysms has long represented one of the most intricate and demanding endeavors in microneurosurgery. Since the pioneering achievement of Charles G. Drake in the direct clipping of a BAT aneurysm through a subtemporal transtentorial approach during the 1960s [ 7 ], the field has undergone significant evolution in the pursuit of safer and more effective access routes. Drake’s subtemporal transtentorial approach was revolutionary, offering a relatively direct anterolateral path to the BAB [ 8 ]. However, it posed several limitations: the need for significant temporal lobe retraction with an associated risk of venous infarction, a limited superior viewing angle for high-riding aneurysms, and the challenge of achieving proximal control without tentorial sectioning . These limitations prompted the refinement of skull base techniques, particularly the cranio-orbito-zygomatic (COZ) approach, which offers improved surgical freedom and enhanced angles of attack [ 1 , 3 , 19 , 22 – 25 ]. Today, the COZ approach is considered especially advantageous for high-riding BAT aneurysms (i.e., those located > 10 mm above the CL, Type 4 in our classification). By incorporating the removal of the orbital rim and zygomatic arch and an extended frontotemporal craniotomy, the COZ approach provides a superior and broader trajectory, allowing for safer clip application and better visualization of the aneurysm neck and surrounding perforators. Its expanded working angles reduce the need for excessive brain retraction and facilitate multi-angled access to the interpeduncular cistern. In contrast, low-riding bifurcations (Types 1 and 2), located below or near the CL, are better addressed through the pretemporal trans-cavernous approach, which provides more direct exposure to the lower interpeduncular fossa with minimal brain retraction. This approach is typically performed via an extended pterional craniotomy, enabling anterior clinoidectomy, unroofing of the optic canal, and mobilization of the oculomotor nerve to access the basilar apex while preserving crucial neurovascular structures [ 13 , 23 ]. In select cases—mainly when the aneurysm is low-lying, projects posteriorly, or is obscured by the petrous apex—the Kawase approach (anterior petrosectomy) may be indicated. This technique involves drilling the petrous apex to create a direct anterolateral corridor to the ventral brainstem and upper clivus [ 2 , 9 , 15 , 16 ]. Although technically demanding, it is beneficial when additional exposure of the lower BA trunk is required beyond what the pretemporal route can offer. Its use, however, should be judicious, given the increased risk of morbidity associated with temporal bone drilling and potential cranial nerve manipulation. Lastly, from a surgical standpoint, the critical observation that the FPCA affects the position of the BAT could be valuable. Accurate preoperative recognition of a FPCA could inform the neurosurgeon that a lower-riding BAB will likely be encountered. This, in turn, supports early consideration of the pretemporal trans-cavernous approach, with or without anterior petrosectomy, as the most direct and least invasive corridor for aneurysm access. By avoiding unnecessarily extensive skull base exposures—such as a full COZ approach—in cases where the BAB lies low, surgeons may reduce operative time, minimize morbidity, and preserve surrounding neurovascular structures. This anatomical correlation, revealed through non-invasive imaging, thus offers a practical, reproducible marker that can enhance surgical strategy and tailor interventions to individual vascular morphology. It also underlines the enduring relevance of detailed preoperative vascular analysis, even in an era increasingly shaped by endovascular techniques. While these results are promising, several limitations must be acknowledged. First, this was a retrospective study based solely on CTA imaging; although CTA provides high-resolution vascular detail, it lacks the intraoperative perspective and real-time dynamics of microsurgical dissection. Second, we used the CL as a reference, which, while practical and reproducible, may be influenced by individual variations in skull base morphology. Third, the study did not include a correlation with intraoperative findings or clinical outcomes, which would be necessary to confirm the functional relevance of our morphometric data. Finally, the FPCA was documented without further analysis of aneurysm formation. Despite these limitations, the current radioanatomical study highlights a measurable and surgically relevant relationship between PCA configuration and BAB height. Neurosurgeons can refine approach selection, reduce surgical burden, and enhance overall procedural safety and precision by integrating vascular variants into preoperative planning. Conclusions The current anatomical-imaging study emphasizes the vertical position of the BAB as a crucial morphometric variable, which is significantly affected by the presence of an FPCA. Using a simple radiological method, a four-typed classification system for the BAT position was proposed. The preoperative demonstration of BAT types 3 and 4 may suggest the utilization of the COZ approach. In contrast, the pretemporal trans-cavernous pathway may address aneurysms defined by BAT types 1 and 2. Traditionally, the FPCA has been discussed in the context of aneurysm development; however, our findings elucidate its significance as a radiological marker linked to a lower-riding BAT. The preoperative identification of this variant may contribute to predicting aneurysm height and optimizing the surgical approach, particularly favoring the pretemporal trans-cavernous route in cases demonstrating favorable anatomy. This study advocates for a more individualized, anatomy-based methodology in surgical planning, correlating vascular configurations with bifurcation height. Such a personalized approach can potentially enhance operative exposure, minimize the extent of skull base dissection, and improve the overall safety and precision of BAT aneurysm surgeries. Declarations Acknowledgments None. Ethical approval and consent to participate. The General Hospital of Nikaia-Piraeus Ethics Committee approved the study (approval number: 56485/13.11.2024). The research was conducted ethically according to the Code of Ethics of the World Medical Association (Declaration of Helsinki). Data availability Please contact the authors for data requests (Professor Maria Piagkou - email address: [email protected] ). Competing interests None. Funding None. Authors’ contribution George Triantafyllou – student – conceptualization, project development, data analysis, writing- original draft, final version approval. Panagiotis Papadopoulos-Manolarakis (MD, MSc) – neurosurgeon – data collection, data analysis, writing- review/editing, final version approval. Maria Piagkou (DDS, MD, MSc, PhD) – professor – data analysis, writing- review/editing, final version approval. George Tsakotos (MD, MSc, PhD) – assistant professor – data analysis, writing- review/editing, final version approval. Renato Galzio (MD, PhD) – neurosurgeon, professor – data analysis, writing- review/editing, final version approval. Sabino Luzzi (MD, PhD) – neurosurgeon, professor - supervision, writing- original draft, final version approval. References Andaluz N, van Loveren HR, Keller JT, Zuccarello M (2003) The One-Piece Orbitopterional Approach. Skull Base 13:241–246. 10.1055/s-2004-817701 Aziz K, van Loveren HR, Tew J, Chicoine M (1999) The Kawase approach to retrosellar and upper clival basilar aneurysms. Neurosurgery 44:1225–1234 discussion 1234-6 Campero A, Martins C, Socolovsky M, Torino R, Yasuda A, Domitrovic L, Rhoton A (2010) Three-Piece Orbitozygomatic Approach. Operative Neurosurg 66:onsE119–onsE120. 10.1227/01.NEU.0000348559.82835.21 Campos J, Fox AJ, Viñuela F, Lylyk P, Ferguson GG, Drake CG, Peerless SJ (1987) Saccular aneurysms in basilar artery fenestration. AJNR Am J Neuroradiol 8:233–236 Choi HH, Cho YD, Yoo DH, Lee HS, Kim S-H, Jang D, Lee SH, Cho W-S, Kang H-S, Kim JE (2020) Impact of fetal-type posterior cerebral artery on recanalization of posterior communicating artery aneurysms after coil embolization: matched-pair case–control study. J Neurointerv Surg 12:783–787. 10.1136/neurintsurg-2019-015531 Davidoiu AM, Mincă DI, Rusu MC, Hostiuc S, Toader C (2023) The Fetal Type of Posterior Cerebral Artery. Med (Lithuania) 59. 10.3390/medicina59020231 Drake CG (1961) Bleeding Aneurysms of the Basilar Artery. J Neurosurg 18:230–238. 10.3171/jns.1961.18.2.0230 Drake CG (1965) Surgical Treatment of Ruptured Aneurysms of the Basilar Artery. J Neurosurg 23:457–473. 10.3171/jns.1965.23.5.0457 Flores-Justa A, Luzzi S, Giotta Lucifero A, Villalonga JF, Saenz A, Santin-Amo JM, Baldoncini M, Campero A (2021) Use of Neuroanatomic Knowledge and Neuronavigation System for a Safe Anterior Petrosectomy. Brain Sci 11:488. 10.3390/brainsci11040488 Giotta Lucifero A, Baldoncini M, Bruno N, Galzio R, Hernesniemi J, Luzzi S (2021) Shedding the Light on the Natural History of Intracranial Aneurysms: An Updated Overview. Med (B Aires) 57:742. 10.3390/medicina57080742 Giotta Lucifero A, Baldoncini M, Bruno N, Tartaglia N, Ambrosi A, Marseglia GL, Galzio R, Campero A, Hernesniemi J, Luzzi S (2021) Microsurgical Neurovascular Anatomy of the Brain: The Anterior Circulation (Part I). Acta Biomed 92:e2021412. 10.23750/abm.v92iS4.12116 Giotta Lucifero A, Baldoncini M, Bruno N, Tartaglia N, Ambrosi A, Marseglia GL, Galzio R, Campero A, Hernesniemi J, Luzzi S (2021) Microsurgical Neurovascular Anatomy of the Brain: The Posterior Circulation (Part II). Acta Biomed 92:e2021413. 10.23750/abm.v92iS4.12119 Hendricks BK, Cohen-Gadol AA (2020) The Extended Pterional Craniotomy: A Contemporary and Balanced Approach. Operative Neurosurg 18:225–231. 10.1093/ons/opz117 Kato Y, Sano H, Behari S, Kumar S, Nagahisa S, Iwata S, Kanno T (2002) Surgical Clipping of Basilar Aneurysms: Relationship Between the Different Approaches and the Surgical Corridors. min -. Minim Invasive Neurosurg 45:142–145. 10.1055/s-2002-34351 Kawase T, Shiobara R, Toya S (1991) Anterior transpetrosal-transtentorial approach for sphenopetroclival meningiomas: surgical method and results in 10 patients. Neurosurgery 28:869–875 discussion 875-6 Kawase T, Shiobara R, Toya S (1994) Middle fossa transpetrosal-transtentorial approaches for petroclival meningiomas selective pyramid resection and radicality. Acta Neurochir (Wien) 129:113–120. 10.1007/BF01406489 Krisht AF, Kadri PAS (2005) Surgical Clipping of Complex Basilar Apex Aneurysms: A Strategy for Successful Outcome Using the Pretemporal Transzygomatic Transcavernous Approach. Operative Neurosurgery 56:ONS-261-ONS-273. 10.1227/01.NEU.0000156785.63530.4E Lawton MT (2002) Basilar Apex Aneurysms: Surgical Results and Perspectives from an Initial Experience. Neurosurgery 50:1–10. 10.1097/00006123-200201000-00002 Lemole GM, Henn JS, Zabramski JM, Spetzler RF (2003) Modifications to the orbitozygomatic approach. J Neurosurg 99:924–930. 10.3171/jns.2003.99.5.0924 Lozier AP, Kim GH, Sciacca RR, Connolly ES, Solomon RA (2004) Microsurgical Treatment of Basilar Apex Aneurysms: Perioperative and Long-term Clinical Outcome. Neurosurgery 54:286–299. 10.1227/01.NEU.0000103222.13642.00 Luzzi S, Gallieni M, Del Maestro M, Trovarelli D, Ricci A, Galzio R (2018) Giant and Very Large Intracranial Aneurysms: Surgical Strategies and Special Issues. pp 25–31 Luzzi S, Giotta Lucifero A, Bruno N, Baldoncini M, Campero A, Galzio R (2022) Cranio-Orbito-Zygomatic Approach. Acta Biomed 92:e2021350. 10.23750/abm.v92iS4.12784 Luzzi S, Giotta Lucifero A, Bruno N, Baldoncini M, Campero A, Galzio R (2022) Pterional Approach. Acta Biomed 92:e2021346. 10.23750/abm.v92iS4.12775 Luzzi S, Giotta Lucifero A, Spina A, Baldoncini M, Campero A, Elbabaa SK, Galzio R (2022) Cranio-Orbito-Zygomatic Approach: Core Techniques for Tailoring Target Exposure and Surgical Freedom. Brain Sci 12:405. 10.3390/brainsci12030405 Luzzi S, Gragnaniello C, Giotta Lucifero A, Del Maestro M, Galzio R (2020) Surgical Management of Giant Intracranial Aneurysms: Overall Results of a Large Series. World Neurosurg 144:e119–e137. 10.1016/j.wneu.2020.08.004 Luzzi S, Del Maestro M, Galzio R (2021) Posterior Circulation Aneurysms: A Critical Appraisal of a Surgical Series in Endovascular Era. pp 39–45 Luzzi S, Del Maestro M, Galzio R (2021) Posterior Circulation Aneurysms: A Critical Appraisal of a Surgical Series in Endovascular Era. pp 39–45 McDougall CG, Spetzler RF, Zabramski JM, Partovi S, Hills NK, Nakaji P, Albuquerque FC (2012) The Barrow Ruptured Aneurysm Trial. J Neurosurg 116:135–144. 10.3171/2011.8.JNS101767 Molyneux AJ, Kerr RS, Yu L-M, Clarke M, Sneade M, Yarnold JA, Sandercock P (2005) International subarachnoid aneurysm trial (ISAT) of neurosurgical clipping versus endovascular coiling in 2143 patients with ruptured intracranial aneurysms: a randomised comparison of effects on survival, dependency, seizures, rebleeding, subgroups, and aneurysm occlusion. Lancet 366:809–817. 10.1016/S0140-6736(05)67214-5 Nanda A, Sonig A, Banerjee AD, Javalkar VK (2014) Microsurgical Management of Basilar Artery Apex Aneurysms: A Single Surgeon’s Experience from Louisiana State University, Shreveport. World Neurosurg 82:118–129. 10.1016/j.wneu.2013.06.016 Pia HW (1979) Classification of vertebro-basilar aneurysms. Acta Neurochir (Wien) 47:3–30. 10.1007/BF01404659 Saeki N, Rhoton AL (1977) Microsurgical anatomy of the upper basilar artery and the posterior circle of Willis. J Neurosurg 46:563–578. 10.3171/jns.1977.46.5.0563 Saliou G, Sacho RH, Power S, Kostynskyy A, Willinsky RA, Tymianski M, terBrugge KG, Rawal S, Krings T (2015) Natural History and Management of Basilar Trunk Artery Aneurysms. Stroke 46:948–953. 10.1161/STROKEAHA.114.006909 Sanai N, Tarapore P, Lee AC, Lawton MT (2008) THE CURRENT ROLE OF MICROSURGERY FOR POSTERIOR CIRCULATION ANEURYSMS. Neurosurgery 62:1236–1253. 10.1227/01.neu.0000333295.59738.de Sano H, Kato Y, Akashi K, Yamaguchi S, Hayakawa M, Arunkumar R, Kanno T (1997) Operation on High-Lying Basilar Bifurcation Aneurysms. Surg Neurol 48:458–464. 10.1016/S0090-3019(97)00036-0 Sekhar LN, Tariq F, Morton RP, Ghodke B, Hallam DK, Barber J, Kim LJ (2013) Basilar Tip Aneurysms. Neurosurgery 72:284–299. 10.1227/NEU.0b013e3182797952 de SOUSA AA (1998) Basilar Bifurcation Aneurysms. Neurol Med Chir (Tokyo) 38:70–73. 10.2176/nmc.38.suppl_70 Troupp H, THE NATURAL HISTORY OF ANEURYSMS OF THE BASILAR BIFURCATION (1971) Acta Neurol Scand 47:350–356. 10.1111/j.1600-0404.1971.tb07489.x Tubbs RS, Shoja MM, Loukas M (2016) Bergman’s comprehensive encyclopedia of human anatomic variation Uchino A, Saito N, Okada Y, Kozawa E, Nishi N, Mizukoshi W, Inoue K, Nakajima R, Takahashi M (2012) Fenestrations of the intracranial vertebrobasilar system diagnosed by MR angiography. Neuroradiology 54:445–450 Wiebers DO (2003) Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet 362:103–110. 10.1016/S0140-6736(03)13860-3 Winkler EA, Lee A, Yue JK, Raygor KP, Rutledge WC, Rubio RR, Josephson SA, Berger MS, Raper DMS, Abla AA (2021) Endovascular embolization versus surgical clipping in a single surgeon series of basilar artery aneurysms: a complementary approach in the endovascular era. Acta Neurochir (Wien) 163:1527–1540. 10.1007/s00701-021-04803-5 Yasargil MG (1984) Microneurosurgery, Volume II: Clinical Considerations, Surgery of the Intracranial Aneurysms and Results. Thieme Yasargil MG, Antic J, Laciga R, Jain KK, Hodosh RM, Smith RD (1976) Microsurgical pterional approach to aneurysms of the basilar bifurcation. Surg Neurol 6:83–91 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 09 Dec, 2025 Read the published version in Surgical and Radiologic Anatomy → Version 1 posted Editorial decision: Revision requested 25 Jul, 2025 Reviews received at journal 12 Jul, 2025 Reviews received at journal 09 Jul, 2025 Reviewers agreed at journal 25 Jun, 2025 Reviews received at journal 23 Jun, 2025 Reviewers agreed at journal 04 May, 2025 Reviews received at journal 01 May, 2025 Reviewers agreed at journal 30 Apr, 2025 Reviewers agreed at journal 29 Apr, 2025 Reviewers invited by journal 28 Apr, 2025 Editor assigned by journal 25 Apr, 2025 Submission checks completed at journal 24 Apr, 2025 First submitted to journal 24 Apr, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-6518553","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":449824940,"identity":"294f5050-9d9a-492b-9b46-fc69ea5b8e27","order_by":0,"name":"George Triantafyllou","email":"","orcid":"","institution":"Department of Anatomy, School of Medicine, Faculty of Health Sciences, National and Kapodistrian University of Athens","correspondingAuthor":false,"prefix":"","firstName":"George","middleName":"","lastName":"Triantafyllou","suffix":""},{"id":449824941,"identity":"4d4ffe05-b1e0-46da-bef8-9eff540c511e","order_by":1,"name":"Panagiotis Papadopoulos-Manolarakis","email":"","orcid":"","institution":"Department of Neurosurgery, General Hospital of Nikaia-Piraeus","correspondingAuthor":false,"prefix":"","firstName":"Panagiotis","middleName":"","lastName":"Papadopoulos-Manolarakis","suffix":""},{"id":449824943,"identity":"45caeaeb-9047-49aa-8e0f-5ef59a82afb7","order_by":2,"name":"Maria Piagkou","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAyUlEQVRIiWNgGAWjYJCCAwwMNkAqgTQtaSRqAYLDJGjRbT978MDPHeej+dkT2CQ+1DDYbW8goMXsTF7Cwd4zt3Nn9jxgk5xxjCF5zgFCWg7kGBzgbbudu+FGAps0DxtDsgQhh5mdf2Nw8G/budz9YC3/iNFyI8fgMG/bgdwNEkAtvG0MdkRoeZdwWLYtOXfGmYfNljP7JBKIcFju4Y9v2+xy+9uTD9748M3GnqAWBgYeGIOxAUhIJDaQoAUC7AnrGAWjYBSMgpEGAAdARBSvZUIoAAAAAElFTkSuQmCC","orcid":"","institution":"Department of Anatomy, School of Medicine, Faculty of Health Sciences, National and Kapodistrian University of Athens","correspondingAuthor":true,"prefix":"","firstName":"Maria","middleName":"","lastName":"Piagkou","suffix":""},{"id":449824944,"identity":"4bbc63d4-d68d-4603-ba88-7213195a96e1","order_by":3,"name":"George Tsakotos","email":"","orcid":"","institution":"Department of Anatomy, School of Medicine, Faculty of Health Sciences, National and Kapodistrian University of Athens","correspondingAuthor":false,"prefix":"","firstName":"George","middleName":"","lastName":"Tsakotos","suffix":""},{"id":449824945,"identity":"cd843526-f3ee-497e-876b-d42d7e5446da","order_by":4,"name":"Renato Galzio","email":"","orcid":"","institution":"Department of Clinical-Surgical, Diagnostic and Pediatric Sciences, University of Pavia","correspondingAuthor":false,"prefix":"","firstName":"Renato","middleName":"","lastName":"Galzio","suffix":""},{"id":449824946,"identity":"a7841b3d-12d5-46fd-aea0-114616ab5e2d","order_by":5,"name":"Sabino Luzzi","email":"","orcid":"","institution":"Department of Medicine, Surgery, and Pharmacy, University of Sassari","correspondingAuthor":false,"prefix":"","firstName":"Sabino","middleName":"","lastName":"Luzzi","suffix":""}],"badges":[],"createdAt":"2025-04-24 08:08:29","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6518553/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6518553/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00276-025-03790-x","type":"published","date":"2025-12-09T15:58:15+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":82141524,"identity":"f8b9725a-4bd9-4dd4-b1a4-74f768ed3ed8","added_by":"auto","created_at":"2025-05-07 06:34:39","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":107453,"visible":true,"origin":"","legend":"\u003cp\u003e(A) The clinoidal line (CL) depicted on a sagittal slice between the anterior and posterior clinoid processes (ACP and PCP), (B) The measurement from the basilar artery (BA) tip to the CL on coronal slices. PCA- posterior cerebral artery, and SCA- superior cerebellar artery.\u003c/p\u003e","description":"","filename":"Figure1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6518553/v1/68b6e71eb9734168297a27b1.jpeg"},{"id":82143800,"identity":"3f398304-2ce9-45bb-b533-8e5f1f9951ae","added_by":"auto","created_at":"2025-05-07 06:42:39","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":195364,"visible":true,"origin":"","legend":"\u003cp\u003eClassification of the basilar artery (BA) into four types according to the measurements of the clinoidal line (CL). Examples of patients demonstrating: Type 1: Infraclinoidal bifurcation (\u0026lt;−5 mm below the CL), Type 2: Clinoidal bifurcation (−5 to +5 mm from the CL), Type 3: Supraclinoidal bifurcation (\u0026gt;+5 mm above the CL), Type 4: High-riding bifurcation (\u0026gt;+10 mm above the CL).\u003c/p\u003e","description":"","filename":"Figure2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6518553/v1/f9a3ab1b6e5c53da739f9f3b.jpeg"},{"id":82141541,"identity":"34281b03-bcda-4d08-89e1-d7be46835884","added_by":"auto","created_at":"2025-05-07 06:34:40","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":20758804,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustration of the proposed classification of the basilar artery tip (BAT) location (A) and the potential relationship with the presence of BAT aneurysm (B).\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6518553/v1/c68c4d94909a4adf8ed5c704.jpg"},{"id":82141527,"identity":"dde6ee9b-e617-49d0-a8bb-0ecf2c770c78","added_by":"auto","created_at":"2025-05-07 06:34:39","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":185648,"visible":true,"origin":"","legend":"\u003cp\u003eBox plots comparing patients with typical and bilateral (A), right (B), and left (C) fetal posterior cerebral arteries (FPCA). The plots demonstrate the vertical distance from the clinoidal line (CL) between patients with typical PCA (left boxes) and with FPCA (right boxes).\u003c/p\u003e","description":"","filename":"Figure4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6518553/v1/e8924e7ffb3a656e295f94bc.jpeg"},{"id":82141526,"identity":"c864b4bb-d898-42f8-8fd8-d05617dbf502","added_by":"auto","created_at":"2025-05-07 06:34:39","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":369606,"visible":true,"origin":"","legend":"\u003cp\u003eBilateral (A) and unilateral left-sided (B) fetal origin of the posterior cerebral artery (fPCA). Three-dimensional reconstruction (A1 and B1) and axial slices (A2 and B2) depicting the variation. tPCA: typical posterior cerebral artery, BA: basilar artery.\u003c/p\u003e","description":"","filename":"Figure5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6518553/v1/8ca376546b83097664b67227.jpeg"},{"id":98244297,"identity":"21cc665f-157b-4eea-80af-15d85e77ea41","added_by":"auto","created_at":"2025-12-15 16:13:57","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":20774161,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6518553/v1/c0d1491c-eb12-49a3-8ee7-339c8113e098.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"A novel classification of the basilar artery bifurcation height and the impact of fetal-type posterior cerebral artery: a radioanatomical study with implications for neurosurgical planning","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe microneurosurgical management of basilar artery tip (BAT) aneurysms continues to represent one of the most technically intricate challenges in vascular neurosurgery. This complexity is predominantly attributed to the deep and central positioning of the basilar artery (BA), the restricted operative pathways offered by standard skull base approaches, and the proximity of vital neurovascular structures. These considerations necessitate thorough preoperative planning and exact intraoperative execution. Intracranial aneurysms in the posterior circulation are linked to a significantly higher risk of rupture and worse clinical outcomes [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. Among these, BAT aneurysms present significant challenges owing to their deep anatomical location, propensity for earlier rupture, and complicated clinical behavior. Emphasizing the exceptional results of microneurosurgery, numerous studies advocate for timely or proactive intervention in such cases, considering their elevated risk profile and complex treatment landscape [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan additionalcitationids=\"CR34 CR35 CR36\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan additionalcitationids=\"CR43\" citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. Our research team has previously highlighted that these aneurysms often manifest at significantly large or, in some instances, giant sizes, which further complicates their management [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Aneurysms of such magnitude may obscure vital anatomical structures, elevate the risk of intraoperative rupture, and restrict surgical maneuverability, thereby rendering anatomical assessment essential.\u003c/p\u003e \u003cp\u003eThe choice of surgical approach for BAT aneurysms depends on multiple factors, including aneurysm size, projection, and the surrounding vascular anatomy. One crucial yet often underrecognized parameter is the vertical position of the basilar artery bifurcation (BAB) to fixed cranial landmarks, especially the clinoidal line (CL), defined by a plane connecting the anterior and posterior clinoid processes (ACPs and PCPs). The BAB height relative to the CL significantly impacts surgical exposure: high-riding BABs may require more extensive skull base approaches, while low-riding bifurcations can be challenging to access due to their depth and proximity to brainstem perforators and cranial nerves. Despite the surgical significance of BAB height, standard anatomical references fail to describe specific topographical variants of the BAB [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMeanwhile, several morphological variants of the posterior circulation have been associated with aneurysm formation. The fetal-type posterior cerebral artery (FPCA), defined by a dominant posterior communicating artery (PComA) and a hypoplastic or absent P1 segment [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e], has been linked to altered hemodynamics and a higher risk of aneurysm development, as well as increased rates of recanalization after coil embolization of PComA aneurysms [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Likewise, BA duplication and fenestration have been correlated with increased aneurysm incidence due to localized flow disturbances and structural vessel wall weakness [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAlthough the relationship between vascular variants and aneurysm formation has been extensively researched, their influence on the vertical topography of the BAT\u0026mdash;and, consequently, their ramifications for surgical access and approach planning\u0026mdash;has garnered considerably less consideration. Specifically, the potential impact of an FPCA on BAB height remains unclear. The present anatomical-imaging study seeks to bridge the gap by assessing a novel classification for the BAT position and the FPCA influence on the BAB's elevation to the CL. The primary objective is to improve anatomical comprehension and facilitate more precise and individualized surgical planning to manage basilar tip aneurysms.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003eA retrospective radioanatomical study was conducted on 250 randomly selected computed tomography angiograms (CTAs) acquired with a slice thickness of 0.8 mm. The study cohort included 138 male and 112 female patients with a mean age of 58.54\u0026thinsp;\u0026plusmn;\u0026thinsp;15 years. Inclusion criteria required high-quality imaging and the absence of pathological processes affecting the BA, ACPs, and PCPs.\u003c/p\u003e \u003cp\u003eImage analysis was performed using Horos software (Horos Project, New York, NY, USA). Multiplanar reconstructions in axial, coronal, and sagittal planes and three-dimensional volume renderings were utilized to evaluate the topographical relationship between the BAT and the CL. The CL was a straight line connecting the ACPs and PCPs, visualized in sagittal reconstructions \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e. The vertical distance from the BAB point to the CL was measured on coronal slices. Positive (+) values indicated a BAB located above the CL, and negative (\u0026minus;) values denoted a BAB below it \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBased on this vertical distance, the height of the BAB was classified into four types:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eType 1: Infraclinoidal bifurcation (\u0026thinsp;\u0026lt;\u0026thinsp;\u0026minus;\u0026thinsp;5 mm below the CL),\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eType 2: Clinoidal bifurcation (\u0026minus;\u0026thinsp;5 to +\u0026thinsp;5 mm from the CL),\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eType 3: Supraclinoidal bifurcation (\u0026thinsp;\u0026gt;\u0026thinsp;+\u0026thinsp;5 mm above the CL),\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eType 4: High-riding bifurcation (\u0026thinsp;\u0026gt;\u0026thinsp;+\u0026thinsp;10 mm above the CL).\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eMoreover, the presence of a FPCA was defined by a dominant PComA and a hypoplastic or absent P1 segment arising from the BA.\u003c/p\u003e \u003cp\u003eStatistical analyses were performed using IBM SPSS Statistics for MacOS, Version 29 (IBM Corp., Armonk, NY, USA). Categorical variables were compared using the Chi-square test for unpaired data and McNemar\u0026rsquo;s test for paired observations. The Shapiro-Wilk test assessed the normality of continuous variables. For normally distributed unpaired continuous variables, the independent t-test was used; otherwise, the Mann-Whitney U test was applied. A paired t-test was employed for paired continuous data when normality was met. For comparisons involving more than two groups, one-way ANOVA or the Kruskal-Wallis test was used based on the data distribution. All results are presented as means\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviations unless stated otherwise. A p-value of \u0026lt;\u0026thinsp;0.05 was deemed statistically significant.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eThe mean distance of the BAT to the CL (BAT-CL) was +\u0026thinsp;2.88\u0026thinsp;\u0026plusmn;\u0026thinsp;4.8 mm. Stratification by gender showed a mean BAT-CL distance of +\u0026thinsp;3.37\u0026thinsp;\u0026plusmn;\u0026thinsp;5.0 mm in females and +\u0026thinsp;2.49\u0026thinsp;\u0026plusmn;\u0026thinsp;4.6 mm in males, with no significant difference (p\u0026thinsp;=\u0026thinsp;0.231) \u003cstrong\u003e(\u003c/strong\u003eTable \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e\u003cstrong\u003e)\u003c/strong\u003e. Concerning, the vertical classification of the BAB, BAB of type 2 (clinoidal level) was the most frequently configuration (55.6%), followed by type 3 (supraclinoidal, 24%), type 1 (infraclinoidal, 12.4%), and type 4 (high-riding, 8%) \u003cstrong\u003e(\u003c/strong\u003eFigs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e\u003cstrong\u003e).\u003c/strong\u003e The distribution of these types did not differ significantly between males and females (p\u0026thinsp;=\u0026thinsp;0.545).\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eDemographic and radio-anatomic data of the current study\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eParameter\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eTotal\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eGender\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"3\"\u003e\n \u003cp\u003e\u003cem\u003ep\u003c/em\u003e-value\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFemale\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMale\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePatients - n.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e250\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e112\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e138\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePatients\u0026rsquo; age - year (\u0026plusmn;SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e56.4 (15.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e55.7 (15.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e57.2 (14.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.440\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBAT-CL distance - mean mm (\u0026plusmn;SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e+\u0026thinsp;2.88 (4.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e+\u0026thinsp;3.37 (5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e+\u0026thinsp;2.49 (4.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.231\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"5\"\u003e\n \u003cp\u003eBAT Types\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eType 1 - n. (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e31 (12.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13 (11.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18 (13%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"4\"\u003e\n \u003cp\u003e0.545\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eType 2 - n. (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e139 (55.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e59 (52.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e80 (57%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eType 3 - n. (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e60 (24%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e29 (25.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e31 (23%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eType 4 - n. (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e20 (8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11 (9.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9 (7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"5\"\u003e\n \u003cp\u003ePCA origin\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFetal-type - n. (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e74 (29.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e31 (27.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e43 (31.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.606\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLeft - n. (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e35 (14)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15 (13.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e20 (14.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"3\"\u003e\n \u003cp\u003e0.687\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRight - n. (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25 (10)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9 (8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e16 (11.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBilateral - n. (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14 (5.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7 (6.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7 (5.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\"\u003eSD: Standard Deviation. BAT-CL: basilar artery tip-clinoidal line.\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eAn FPCA was identified in 74 patients (29.6%), including 35 cases (14%) with a left-sided FPCA, 25 cases (10%) with a right-sided variant, and 14 cases (5.6%) with a bilateral configuration (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e) \u003cstrong\u003e(\u003c/strong\u003eTable \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e\u003cstrong\u003e)\u003c/strong\u003e. Analysis of the BAT-CL distance to PCA configuration showed lower mean values in all fetal-type groups compared to the typical PCA origin \u003cstrong\u003e(\u003c/strong\u003eTable \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e\u003cstrong\u003e)\u003c/strong\u003e. In patients with bilateral FPCA, the mean BAT-CL distance was \u0026minus;\u0026thinsp;0.9\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2 mm, compared to +\u0026thinsp;3.1\u0026thinsp;\u0026plusmn;\u0026thinsp;4.8 mm in those with a bilateral typical PCA (p\u0026thinsp;=\u0026thinsp;0.002). In cases with a left FPCA, the mean distance was \u0026minus;\u0026thinsp;1.1\u0026thinsp;\u0026plusmn;\u0026thinsp;4.5 mm versus +\u0026thinsp;3.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4.8 mm in typical left PCA cases (p\u0026thinsp;=\u0026thinsp;0.005). For right-sided variants, the fetal-type group showed a mean distance of \u0026minus;\u0026thinsp;0.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.9 mm, compared to +\u0026thinsp;3.4\u0026thinsp;\u0026plusmn;\u0026thinsp;4.8 mm in the typical configuration (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) \u003cstrong\u003e(\u003c/strong\u003eTable \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e \u003cstrong\u003eand\u003c/strong\u003e Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e\u003cstrong\u003e)\u003c/strong\u003e.\u0026nbsp;\u003c/p\u003e\n\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eEffect of Fetal-Type PCA on Basilar Tip Height by Sidedness\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eSidedness\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003ePCA variant\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cem\u003ep\u003c/em\u003e-value\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTypical\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFetal-type\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBilateral - mean BAT-CL distance mm (\u0026plusmn;SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e+\u0026thinsp;3.1 (4.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-0.9 (3.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.002*\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLeft - mean BAT-CL distance mm (\u0026plusmn;SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e+\u0026thinsp;3.3 (4.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-1.1 (4.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.005*\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRight - mean BAT-CL distance mm (\u0026plusmn;SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e+\u0026thinsp;3.4 (4.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-0.3 (3.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001*\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"4\"\u003ePCA: posterior cerebral artery. BAT-CL: basilar artery tip-clinoidal line. SD: Standard Deviation.\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n\u003c/table\u003e"},{"header":"Discussion","content":"\u003cp\u003eOur study underscores the necessity of individualized surgical planning by quantifying variability in BAT height and, importantly, identifying a clear association between vascular configuration and vertical positioning of the BAT. First, we proposed a classification system for the BAT height \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e, followed by an analysis of the results based on sex and the potential influence of the FPCA. Among the 250 patients analyzed, we found a significant correlation between an FPCA and a caudally displaced BAT \u003cb\u003e(\u003c/b\u003eTables\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u003cb\u003e).\u003c/b\u003e Specifically, patients with an FPCA consistently exhibited lower BAT-CL distances than those with a typical PCA configuration, regardless of sidedness. This finding suggests that the FPCA\u0026mdash;characterized by a dominant PComA and hypoplastic or absent P1 segment\u0026mdash;may be a reliable radiological predictor of low bifurcation height. These anatomical findings are novel and should properly correlate with their neurosurgical significance; therefore, it is further discussed.\u003c/p\u003e \u003cp\u003eSurgical management of BAT aneurysms has long represented one of the most intricate and demanding endeavors in microneurosurgery. Since the pioneering achievement of Charles G. Drake in the direct clipping of a BAT aneurysm through a subtemporal transtentorial approach during the 1960s [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], the field has undergone significant evolution in the pursuit of safer and more effective access routes. Drake\u0026rsquo;s subtemporal transtentorial approach was revolutionary, offering a relatively direct anterolateral path to the BAB [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. However, it posed several limitations: \u003cem\u003ethe need for significant temporal lobe retraction with an associated risk of venous infarction, a limited superior viewing angle for high-riding aneurysms, and the challenge of achieving proximal control without tentorial sectioning\u003c/em\u003e. These limitations prompted the refinement of skull base techniques, particularly the cranio-orbito-zygomatic (COZ) approach, which offers improved surgical freedom and enhanced angles of attack [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan additionalcitationids=\"CR23 CR24\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Today, the COZ approach is considered especially advantageous for high-riding BAT aneurysms (i.e., those located\u0026thinsp;\u0026gt;\u0026thinsp;10 mm above the CL, Type 4 in our classification). By incorporating the removal of the orbital rim and zygomatic arch and an extended frontotemporal craniotomy, the COZ approach provides a superior and broader trajectory, allowing for safer clip application and better visualization of the aneurysm neck and surrounding perforators. Its expanded working angles reduce the need for excessive brain retraction and facilitate multi-angled access to the interpeduncular cistern.\u003c/p\u003e \u003cp\u003eIn contrast, low-riding bifurcations (Types 1 and 2), located below or near the CL, are better addressed through the pretemporal trans-cavernous approach, which provides more direct exposure to the lower interpeduncular fossa with minimal brain retraction. This approach is typically performed via an extended pterional craniotomy, enabling anterior clinoidectomy, unroofing of the optic canal, and mobilization of the oculomotor nerve to access the basilar apex while preserving crucial neurovascular structures [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn select cases\u0026mdash;mainly when the aneurysm is low-lying, projects posteriorly, or is obscured by the petrous apex\u0026mdash;the Kawase approach (anterior petrosectomy) may be indicated. This technique involves drilling the petrous apex to create a direct anterolateral corridor to the ventral brainstem and upper clivus [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Although technically demanding, it is beneficial when additional exposure of the lower BA trunk is required beyond what the pretemporal route can offer. Its use, however, should be judicious, given the increased risk of morbidity associated with temporal bone drilling and potential cranial nerve manipulation.\u003c/p\u003e \u003cp\u003eLastly, from a surgical standpoint, the critical observation that the FPCA affects the position of the BAT could be valuable. Accurate preoperative recognition of a FPCA could inform the neurosurgeon that a lower-riding BAB will likely be encountered. This, in turn, supports early consideration of the pretemporal trans-cavernous approach, with or without anterior petrosectomy, as the most direct and least invasive corridor for aneurysm access. By avoiding unnecessarily extensive skull base exposures\u0026mdash;such as a full COZ approach\u0026mdash;in cases where the BAB lies low, surgeons may reduce operative time, minimize morbidity, and preserve surrounding neurovascular structures. This anatomical correlation, revealed through non-invasive imaging, thus offers a practical, reproducible marker that can enhance surgical strategy and tailor interventions to individual vascular morphology. It also underlines the enduring relevance of detailed preoperative vascular analysis, even in an era increasingly shaped by endovascular techniques.\u003c/p\u003e \u003cp\u003eWhile these results are promising, several limitations must be acknowledged. First, this was a retrospective study based solely on CTA imaging; although CTA provides high-resolution vascular detail, it lacks the intraoperative perspective and real-time dynamics of microsurgical dissection. Second, we used the CL as a reference, which, while practical and reproducible, may be influenced by individual variations in skull base morphology. Third, the study did not include a correlation with intraoperative findings or clinical outcomes, which would be necessary to confirm the functional relevance of our morphometric data. Finally, the FPCA was documented without further analysis of aneurysm formation.\u003c/p\u003e \u003cp\u003eDespite these limitations, the current radioanatomical study highlights a measurable and surgically relevant relationship between PCA configuration and BAB height. Neurosurgeons can refine approach selection, reduce surgical burden, and enhance overall procedural safety and precision by integrating vascular variants into preoperative planning.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe current anatomical-imaging study emphasizes the vertical position of the BAB as a crucial morphometric variable, which is significantly affected by the presence of an FPCA. Using a simple radiological method, a four-typed classification system for the BAT position was proposed. The preoperative demonstration of BAT types 3 and 4 may suggest the utilization of the COZ approach. In contrast, the pretemporal trans-cavernous pathway may address aneurysms defined by BAT types 1 and 2. Traditionally, the FPCA has been discussed in the context of aneurysm development; however, our findings elucidate its significance as a radiological marker linked to a lower-riding BAT. The preoperative identification of this variant may contribute to predicting aneurysm height and optimizing the surgical approach, particularly favoring the pretemporal trans-cavernous route in cases demonstrating favorable anatomy. This study advocates for a more individualized, anatomy-based methodology in surgical planning, correlating vascular configurations with bifurcation height. Such a personalized approach can potentially enhance operative exposure, minimize the extent of skull base dissection, and improve the overall safety and precision of BAT aneurysm surgeries.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNone.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval and consent to participate.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe General Hospital of Nikaia-Piraeus Ethics Committee approved the study (approval number: 56485/13.11.2024). The research was conducted ethically according to the Code of Ethics of the World Medical Association (Declaration of Helsinki).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePlease contact the authors for data requests (Professor Maria Piagkou - email address: [email protected]).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNone.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNone.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; contribution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eGeorge Triantafyllou \u0026ndash; student \u0026ndash; conceptualization, project development, data analysis, writing- original draft, final version approval.\u003c/p\u003e\n\u003cp\u003ePanagiotis Papadopoulos-Manolarakis (MD, MSc) \u0026ndash; neurosurgeon \u0026ndash; data collection, data analysis, writing- review/editing, final version approval.\u003c/p\u003e\n\u003cp\u003eMaria Piagkou (DDS, MD, MSc, PhD) \u0026ndash; professor \u0026ndash; data analysis, writing- review/editing, final version approval.\u003c/p\u003e\n\u003cp\u003eGeorge Tsakotos (MD, MSc, PhD) \u0026ndash; assistant professor \u0026ndash; data analysis, writing- review/editing, final version approval.\u003c/p\u003e\n\u003cp\u003eRenato Galzio (MD, PhD) \u0026ndash; neurosurgeon, professor \u0026ndash; data analysis, writing- review/editing, final version approval.\u003c/p\u003e\n\u003cp\u003eSabino Luzzi (MD, PhD) \u0026ndash; neurosurgeon, professor - supervision, writing- original draft, final version approval.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAndaluz N, van Loveren HR, Keller JT, Zuccarello M (2003) The One-Piece Orbitopterional Approach. Skull Base 13:241\u0026ndash;246. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1055/s-2004-817701\u003c/span\u003e\u003cspan address=\"10.1055/s-2004-817701\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAziz K, van Loveren HR, Tew J, Chicoine M (1999) The Kawase approach to retrosellar and upper clival basilar aneurysms. Neurosurgery 44:1225\u0026ndash;1234 discussion 1234-6\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCampero A, Martins C, Socolovsky M, Torino R, Yasuda A, Domitrovic L, Rhoton A (2010) Three-Piece Orbitozygomatic Approach. Operative Neurosurg 66:onsE119\u0026ndash;onsE120. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1227/01.NEU.0000348559.82835.21\u003c/span\u003e\u003cspan address=\"10.1227/01.NEU.0000348559.82835.21\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCampos J, Fox AJ, Vi\u0026ntilde;uela F, Lylyk P, Ferguson GG, Drake CG, Peerless SJ (1987) Saccular aneurysms in basilar artery fenestration. AJNR Am J Neuroradiol 8:233\u0026ndash;236\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChoi HH, Cho YD, Yoo DH, Lee HS, Kim S-H, Jang D, Lee SH, Cho W-S, Kang H-S, Kim JE (2020) Impact of fetal-type posterior cerebral artery on recanalization of posterior communicating artery aneurysms after coil embolization: matched-pair case\u0026ndash;control study. J Neurointerv Surg 12:783\u0026ndash;787. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1136/neurintsurg-2019-015531\u003c/span\u003e\u003cspan address=\"10.1136/neurintsurg-2019-015531\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDavidoiu AM, Mincă DI, Rusu MC, Hostiuc S, Toader C (2023) The Fetal Type of Posterior Cerebral Artery. Med (Lithuania) 59. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3390/medicina59020231\u003c/span\u003e\u003cspan address=\"10.3390/medicina59020231\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDrake CG (1961) Bleeding Aneurysms of the Basilar Artery. J Neurosurg 18:230\u0026ndash;238. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3171/jns.1961.18.2.0230\u003c/span\u003e\u003cspan address=\"10.3171/jns.1961.18.2.0230\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDrake CG (1965) Surgical Treatment of Ruptured Aneurysms of the Basilar Artery. J Neurosurg 23:457\u0026ndash;473. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3171/jns.1965.23.5.0457\u003c/span\u003e\u003cspan address=\"10.3171/jns.1965.23.5.0457\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFlores-Justa A, Luzzi S, Giotta Lucifero A, Villalonga JF, Saenz A, Santin-Amo JM, Baldoncini M, Campero A (2021) Use of Neuroanatomic Knowledge and Neuronavigation System for a Safe Anterior Petrosectomy. Brain Sci 11:488. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3390/brainsci11040488\u003c/span\u003e\u003cspan address=\"10.3390/brainsci11040488\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGiotta Lucifero A, Baldoncini M, Bruno N, Galzio R, Hernesniemi J, Luzzi S (2021) Shedding the Light on the Natural History of Intracranial Aneurysms: An Updated Overview. Med (B Aires) 57:742. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3390/medicina57080742\u003c/span\u003e\u003cspan address=\"10.3390/medicina57080742\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGiotta Lucifero A, Baldoncini M, Bruno N, Tartaglia N, Ambrosi A, Marseglia GL, Galzio R, Campero A, Hernesniemi J, Luzzi S (2021) Microsurgical Neurovascular Anatomy of the Brain: The Anterior Circulation (Part I). Acta Biomed 92:e2021412. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.23750/abm.v92iS4.12116\u003c/span\u003e\u003cspan address=\"10.23750/abm.v92iS4.12116\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGiotta Lucifero A, Baldoncini M, Bruno N, Tartaglia N, Ambrosi A, Marseglia GL, Galzio R, Campero A, Hernesniemi J, Luzzi S (2021) Microsurgical Neurovascular Anatomy of the Brain: The Posterior Circulation (Part II). Acta Biomed 92:e2021413. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.23750/abm.v92iS4.12119\u003c/span\u003e\u003cspan address=\"10.23750/abm.v92iS4.12119\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHendricks BK, Cohen-Gadol AA (2020) The Extended Pterional Craniotomy: A Contemporary and Balanced Approach. Operative Neurosurg 18:225\u0026ndash;231. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1093/ons/opz117\u003c/span\u003e\u003cspan address=\"10.1093/ons/opz117\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKato Y, Sano H, Behari S, Kumar S, Nagahisa S, Iwata S, Kanno T (2002) Surgical Clipping of Basilar Aneurysms: Relationship Between the Different Approaches and the Surgical Corridors. min -. Minim Invasive Neurosurg 45:142\u0026ndash;145. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1055/s-2002-34351\u003c/span\u003e\u003cspan address=\"10.1055/s-2002-34351\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKawase T, Shiobara R, Toya S (1991) Anterior transpetrosal-transtentorial approach for sphenopetroclival meningiomas: surgical method and results in 10 patients. Neurosurgery 28:869\u0026ndash;875 discussion 875-6\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKawase T, Shiobara R, Toya S (1994) Middle fossa transpetrosal-transtentorial approaches for petroclival meningiomas selective pyramid resection and radicality. Acta Neurochir (Wien) 129:113\u0026ndash;120. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/BF01406489\u003c/span\u003e\u003cspan address=\"10.1007/BF01406489\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKrisht AF, Kadri PAS (2005) Surgical Clipping of Complex Basilar Apex Aneurysms: A Strategy for Successful Outcome Using the Pretemporal Transzygomatic Transcavernous Approach. Operative Neurosurgery 56:ONS-261-ONS-273. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1227/01.NEU.0000156785.63530.4E\u003c/span\u003e\u003cspan address=\"10.1227/01.NEU.0000156785.63530.4E\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLawton MT (2002) Basilar Apex Aneurysms: Surgical Results and Perspectives from an Initial Experience. Neurosurgery 50:1\u0026ndash;10. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1097/00006123-200201000-00002\u003c/span\u003e\u003cspan address=\"10.1097/00006123-200201000-00002\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLemole GM, Henn JS, Zabramski JM, Spetzler RF (2003) Modifications to the orbitozygomatic approach. J Neurosurg 99:924\u0026ndash;930. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3171/jns.2003.99.5.0924\u003c/span\u003e\u003cspan address=\"10.3171/jns.2003.99.5.0924\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLozier AP, Kim GH, Sciacca RR, Connolly ES, Solomon RA (2004) Microsurgical Treatment of Basilar Apex Aneurysms: Perioperative and Long-term Clinical Outcome. Neurosurgery 54:286\u0026ndash;299. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1227/01.NEU.0000103222.13642.00\u003c/span\u003e\u003cspan address=\"10.1227/01.NEU.0000103222.13642.00\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLuzzi S, Gallieni M, Del Maestro M, Trovarelli D, Ricci A, Galzio R (2018) Giant and Very Large Intracranial Aneurysms: Surgical Strategies and Special Issues. pp 25\u0026ndash;31\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLuzzi S, Giotta Lucifero A, Bruno N, Baldoncini M, Campero A, Galzio R (2022) Cranio-Orbito-Zygomatic Approach. Acta Biomed 92:e2021350. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.23750/abm.v92iS4.12784\u003c/span\u003e\u003cspan address=\"10.23750/abm.v92iS4.12784\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLuzzi S, Giotta Lucifero A, Bruno N, Baldoncini M, Campero A, Galzio R (2022) Pterional Approach. Acta Biomed 92:e2021346. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.23750/abm.v92iS4.12775\u003c/span\u003e\u003cspan address=\"10.23750/abm.v92iS4.12775\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLuzzi S, Giotta Lucifero A, Spina A, Baldoncini M, Campero A, Elbabaa SK, Galzio R (2022) Cranio-Orbito-Zygomatic Approach: Core Techniques for Tailoring Target Exposure and Surgical Freedom. Brain Sci 12:405. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3390/brainsci12030405\u003c/span\u003e\u003cspan address=\"10.3390/brainsci12030405\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLuzzi S, Gragnaniello C, Giotta Lucifero A, Del Maestro M, Galzio R (2020) Surgical Management of Giant Intracranial Aneurysms: Overall Results of a Large Series. World Neurosurg 144:e119\u0026ndash;e137. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.wneu.2020.08.004\u003c/span\u003e\u003cspan address=\"10.1016/j.wneu.2020.08.004\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLuzzi S, Del Maestro M, Galzio R (2021) Posterior Circulation Aneurysms: A Critical Appraisal of a Surgical Series in Endovascular Era. pp 39\u0026ndash;45\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLuzzi S, Del Maestro M, Galzio R (2021) Posterior Circulation Aneurysms: A Critical Appraisal of a Surgical Series in Endovascular Era. pp 39\u0026ndash;45\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMcDougall CG, Spetzler RF, Zabramski JM, Partovi S, Hills NK, Nakaji P, Albuquerque FC (2012) The Barrow Ruptured Aneurysm Trial. J Neurosurg 116:135\u0026ndash;144. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3171/2011.8.JNS101767\u003c/span\u003e\u003cspan address=\"10.3171/2011.8.JNS101767\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMolyneux AJ, Kerr RS, Yu L-M, Clarke M, Sneade M, Yarnold JA, Sandercock P (2005) International subarachnoid aneurysm trial (ISAT) of neurosurgical clipping versus endovascular coiling in 2143 patients with ruptured intracranial aneurysms: a randomised comparison of effects on survival, dependency, seizures, rebleeding, subgroups, and aneurysm occlusion. Lancet 366:809\u0026ndash;817. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/S0140-6736(05)67214-5\u003c/span\u003e\u003cspan address=\"10.1016/S0140-6736(05)67214-5\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNanda A, Sonig A, Banerjee AD, Javalkar VK (2014) Microsurgical Management of Basilar Artery Apex Aneurysms: A Single Surgeon\u0026rsquo;s Experience from Louisiana State University, Shreveport. World Neurosurg 82:118\u0026ndash;129. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.wneu.2013.06.016\u003c/span\u003e\u003cspan address=\"10.1016/j.wneu.2013.06.016\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePia HW (1979) Classification of vertebro-basilar aneurysms. Acta Neurochir (Wien) 47:3\u0026ndash;30. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/BF01404659\u003c/span\u003e\u003cspan address=\"10.1007/BF01404659\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSaeki N, Rhoton AL (1977) Microsurgical anatomy of the upper basilar artery and the posterior circle of Willis. J Neurosurg 46:563\u0026ndash;578. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3171/jns.1977.46.5.0563\u003c/span\u003e\u003cspan address=\"10.3171/jns.1977.46.5.0563\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSaliou G, Sacho RH, Power S, Kostynskyy A, Willinsky RA, Tymianski M, terBrugge KG, Rawal S, Krings T (2015) Natural History and Management of Basilar Trunk Artery Aneurysms. Stroke 46:948\u0026ndash;953. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1161/STROKEAHA.114.006909\u003c/span\u003e\u003cspan address=\"10.1161/STROKEAHA.114.006909\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSanai N, Tarapore P, Lee AC, Lawton MT (2008) THE CURRENT ROLE OF MICROSURGERY FOR POSTERIOR CIRCULATION ANEURYSMS. Neurosurgery 62:1236\u0026ndash;1253. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1227/01.neu.0000333295.59738.de\u003c/span\u003e\u003cspan address=\"10.1227/01.neu.0000333295.59738.de\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSano H, Kato Y, Akashi K, Yamaguchi S, Hayakawa M, Arunkumar R, Kanno T (1997) Operation on High-Lying Basilar Bifurcation Aneurysms. Surg Neurol 48:458\u0026ndash;464. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/S0090-3019(97)00036-0\u003c/span\u003e\u003cspan address=\"10.1016/S0090-3019(97)00036-0\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSekhar LN, Tariq F, Morton RP, Ghodke B, Hallam DK, Barber J, Kim LJ (2013) Basilar Tip Aneurysms. Neurosurgery 72:284\u0026ndash;299. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1227/NEU.0b013e3182797952\u003c/span\u003e\u003cspan address=\"10.1227/NEU.0b013e3182797952\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ede SOUSA AA (1998) Basilar Bifurcation Aneurysms. Neurol Med Chir (Tokyo) 38:70\u0026ndash;73. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.2176/nmc.38.suppl_70\u003c/span\u003e\u003cspan address=\"10.2176/nmc.38.suppl_70\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTroupp H, THE NATURAL HISTORY OF ANEURYSMS OF THE BASILAR BIFURCATION (1971) Acta Neurol Scand 47:350\u0026ndash;356. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1111/j.1600-0404.1971.tb07489.x\u003c/span\u003e\u003cspan address=\"10.1111/j.1600-0404.1971.tb07489.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTubbs RS, Shoja MM, Loukas M (2016) Bergman\u0026rsquo;s comprehensive encyclopedia of human anatomic variation\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eUchino A, Saito N, Okada Y, Kozawa E, Nishi N, Mizukoshi W, Inoue K, Nakajima R, Takahashi M (2012) Fenestrations of the intracranial vertebrobasilar system diagnosed by MR angiography. Neuroradiology 54:445\u0026ndash;450\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWiebers DO (2003) Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet 362:103\u0026ndash;110. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/S0140-6736(03)13860-3\u003c/span\u003e\u003cspan address=\"10.1016/S0140-6736(03)13860-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWinkler EA, Lee A, Yue JK, Raygor KP, Rutledge WC, Rubio RR, Josephson SA, Berger MS, Raper DMS, Abla AA (2021) Endovascular embolization versus surgical clipping in a single surgeon series of basilar artery aneurysms: a complementary approach in the endovascular era. Acta Neurochir (Wien) 163:1527\u0026ndash;1540. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s00701-021-04803-5\u003c/span\u003e\u003cspan address=\"10.1007/s00701-021-04803-5\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYasargil MG (1984) Microneurosurgery, Volume II: Clinical Considerations, Surgery of the Intracranial Aneurysms and Results. Thieme\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYasargil MG, Antic J, Laciga R, Jain KK, Hodosh RM, Smith RD (1976) Microsurgical pterional approach to aneurysms of the basilar bifurcation. Surg Neurol 6:83\u0026ndash;91\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"surgical-and-radiologic-anatomy","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"sara","sideBox":"Learn more about [Surgical and Radiologic Anatomy](http://link.springer.com/journal/276)","snPcode":"276","submissionUrl":"https://submission.nature.com/new-submission/276/3","title":"Surgical and Radiologic Anatomy","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Basilar artery bifurcation, Clinoidal line, Fetal-type posterior cerebral artery, Pretemporal trans-cavernous approach, Skull base surgery","lastPublishedDoi":"10.21203/rs.3.rs-6518553/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6518553/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003ePurpose\u003c/h2\u003e \u003cp\u003eThe vertical location of the basilar artery bifurcation (BAB) is a crucial factor in determining the best surgical approach for basilar tip (BAT) aneurysms. Although anatomical variants, such as the fetal-type posterior cerebral artery (FPCA), have been linked to aneurysm formation, their impact on BAB height remains unclear.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eA retrospective anatomical-imaging analysis of 250 high-resolution computed tomography angiograms (CTAs) was conducted to measure the vertical distance from the BAT to the clinoidal line (CL). A dominant posterior communicating artery and/or a hypoplastic or absent P1 segment defines the FPCA.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eBATs were classified into four types based on their BAT-CL distance, with Type 2 BATs (within \u0026plusmn;\u0026thinsp;5 mm of the CL) being the most common. The mean BAT-CL distance was +\u0026thinsp;2.88\u0026thinsp;\u0026plusmn;\u0026thinsp;4.8 mm. An FPCA was identified in 74 patients (29.6%). The BAT was significantly lower in all fetal-type subgroups than in patients with typical PCA anatomy (p\u0026thinsp;\u0026lt;\u0026thinsp;0.005). Bilateral FPCA exhibited the lowest BAT-CL distance (-0.9\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2 mm). An FPCA is significantly associated with a caudally positioned BAT.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eThis finding can assist in surgical planning by predicting aneurysm height based on vascular configuration. In such cases, the pretemporal trans-cavernous approach through extended pterional craniotomy may offer safer and more direct access, thereby reducing surgical morbidity. These results support incorporating vascular variants in preoperative assessments to optimize personalized neurosurgical strategies.\u003c/p\u003e","manuscriptTitle":"A novel classification of the basilar artery bifurcation height and the impact of fetal-type posterior cerebral artery: a radioanatomical study with implications for neurosurgical planning","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-07 06:34:35","doi":"10.21203/rs.3.rs-6518553/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-25T08:19:43+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-12T14:44:23+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-10T01:52:56+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"38557235079892927725465419880947491629","date":"2025-06-25T20:05:39+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-24T02:00:08+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"115354807361523242507362980487181516227","date":"2025-05-04T07:09:54+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-01T07:55:46+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"148000870430937486434604681822524640450","date":"2025-04-30T21:04:09+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"174247844021247268043442118875060151123","date":"2025-04-29T16:54:04+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-04-28T16:03:29+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-04-25T09:59:12+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-04-24T08:19:41+00:00","index":"","fulltext":""},{"type":"submitted","content":"Surgical and Radiologic Anatomy","date":"2025-04-24T07:59:19+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"surgical-and-radiologic-anatomy","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"sara","sideBox":"Learn more about [Surgical and Radiologic Anatomy](http://link.springer.com/journal/276)","snPcode":"276","submissionUrl":"https://submission.nature.com/new-submission/276/3","title":"Surgical and Radiologic Anatomy","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"6b975037-692b-43ce-8246-756649c29287","owner":[],"postedDate":"May 7th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-12-15T16:07:23+00:00","versionOfRecord":{"articleIdentity":"rs-6518553","link":"https://doi.org/10.1007/s00276-025-03790-x","journal":{"identity":"surgical-and-radiologic-anatomy","isVorOnly":false,"title":"Surgical and Radiologic Anatomy"},"publishedOn":"2025-12-09 15:58:15","publishedOnDateReadable":"December 9th, 2025"},"versionCreatedAt":"2025-05-07 06:34:35","video":"","vorDoi":"10.1007/s00276-025-03790-x","vorDoiUrl":"https://doi.org/10.1007/s00276-025-03790-x","workflowStages":[]},"version":"v1","identity":"rs-6518553","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6518553","identity":"rs-6518553","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}