Syncope Associated with a Congenital Variant of the Circle of Willis: Absence of the Right Anterior Cerebral Artery and Anterior Communicating Artery

Syncope Associated with a Congenital Variant of the Circle of Willis: Absence of the Right Anterior Cerebral Artery and Anterior Communicating Artery | 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 Case Report Syncope Associated with a Congenital Variant of the Circle of Willis: Absence of the Right Anterior Cerebral Artery and Anterior Communicating Artery Isabel Echevarría Frutos, Gutenberg Navarro Zambrano, Amaury León Sosa, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7335489/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background: Syncope is a transient loss of consciousness caused by global cerebral hypoperfusion. Although most commonly attributed to vasovagal or cardiac etiologies, anatomical variants of the Circle of Willis may alter cerebral hemodynamics and, in rare cases, contribute to syncope. Case presentation: We report the case of an 18-year-old female patient with no significant personal medical history and a family history of cerebral cavernoma. She experienced a single syncopal episode upon sudden standing, with brief loss of consciousness lasting approximately one minute and no subsequent neurological deficits. Laboratory tests and electroencephalogram were within normal limits. Brain magnetic resonance imaging (MRI) and time-of-flight magnetic resonance angiography (TOF-MRA) revealed absence of the right anterior cerebral artery (ACA) A1 segment and complete absence of the anterior communicating artery (ACoA). The left ACA was dominant, supplying both cerebral hemispheres. Cardiac causes were excluded, and a diagnosis of classic vasovagal syncope was established. The patient has remained asymptomatic after nearly three years of follow-up. Discussion: Congenital variants of the Circle of Willis are common anatomical findings but rarely linked to syncope. In this case, the bilateral absence of key vascular segments may have reduced cerebrovascular reserve during orthostatic stress, precipitating the syncopal event. This case underscores the importance of advanced neuroimaging techniques in the evaluation of atypical syncope. Conclusions: This report highlights the clinical significance of Circle of Willis anatomical variants as potential contributors to syncope when other causes have been excluded. A multidisciplinary approach and the use of appropriate imaging modalities are critical for accurate diagnosis. syncope Circle of Willis anterior cerebral artery anterior communicating artery congenital vascular anomaly cerebral blood flow vasovagal syncope Figures Figure 1 Figure 2 Introduction Syncope, defined as a transient loss of consciousness secondary to global cerebral hypoperfusion, is a common clinical complaint. Although vasovagal syncope is the most frequent cause, anatomical variants of the Circle of Willis may contribute in cases unexplained by conventional causes. The Circle of Willis is a fundamental anastomotic arterial network for cerebral collateral circulation and adequate brain perfusion. Congenital variations in its configuration are common, with reported prevalence ranging between 40% and 60% in population studies ( 1 , 2 ). Hypoplasia or absence of the A1 segment of the anterior cerebral artery (ACA) and the anterior communicating artery (ACoA) are uncommon anomalies, with estimated frequencies between 1% and 15% for the A1 segment and approximately 1–5% for the ACoA ( 3 , 4 ). These variants can alter cerebral hemodynamics and have been associated with an increased risk of ischemic cerebrovascular events ( 5 ). However, the direct association between these variants and syncope episodes is rarely reported in the literature. We present the case of an 18-year-old female patient with syncope associated with a congenital variant of the Circle of Willis, characterized by absence of the right anterior cerebral artery (A1 segment) and the anterior communicating artery. This report emphasizes the importance of considering cerebral vascular anatomical variants in the differential diagnosis of syncope and discusses their clinical implications. Case Presentation An 18-year-old female patient without significant personal pathological history, except sulfa allergy and allergic rhinitis. Family history includes cerebral cavernoma and absence seizures in her father. The patient reported a single syncope episode occurring upon sudden standing after lying down, with brief loss of consciousness (approximately 1 minute), spontaneous recovery, and no subsequent neurological focality. She also reported prior exposure to solvents (thinner and paint) and moderate alcohol consumption. Initial evaluation by neurology and neurosurgery included electroencephalogram (normal during wakefulness and light sleep) and laboratory studies within normal limits. Consideration was given to performing contrast neuroimaging studies, which were authorized after allergy evaluation. Brain magnetic resonance imaging (MRI) and time-of-flight (TOF) MR angiography showed absence of the right anterior cerebral artery (ACA A1) and complete absence of the anterior communicating artery (ACoA) (Fig. 1 ). The left ACA was dominant, supplying both hemispheres. The rest of the Circle of Willis had a normal configuration without evidence of aneurysms, arteriovenous malformations, or other pathological findings (Fig. 2 ). The patient remained asymptomatic without new syncope episodes or neurological deficits. Cardiology evaluation diagnosed classical vasovagal syncope. Follow-up included isolated arterial hypertension and mild dyslipidemia, without pharmacological treatment requirement. Complementary care was provided by ENT and ophthalmology for unrelated findings. At 2 years and 11 months follow-up, the patient remains asymptomatic. Discussion Syncope is a transient loss of consciousness caused by global cerebral hypoperfusion, commonly attributed to vasovagal or cardiac causes. However, anatomical variants of the cerebral arteries, such as those affecting the Circle of Willis, can influence cerebral hemodynamics and, in rare cases, contribute to syncope. The Circle of Willis is a crucial collateral network ensuring adequate cerebral perfusion even in cases of vascular occlusion or stenosis. Anatomical variations in this structure are common, occurring in up to 50–60% of individuals in population studies ( 6 , 7 ). Among these, absence or hypoplasia of the anterior cerebral artery (ACA) segments and the anterior communicating artery (ACoA) are less frequent but clinically relevant ( 8 , 9 ). In our patient, congenital absence of the right ACA A1 segment and ACoA likely compromised cerebral collateral flow, lowering the threshold for cerebral hypoperfusion during orthostatic stress, explaining the syncopal episode. This is consistent with McKinstry et al., who described reduced cerebrovascular reserve in patients with similar arterial anomalies ( 1 ). Additionally, the presence of a dominant left ACA supplying both hemispheres may partially compensate for this absence, explaining the lack of permanent neurological deficits. Previous studies have mainly associated these anatomical variants with ischemic stroke and aneurysm formation ( 6 , 7 ). However, their role in transient neurological symptoms, including syncope, is less documented. Our case contributes to the emerging literature emphasizing the clinical significance of Circle of Willis variants beyond cerebrovascular events. The differential diagnosis ruled out cardiac and neurogenic causes, supporting a vascular anatomical etiology for the syncope. MRI and MR angiography were essential in identifying these variants, demonstrating the value of advanced neuroimaging in unexplained syncope ( 8 , 9 ). Management of patients with these vascular variants is mostly conservative, focusing on monitoring and controlling vascular risk factors. The favorable prognosis observed in our patient after nearly three years of follow-up supports this strategy. Further studies are needed to clarify the prevalence and clinical implications of Circle of Willis variants in syncope and other transient cerebral hypoperfusion syndromes, which may improve diagnostic accuracy and guide therapeutic management. Conclusion This case highlights that anatomical variants of the Circle of Willis, although often considered incidental, may contribute to transient neurological manifestations such as syncope by reducing cerebral hemodynamic reserve under orthostatic stress. The combination of an absent A1 segment of the anterior cerebral artery and the anterior communicating artery with a dominant left ACA represents a rare vascular configuration that is identifiable only through advanced neuroimaging. While a single case does not allow for generalization, timely recognition of such variants can support appropriate conservative management and help avoid unnecessary interventions. The main limitation of this report is that causality between the vascular anomaly and syncope cannot be definitively established; nonetheless, the observation raises awareness of the potential clinical relevance of Circle of Willis variants in young patients without major comorbidities. Abbreviations ACA Anterior cerebral artery ACoA Anterior communicating artery MRI Magnetic resonance imaging TOF-MRA Time-of-flight magnetic resonance angiography Declarations Ethics approval and consent to participate: Not applicable. Consent to Publish declaration: Written informed consent was obtained from the patient’s legal guardian for the publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor of this journal. Availability of data and materials: Not applicable. Competing interests: The authors declare that they have no competing interests. Funding: No funding was received for this study. Conflict of interest: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Acknowledgements: We acknowledge Universidad Israel for their valuable contribution to this work. Clinical trial number: Not applicable. References McKinstry RC, et al. Population-based study of Circle of Willis variants using MR angiography. PLoS ONE. 2021;16(9):e0257052. 10.1371/journal.pone.0257052 . De Caro R, et al. Anatomical variations of the Circle of Willis: A systematic review. J Neurol. 2021;268(9):3337–53. 10.1007/s00415-021-10454-4 . Jímenez-Sosa A, et al. Anatomical variations of the anterior communicating artery complex in a Mexican population. Int J Morphol. 2017;35(3):1115–20. 10.4067/S0717-95022017000301115 . Radiopaedia. Anterior cerebral artery hypoplasia or absence. Available from: https://radiopaedia.org/articles/anterior-cerebral-artery-hypoplasia-or-absence Schramm P, et al. Impact of absent anterior communicating artery on cerebrovascular reactivity and ischemic risk. AJNR Am J Neuroradiol. 2022;43(8):1124–30. 10.3174/ajnr.A7385 . Yu S, et al. Circle of Willis anomalies and cerebral ischemic stroke risk: A meta-analysis. Stroke. 2020;51(3):909–16. 10.1161/STROKEAHA.119.027494 . Kang HS, et al. Association between Circle of Willis variations and intracranial aneurysms: A systematic review. J Neurosurg. 2019;131(3):912–9. 10.3171/2018.6.JNS18305 . Brignole M, Moya A, de Lange FJ, et al. 2018 ESC Guidelines for the diagnosis and management of syncope. Eur Heart J. 2018;39(21):1883–948. 10.1093/eurheartj/ehy037 . Sheldon R, Rose S, Ritchie D, et al. Historical criteria that distinguish syncope from seizures. J Am Coll Cardiol. 2002;40(1):142–8. 10.1016/s0735-1097(02)01943-4 . Additional Declarations No competing interests reported. Supplementary Files RequestforfullArticleProcessingCharge.pdf Cite Share Download PDF Status: Posted Version 1 posted 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-7335489","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Case Report","associatedPublications":[],"authors":[{"id":519155724,"identity":"cf0d8070-5db2-4c3c-ae87-705a367bd2dc","order_by":0,"name":"Isabel Echevarría Frutos","email":"data:image/png;base64,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","orcid":"","institution":"Universidad Israel","correspondingAuthor":true,"prefix":"","firstName":"Isabel","middleName":"Echevarría","lastName":"Frutos","suffix":""},{"id":519155725,"identity":"61a90acd-12e6-4b43-b24f-a088a986b81b","order_by":1,"name":"Gutenberg Navarro Zambrano","email":"","orcid":"","institution":"Universidad Israel","correspondingAuthor":false,"prefix":"","firstName":"Gutenberg","middleName":"Navarro","lastName":"Zambrano","suffix":""},{"id":519155726,"identity":"c4dd6afc-8213-4c60-8c02-13655b7d3196","order_by":2,"name":"Amaury León Sosa","email":"","orcid":"","institution":"Universidad Israel","correspondingAuthor":false,"prefix":"","firstName":"Amaury","middleName":"León","lastName":"Sosa","suffix":""},{"id":519155727,"identity":"814b7f85-d57c-4835-a9c1-5586db281c8f","order_by":3,"name":"Arianne Llamos Paneque","email":"","orcid":"","institution":"Universidad Israel","correspondingAuthor":false,"prefix":"","firstName":"Arianne","middleName":"Llamos","lastName":"Paneque","suffix":""},{"id":519155729,"identity":"93ac0ed2-f35a-4b3d-8660-a2ec8350af97","order_by":4,"name":"Wilfredo Ruiz Marcano","email":"","orcid":"","institution":"Universidad Israel","correspondingAuthor":false,"prefix":"","firstName":"Wilfredo","middleName":"Ruiz","lastName":"Marcano","suffix":""},{"id":519155730,"identity":"85a8fc46-6105-421e-b3d9-b9fc540b2947","order_by":5,"name":"Karina Bravo Cañar","email":"","orcid":"","institution":"Universidad Israel","correspondingAuthor":false,"prefix":"","firstName":"Karina","middleName":"Bravo","lastName":"Cañar","suffix":""}],"badges":[],"createdAt":"2025-08-09 18:23:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7335489/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7335489/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":92088355,"identity":"653ed2a4-7bec-4bf5-ba37-88d8a46e6e71","added_by":"auto","created_at":"2025-09-24 13:10:43","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":3807975,"visible":true,"origin":"","legend":"","description":"","filename":"ManuscriptRevision.docx.docx","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/48a9974250affc8e6f1ad4b2.docx"},{"id":92086361,"identity":"32873d26-9e6f-49b6-86c2-87e0e0320f44","added_by":"auto","created_at":"2025-09-24 13:02:43","extension":"json","order_by":3,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":7978,"visible":true,"origin":"","legend":"","description":"","filename":"6852081a097d448bae76e723e807ceef.json","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/82f39e7647166a82be9705e2.json"},{"id":92086375,"identity":"3bd67af6-ce72-427b-a8ff-848bb4995637","added_by":"auto","created_at":"2025-09-24 13:02:43","extension":"pdf","order_by":4,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":159773,"visible":true,"origin":"","legend":"","description":"","filename":"RequestforfullArticleProcessingCharged1.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/6908ae7d5d0330d28567844a.pdf"},{"id":92086359,"identity":"e3e7b2c1-ac3e-458f-ae0e-a563185e8fb6","added_by":"auto","created_at":"2025-09-24 13:02:43","extension":"xml","order_by":5,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":33916,"visible":true,"origin":"","legend":"","description":"","filename":"6852081a097d448bae76e723e807ceef1enriched.xml","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/5f93a8a02cdb68f2a48db367.xml"},{"id":92086370,"identity":"4a006699-080f-4bc4-9f74-a547b8300d96","added_by":"auto","created_at":"2025-09-24 13:02:43","extension":"jpeg","order_by":6,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":159423,"visible":true,"origin":"","legend":"","description":"","filename":"FIGURE1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/d294881925c35bf2d84eb7b8.jpeg"},{"id":92086363,"identity":"399ca179-5d77-49b2-a857-0e4a341f3b7e","added_by":"auto","created_at":"2025-09-24 13:02:43","extension":"jpeg","order_by":7,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":195067,"visible":true,"origin":"","legend":"","description":"","filename":"FIGURE2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/7832c58c13cb954d4f4f529a.jpeg"},{"id":92086366,"identity":"b61772cc-cdb4-4201-bc29-1e5613a0c03f","added_by":"auto","created_at":"2025-09-24 13:02:43","extension":"jpeg","order_by":8,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":482565,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/b10d429e6352de3722d85976.jpeg"},{"id":92088824,"identity":"63e7c4d9-1d4e-42f8-9da8-ea9fe8387809","added_by":"auto","created_at":"2025-09-24 13:18:43","extension":"jpeg","order_by":9,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":884356,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/43cca47b045b0cb2a33eeba0.jpeg"},{"id":92089906,"identity":"773c5951-2dda-4623-b002-37789a669780","added_by":"auto","created_at":"2025-09-24 13:26:43","extension":"png","order_by":10,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":249841,"visible":true,"origin":"","legend":"","description":"","filename":"OnlineFIGURE1.png","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/0a5c7f7e00357d454c985839.png"},{"id":92086372,"identity":"c713d4c9-40e3-433d-b721-cf98131136bc","added_by":"auto","created_at":"2025-09-24 13:02:43","extension":"png","order_by":11,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":277416,"visible":true,"origin":"","legend":"","description":"","filename":"OnlineFIGURE2.png","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/466eabcd545be9ac92868ec2.png"},{"id":92086371,"identity":"63a38e1a-c621-462f-b626-9873272e3319","added_by":"auto","created_at":"2025-09-24 13:02:43","extension":"png","order_by":12,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":288847,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/2e68dae45a51e5758df5eb02.png"},{"id":92086373,"identity":"9581bfb9-cc06-469f-9743-8826c3617ef3","added_by":"auto","created_at":"2025-09-24 13:02:43","extension":"png","order_by":13,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":479306,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/c8b786e59abad5b4ad89d1f8.png"},{"id":92086365,"identity":"f31e6d76-c8f3-4a37-9a72-758a291a446e","added_by":"auto","created_at":"2025-09-24 13:02:43","extension":"xml","order_by":14,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":31968,"visible":true,"origin":"","legend":"","description":"","filename":"6852081a097d448bae76e723e807ceef1structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/515d1a8dd4a20959256f6ccd.xml"},{"id":92088352,"identity":"9ad93b53-c75d-4459-a742-d0afcbb04c13","added_by":"auto","created_at":"2025-09-24 13:10:43","extension":"html","order_by":15,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":39268,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/923e02a89afc7cfec55e2315.html"},{"id":92088350,"identity":"36a73433-83c6-4b27-a85d-cc7f2e7c4143","added_by":"auto","created_at":"2025-09-24 13:10:43","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":159423,"visible":true,"origin":"","legend":"\u003cp\u003eCerebral MR angiography (TOF technique: Time-of-Flight) in (a) axial, (b) sagittal, and (c) coronal planes, showing congenital absence of the right anterior cerebral artery A1 segment and complete absence of the anterior communicating artery.\u003c/p\u003e","description":"","filename":"FIGURE1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/91ec80fdd1579c6c5e6cdc15.jpeg"},{"id":92086362,"identity":"ff655015-78e6-437b-b218-cbd12f7c6964","added_by":"auto","created_at":"2025-09-24 13:02:43","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":195067,"visible":true,"origin":"","legend":"\u003cp\u003eCoronal projection reconstruction of the Circle of Willis showing dominance of the left anterior cerebral artery supplying both hemispheres, with no evidence of aneurysms or arteriovenous malformations, and congenital absence of the right anterior cerebral artery A1 segment (white arrow).\u003c/p\u003e","description":"","filename":"FIGURE2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/ace2d9533c359ed16a0a703a.jpeg"},{"id":96592140,"identity":"f5c5bb31-8d00-4e38-bb4f-25a204d78a1c","added_by":"auto","created_at":"2025-11-24 06:39:25","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":784046,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/5187fd41-cbaa-4ab5-9236-c3019a5c7c12.pdf"},{"id":92088351,"identity":"d155ed49-485e-44d0-92e0-6a785f5f1a3a","added_by":"auto","created_at":"2025-09-24 13:10:43","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":159773,"visible":true,"origin":"","legend":"","description":"","filename":"RequestforfullArticleProcessingCharge.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7335489/v1/6ed11f3fbdbcb6eb108773ee.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Syncope Associated with a Congenital Variant of the Circle of Willis: Absence of the Right Anterior Cerebral Artery and Anterior Communicating Artery","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSyncope, defined as a transient loss of consciousness secondary to global cerebral hypoperfusion, is a common clinical complaint. Although vasovagal syncope is the most frequent cause, anatomical variants of the Circle of Willis may contribute in cases unexplained by conventional causes. The Circle of Willis is a fundamental anastomotic arterial network for cerebral collateral circulation and adequate brain perfusion. Congenital variations in its configuration are common, with reported prevalence ranging between 40% and 60% in population studies (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eHypoplasia or absence of the A1 segment of the anterior cerebral artery (ACA) and the anterior communicating artery (ACoA) are uncommon anomalies, with estimated frequencies between 1% and 15% for the A1 segment and approximately 1\u0026ndash;5% for the ACoA (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e). These variants can alter cerebral hemodynamics and have been associated with an increased risk of ischemic cerebrovascular events (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e). However, the direct association between these variants and syncope episodes is rarely reported in the literature.\u003c/p\u003e\u003cp\u003eWe present the case of an 18-year-old female patient with syncope associated with a congenital variant of the Circle of Willis, characterized by absence of the right anterior cerebral artery (A1 segment) and the anterior communicating artery. This report emphasizes the importance of considering cerebral vascular anatomical variants in the differential diagnosis of syncope and discusses their clinical implications.\u003c/p\u003e"},{"header":"Case Presentation","content":"\u003cp\u003eAn 18-year-old female patient without significant personal pathological history, except sulfa allergy and allergic rhinitis. Family history includes cerebral cavernoma and absence seizures in her father. The patient reported a single syncope episode occurring upon sudden standing after lying down, with brief loss of consciousness (approximately 1 minute), spontaneous recovery, and no subsequent neurological focality. She also reported prior exposure to solvents (thinner and paint) and moderate alcohol consumption. Initial evaluation by neurology and neurosurgery included electroencephalogram (normal during wakefulness and light sleep) and laboratory studies within normal limits. Consideration was given to performing contrast neuroimaging studies, which were authorized after allergy evaluation.\u003c/p\u003e\u003cp\u003eBrain magnetic resonance imaging (MRI) and time-of-flight (TOF) MR angiography showed absence of the right anterior cerebral artery (ACA A1) and complete absence of the anterior communicating artery (ACoA) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The left ACA was dominant, supplying both hemispheres. The rest of the Circle of Willis had a normal configuration without evidence of aneurysms, arteriovenous malformations, or other pathological findings (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The patient remained asymptomatic without new syncope episodes or neurological deficits. Cardiology evaluation diagnosed classical vasovagal syncope. Follow-up included isolated arterial hypertension and mild dyslipidemia, without pharmacological treatment requirement. Complementary care was provided by ENT and ophthalmology for unrelated findings. At 2 years and 11 months follow-up, the patient remains asymptomatic.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eSyncope is a transient loss of consciousness caused by global cerebral hypoperfusion, commonly attributed to vasovagal or cardiac causes. However, anatomical variants of the cerebral arteries, such as those affecting the Circle of Willis, can influence cerebral hemodynamics and, in rare cases, contribute to syncope. The Circle of Willis is a crucial collateral network ensuring adequate cerebral perfusion even in cases of vascular occlusion or stenosis. Anatomical variations in this structure are common, occurring in up to 50\u0026ndash;60% of individuals in population studies (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e). Among these, absence or hypoplasia of the anterior cerebral artery (ACA) segments and the anterior communicating artery (ACoA) are less frequent but clinically relevant (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eIn our patient, congenital absence of the right ACA A1 segment and ACoA likely compromised cerebral collateral flow, lowering the threshold for cerebral hypoperfusion during orthostatic stress, explaining the syncopal episode. This is consistent with McKinstry et al., who described reduced cerebrovascular reserve in patients with similar arterial anomalies (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e). Additionally, the presence of a dominant left ACA supplying both hemispheres may partially compensate for this absence, explaining the lack of permanent neurological deficits.\u003c/p\u003e\u003cp\u003ePrevious studies have mainly associated these anatomical variants with ischemic stroke and aneurysm formation (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e). However, their role in transient neurological symptoms, including syncope, is less documented. Our case contributes to the emerging literature emphasizing the clinical significance of Circle of Willis variants beyond cerebrovascular events.\u003c/p\u003e\u003cp\u003eThe differential diagnosis ruled out cardiac and neurogenic causes, supporting a vascular anatomical etiology for the syncope. MRI and MR angiography were essential in identifying these variants, demonstrating the value of advanced neuroimaging in unexplained syncope (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eManagement of patients with these vascular variants is mostly conservative, focusing on monitoring and controlling vascular risk factors. The favorable prognosis observed in our patient after nearly three years of follow-up supports this strategy.\u003c/p\u003e\u003cp\u003eFurther studies are needed to clarify the prevalence and clinical implications of Circle of Willis variants in syncope and other transient cerebral hypoperfusion syndromes, which may improve diagnostic accuracy and guide therapeutic management.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis case highlights that anatomical variants of the Circle of Willis, although often considered incidental, may contribute to transient neurological manifestations such as syncope by reducing cerebral hemodynamic reserve under orthostatic stress. The combination of an absent A1 segment of the anterior cerebral artery and the anterior communicating artery with a dominant left ACA represents a rare vascular configuration that is identifiable only through advanced neuroimaging. While a single case does not allow for generalization, timely recognition of such variants can support appropriate conservative management and help avoid unnecessary interventions. The main limitation of this report is that causality between the vascular anomaly and syncope cannot be definitively established; nonetheless, the observation raises awareness of the potential clinical relevance of Circle of Willis variants in young patients without major comorbidities.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eACA\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eAnterior cerebral artery\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eACoA\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eAnterior communicating artery\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eMRI\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eMagnetic resonance imaging\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eTOF-MRA\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eTime-of-flight magnetic resonance angiography\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate:\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish declaration: \u003c/strong\u003eWritten informed consent was obtained from the patient\u0026rsquo;s legal guardian for the publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor of this journal.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials:\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests:\u003c/strong\u003e The authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e No funding was received for this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest:\u003c/strong\u003e The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements:\u003c/strong\u003e We acknowledge Universidad Israel for their valuable contribution to this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical trial number:\u003c/strong\u003e Not applicable.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMcKinstry RC, et al. Population-based study of Circle of Willis variants using MR angiography. PLoS ONE. 2021;16(9):e0257052. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1371/journal.pone.0257052\u003c/span\u003e\u003cspan address=\"10.1371/journal.pone.0257052\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDe Caro R, et al. Anatomical variations of the Circle of Willis: A systematic review. J Neurol. 2021;268(9):3337\u0026ndash;53. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s00415-021-10454-4\u003c/span\u003e\u003cspan address=\"10.1007/s00415-021-10454-4\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eJ\u0026iacute;menez-Sosa A, et al. Anatomical variations of the anterior communicating artery complex in a Mexican population. Int J Morphol. 2017;35(3):1115\u0026ndash;20. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.4067/S0717-95022017000301115\u003c/span\u003e\u003cspan address=\"10.4067/S0717-95022017000301115\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRadiopaedia. Anterior cerebral artery hypoplasia or absence. Available from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://radiopaedia.org/articles/anterior-cerebral-artery-hypoplasia-or-absence\u003c/span\u003e\u003cspan address=\"https://radiopaedia.org/articles/anterior-cerebral-artery-hypoplasia-or-absence\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSchramm P, et al. Impact of absent anterior communicating artery on cerebrovascular reactivity and ischemic risk. AJNR Am J Neuroradiol. 2022;43(8):1124\u0026ndash;30. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3174/ajnr.A7385\u003c/span\u003e\u003cspan address=\"10.3174/ajnr.A7385\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eYu S, et al. Circle of Willis anomalies and cerebral ischemic stroke risk: A meta-analysis. Stroke. 2020;51(3):909\u0026ndash;16. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1161/STROKEAHA.119.027494\u003c/span\u003e\u003cspan address=\"10.1161/STROKEAHA.119.027494\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKang HS, et al. Association between Circle of Willis variations and intracranial aneurysms: A systematic review. J Neurosurg. 2019;131(3):912\u0026ndash;9. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3171/2018.6.JNS18305\u003c/span\u003e\u003cspan address=\"10.3171/2018.6.JNS18305\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBrignole M, Moya A, de Lange FJ, et al. 2018 ESC Guidelines for the diagnosis and management of syncope. Eur Heart J. 2018;39(21):1883\u0026ndash;948. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1093/eurheartj/ehy037\u003c/span\u003e\u003cspan address=\"10.1093/eurheartj/ehy037\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSheldon R, Rose S, Ritchie D, et al. Historical criteria that distinguish syncope from seizures. J Am Coll Cardiol. 2002;40(1):142\u0026ndash;8. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/s0735-1097(02)01943-4\u003c/span\u003e\u003cspan address=\"10.1016/s0735-1097(02)01943-4\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"syncope, Circle of Willis, anterior cerebral artery, anterior communicating artery, congenital vascular anomaly, cerebral blood flow, vasovagal syncope","lastPublishedDoi":"10.21203/rs.3.rs-7335489/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7335489/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground:\u003c/strong\u003e Syncope is a transient loss of consciousness caused by global cerebral hypoperfusion. Although most commonly attributed to vasovagal or cardiac etiologies, anatomical variants of the Circle of Willis may alter cerebral hemodynamics and, in rare cases, contribute to syncope.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCase presentation:\u003c/strong\u003e We report the case of an 18-year-old female patient with no significant personal medical history and a family history of cerebral cavernoma. She experienced a single syncopal episode upon sudden standing, with brief loss of consciousness lasting approximately one minute and no subsequent neurological deficits. Laboratory tests and electroencephalogram were within normal limits. Brain magnetic resonance imaging (MRI) and time-of-flight magnetic resonance angiography (TOF-MRA) revealed absence of the right anterior cerebral artery (ACA) A1 segment and complete absence of the anterior communicating artery (ACoA). The left ACA was dominant, supplying both cerebral hemispheres. Cardiac causes were excluded, and a diagnosis of classic vasovagal syncope was established. The patient has remained asymptomatic after nearly three years of follow-up.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDiscussion:\u003c/strong\u003e Congenital variants of the Circle of Willis are common anatomical findings but rarely linked to syncope. In this case, the bilateral absence of key vascular segments may have reduced cerebrovascular reserve during orthostatic stress, precipitating the syncopal event. This case underscores the importance of advanced neuroimaging techniques in the evaluation of atypical syncope.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions:\u003c/strong\u003e This report highlights the clinical significance of Circle of Willis anatomical variants as potential contributors to syncope when other causes have been excluded. A multidisciplinary approach and the use of appropriate imaging modalities are critical for accurate diagnosis.\u003c/p\u003e","manuscriptTitle":"Syncope Associated with a Congenital Variant of the Circle of Willis: Absence of the Right Anterior Cerebral Artery and Anterior Communicating Artery","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-24 13:02:38","doi":"10.21203/rs.3.rs-7335489/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"fdadedd5-c437-4f31-a936-2518a8f9d010","owner":[],"postedDate":"September 24th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-11-24T06:39:16+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-24 13:02:38","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7335489","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7335489","identity":"rs-7335489","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}