Bilateral anterior cerebral artery-anterior communicating artery junction arterial ring associated with unilateral A1 aplasia diagnosed by magnetic resonance angiography

Bilateral anterior cerebral artery-anterior communicating artery junction arterial ring associated with unilateral A1 aplasia diagnosed by magnetic resonance angiography | 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 Bilateral anterior cerebral artery-anterior communicating artery junction arterial ring associated with unilateral A1 aplasia diagnosed by magnetic resonance angiography Akira Uchino, Shunpei Andoh This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7152541/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 30 Aug, 2025 Read the published version in Surgical and Radiologic Anatomy → Version 1 posted 9 You are reading this latest preprint version Abstract Purpose To describe a case of two arterial rings of the anterior cerebral artery (ACA)-anterior communicating artery (ACoA) complex diagnosed by magnetic resonance angiography (MRA). Methods A 72-year-old woman with a brain tumor underwent cranial magnetic resonance imaging (MRI) and MRA using a 3-Tesla scanner. MRA was performed using a standard 3-dimensional time-of-flight technique. Results MRI showed a small convexity meningioma in the right parietal region. MRA showed no pathological lesions. The A1 segment of the left ACA was absent and the bilateral A2 segments were supplied by the right ACA. Two arterial rings were present bilaterally at the ACA-ACoA junction. The arterial rings showed a triangular configuration, suggesting a duplicate origin of A2 rather than A2 origin fenestration or partial duplication of the ACoA. A fetal-type right posterior cerebral artery was also observed. Conclusion The ACA-ACoA complex is the most frequent site of cerebral arterial fenestration. However, ACoA duplication, partial ACoA duplication, and other arterial rings of the ACA-ACoA complex have been confused and reported as ACoA fenestration. True fenestration of the ACoA is rarely been reported. The present case had bilateral ACA-ACoA junction triangular rings, suggesting a bilateral duplicate origin of the A2 segment of the ACAs. No similar case has been reported in relevant English-language literature. Careful observation using MRA is important for the detection of rare arterial variations. Partial volume-rendering MRA images are useful for identifying complicated small arterial variations. Anterior cerebral artery Anterior communicating artery Arterial ring Cerebral arterial variations Fenestration Magnetic resonance angiography Figures Figure 1 Figure 2 Figure 3 Introduction There are many types of arterial variations in the anterior cerebral artery (ACA)-anterior communicating artery (ACoA) complex. According to a review by Kashtiara et al. [ 5 ], 12 types have been reported. Arterial rings in the ACA-ACoA complex have been reported, including duplication, triplication, fenestration, partial duplication (Y-shaped), and double partial duplication (H-shaped) [ 5 , 14 ]. True fenestration of the ACoA visualized using magnetic resonance angiography (MRA) has rarely been reported [ 1 , 14 ]. We herein report a case of double arterial rings of the ACA-ACoA complex that has not been previously reported in the relevant English-language literature. Case report A 72-year-old woman with a brain tumor underwent cranial magnetic resonance imaging (MRI) and MRA using a 3-Tesla scanner. MRA was performed using a 3-Tesla scanner (MAGNETOM Skyra; Siemens Healthineers, Erlangen, Germany) for the evaluation of brain lesions. MRA was performed using a standard 3-dimensional time-of-flight technique. The imaging parameters were as follows: flip angle, 15°; repetition time, 29.3 s; echo time, 3.7 s; slice thickness, 0.6 mm; number of slices, 209; slab thickness, 125 mm; field of view, 28.0 × 20.0 cm. MRI showed a small convexity meningioma in the right parietal region. MRA showed no pathological lesions. The A1 segment of the left ACA was absent and the bilateral A2 segments were supplied by the right ACA. Two arterial rings were bilaterally present at the ACA-ACoA junction. The arterial rings showed a triangular configuration, suggesting a duplicate origin of A2 rather than A2 origin fenestration or partial duplication of the ACoA. There was also a fetal-type right posterior cerebral artery (PCA) (Figs. 1 , 2 ). Figure 3 shows a schematic illustration of the arterial variations in this patient. Additional radiological examinations, such as computed tomography angiography (CTA) and three-dimensional rotational angiography (3D-RA), were not performed. Because the patient’s clinical symptoms were mild, the brain tumor was followed conservatively. The patient’s clinical symptoms did not change. Discussion Embryologically, there is a primitive cerebral arterial network in the early gestational stage. The most distal segment of the ICA divides into rostral and caudal branches, and the rostral branches become the ACA and middle cerebral arteries. Primitive cerebral arteries usually regress or fuse to form normal adult arteries. The ACoA develops from plexiform anastomoses between two ACAs [ 9 ]. Therefore, abnormal persistence or abnormal regression/fusion of these primitive arteries between bilateral ACAs can lead to variations in the ACA-ACoA complex [ 5 ]. As mentioned in the Introduction , there are several types of arterial rings in the ACA-ACoA complex [ 5 , 14 ]. These arterial rings have been confused and reported as fenestrations based on radiological investigations [ 2 – 4 , 8 , 12 , 15 ]. Using CTA, Bharatha et al. [ 2 ] reported that the ACA-ACoA complex was the most frequent site of intracranial fenestrations, with an overall prevalence of 35/504 (6.9%). Using 3D-RA, de Gast et al. [ 4 ] reported that ACoA fenestration was present in 12 of 227 (5.3%) patients. However, several types of arterial rings have also been regarded as fenestrations in these reports. The MRA findings of true fenestration of the ACoA have rarely been reported [ 1 , 14 ]. In contrast, when using cadaver dissection, the prevalence of true fenestrations of the ACoA was reported to be extremely high. Among 30 cadaver brains, Serizawa et al. [ 11 ] found ACoA fenestration in 6 (20%). Recently, Saha et al. 10] reported the prevalence of ACoA fenestration as 1.78% in cadaver dissection. Microsurgical evaluation of the ACA-ACoA complex can detect small fenestrations that are not diagnosed by radiological imaging studies, such as MRA and CTA. 3D-RA has a much higher spatial resolution than MRA and CTA and can detect smaller fenestrations. However, some of the tiny fenestrations may not be detected, even on 3D-RA. Using CTA, Krzyżewski et al. [ 6 ] reported that the prevalence of ACoA duplication is only 0.49%. López-Sala et al. [ 8 ] reported that the prevalence of ACoA duplication/fenestration on CTA was 0.9%. According to a meta-analysis by Triantafyllou et al. [ 12 ], the prevalence of ACoA fenestration and duplication was 5.0% and 4.3%, respectively. However, as mentioned above, true fenestration of the ACoA and other arterial rings of the ACA-ACoA complex are reported to have been confused. In our patient, a small arterial ring with a triangular configuration was observed on the bilateral sides of the ACA-ACoA junction. We suggest that these ACA-ACoA junction arterial rings can be regarded as duplicate origins of A2 rather than A2 origin fenestration or partial duplication of ACoA. No similar case has been reported in the relevant English-language literature. A cerebral aneurysm can be observed at the proximal end of the fenestration. Using 3D-RA, van Rooij et al. [ 15 ] detected 210 aneurysms and 45 intracranial fenestrations (arterial rings) in 140 patients with subarachnoid hemorrhage. The ACA-ACoA complex arterial ring, including fenestrations, was found in of 31 of 45 (69%) patients, and 14/45 (31%) fenestrations (arterial rings) were associated with an aneurysm. Using 3D-RA, de Gast et al. [ 4 ] reported that among the 12 arterial rings, including fenestrations of the ACA-ACoA complex, 10 (83%) were associated with one or more aneurysms of the ACA-ACoA complex. However, these studies had a strong selection bias. According to a review article by Cooke et al. [ 3 ], there is no definite pathological relationship between cerebral arterial fenestration and cerebral aneurysms. Our patient had left A1 aplasia and a right fetal-type PCA. Using MRA, Lin et al. [ 7 ] reported that an incomplete circle of Willis was seen in 34% of patients, and ACA aplasia/hypoplasia of the A1 segment was seen in 13% of patients. Among 15 cadavers, Saha et al. [ 10 ] found A1 hypoplasia only on the right side, and no aplasia on either side. The clinical significance of the ACA-ACoA complex arterial ring includes aneurysm formation [ 4 ], mimicking an aneurysm on radiological images [ 13 ], and a potential collateral pathway in cases of unilateral channel occlusion. Conclusions We report a case of arterial rings at the bilateral ACA-ACoA junctions. Based on the triangular configuration, we concluded that they represent a duplicate origin of the A2 rather than A2 origin fenestration or partial duplication of the ACoA. Careful observation using MRA is important for the detection of rare arterial variations. Partial VR MRA is useful for identifying small arterial variations. Declarations Acknowledgements We thank Mr. Yasuo Inoue, R.T., for his technical support. Author contributions AU carried out the study design, and drafted the manuscript. AU and SA reviewed the manuscript critically, and have read and approved the final manuscript. Funding The authors did not receive support from any organization for the submitted work. Data availability Not applicable. Conflict of interest The authors declare no competing interests. Ethical approval and consent to participate All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. Consent for publication The patient signed informed consent regarding publishing his data and figures. References Asami S, Uchino A, Usami Y, Nabeshima T, Baba Y (2025) True fenestration of an extremely long anterior communicating artery diagnosed by magnetic resonance angiography. Surg Radiol Anat 47:126. 10.1007/s00276-025-03634-8 Bharatha A, Aviv RI, White J, Fox AJ, Symons SP (2008) Intracranial arterial fenestrations: frequency on CT angiography and association with other vascular lesions. Surg Radiol Anat 30:397–401. 10.1007/s00276-008-0340-7 Cooke DL, Stout CE, Kim WT, Kansagra AP, Yu JP, Gu A, Jewell NP, Hetts SW, Higashida RT, Dowd CF, Halbach VV (2014) Cerebral arterial fenestrations. Interv Neuroradiol 20:261–274. 10.15274/INR-2014-10027 de Gast AN, van Rooij WJ, Sluzewski M (2008) Fenestrations of the anterior communicating artery: incidence on 3D angiography and relationship to aneurysms. AJNR Am J Neuroradiol 29:296–298. 10.3174/ajnr.A0807 Kashtiara A, Beldé S, Menovsky T (2024) Anatomical variations and anomalies of the anterior communicating artery complex. World Neurosurg 183:e218–e227. 10.1016/j.wneu.2023.12.060 Krzyżewski RM, Tomaszewski KA, Kochana M, Kopeć M, Klimek-Piotrowska W, Walocha JA (2015) Anatomical variations of the anterior communicating artery complex: gender relationship. Surg Radiol Anat 37:81–86. 10.1007/s00276-014-1313-7 Lin E, Kamel H, Gupta A, RoyChoudhury A, Girgis P, Glodzik L (2022) Incomplete circle of Willis variants and stroke outcome. Eur J Radiol 153:110383. 10.1016/j.ejrad.2022.110383 López-Sala P, Alberdi N, Mendigaña M, Bacaicoa MC, Cabada T (2020) Anatomical variants of anterior communicating artery complex. A study by computerized tomographic angiography. J Clin Neurosci 80:182–187. 10.1016/j.jocn.2020.08.019 Padget DH (1948) The development of the cranial arteries in the human embryo. Contrib Embryol 32:205–262 Saha A, Bhattacharya A, Ghosh SP, Roy SR (2024) Morphology and morphometry of the anterior cerebral-anterior communicating artery complex. Surg Radiol Anat 46:1585–1593. 10.1007/s00276-024-03451-5 Serizawa T, Saeki N, Yamaura A (1997) Microsurgical anatomy and clinical significance of the anterior communicating artery and its perforating branches. Neurosurgery 40:1211–1216 discussion 1216-8. 10.1097/00006123-199706000-00019 Triantafyllou G, Tudose RC, Tsiouris C, Tsakotos G, Loukas M, Tubbs RS, Kalamatianos T, Chrissicopoulos C, Al-Nasraoui K, Koutserimpas C, Rusu MC, Natsis K, Kotrotsios A, Piagkou M (2024) The anterior communicating artery variants: a meta-analysis with a proposed classification system. Surg Radiol Anat. 2024;46(5):697–716. 10.1007/s00276-024-03336-7 Tsukada A, Yanaka K, Takeda H, Onuma K, Takada M, Nakamura K, Ishikawa E (2023) Fenestrated anterior communicating artery complex mimicking an unruptured aneurysm: diagnostic pitfall. Asian J Neurosurg 18:201–205. 10.1055/s-0043-1764119 Uchino A, Saito N, Uehara T, Neki H, Kohyama S, Yamane F (2016) True fenestration of the anterior communicating artery diagnosed by magnetic resonance angiography. Surg Radiol Anat 38:1095–1098. 10.1007/s00276-016-1646-5 van Rooij SB, Bechan RS, Peluso JP, Sluzewski M, van Rooij WJ (2015) Fenestrations of intracranial arteries. AJNR Am J Neuroradiol 36:1167–1170. 10.3174/ajnr.A4236 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 30 Aug, 2025 Read the published version in Surgical and Radiologic Anatomy → Version 1 posted Editorial decision: Revision requested 11 Aug, 2025 Reviews received at journal 25 Jul, 2025 Reviews received at journal 25 Jul, 2025 Reviewers agreed at journal 25 Jul, 2025 Reviewers agreed at journal 22 Jul, 2025 Reviewers invited by journal 22 Jul, 2025 Editor assigned by journal 22 Jul, 2025 Submission checks completed at journal 18 Jul, 2025 First submitted to journal 17 Jul, 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. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7152541","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":489384626,"identity":"91ca09bf-78ad-4e03-94c2-75af84e95687","order_by":0,"name":"Akira Uchino","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA50lEQVRIiWNgGAWjYHACNoYEBgYe+/bmgw+APB4+YrXIGfAcSzYAaWEjSgsQGBtI5JhJwLn4AP+M5GcPHu6wSdzOkJZW+TXHToaNgfnhoxt4tEjcSDM3SDyTlriz4fCx27LbkoEOYzM2zsFnzY0cNonEtsOJDQfb0m5LbmMGauFhk8anRR6u5TCPWbHktnrCWgygWowNjvGYMX7cdpiwFsMzz8yAWtLkJHvYkqUZtx3nYWMm4Be548nPJH+22fDwyz8++PHntmp7fvbmh4/xeh8ZMPOASWKVgwDjD1JUj4JRMApGwYgBAKOfRxxHpWQSAAAAAElFTkSuQmCC","orcid":"","institution":"Saitama Sekishinkai Hospital","correspondingAuthor":true,"prefix":"","firstName":"Akira","middleName":"","lastName":"Uchino","suffix":""},{"id":489384627,"identity":"cb93b63c-ffff-4370-97b2-11562e87833d","order_by":1,"name":"Shunpei Andoh","email":"","orcid":"","institution":"Saitama Sekishinkai Hospital","correspondingAuthor":false,"prefix":"","firstName":"Shunpei","middleName":"","lastName":"Andoh","suffix":""}],"badges":[],"createdAt":"2025-07-17 23:23:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7152541/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7152541/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00276-025-03708-7","type":"published","date":"2025-08-30T15:57:14+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":87551364,"identity":"c90d20eb-15ef-4169-8949-33f98fc1765f","added_by":"auto","created_at":"2025-07-25 06:23:06","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1419791,"visible":true,"origin":"","legend":"\u003cp\u003eAnteroinferior-posterosuperior projection of volume-rendering (VR) image of magnetic resonance angiography (MRA)\u003c/p\u003e\n\u003cp\u003eThe A1 segment of the left anterior cerebral artery (ACA) is absent (\u003cem\u003elong arrow\u003c/em\u003e). Two arterial rings at the ACA-anterior communicating artery (ACoA) junction are bilaterally present (\u003cem\u003eshort arrows\u003c/em\u003e). The \u003cem\u003edotted arrow\u003c/em\u003eindicates fetal-type right posterior cerebral artery.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-7152541/v1/1c46d04cfa1fd16b7631dcd5.png"},{"id":87551368,"identity":"bdf6dbf9-ef35-4e76-be00-1b2f39980679","added_by":"auto","created_at":"2025-07-25 06:23:06","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1309976,"visible":true,"origin":"","legend":"\u003cp\u003ePartial VR images of MRA of the right carotid system\u003c/p\u003e\n\u003cp\u003eAnteroinferior-posterosuperior (\u003cstrong\u003ea\u003c/strong\u003e) and posterosuperior–anteroinferior (\u003cstrong\u003eb\u003c/strong\u003e) projections clearly show two arterial rings. Large and small arteries arise from the ACoA and fuse soon, suggesting a duplicate origin of the A2 segment, bilaterally rather than A2 origin fenestration or partial duplication of the ACoA (\u003cem\u003earrows\u003c/em\u003e).\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-7152541/v1/27b06809ac8b8eec4216172c.png"},{"id":87554078,"identity":"5d4f7c3f-3d89-4cac-9185-9c736eee86d2","added_by":"auto","created_at":"2025-07-25 06:39:06","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":48750,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustration of arterial variations of this patient (anteroposterior projection)\u003c/p\u003e\n\u003cp\u003eACA, anterior cerebral artery; ACoA, anterior communicating artery; BA, basilar artery; ICA, internal carotid artery; MCA, middle cerebral artery; PCA, posterior cerebral artery.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-7152541/v1/f80329b74bdf550baca9360c.png"},{"id":90345104,"identity":"7dea617a-e224-4194-8ca9-3724ccbcf875","added_by":"auto","created_at":"2025-09-01 16:09:59","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2909070,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7152541/v1/751cf4ed-f130-4428-a976-3fdc0b28f524.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Bilateral anterior cerebral artery-anterior communicating artery junction arterial ring associated with unilateral A1 aplasia diagnosed by magnetic resonance angiography","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThere are many types of arterial variations in the anterior cerebral artery (ACA)-anterior communicating artery (ACoA) complex. According to a review by Kashtiara et al. [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], 12 types have been reported. Arterial rings in the ACA-ACoA complex have been reported, including duplication, triplication, fenestration, partial duplication (Y-shaped), and double partial duplication (H-shaped) [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. True fenestration of the ACoA visualized using magnetic resonance angiography (MRA) has rarely been reported [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eWe herein report a case of double arterial rings of the ACA-ACoA complex that has not been previously reported in the relevant English-language literature.\u003c/p\u003e"},{"header":"Case report","content":"\u003cp\u003eA 72-year-old woman with a brain tumor underwent cranial magnetic resonance imaging (MRI) and MRA using a 3-Tesla scanner. MRA was performed using a 3-Tesla scanner (MAGNETOM Skyra; Siemens Healthineers, Erlangen, Germany) for the evaluation of brain lesions. MRA was performed using a standard 3-dimensional time-of-flight technique. The imaging parameters were as follows: flip angle, 15\u0026deg;; repetition time, 29.3 s; echo time, 3.7 s; slice thickness, 0.6 mm; number of slices, 209; slab thickness, 125 mm; field of view, 28.0 \u0026times; 20.0 cm.\u003c/p\u003e\u003cp\u003eMRI showed a small convexity meningioma in the right parietal region. MRA showed no pathological lesions. The A1 segment of the left ACA was absent and the bilateral A2 segments were supplied by the right ACA. Two arterial rings were bilaterally present at the ACA-ACoA junction. The arterial rings showed a triangular configuration, suggesting a duplicate origin of A2 rather than A2 origin fenestration or partial duplication of the ACoA. There was also a fetal-type right posterior cerebral artery (PCA) (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e,\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows a schematic illustration of the arterial variations in this patient.\u003c/p\u003e\u003cp\u003eAdditional radiological examinations, such as computed tomography angiography (CTA) and three-dimensional rotational angiography (3D-RA), were not performed. Because the patient\u0026rsquo;s clinical symptoms were mild, the brain tumor was followed conservatively. The patient\u0026rsquo;s clinical symptoms did not change.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eEmbryologically, there is a primitive cerebral arterial network in the early gestational stage. The most distal segment of the ICA divides into rostral and caudal branches, and the rostral branches become the ACA and middle cerebral arteries. Primitive cerebral arteries usually regress or fuse to form normal adult arteries. The ACoA develops from plexiform anastomoses between two ACAs [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Therefore, abnormal persistence or abnormal regression/fusion of these primitive arteries between bilateral ACAs can lead to variations in the ACA-ACoA complex [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eAs mentioned in the \u003cb\u003eIntroduction\u003c/b\u003e, there are several types of arterial rings in the ACA-ACoA complex [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. These arterial rings have been confused and reported as fenestrations based on radiological investigations [\u003cspan additionalcitationids=\"CR3\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Using CTA, Bharatha et al. [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] reported that the ACA-ACoA complex was the most frequent site of intracranial fenestrations, with an overall prevalence of 35/504 (6.9%). Using 3D-RA, de Gast et al. [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] reported that ACoA fenestration was present in 12 of 227 (5.3%) patients. However, several types of arterial rings have also been regarded as fenestrations in these reports. The MRA findings of true fenestration of the ACoA have rarely been reported [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. In contrast, when using cadaver dissection, the prevalence of true fenestrations of the ACoA was reported to be extremely high. Among 30 cadaver brains, Serizawa et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] found ACoA fenestration in 6 (20%). Recently, Saha et al. 10] reported the prevalence of ACoA fenestration as 1.78% in cadaver dissection. Microsurgical evaluation of the ACA-ACoA complex can detect small fenestrations that are not diagnosed by radiological imaging studies, such as MRA and CTA. 3D-RA has a much higher spatial resolution than MRA and CTA and can detect smaller fenestrations. However, some of the tiny fenestrations may not be detected, even on 3D-RA.\u003c/p\u003e\u003cp\u003eUsing CTA, Krzyżewski et al. [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] reported that the prevalence of ACoA duplication is only 0.49%. L\u0026oacute;pez-Sala et al. [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] reported that the prevalence of ACoA duplication/fenestration on CTA was 0.9%. According to a meta-analysis by Triantafyllou et al. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], the prevalence of ACoA fenestration and duplication was 5.0% and 4.3%, respectively. However, as mentioned above, true fenestration of the ACoA and other arterial rings of the ACA-ACoA complex are reported to have been confused. In our patient, a small arterial ring with a triangular configuration was observed on the bilateral sides of the ACA-ACoA junction. We suggest that these ACA-ACoA junction arterial rings can be regarded as duplicate origins of A2 rather than A2 origin fenestration or partial duplication of ACoA. No similar case has been reported in the relevant English-language literature.\u003c/p\u003e\u003cp\u003eA cerebral aneurysm can be observed at the proximal end of the fenestration. Using 3D-RA, van Rooij et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] detected 210 aneurysms and 45 intracranial fenestrations (arterial rings) in 140 patients with subarachnoid hemorrhage. The ACA-ACoA complex arterial ring, including fenestrations, was found in of 31 of 45 (69%) patients, and 14/45 (31%) fenestrations (arterial rings) were associated with an aneurysm. Using 3D-RA, de Gast et al. [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] reported that among the 12 arterial rings, including fenestrations of the ACA-ACoA complex, 10 (83%) were associated with one or more aneurysms of the ACA-ACoA complex. However, these studies had a strong selection bias. According to a review article by Cooke et al. [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], there is no definite pathological relationship between cerebral arterial fenestration and cerebral aneurysms.\u003c/p\u003e\u003cp\u003eOur patient had left A1 aplasia and a right fetal-type PCA. Using MRA, Lin et al. [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] reported that an incomplete circle of Willis was seen in 34% of patients, and ACA aplasia/hypoplasia of the A1 segment was seen in 13% of patients. Among 15 cadavers, Saha et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] found A1 hypoplasia only on the right side, and no aplasia on either side.\u003c/p\u003e\u003cp\u003eThe clinical significance of the ACA-ACoA complex arterial ring includes aneurysm formation [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], mimicking an aneurysm on radiological images [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], and a potential collateral pathway in cases of unilateral channel occlusion.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eWe report a case of arterial rings at the bilateral ACA-ACoA junctions. Based on the triangular configuration, we concluded that they represent a duplicate origin of the A2 rather than A2 origin fenestration or partial duplication of the ACoA. Careful observation using MRA is important for the detection of rare arterial variations. Partial VR MRA is useful for identifying small arterial variations.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e We thank Mr. Yasuo Inoue, R.T., for his technical support.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u0026nbsp;\u003c/strong\u003eAU carried out the study design, and drafted the manuscript. AU and SA reviewed the manuscript critically, and have read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e The authors did not receive support from any organization for the submitted work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e The authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval and consent to participate\u003c/strong\u003e All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e The patient signed informed consent regarding publishing his data and figures.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAsami S, Uchino A, Usami Y, Nabeshima T, Baba Y (2025) True fenestration of an extremely long anterior communicating artery diagnosed by magnetic resonance angiography. 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AJNR Am J Neuroradiol 36:1167\u0026ndash;1170. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3174/ajnr.A4236\u003c/span\u003e\u003cspan address=\"10.3174/ajnr.A4236\" 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":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":"Anterior cerebral artery, Anterior communicating artery, Arterial ring, Cerebral arterial variations, Fenestration, Magnetic resonance angiography","lastPublishedDoi":"10.21203/rs.3.rs-7152541/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7152541/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003ePurpose\u003c/h2\u003e\u003cp\u003eTo describe a case of two arterial rings of the anterior cerebral artery (ACA)-anterior communicating artery (ACoA) complex diagnosed by magnetic resonance angiography (MRA).\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003eA 72-year-old woman with a brain tumor underwent cranial magnetic resonance imaging (MRI) and MRA using a 3-Tesla scanner. MRA was performed using a standard 3-dimensional time-of-flight technique.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eMRI showed a small convexity meningioma in the right parietal region. MRA showed no pathological lesions. The A1 segment of the left ACA was absent and the bilateral A2 segments were supplied by the right ACA. Two arterial rings were present bilaterally at the ACA-ACoA junction. The arterial rings showed a triangular configuration, suggesting a duplicate origin of A2 rather than A2 origin fenestration or partial duplication of the ACoA. A fetal-type right posterior cerebral artery was also observed.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e\u003cp\u003eThe ACA-ACoA complex is the most frequent site of cerebral arterial fenestration. However, ACoA duplication, partial ACoA duplication, and other arterial rings of the ACA-ACoA complex have been confused and reported as ACoA fenestration. True fenestration of the ACoA is rarely been reported. The present case had bilateral ACA-ACoA junction triangular rings, suggesting a bilateral duplicate origin of the A2 segment of the ACAs. No similar case has been reported in relevant English-language literature. Careful observation using MRA is important for the detection of rare arterial variations. Partial volume-rendering MRA images are useful for identifying complicated small arterial variations.\u003c/p\u003e","manuscriptTitle":"Bilateral anterior cerebral artery-anterior communicating artery junction arterial ring associated with unilateral A1 aplasia diagnosed by magnetic resonance angiography","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-25 06:23:01","doi":"10.21203/rs.3.rs-7152541/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-08-11T10:43:49+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-25T21:23:01+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-25T20:55:24+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"260213394802975184159665688428434391027","date":"2025-07-25T10:41:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"90877766134508558192278980512938176736","date":"2025-07-22T21:02:55+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-22T06:56:37+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-22T05:44:39+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-18T07:04:55+00:00","index":"","fulltext":""},{"type":"submitted","content":"Surgical and Radiologic Anatomy","date":"2025-07-17T23:20:03+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":"59514b13-280a-41af-a43f-5ac7a3f1ca97","owner":[],"postedDate":"July 25th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-09-01T16:06:16+00:00","versionOfRecord":{"articleIdentity":"rs-7152541","link":"https://doi.org/10.1007/s00276-025-03708-7","journal":{"identity":"surgical-and-radiologic-anatomy","isVorOnly":false,"title":"Surgical and Radiologic Anatomy"},"publishedOn":"2025-08-30 15:57:14","publishedOnDateReadable":"August 30th, 2025"},"versionCreatedAt":"2025-07-25 06:23:01","video":"","vorDoi":"10.1007/s00276-025-03708-7","vorDoiUrl":"https://doi.org/10.1007/s00276-025-03708-7","workflowStages":[]},"version":"v1","identity":"rs-7152541","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7152541","identity":"rs-7152541","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}