{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T04:58:19Z","timestamp":1790657899057,"version":"4.1.0"},"reference-count":28,"publisher":"Springer Science and Business Media LLC","issue":"1","license":[{"start":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T00:00:00Z","timestamp":1790640000000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0"},{"start":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T00:00:00Z","timestamp":1790640000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0"}],"content-domain":{"domain":["link.springer.com"],"crossmark-restriction":false},"short-container-title":["Neurosurg Rev"],"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:p>The clinical management of small, unruptured intracranial aneurysms, particularly those measuring less than 5 mm, represents a significant area of debate in neurovascular surgery. The decision to pursue invasive treatment versus conservative surveillance is often guided by limited and sometimes conflicting evidence, leaving a critical gap in clinical decision-making. This study aimed to meticulously characterize the five-year natural history and morphological evolution of a cohort of patients with untreated small intracranial aneurysms (defined as &lt;\u20095 mm), managed conservatively with serial angiographic surveillance. We conducted a longitudinal cohort study at a single tertiary academic center, enrolling 113 patients (101 female, 89.4%; 12 male, 10.6%; mean age 59 years) with at least one unruptured intracranial aneurysm measuring\u2009&lt;\u20095 mm, diagnosed by digital subtraction angiography (DSA). All patients were managed with a conservative \u201cwatch-and-wait\u201d protocol, which included a follow-up DSA at five years. The primary endpoints were morphological changes, including dimensional growth, shrinkage, complete resolution, de novo formation of new aneurysms, and the incidence of aneurysmal subarachnoid hemorrhage (SAH). Over the cumulative 565 patient-years of follow-up, no instances of aneurysmal rupture or SAH were observed. Most aneurysms were located in the anterior circulation (92.2%). The vast majority of aneurysms (n\u2009=\u200987; 77.0%) demonstrated complete morphological stability. A small subset of aneurysms exhibited dynamic changes: 12 (10.6%) demonstrated minor growth but remained within the &lt;\u20095 mm size category, 6 (5.3%) decreased in size, and 5 (4.4%) underwent complete spontaneous resolution. De novo aneurysm formation was identified in 3 patients (2.7%). While traditional vascular risk factors like hypertension and oral contraceptive use showed no significant correlation with aneurysm behavior, a paradoxical and statistically significant association was found with smoking, which correlated with a higher likelihood of aneurysm resolution (p\u2009=\u20090.016). This study supports that a conservative management strategy with planned imaging surveillance is a safe and viable option for patients with unruptured intracranial aneurysms smaller than 5 mm. The absence of rupture over five years, coupled with the low rate of significant growth, suggests that these lesions have a very low observed risk of rupture and morphological progression over five years. These findings support conservative management for most patients with UIAs\u2009&lt;\u20095 mm, although treatment decisions should remain individualized according to patient- and aneurysm-specific risk factors.<\/jats:p>","DOI":"10.1007\/s10143-026-04507-3","type":"journal-article","created":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T04:26:03Z","timestamp":1790655963000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["The natural history of untreated small (&lt;\u20095\u00a0mm) intracranial aneurysms: a five-year angiographic follow-up study"],"prefix":"10.1007","volume":"49","author":[{"suffix":"Jr","given":"Jefferson","family":"Rosi","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Juliana Gozzo","family":"Sekula","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0009-5612-556X","authenticated-orcid":false,"given":"Leonardo B. O.","family":"Brenner","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Manoel Jacobsen","family":"Teixeira","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Saul Almeida","family":"da Silva","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jose Guilherme Mendes Pereira","family":"Caldas","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Carlos Gilberto Carlotti","family":"Junior","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Eberval Gadelha","family":"Figueiredo","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2026,9,29]]},"reference":[{"issue":"7","key":"4507_CR1","doi-asserted-by":"publisher","first-page":"626","DOI":"10.1016\/S1474-4422(11)70109-0","volume":"10","author":"MH Vlak","year":"2011","unstructured":"Vlak MH, Algra A, Brandenburg R, Rinkel GJ (2011) Prevalence of unruptured intracranial aneurysms, with emphasis on sex, age, comorbidity, country, and time period: a systematic review and meta-analysis. Lancet Neurol 10(7):626\u2013636","journal-title":"Lancet Neurol"},{"issue":"9488","key":"4507_CR2","doi-asserted-by":"publisher","first-page":"809","DOI":"10.1016\/S0140-6736(05)67214-5","volume":"366","author":"AJ Molyneux","year":"2005","unstructured":"Molyneux AJ, Kerr RS, Yu LM, 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 trial. Lancet 366(9488):809\u2013817","journal-title":"Lancet"},{"issue":"9378","key":"4507_CR3","doi-asserted-by":"publisher","first-page":"103","DOI":"10.1016\/S0140-6736(03)13860-3","volume":"362","author":"DO Wiebers","year":"2003","unstructured":"Wiebers DO, Whisnant JP, Huston J, Meissner I, Brown RD, Piepgras DG, O\u2019Fallon WM (2003) Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet 362(9378):103\u2013110","journal-title":"Lancet"},{"issue":"26","key":"4507_CR4","doi-asserted-by":"publisher","first-page":"2474","DOI":"10.1056\/NEJMoa1113260","volume":"366","author":"UCAS Japan Investigators","year":"2012","unstructured":"UCAS Japan Investigators (2012) The natural course of unruptured cerebral aneurysms in a Japanese cohort. N Engl J Med 366(26):2474\u20132482","journal-title":"N Engl J Med"},{"issue":"4","key":"4507_CR5","doi-asserted-by":"publisher","first-page":"393","DOI":"10.1016\/S1474-4422(14)70015-8","volume":"13","author":"RD Brown","year":"2014","unstructured":"Brown RD, Broderick JP (2014) Unruptured intracranial aneurysms: epidemiology, natural history, management options, and familial screening. Lancet Neurol 13(4):393\u2013404","journal-title":"Lancet Neurol"},{"issue":"1","key":"4507_CR6","doi-asserted-by":"publisher","first-page":"258","DOI":"10.1148\/radiol.13121188","volume":"269","author":"JP Villablanca","year":"2013","unstructured":"Villablanca JP, Duckwiler GR, Jahan R, Tateshima S, Martin NA, Frazee J, Vi\u00f1uela F (2013) Natural history of asymptomatic unruptured cerebral aneurysms evaluated at CT angiography: growth and rupture incidence and correlation with epidemiologic risk factors. Radiology 269(1):258\u2013265","journal-title":"Radiology"},{"issue":"11","key":"4507_CR7","doi-asserted-by":"publisher","first-page":"3027","DOI":"10.1161\/STROKEAHA.113.001107","volume":"44","author":"E G\u00fcresir","year":"2013","unstructured":"G\u00fcresir E, Schuss P, Seifert V, Vatter H (2013) Natural history of small unruptured anterior circulation aneurysms: a prospective cohort study. Stroke 44(11):3027\u20133031","journal-title":"Stroke"},{"key":"4507_CR8","first-page":"108139","volume":"230","author":"L Davies","year":"2025","unstructured":"Davies L, Khurana VG, Laidlaw JD, Kitchen N (2025) Natural history of small incidental intracranial aneurysms: a systematic review and meta-analysis. Clin Neurol Neurosurg 230:108139","journal-title":"Clin Neurol Neurosurg"},{"key":"4507_CR9","volume-title":"Essential medical statistics","author":"BR Kirkwood","year":"2006","unstructured":"Kirkwood BR, Sterne JAC (2006) Essential medical statistics. Blackwell Science"},{"key":"4507_CR10","doi-asserted-by":"crossref","unstructured":"Hosmer DW Jr, Lemeshow S, Sturdivant RX (2013) Applied logistic regression. John Wiley & Sons","DOI":"10.1002\/9781118548387"},{"issue":"9","key":"4507_CR11","doi-asserted-by":"publisher","first-page":"2414","DOI":"10.1161\/STROKEAHA.113.001838","volume":"44","author":"S Juvela","year":"2013","unstructured":"Juvela S, Poussa K, Lehto H, Porras M (2013) Natural history of unruptured intracranial aneurysms: a long-term follow-up study. Stroke 44(9):2414\u20132421","journal-title":"Stroke"},{"key":"4507_CR12","first-page":"e472","volume":"86","author":"MJ Fr\u0105czek","year":"2021","unstructured":"Fr\u0105czek MJ, Kluczewska E, Jab\u0142o\u0144ski M (2021) Unruptured intracranial aneurysms: Why should we focus on small aneurysms? A comprehensive review. Pol J Radiol 86:e472\u2013e481","journal-title":"Pol J Radiol"},{"issue":"4","key":"4507_CR13","first-page":"717","volume":"110","author":"DR Buis","year":"2009","unstructured":"Buis DR, van den Berg R, van der Sprenkel JWB, Rinkel GJE, Vandertop WP (2009) Spontaneous thrombosis of an unruptured intracranial aneurysm. J Neurosurg 110(4):717\u2013720","journal-title":"J Neurosurg"},{"issue":"3","key":"4507_CR14","doi-asserted-by":"publisher","first-page":"887","DOI":"10.1148\/radiol.10091982","volume":"256","author":"ON Naggara","year":"2010","unstructured":"Naggara ON, White PM, Guilbert F, Roy D, Weill A, Raymond J (2010) Endovascular treatment of intracranial unruptured aneurysms: systematic review and meta-analysis of the literature on safety and efficacy. Radiology 256(3):887\u2013897","journal-title":"Radiology"},{"key":"4507_CR15","doi-asserted-by":"publisher","first-page":"271582","DOI":"10.1155\/2012\/271582","volume":"2012","author":"N Chalouhi","year":"2012","unstructured":"Chalouhi N, Ali MS, Jabbour PM, Tjoumakaris SI, Gonzalez LF, Rosenwasser RH, Dumont AS (2012) Cigarette smoke and inflammation: role in cerebral aneurysm formation and rupture. Mediat Inflamm 2012:271582","journal-title":"Mediat Inflamm"},{"key":"4507_CR16","first-page":"917666","volume":"13","author":"H Wang","year":"2022","unstructured":"Wang H, Li W, He H, Zhou Y, Xia D, Bi J (2022) The biological effects of smoking on the formation and rupture of intracranial aneurysms: A systematic review and meta-analysis. Front Physiol 13:917666","journal-title":"Front Physiol"},{"issue":"4","key":"4507_CR17","doi-asserted-by":"publisher","first-page":"431","DOI":"10.1093\/neuros\/nyx238","volume":"82","author":"R Kleinloog","year":"2018","unstructured":"Kleinloog R, de Mul N, Verweij BH, Post JA, Rinkel GJ, Ruigrok YM (2018) Risk factors for intracranial aneurysm rupture: a systematic review. Neurosurgery 82(4):431\u2013440","journal-title":"Neurosurgery"},{"issue":"5","key":"4507_CR18","doi-asserted-by":"publisher","first-page":"978","DOI":"10.3171\/2012.11.JNS121210","volume":"118","author":"H Matsukawa","year":"2013","unstructured":"Matsukawa H, Uemura A, Fujii M, Kamo M, Takahashi O, Sumiyoshi S (2013) Morphological and clinical risk factors for the rupture of anterior communicating artery aneurysms. J Neurosurg 118(5):978\u2013983","journal-title":"J Neurosurg"},{"issue":"3","key":"4507_CR19","doi-asserted-by":"publisher","first-page":"941","DOI":"10.1148\/radiol.2017162290","volume":"285","author":"ZL Yang","year":"2017","unstructured":"Yang ZL, Zhang LJ, Lu GM, Xu XQ, Chen KM (2017) Small intracranial aneurysms: diagnostic accuracy of CT angiography. Radiology 285(3):941\u2013952","journal-title":"Radiology"},{"issue":"7","key":"4507_CR20","doi-asserted-by":"publisher","first-page":"1803","DOI":"10.1161\/01.STR.0000019510.32145.A9","volume":"33","author":"M Okahara","year":"2002","unstructured":"Okahara M, Kiyosue H, Yamashita M, Nagatomi H, Hata H, Saginoya T\u2026Mori, H. (2002) Diagnostic accuracy of magnetic resonance angiography for cerebral aneurysms in correlation with 3D-digital subtraction angiographic images: a study of 133 aneurysms. Stroke 33(7):1803\u20131808","journal-title":"Stroke"},{"issue":"12","key":"4507_CR21","doi-asserted-by":"publisher","first-page":"1163","DOI":"10.1016\/j.diii.2014.10.005","volume":"95","author":"C Rodriguez-R\u00e9gent","year":"2014","unstructured":"Rodriguez-R\u00e9gent C, Edjlali-Goujon M, Trystram D, Boulouis G, Ben Hassen W, Godon-Hardy S, Oppenheim C (2014) Non-invasive diagnosis of intracranial aneurysms. Diagn Interv Imaging 95(12):1163\u20131174","journal-title":"Diagn Interv Imaging"},{"issue":"6","key":"4507_CR22","doi-asserted-by":"publisher","first-page":"1322","DOI":"10.3171\/jns.2002.97.6.1322","volume":"97","author":"JP Villablanca","year":"2002","unstructured":"Villablanca JP, Hooshi P, Martin N, Jahan R, Duckwiler G, Lim S, Frazee J, Gobin YP, Sayre J, Bentson J, Vi\u00f1uela F (2002) Three-dimensional helical computerized tomography angiography in the diagnosis, characterization, and management of middle cerebral artery aneurysms: comparison with conventional angiography and intraoperative findings. J Neurosurg 97(6):1322\u20131332","journal-title":"J Neurosurg"},{"issue":"8","key":"4507_CR23","doi-asserted-by":"publisher","first-page":"514","DOI":"10.7326\/0003-4819-159-8-201310150-00004","volume":"159","author":"MH Li","year":"2012","unstructured":"Li MH, Chen SW, Li YD, Chen YC, Cheng YS, Hu DJ, Wang W (2012) Prevalence of unruptured cerebral aneurysms in Chinese adults aged 35 to 75 years: a cross-sectional study. Ann Intern Med 159(8):514\u2013521","journal-title":"Ann Intern Med"},{"issue":"1","key":"4507_CR24","doi-asserted-by":"publisher","first-page":"251","DOI":"10.1161\/01.STR.29.1.251","volume":"29","author":"GJ Rinkel","year":"1998","unstructured":"Rinkel GJ, Djibuti M, Algra A, van Gijn J (1998) Prevalence and risk of rupture of intracranial aneurysms: a systematic review. Stroke 29(1):251\u2013256","journal-title":"Stroke"},{"key":"4507_CR25","doi-asserted-by":"crossref","unstructured":"Li MH, Li YD, Tan HQ, Luo QY, Cheng YS, Wang W, Fang C (2014) Accurate diagnosis of small cerebral aneurysms\u2009\u2264\u20095\u00a0mm in diameter with 3.0-T MR angiography. Radiology, 271(2), 553\u2013560","DOI":"10.1148\/radiol.14122770"},{"issue":"4","key":"4507_CR26","doi-asserted-by":"publisher","first-page":"879","DOI":"10.4103\/0028-3886.323897","volume":"69","author":"X Lv","year":"2021","unstructured":"Lv X, Zhang W, Zhao X, Zhang H, Wang J (2021) Endovascular Treatment of Small Wide-Neck Bifurcation Aneurysms with Single Solitaire AB Stent Technique. Neurol India 69(4):879\u2013882. https:\/\/doi.org\/10.4103\/0028-3886.323897","journal-title":"Neurol India"},{"key":"4507_CR27","doi-asserted-by":"publisher","first-page":"110766","DOI":"10.1016\/j.jocn.2024.110766","volume":"127","author":"S Batista","year":"2024","unstructured":"Batista S, Ferreira MY, Brenner LBO, Semione G, Bocanegra-Becerra JE, Bertani R, Palavani LB, de Mac\u00eado Filho LJM, Bertoli ED, Rabelo NN, Welling LC, Figueiredo EG, Lawton MT (2024) Surgical clipping and endovascular treatments for small or very small anterior communicating artery aneurysms: A comparative pooled analysis. J Clin neuroscience: official J Neurosurgical Soc Australasia 127:110766. https:\/\/doi.org\/10.1016\/j.jocn.2024.110766","journal-title":"J Clin neuroscience: official J Neurosurgical Soc Australasia"},{"key":"4507_CR28","doi-asserted-by":"publisher","unstructured":"Goertz L, Hohenstatt S, Siebert E, Styczen H, Ranft A, Zopfs D, Kaiser D, Krukowski P, Schlamann M, Kottlors J, Janssen JP, Deuschl C, Dorn F, M\u00f6hlenbruch MA, Liebig T, Kabbasch C (2025) Feasibility, safety and efficacy of Woven EndoBridge embolization of intracranial aneurysms with the 2\u00a0mm height variants. Neuroradiology 67(11):3229\u20133238. https:\/\/doi.org\/10.1007\/s00234-025-03806-8","DOI":"10.1007\/s00234-025-03806-8"}],"container-title":["Neurosurgical Review"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/link.springer.com\/content\/pdf\/10.1007\/s10143-026-04507-3.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/link.springer.com\/article\/10.1007\/s10143-026-04507-3","content-type":"text\/html","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/link.springer.com\/content\/pdf\/10.1007\/s10143-026-04507-3.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T04:26:06Z","timestamp":1790655966000},"score":1,"resource":{"primary":{"URL":"https:\/\/link.springer.com\/10.1007\/s10143-026-04507-3"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,9,29]]},"references-count":28,"journal-issue":{"issue":"1","published-online":{"date-parts":[[2026,12]]}},"alternative-id":["4507"],"URL":"https:\/\/doi.org\/10.1007\/s10143-026-04507-3","relation":{},"ISSN":["1437-2320"],"issn-type":[{"value":"1437-2320","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,9,29]]},"assertion":[{"value":"15 November 2025","order":1,"name":"received","label":"Received","group":{"name":"ArticleHistory","label":"Article History"}},{"value":"10 August 2026","order":2,"name":"revised","label":"Revised","group":{"name":"ArticleHistory","label":"Article History"}},{"value":"15 September 2026","order":3,"name":"accepted","label":"Accepted","group":{"name":"ArticleHistory","label":"Article History"}},{"value":"29 September 2026","order":4,"name":"first_online","label":"First Online","group":{"name":"ArticleHistory","label":"Article History"}},{"value":"This study was approved by the Institutional Review Board of our institution. All procedures were conducted in accordance with institutional guidelines and the Declaration of Helsinki.","order":1,"name":"Ethics","label":"Ethical approval","group":{"name":"EthicsHeading","label":"Declarations"}},{"value":"This study was conducted in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki Declaration and its later amendments. Ethical approval was obtained from the appropriate ethics committee, and the study was duly registered on Plataforma Brasil under protocol number 78627123.5.0000.00681. All participants were informed about the objectives, procedures, potential risks, and benefits of the study and provided written informed consent prior to their participation. The confidentiality and anonymity of all participants were strictly preserved throughout the research process.","order":2,"name":"Ethics","label":"Consent to participate","group":{"name":"EthicsHeading","label":"Declarations"}},{"value":"Not applicable.","order":3,"name":"Ethics","label":"Clinical trial number","group":{"name":"EthicsHeading","label":"Declarations"}},{"value":"The authors declare no competing interests.","order":4,"name":"Ethics","label":"Competing interests","group":{"name":"EthicsHeading","label":"Declarations"}}],"article-number":"590"}}