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Unruptured intracranial aneurysms

Robert J Singer, MD
Christopher S Ogilvy, MD
Guy Rordorf, MD
Section Editor
Jose Biller, MD, FACP, FAAN, FAHA
Deputy Editor
Janet L Wilterdink, MD


Most subarachnoid hemorrhages (SAH) are caused by ruptured intracranial saccular (berry) aneurysms. The epidemiology and pathogenesis of intracranial aneurysms and the management of unruptured aneurysms are discussed here. The epidemiology, etiology, clinical manifestations, diagnosis, and treatment of SAH, and issues related to screening for aneurysms are discussed separately. (See "Clinical manifestations and diagnosis of aneurysmal subarachnoid hemorrhage" and "Treatment of aneurysmal subarachnoid hemorrhage" and "Screening for intracranial aneurysm".)


The prevalence of intracranial saccular aneurysms by radiographic and autopsy series is estimated to be 3.2 percent in a population without comorbidity, a mean age of 50 years, and a 1:1 gender ratio [1,2],. Of patients with cerebral aneurysms, 20 to 30 percent have multiple aneurysms [3]. Aneurysmal SAH occurs at an estimated rate of 6 to 16 per 100,000 population [4]. In North America, this translates into approximately 30,000 affected persons per year. Thus, most aneurysms, particularly small aneurysms, do not rupture (see 'Risk of aneurysm rupture' below).

Rupture of an intracranial aneurysm is believed to account for 0.4 to 0.6 percent of all deaths. Approximately 10 percent of patients die prior to reaching the hospital, and only one-third has a "good result" after treatment. (See "Treatment of aneurysmal subarachnoid hemorrhage".)

Most intracranial aneurysms (approximately 85 percent) are located in the anterior circulation, predominantly on the circle of Willis. Common sites include the junction of the anterior communicating artery with the anterior cerebral artery, the junction of the posterior communicating artery with the internal carotid artery, and the bifurcation of the middle cerebral artery. Posterior circulation sites often include the top of the basilar artery, the junction of the basilar artery and the superior or anterior inferior cerebellar arteries, and the junction of the vertebral artery and the posterior inferior cerebellar artery [5].

There is a female preponderance for aneurysms ranging from 54 to 61 percent [2,4]. In populations older than 50 years, the increased prevalence in women may approach a 2 to 1 ratio or greater. (See 'Estrogen deficiency' below.)

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Literature review current through: Nov 2017. | This topic last updated: Sep 26, 2013.
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  1. Vernooij MW, Ikram MA, Tanghe HL, et al. Incidental findings on brain MRI in the general population. N Engl J Med 2007; 357:1821.
  2. Vlak MH, Algra A, Brandenburg R, Rinkel GJ. Prevalence of unruptured intracranial aneurysms, with emphasis on sex, age, comorbidity, country, and time period: a systematic review and meta-analysis. Lancet Neurol 2011; 10:626.
  4. Sarti C, Tuomilehto J, Salomaa V, et al. Epidemiology of subarachnoid hemorrhage in Finland from 1983 to 1985. Stroke 1991; 22:848.
  5. Schievink WI. Intracranial aneurysms. N Engl J Med 1997; 336:28.
  6. Alg VS, Sofat R, Houlden H, Werring DJ. Genetic risk factors for intracranial aneurysms: a meta-analysis in more than 116,000 individuals. Neurology 2013; 80:2154.
  7. Neil-Dwyer G, Bartlett JR, Nicholls AC, et al. Collagen deficiency and ruptured cerebral aneurysms. A clinical and biochemical study. J Neurosurg 1983; 59:16.
  8. Pepin M, Schwarze U, Superti-Furga A, Byers PH. Clinical and genetic features of Ehlers-Danlos syndrome type IV, the vascular type. N Engl J Med 2000; 342:673.
  9. Conway JE, Hutchins GM, Tamargo RJ. Marfan syndrome is not associated with intracranial aneurysms. Stroke 1999; 30:1632.
  10. Litchfield WR, Anderson BF, Weiss RJ, et al. Intracranial aneurysm and hemorrhagic stroke in glucocorticoid-remediable aldosteronism. Hypertension 1998; 31:445.
  11. Chalhoub V, Abi-Rafeh L, Hachem K, et al. Intracranial aneurysm and recessive polycystic kidney disease: the third reported case. JAMA Neurol 2013; 70:114.
  12. Ronkainen A, Hernesniemi J, Puranen M, et al. Familial intracranial aneurysms. Lancet 1997; 349:380.
  13. Raaymakers TW. Aneurysms in relatives of patients with subarachnoid hemorrhage: frequency and risk factors. MARS Study Group. Magnetic Resonance Angiography in Relatives of patients with Subarachnoid hemorrhage. Neurology 1999; 53:982.
  14. Bromberg JE, Rinkel GJ, Algra A, et al. Familial subarachnoid hemorrhage: distinctive features and patterns of inheritance. Ann Neurol 1995; 38:929.
  15. Wills S, Ronkainen A, van der Voet M, et al. Familial intracranial aneurysms: an analysis of 346 multiplex Finnish families. Stroke 2003; 34:1370.
  16. Onda H, Kasuya H, Yoneyama T, et al. Genomewide-linkage and haplotype-association studies map intracranial aneurysm to chromosome 7q11. Am J Hum Genet 2001; 69:804.
  17. Hashikata H, Liu W, Inoue K, et al. Confirmation of an association of single-nucleotide polymorphism rs1333040 on 9p21 with familial and sporadic intracranial aneurysms in Japanese patients. Stroke 2010; 41:1138.
  18. van der Voet M, Olson JM, Kuivaniemi H, et al. Intracranial aneurysms in Finnish families: confirmation of linkage and refinement of the interval to chromosome 19q13.3. Am J Hum Genet 2004; 74:564.
  19. Deka R, Koller DL, Lai D, et al. The relationship between smoking and replicated sequence variants on chromosomes 8 and 9 with familial intracranial aneurysm. Stroke 2010; 41:1132.
  20. Foroud T, Koller DL, Lai D, et al. Genome-wide association study of intracranial aneurysms confirms role of Anril and SOX17 in disease risk. Stroke 2012; 43:2846.
  21. St Jean P, Hart B, Webster M, et al. Alpha-1-antitrypsin deficiency in aneurysmal disease. Hum Hered 1996; 46:92.
  22. Broderick JP, Brown RD Jr, Sauerbeck L, et al. Greater rupture risk for familial as compared to sporadic unruptured intracranial aneurysms. Stroke 2009; 40:1952.
  23. Mackey J, Brown RD Jr, Moomaw CJ, et al. Familial intracranial aneurysms: is anatomic vulnerability heritable? Stroke 2013; 44:38.
  24. Teunissen LL, Rinkel GJ, Algra A, van Gijn J. Risk factors for subarachnoid hemorrhage: a systematic review. Stroke 1996; 27:544.
  25. Knekt P, Reunanen A, Aho K, et al. Risk factors for subarachnoid hemorrhage in a longitudinal population study. J Clin Epidemiol 1991; 44:933.
  26. Leppälä JM, Paunio M, Virtamo J, et al. Alcohol consumption and stroke incidence in male smokers. Circulation 1999; 100:1209.
  27. Vlak MH, Rinkel GJ, Greebe P, Algra A. Independent risk factors for intracranial aneurysms and their joint effect: a case-control study. Stroke 2013; 44:984.
  28. Bonita R. Cigarette smoking, hypertension and the risk of subarachnoid hemorrhage: a population-based case-control study. Stroke 1986; 17:831.
  29. Stober T, Sen S, Anstätt T, et al. Direct evidence of hypertension and the possible role of post-menopause oestrogen deficiency in the pathogenesis of berry aneurysms. J Neurol 1985; 232:67.
  30. Taylor CL, Yuan Z, Selman WR, et al. Cerebral arterial aneurysm formation and rupture in 20,767 elderly patients: hypertension and other risk factors. J Neurosurg 1995; 83:812.
  31. Longstreth WT, Nelson LM, Koepsell TD, van Belle G. Subarachnoid hemorrhage and hormonal factors in women. A population-based case-control study. Ann Intern Med 1994; 121:168.
  32. Mhurchu CN, Anderson C, Jamrozik K, et al. Hormonal factors and risk of aneurysmal subarachnoid hemorrhage: an international population-based, case-control study. Stroke 2001; 32:606.
  33. Perloff JK. The Clinical Recognition of Congenital Heart Disease, 4th, WB Saunders, Philadelphia 1994.
  34. HODES HL, STEINFELD L, BLUMENTHAL S. Congenital cerebral aneurysms and coarctation of the aorta. Arch Pediatr 1959; 76:28.
  35. Austin G, Fisher S, Dickson D, et al. The significance of the extracellular matrix in intracranial aneurysms. Ann Clin Lab Sci 1993; 23:97.
  36. Patel RL, Richards P, Chambers DJ, Venn G. Infective endocarditis complicated by ruptured cerebral mycotic aneurysm. J R Soc Med 1991; 84:746.
  37. Wiebers DO, Piepgras DG, Meyer FB, et al. Pathogenesis, natural history, and treatment of unruptured intracranial aneurysms. Mayo Clin Proc 2004; 79:1572.
  38. Starke RM, Chalouhi N, Ali MS, et al. The role of oxidative stress in cerebral aneurysm formation and rupture. Curr Neurovasc Res 2013; 10:247.
  39. Chalouhi N, Ali MS, Starke RM, et al. Cigarette smoke and inflammation: role in cerebral aneurysm formation and rupture. Mediators Inflamm 2012; 2012:271582.
  40. Aoki T, Nishimura M. Targeting chronic inflammation in cerebral aneurysms: focusing on NF-kappaB as a putative target of medical therapy. Expert Opin Ther Targets 2010; 14:265.
  41. Frösen J, Piippo A, Paetau A, et al. Remodeling of saccular cerebral artery aneurysm wall is associated with rupture: histological analysis of 24 unruptured and 42 ruptured cases. Stroke 2004; 35:2287.
  42. Raps EC, Rogers JD, Galetta SL, et al. The clinical spectrum of unruptured intracranial aneurysms. Arch Neurol 1993; 50:265.
  43. Friedman JA, Piepgras DG, Pichelmann MA, et al. Small cerebral aneurysms presenting with symptoms other than rupture. Neurology 2001; 57:1212.
  44. Huston J 3rd, Nichols DA, Luetmer PH, et al. Blinded prospective evaluation of sensitivity of MR angiography to known intracranial aneurysms: importance of aneurysm size. AJNR Am J Neuroradiol 1994; 15:1607.
  45. Schwartz RB, Tice HM, Hooten SM, et al. Evaluation of cerebral aneurysms with helical CT: correlation with conventional angiography and MR angiography. Radiology 1994; 192:717.
  46. White PM, Teadsale E, Wardlaw JM, Easton V. What is the most sensitive non-invasive imaging strategy for the diagnosis of intracranial aneurysms? J Neurol Neurosurg Psychiatry 2001; 71:322.
  47. van Gelder JM. Computed tomographic angiography for detecting cerebral aneurysms: implications of aneurysm size distribution for the sensitivity, specificity, and likelihood ratios. Neurosurgery 2003; 53:597.
  48. Menke J, Larsen J, Kallenberg K. Diagnosing cerebral aneurysms by computed tomographic angiography: meta-analysis. Ann Neurol 2011; 69:646.
  49. Li MH, Li YD, Tan HQ, et al. Contrast-free MRA at 3.0 T for the detection of intracranial aneurysms. Neurology 2011; 77:667.
  50. Wiebers DO, Whisnant JP, Huston J 3rd, et al. Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet 2003; 362:103.
  51. UCAS Japan Investigators, Morita A, Kirino T, et al. The natural course of unruptured cerebral aneurysms in a Japanese cohort. N Engl J Med 2012; 366:2474.
  52. International Study of Unruptured Intracranial Aneurysms Investigators. Unruptured intracranial aneurysms--risk of rupture and risks of surgical intervention. N Engl J Med 1998; 339:1725.
  53. Wiebers DO, Whisnant JP, O'Fallon WM. The natural history of unruptured intracranial aneurysms. N Engl J Med 1981; 304:696.
  54. Wiebers DO, Whisnant JP, Sundt TM Jr, O'Fallon WM. The significance of unruptured intracranial saccular aneurysms. J Neurosurg 1987; 66:23.
  55. Sonobe M, Yamazaki T, Yonekura M, Kikuchi H. Small unruptured intracranial aneurysm verification study: SUAVe study, Japan. Stroke 2010; 41:1969.
  56. Matsubara S, Hadeishi H, Suzuki A, et al. Incidence and risk factors for the growth of unruptured cerebral aneurysms: observation using serial computerized tomography angiography. J Neurosurg 2004; 101:908.
  57. Burns JD, Huston J 3rd, Layton KF, et al. Intracranial aneurysm enlargement on serial magnetic resonance angiography: frequency and risk factors. Stroke 2009; 40:406.
  58. Kashiwazaki D, Kuroda S, Sapporo SAH Study Group. Size ratio can highly predict rupture risk in intracranial small (<5 mm) aneurysms. Stroke 2013; 44:2169.
  59. Forget TR Jr, Benitez R, Veznedaroglu E, et al. A review of size and location of ruptured intracranial aneurysms. Neurosurgery 2001; 49:1322.
  60. White PM, Wardlaw J. Unruptured intracranial aneurysms: prospective data have arrived. Lancet 2003; 362:90.
  61. Sato K, Yoshimoto Y. Risk profile of intracranial aneurysms: rupture rate is not constant after formation. Stroke 2011; 42:3376.
  62. Chien A, Liang F, Sayre J, et al. Enlargement of small, asymptomatic, unruptured intracranial aneurysms in patients with no history of subarachnoid hemorrhage: the different factors related to the growth of single and multiple aneurysms. J Neurosurg 2013; 119:190.
  63. Ingall T, Asplund K, Mähönen M, Bonita R. A multinational comparison of subarachnoid hemorrhage epidemiology in the WHO MONICA stroke study. Stroke 2000; 31:1054.
  64. Morita A, Fujiwara S, Hashi K, et al. Risk of rupture associated with intact cerebral aneurysms in the Japanese population: a systematic review of the literature from Japan. J Neurosurg 2005; 102:601.
  65. Morita A. [On-line outcome study of unruptured cerebral aneurysm in Japan (UCAS Japan)]. Rinsho Shinkeigaku 2002; 42:1188.
  66. Yonekura M. Small unruptured aneurysm verification (SUAVe Study, Japan)--interim report. Neurol Med Chir (Tokyo) 2004; 44:213.
  67. Hasan D, Chalouhi N, Jabbour P, et al. Early change in ferumoxytol-enhanced magnetic resonance imaging signal suggests unstable human cerebral aneurysm: a pilot study. Stroke 2012; 43:3258.
  68. Vlak MH, Rinkel GJ, Greebe P, Algra A. Risk of rupture of an intracranial aneurysm based on patient characteristics: a case-control study. Stroke 2013; 44:1256.
  69. Johnston SC, Wilson CB, Halbach VV, et al. Endovascular and surgical treatment of unruptured cerebral aneurysms: comparison of risks. Ann Neurol 2000; 48:11.
  70. Kotowski M, Naggara O, Darsaut TE, et al. Safety and occlusion rates of surgical treatment of unruptured intracranial aneurysms: a systematic review and meta-analysis of the literature from 1990 to 2011. J Neurol Neurosurg Psychiatry 2013; 84:42.
  71. Alshekhlee A, Mehta S, Edgell RC, et al. Hospital mortality and complications of electively clipped or coiled unruptured intracranial aneurysm. Stroke 2010; 41:1471.
  72. Ogilvy CS, Carter BS. Stratification of outcome for surgically treated unruptured intracranial aneurysms. Neurosurgery 2003; 52:82.
  73. Johnston SC, Gress DR, Kahn JG. Which unruptured cerebral aneurysms should be treated? A cost-utility analysis. Neurology 1999; 52:1806.
  74. Takao H, Nojo T. Treatment of unruptured intracranial aneurysms: decision and cost-effectiveness analysis. Radiology 2007; 244:755.
  75. Wiebers DO, Torres VE. Screening for unruptured intracranial aneurysms in autosomal dominant polycystic kidney disease. N Engl J Med 1992; 327:953.
  76. Héman LM, Jongen LM, van der Worp HB, et al. Incidental intracranial aneurysms in patients with internal carotid artery stenosis: a CT angiography study and a metaanalysis. Stroke 2009; 40:1341.
  77. Hasan DM, Mahaney KB, Brown RD Jr, et al. Aspirin as a promising agent for decreasing incidence of cerebral aneurysm rupture. Stroke 2011; 42:3156.
  78. Bederson JB, Awad IA, Wiebers DO, et al. Recommendations for the management of patients with unruptured intracranial aneurysms: A statement for healthcare professionals from the Stroke Council of the American Heart Association. Circulation 2000; 102:2300.
  79. Greving JP, Rinkel GJ, Buskens E, Algra A. Cost-effectiveness of preventive treatment of intracranial aneurysms: new data and uncertainties. Neurology 2009; 73:258.
  80. Johnston SC, Zhao S, Dudley RA, et al. Treatment of unruptured cerebral aneurysms in California. Stroke 2001; 32:597.
  81. Vallee JN, Aymard A, Vicaut E, et al. Endovascular treatment of basilar tip aneurysms with Guglielmi detachable coils: predictors of immediate and long-term results with multivariate analysis 6-year experience. Radiology 2003; 226:867.
  82. Raftopoulos C, Goffette P, Vaz G, et al. Surgical clipping may lead to better results than coil embolization: results from a series of 101 consecutive unruptured intracranial aneurysms. Neurosurgery 2003; 52:1280.
  83. Zacharia BE, Ducruet AF, Hickman ZL, et al. Technological advances in the management of unruptured intracranial aneurysms fail to improve outcome in New York state. Stroke 2011; 42:2844.
  84. McDonald JS, McDonald RJ, Fan J, et al. Comparative effectiveness of unruptured cerebral aneurysm therapies: propensity score analysis of clipping versus coiling. Stroke 2013; 44:988.
  85. De Vries J, Boogaarts J, Van Norden A, Wakhloo AK. New generation of Flow Diverter (surpass) for unruptured intracranial aneurysms: a prospective single-center study in 37 patients. Stroke 2013; 44:1567.