Introduction: Due to observational studies finding small anterior circulation unruptured intracranial aneurysms (UIA) to be at low risk for subarachnoid hemorrhage (SAH), any UIAs are now followed with surveillance imaging. The incidence of growth of UIAs, incidence of de novo aneurysm formation, and risk factors for growth or de novo aneurysm formation require further research. We report our experience with an aneurysm surveillance protocol and review the literature on this topic.

Methods: We retrospectively identified 192 patients with 234 UIAs that were recommended for observation with surveillance imaging and obtained at least 1 follow-up study. The incidence of UIA growth and de novo aneurysm formation was assessed. Risk factors for UIA growth and de novo aneurysm formation were evaluated. Patient compliance with the surveillance protocol and results after treatment were assessed.

Results: Over 749 aneurysm-years of follow-up, 28 of 234 UIAs grew resulting in an annual risk of growth of 3.74%. At 6-months, 7.0% of patients had a growth of the aneurysm identified. Initial aneurysm size was the only predictor of aneurysm growth (p=0.002). The incidence of growth for UIAs < 5 mm versus UIA = 5 mm was 1.6% and 8.7% per aneurysm-year, respectively. Over 614 patient-years of follow-up, 4 de novo aneurysms formed in 192 patients resulting in a 0.64% annual risk of de novo aneurysm formation. The rate of aneurysm growth or de novo aneurysm formation was 5.0% per patient-year of follow-up. Patient compliance with our protocol was 65% with younger age predictive of patient compliance (p = 0.01).

Conclusions: Observation of low risk UIAs with surveillance imaging can be safely implemented into clinical practice with good adherence. More frequent surveillance imaging for newly diagnosed UIAs is warranted. Future guidelines should recommend a specific frequency and duration of aneurysm surveillance.

Patient Care: Our research will contribute to the development of future guidelines regarding the specific frequency and duration of surveillance imaging of unruptured intracranial aneurysms.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Identify the risk factor(s)for growth of unruptured intracranial aneurysms, 2) Identify patients which may warrant immediate occlusion or at least more frequent surveillance imaging, 3) Describe the annual risk of growth for unruptured intracranial aneurysms and the risk of de novo aneurysm formation.

References: 1.Brown, R.D., Unruptured intracranial aneurysms. Semin Neurol, 2010. 30(5): p. 537-44. 2.Morita, A., et al., The natural course of unruptured cerebral aneurysms in a Japanese cohort. N Engl J Med, 2012. 366(26): p. 2474-82. 3.Wiebers, D.O., Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. The Lancet, 2003. 362(9378): p. 103-110. 4.Juvela, S., et al., Natural history of unruptured intracranial aneurysms: a long-term follow-up study. Stroke, 2013. 44(9): p. 2414-21. 5.Sonobe, M., et al., Small unruptured intracranial aneurysm verification study: SUAVe study, Japan. Stroke, 2010. 41(9): p. 1969-77. 6.Wermer, M.J., et al., Yield of short-term follow-up CT/MR angiography for small aneurysms detected at screening. Stroke, 2006. 37(2): p. 414-8. 7.Lee, E.J., et al., Rupture rate for patients with untreated unruptured intracranial aneurysms in South Korea during 2006-2009. J Neurosurg, 2012. 117(1): p. 53-9. 8.Ishibashi, T., et al., Unruptured intracranial aneurysms: incidence of rupture and risk factors. Stroke, 2009. 40(1): p. 313-6. 9.Greving, J.P., et al., Development of the PHASES score for prediction of risk of rupture of intracranial aneurysms: a pooled analysis of six prospective cohort studies. Lancet Neurol, 2014. 13(1): p. 59-66. 10.Bederson, J.B., 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. Stroke, 2000. 31(11): p. 2742-2750. 11.Zipfel, G.J. and R.G. Dacey, Update on the management of unruptured intracranial aneurysms. Neurosurg Focus, 2004. 17(5): p. E2. 12.Komotar, R.J., J. Mocco, and R.A. Solomon, Guidelines for the surgical treatment of unruptured intracranial aneurysms: the first annual J. Lawrence pool memorial research symposium--controversies in the management of cerebral aneurysms. Neurosurgery, 2008. 62(1): p. 183-93; discussion 193-4. 13.Inoue, T., et al., Annual rupture risk of growing unruptured cerebral aneurysms detected by magnetic resonance angiography. J Neurosurg, 2012. 117(1): p. 20-5. 14.Villablanca, J.P., et al., Natural history of asymptomatic unruptured cerebral aneurysms evaluated at CT angiography: growth and rupture incidence and correlation with epidemiologic risk factors. Radiology, 2013. 269(1): p. 258-65. 15.Koffijberg, H., et al., Growth rates of intracranial aneurysms: exploring constancy. J Neurosurg, 2008. 109(2): p. 176-85. 16.Juvela, S., K. Poussa, and M. Porras, Factors Affecting Formation and Growth of Intracranial Aneurysms : A Long-Term Follow-Up Study. Stroke, 2001. 32(2): p. 485-491. 17.Matsumoto, K., et al., Incidence of growth and rupture of unruptured intracranial aneurysms followed by serial MRA. Acta Neurochir (Wien), 2013. 155(2): p. 211-6. 18.Miyazawa, N., I. Akiyama, and Z. Yamagata, Risk factors for growth of unruptured intracranial aneurysms: follow-up study by serial 0.5-T magnetic resonance angiography. Neurosurgery, 2006. 58(6): p. 1047-53; discussion 1047-53. 19.So, T.Y., et al., Risk of growth in unruptured intracranial aneurysms: a retrospective analysis. J Clin Neurosci, 2010. 17(1): p. 29-33. 20.Ferns, S.P., et al., De novo aneurysm formation and growth of untreated aneurysms: a 5-year MRA follow-up in a large cohort of patients with coiled aneurysms and review of the literature. Stroke, 2011. 42(2): p. 313-8. 21.Burns, J.D., et al., Intracranial aneurysm enlargement on serial magnetic resonance angiography: frequency and risk factors. Stroke, 2009. 40(2): p. 406-11. 22.Matsubara, S., et al., Incidence and risk factors for the growth of unruptured cerebral aneurysms: observation using serial computerized tomography angiography. J Neurosurg, 2004. 101(6): p. 908-14. 23.Chien, A., 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(1): p. 190-7. 24.David, C.A., et al., Late angiographic follow-up review of surgically treated aneurysms. J Neurosurg, 1999. 91(3): p. 396-401. 25.Tsutsumi, K., et al., Risk of Aneurysm Recurrence in Patients With Clipped Cerebral Aneurysms : Results of Long-Term Follow-Up Angiography. Stroke, 2001. 32(5): p. 1191-1194. 26.Wermer, M.J., et al., Follow-up screening after subarachnoid haemorrhage: frequency and determinants of new aneurysms and enlargement of existing aneurysms. Brain, 2005. 128(Pt 10): p. 2421-9. 27.Sprengers, M.E., et al., Evaluation of the occlusion status of coiled intracranial aneurysms with MR angiography at 3T: is contrast enhancement necessary? AJNR Am J Neuroradiol, 2009. 30(9): p. 1665-71. 28.Wiebers, D.O., et al., Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet, 2003. 362(9378): p. 103-10. 29.Ronkainen, A., et al., Intracranial aneurysms: MR angiographic screening in 400 asymptomatic individuals with increased familial risk. Radiology, 1995. 195(1): p. 35-40. 30.Grandin, C.B., et al., Diagnosis of intracranial aneurysms: accuracy of MR angiography at 0.5 T. AJNR Am J Neuroradiol, 1998. 19(2): p. 245-52. 31.Yonekura, M., Small unruptured aneurysm verification (SUAVe Study, Japan)--interim report. Neurol Med Chir (Tokyo), 2004. 44(4): p. 213-4. 32.Frosen, J., 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(10): p. 2287-93. 33.Frosen, J., Smooth muscle cells and the formation, degeneration, and rupture of saccular intracranial aneurysm wall--a review of current pathophysiological knowledge. Transl Stroke Res, 2014. 5(3): p. 347-56. 34.Wiebers, D.O., et al., Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet, 2003. 362(9378): p. 103-10. 35.Allcock, J.M. and P.B. Canham, Angiographic study of the growth of intracranial aneurysms. J Neurosurg, 1976. 45(6): p. 617-21. 36.Juvela, S., M. Porras, and O. Heiskanen, Natural history of unruptured intracranial aneurysms: a long-term follow-up study. J Neurosurg, 1993. 79(2): p. 174-82. 37.Chmayssani, M., et al., Relationship of growth to aneurysm rupture in asymptomatic aneurysms </= 7 mm: a systematic analysis of the literature. Neurosurgery, 2011. 68(5): p. 1164-71; discussion 1171. 38.Brown, R.D., Jr. and J.P. Broderick, Unruptured intracranial aneurysms: epidemiology, natural history, management options, and familial screening. Lancet Neurol, 2014. 13(4): p. 393-404.