- To analyze the controversy concerning the risk of rupture of small intracranial aneurysms.
In the last post, we have concluded that when an unruptured intracranial aneurysm is identified we have to decide whether the "patient" (and not only the aneurysm) should be treated and whether it should be treated with endovascular or neurosurgical techniques. But for years our decision making has been influenced by results of the International Study of Unruptured Intracranial Aneurysms (ISUIA).
ISUIA is a longitudinal prospective study, which found that larger aneurysms are more likely to rupture.
The problem is that ISUIA study failed to resolve one of the fundamental clinical problems: the discrepancy between their reported extremely low rupture risk in asymptomatic aneurysms <7 mm at 0.7% per year compared to the large proportion of ruptured aneurysms in the same category. In fact, in contrast to the findings of the ISUIA, several studies showed that the majority of SAHs result from aneurysms <10 mm in size and a significant proportion of patients present with ruptured aneurysms <5 mm in diameter (Korja et al.). The high percentage of ruptured small IAs among ruptured IAs clearly indicates that small IAs can rupture without becoming large IAs. This thing suggests that there are some intrinsic differences between small and large IAs in morphological and hemodynamic features.
Varble et al. inquired whether small and large IAs might have different rupture risk profiles. They used a cutoff of 5 mm and they found that there are some different hemodynamic and clinical, but not morphological, rupture discriminants.
This previous study indicated that small and large IAs have different paths to rupture and demonstrated that 5 mm is the best cutoff.
In conclusion what is evident from these articles is that:
- Growth and rupture of IAs are dynamic conditions, related to hemodynamic changes.
- "Larger size = higher risk" is an old idea, because small aneurysms need to be carefully evaluated by relying on different indicators.
- * Johnson AK, Heiferman DM, Lopes DK. Stent-assisted embolization of 100 middle cerebral artery aneurysms. J Neurosurg. 2013 May;118(5):950-5. doi: 10.3171/2013.1.JNS121298. Epub 2013 Feb 8.
- Alreshidi M, Cote DJ, Dasenbrock HH, Acosta M, Can A, Doucette J, Simjian T, Hulou MM, Wheeler LA, Huang K, Zaidi HA, Du R, Aziz-Sultan MA, Mekary RA, Smith TR. Coiling Versus Microsurgical Clipping in the Treatment of Unruptured Middle Cerebral Artery Aneurysms: A Meta-Analysis. Neurosurgery. 2018 Feb 9. doi: 10.1093/neuros/nyx623. [Epub ahead of print]
- Varble N, Tutino VM, Yu J, Sonig A, Siddiqui AH, Davies JM, Meng H. Shared and Distinct Rupture Discriminants of Small and Large Intracranial Aneurysms. Stroke. 2018 Apr;49(4):856-864. doi: 10.1161/STROKEAHA.117.019929. Epub 2018 Mar 13.
- Meng H, Tutino VM, Xiang J, Siddiqui A. High WSS or low WSS? Complex interactions of hemodynamics with intracranial aneurysm initiation, growth, and rupture: toward a unifying hypothesis. AJNR Am J Neuroradiol. 2014;35:1254–1262. doi: 10.3174/ajnr.A3558.