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• Large data, but what is the implication comparing the aneurysm discovered by bleeding and those by other reasons?
  Toshikazu Kimura
  Published on: 30 October 2020

• Published on: 30 October 2020

  Large data, but what is the implication comparing the aneurysm discovered by bleeding and those by other reasons?

  • Toshikazu Kimura, Neurosurgeon Department of Neurosurgery, Japanese Red Cross Medical Center

  Dear editor,
  We read with great interest the article by Rousseau et al. “Location of intracranial aneurysms is the main factor associated with rupture in the ICAN population.”1
  They compared ruptured intracranial aneurysms (RIAs) with unruptured cerebral aneurysms (UCAs) in the ICAN registry, and analyzed factors that were considered associated with subarachnoid hemorrhage in previous literature. As a result, they found the location of the aneurysm showed the largest hazard ratio as much as 6.05 and showed their result with beautiful info-graphic.
  We should be careful that their result is derived from comparisons between the aneurysms, which caused subarachnoid hemorrhage and UCAs that was found without bleeding. Hence, the meaning is different from that of ISUIA2, UCAS Japan3, and other studies, which investigated the risk of bleeding from the known UCAs. As noted in the discussion of the headache, which prefers UCAs to RIAs, the factors examined may be seeing factors, which lead to brain examination without causing subarachnoid hemorrhage in France.
  As in the title, they focused on the location of the aneurysm, and found ACA and posterior circulation aneurysms have high odds ratio of 4.99 and 6.05 respectively comparing with ICA aneurysms. As in ISUIA study, they included internal carotid- posterior communicating artery (IC-Pcom) aneurysms in the posterior circulation aneurysms, and “ICA” includes other aneurysms occurring on the ICA. However...

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  Dear editor,
  We read with great interest the article by Rousseau et al. “Location of intracranial aneurysms is the main factor associated with rupture in the ICAN population.”1
  They compared ruptured intracranial aneurysms (RIAs) with unruptured cerebral aneurysms (UCAs) in the ICAN registry, and analyzed factors that were considered associated with subarachnoid hemorrhage in previous literature. As a result, they found the location of the aneurysm showed the largest hazard ratio as much as 6.05 and showed their result with beautiful info-graphic.
  We should be careful that their result is derived from comparisons between the aneurysms, which caused subarachnoid hemorrhage and UCAs that was found without bleeding. Hence, the meaning is different from that of ISUIA2, UCAS Japan3, and other studies, which investigated the risk of bleeding from the known UCAs. As noted in the discussion of the headache, which prefers UCAs to RIAs, the factors examined may be seeing factors, which lead to brain examination without causing subarachnoid hemorrhage in France.
  As in the title, they focused on the location of the aneurysm, and found ACA and posterior circulation aneurysms have high odds ratio of 4.99 and 6.05 respectively comparing with ICA aneurysms. As in ISUIA study, they included internal carotid- posterior communicating artery (IC-Pcom) aneurysms in the posterior circulation aneurysms, and “ICA” includes other aneurysms occurring on the ICA. However, in the real world, we experience subarachnoid hemorrhage due to bleeding from internal carotid- anterior choroidal artery aneurysms and less often (superiorly projecting large) paraclinoid aneurysm, which accounts less than 5%. According to the baseline characteristics of this study (Table 1), the ICA aneurysms occupy 33.4% in the RIA group, while it is only 11.8% in the UCA group. It should be misleading to use such small risk aneurysms as a reference for comparison and to say that the hazard ratio is high.　　The ISUIA study4 was first criticized for its inclusion of aneurysms within the cavernous sinus that did not cause subarachnoid hemorrhage, and they were no longer included in subsequent analyses. Similarly, given the proportion of aneurysms that cause subarachnoid hemorrhage, it is time to stop discussing anterior choroidal artery aneurysms and paraclinoid aneurysms collectively.

  References
  1. Rousseau O, Karakachoff M, Gaignard A, et al. Location of intracranial aneurysms is the main factor associated with rupture in the ICAN population. J Neurol Neurosurg Psychiatry 2020;23(324371):2020-324371.
  2. 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(9378):103-10. [published Online First: 2003/07/18]
  3. Morita A, Kirino T, Hashi K, et al. The natural course of unruptured cerebral aneurysms in a Japanese cohort. N Engl J Med 2012;366(26):2474-82. doi: 10.1056/NEJMoa1113260 [published Online First: 2012/06/29]
  4. International Study of Unruptured Intracranial Aneurysms Investigators. Unruptured intracranial aneurysms--risk of rupture and risks of surgical intervention. N Engl J Med 1998;339(24):1725-33. doi: 10.1056/nejm199812103392401 [published Online First: 1998/12/29]

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  Conflict of Interest:
  None declared.

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