Response to Letter by Sarikaya
We are grateful to Dr Basar Sarikaya for the interest in our article. He has specifically pointed on several issues in our publication that we would like to clarify additionally.
First, it is mentioned that the groups according to size are different from ISUIA study,1 and that makes comparison difficult. There are some reasons for that. Because the patient population accumulation from the ISUIA is earlier in time, and since then resolution of diagnostic imaging and technique of treatment have evolved toward smaller lesions, we considered as a better option the criteria of the Japanese Society for Detection of Asymptomatic Brain Diseases, that applies to some extent different size limits for the subgroups.2 There have been other suggestions for the use of a “cutt-off” size of 5 mm too,3 when setting the guidelines for recommending surgical treatment for unruptured aneurysm. In our study the very small aneurysms have not been studied particularly as a subgroup; however, we agree to the increase of interest on this subgroup and the need to elucidate their clinical evolution,4 as still some controversies exist.
Second, we agree with the observation that very small aneurysms constitute 30% roughly of all unruptured aneurysms that subsequently ruptured. However, comparing this observation with a general pool of already ruptured aneurysms on first detection might have uncertainties. Models on the background differ and the ruptured very small aneurysm rates may not reflect incidences of unruptured very small aneurysms and the rates of their rupture. Even more, in populations with different racial, geographic, gender, etc, distribution, differences may grow.
Third, this last point is also raised by Dr Sarikaya, who mentioned some similarities between Finland, Japan and Turkey. There has been emphasis on the different incidence of aneurysms and their rupture rate in these countries,5 suggesting genetic inferences. At the moment there is no evidence of the intrinsic mechanisms that relate to these differences and on our opinion making connections between racial characteristics, patient origin and aneurysm pathology will be speculative regarding the small aneurysm problem. One of the reasons of different incidence of rupture may be related to our high follow-up rate of the observation patients and uniform measurement method using 3D CTA.
Wiebers DO, Whisnant JP, Huston, Meissner I, Brown, Piepgras DG, Forbes GS, Thielen K, Nichols D, O'Fallon WM, Peacock J, Jaeger L, Kassell NF, Kongable-Beckman GL, Torner JC. International Study of Unruptured Intracranial Aneurysms Investigators. Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet. 2003; 362: 103–110.
Committee of Detection of Asymptomatic Brain Diseases. Guideline for Detection of Asymptomatic Brain Diseases [in Japanese]. 2003.
Rooij WJ, Keeren GJ, Peluso JP, Sluzewski M. Clinical and angiographic results of coiling of 196 very small (<=3 mm) intracranial aneurysms. AJNR Am J Neuroradiol. 2009 Jan 8. [Epub ahead of print].