Commentary

Risk of rupture for incidentally diagnosed aneurysms (ANs) is currently under big controversy, particularly for small AN (<7 mm in diameter) [3]. In this regard, size determination is critical for assessment of bleeding risk. In this article, Beck et al report the size distribution of ruptured and unruptured ANs in consecutive patients using 3-dimensional rotational angiography (3D-RA). They showed that the mean size was 6.7 mm for ruptured and 5.7 mm for unruptured ANs, which were smaller than those in other reported series. In addition, the majority of ruptured aneurysms were less than 7 mm and located in the anterior location. Based on these findings, they claimed that the size measured in 2-dimensional would overestimate the true size or increase the variability, which may change the risk of rupture based on the size of aneurysm (<7 mm by ISUIA II).

As mentioned in the discussion, 3D-RA would be superior in (1) selecting best plane for measurement, (2) magnification errors, (3) visualization of neck dome relations to omit parent artery for dome measurement. However, there is no quantitative comparison between 2-D digital subtraction angiography and 3D-RA in the current study. This is the weakest aspect of this study for validating these points. However, 3D-RA is indeed better for delineation of dome configuration, neck and parent artery relationship. Although still costly, this new diagnostic modality would replace conventional 2D digital subtraction angiography in the future for the management of aneurysms.

Based on their finding that most of the ruptured aneurysms were smaller than 7 mm, they emphasized the growth rate as a risk factor for small aneurysms. Although many aneurysms showing rapid growth along with their risk of rupture are not currently unknown, recently published data showed that 3-year cumulative risk of growth is 17.6 % and dependent on the size of initial aneurysm, which is surprisingly high [1]. One major drawback of ISUIA II is that a substantial number of patients (almost one third) were excluded from the prospective cohort due to crossover to treatment group, and the number of patients at risk at 4 years is only 112 in small incidental aneurysm, which may lead to observation bias [2]. If the patients showing rapid growth within this interval were treated by intervention, reported risk of small aneurysms in ISUIA II might have underestimated true rupture rate. Natural history of unruptured small aneurysms should be reevaluated based on long-term prospective data without bias, although it would be a difficult task.