Objective Several definitions have been proposed to distinguish the daughter sac when treating unruptured intracranial aneurysms. The aim of this study was to evaluate interobserver variability of aneurysm morphology, including the daughter sac, using criteria from the International Study of Unruptured Intracranial Aneurysms (ISUIA) and the Unruptured Cerebral Aneurysm Study of Japan (UCAS).

Materials and methods After approval by the institutional review board, we analyzed three morphological features (daughter sac, lobulation, and irregular margin) from the ISUIA and UCAS using angiographic images from 102 saccular aneurysms. Four independent readers interpreted each morphological criterion using dichotomized scales (existence or not). The κ statistic was used to measure interobserver agreement, and κ>0.6 was considered substantial agreement.

Results For discrimination of the daughter sac, interobserver agreement among the four readers was substantial using the UCAS criteria (k=0.626 for two-dimensional (2D) and 0.659 for three-dimensional (3D) images) but not for the ISUIA criteria (k=0.487 for 2D and 0.473 for 3D images; significant difference). Irrespective of the images used, pairwise pooled κ values for the UCAS were >0.6, except for one case (score of 0.54 between readers A and B). Regarding the proportion of positive reads, there was a significant difference between reads for the daughter sac using the UCAS and ISUIA criteria.

Conclusions For discrimination of the daughter sac, the UCAS definition showed a higher reliability than the ISUIA. However, a further prospective study is necessary to validate this definition as the treatment standard for unruptured intracranial aneurysms.