Introduction: The management of unruptured small intracranial arterial aneurysms (SIAs) remains non-uniform. Recently, there has been growing interest in physical parameters other than maximum aneurysm size for estimating rupture risk in cerebral aneurysms. We report on the differences between stable, unruptured SIAs and ruptured SIAs when volume, surface area, and surface area-to-volume ratio (SAV) are measured using simple techniques in order to better quantify risk of rupture as compared to size alone.
Methods: We retrospectively reviewed the clinical database at our institution and identified patients with unruptured and ruptured SIAs. For unruptured aneurysms, we included patients with stable aneurysm size and morphology at a minimum of one year follow up, saccular morphology, <=7 mm maximum aneurysm diameter and no intervening treatment. Ruptured aneurysms were included into the analysis if they were saccular and <=7 mm in maximum diameter. Computer tomography angiography (CTA) or magnetic resonance angiography (MRA) was used to perform three-dimensional analysis to measure size, surface area, and volume. Results for the two groups were compared using chi-square and Cox-Snell regression modeling.
Results: Of the 100 SIAs analyzed, 71 were unruptured and 29 were ruptured. Analysis of Cox-Snell revealed that volume was the best model in predicting rupture risk of SIAs, followed by SAV, surface area and then size. However, receiver operating characteristic area under curve analyses showed no significant differences between the indices. Decision tree models showed treatment threshold values for volume, SAV, surface area, and size to be >25.4 mm3, <1.5/m, >71.4 mm2, and >5.4 mm, respectively, in unruptured SIAs.
Conclusions: The volume, SAV, and surface area appear to be better indicators of rupture risk for SIAs than size alone and can be used in the decision-making process to identify those patients in whom treatment may be justified, especially for aneurysms in the 4 – 6 mm size range.
Patient Care: There remains a great deal of ambivalence in clinical practice when trying to decide whether or not to treat incidentally discovered small (<7 mm), unruptured intracranial aneurysms. This study provides initial analysis of additional information other than just aneurysm size that could potentially help guide patient care in the future.
Learning Objectives: By the conclusion of this session, participants should be able to recognize the importance of additional characteristics other than size when considering intervention for small, unruptured intracranial aneurysms.