Mervyn Vergouwen
The number of incidentally discovered unruptured intracranial aneurysms increases due to the rising availability and use of brain imaging. Currently, the best available tool to predict the risk of aneurysm rupture is the Population, Hypertension, Age, Size of Aneurysm, Earlier Subarachnoid Hemorrhage from Another Aneurysm, and Site of Aneurysm (PHASES) score. This score is derived from a pooled analysis of individual patient data of 8,382 individuals from 6 prospective cohort studies with 29,166 person years of follow-up.
The most important predictors for aneurysm rupture were aneurysm size, aneurysm location, and population; there is an increased risk in Finnish and Japanese populations. However, the PHASES score has several limitations, such as incomplete data on risk factors (eg, smoking, aneurysm morphology, and family history). Because most patients have a small aneurysm, especially in that subgroup of patients, the PHASES score insufficiently discriminates between those with a high and low risk of rupture, and a better tool is needed to predict aneurysm instability in this large group of patients.
Several recent studies showed that the wall of an intracranial aneurysm can be visualized using MRI. Some, but not all, aneurysm walls show enhancement after the administration of gadolinium. It is believed that aneurysm wall enhancement represents wall inflammation. Inflammation of the aneurysm wall increases the risk of aneurysm instability. The capability of imaging the aneurysm wall instead of only the lumen means a giant step forward, because the actual disease is in the aneurysm wall, and not in the lumen.
Because aneurysm wall enhancement more often occurs in recently ruptured aneurysms (>95%) than in small, unruptured aneurysms (approximately 30%), it may represent aneurysm instability and, therefore, may be a novel biomarker to identify unstable aneurysms. However, all previous studies had a cross-sectional design.
The current study is the first follow-up study in the field of intracranial aneurysm wall imaging. We showed that gadolinium enhancement of the aneurysm wall at baseline is associated with aneurysm instability during follow-up. After a median follow-up of 27 months, growth (n=2) or rupture (n=2) was observed in 4 out of 19 aneurysms (21%; 95% CI, 6–54%) with wall enhancement and in 0 out of 46 aneurysms (0%; 95% CI, 0–8%) without enhancement (risk difference, 21%; 95% CI, 3–39%).