Assessment of angiographic outcomes after flow diversion treatment of intracranial aneurysms: a new grading schema

Flow diverter (FD) devices have emerged as an alternative treatment for a subgroup of intracranial aneurysms. The principle of endovascular flow diversion is inherently different from endosaccular coil embolisation. To monitor the angiographic outcomes for FDs, a sensitive and reliable new measure is required. Oxford Neurovascular and Neuroradiology Research Unit developed a grading schema while conducting a registry to audit outcomes of patients treated using a particular FD (SILK flow diverter; Balt Extrusion, Montmorency, France). The aim of this study is to assess the applicability and reproducibility of the new schema. The proposed grading schema is designed for saccular- or fusiform-shaped aneurysms. For both, it documents the degree of aneurysm occlusion using a five-point scale and the parent artery patency on a three-point scale. Two neuroradiologists used the schema to independently rate 55 angiograms showing comparable treatment and follow-up angiograms of patients treated with a FD. Inter-observer agreement was estimated using the weighted kappa co-efficient. Both readers found the schema easy to apply. Overall, there were ten discordant readings for degrees of aneurysm occlusion and two for parent artery patency. Inter-observer agreement was excellent for both the assessment of aneurysm occlusion (k=0.89; C.I.=0.81-0.99) and parent artery patency (k=0.90; C.I.=0.76-1.0). The proposed schema is sufficiently sensitive to register gradual aneurysm occlusion and parent artery patency on interval angiograms. It is reproducible and is applicable to both saccular and fusiform aneurysms. More data on follow-up of FD-treated aneurysms is needed to prove its efficacy in predicting the long-term behaviour of treated aneurysms.