17 FLOW DIVERSION GRADING SCALES
While flow diversion has become a standard part of the neurointerventionalist′s armamentarium, there is no commonly agreed upon system to grade results. Recently, four different grading systems (OKM scale, Kamran-Byrne scale, SMART scale, and the flow-diverting stent scale) have been published to help address this shortcoming. We review these four different systems in detail and compare and contrast the features among one another. While all of the scales have some merits, currently, no one system has been widely accepted by the neurointerventional world.
As the popularity of flow-diverting stents (FDSs) as an accepted endovascular treatment for large and giant cerebral aneurysms has grown, more and more practitioners are using FDSs for “off-label” indications, including smaller aneurysms and posterior and distal anterior circulation aneurysms. 1 , 2 , 3 This increased usage necessitates a common language to describe the results of treatment and to provide a uniform reporting structure for short-, mid-, and long-term radiographic results.
Because flow diversion represents a vastly different strategy than coil embolization for treatment of cerebral aneurysms, there are concerns that the Roy and Raymond scale, which is used to grade outcomes after endovascular treatment of saccular aneurysms, 4 will be inadequate for classifying these aneurysms. While the initial results after coil embolization are often dramatic with, ideally, complete or near-complete occlusion of the aneurysm, the same cannot be said for aneurysms treated with flow diversion. Often, there is still significant filling of the aneurysm sac that resolves as occlusion occurs over a period of time. 5 Using the Roy and Raymond scale, almost all aneurysms treated with flow diversion would be classified as having residual aneurysm filling.
While the three-point scale of Roy and Raymond has gained wide acceptance as an angiographic classification scheme for assessment after coil embolization, the same cannot be said for the several competing grading scales proposed for flow diversion. 6 , 7 , 8 , 9 These scales, thus far, have not yet reached a critical mass with neurointerventional surgeons and are not widely employed in the literature at the time of this writing.
17.2 Grading Scales
17.2.1 O’ Kelly-Marotta Scale
In 2010, O′Kelly et al attempted to address a deficit in outcome assessment by proposing the first grading scale for the angiographic assessment of aneurysms following flow diversion ( Fig. 17.1). 6 The O′Kelly-Marotta (OKM) scale was designed to account for both the degree of aneurysm filling and the amount of contrast stasis after FDS deployment. This scale requires an angiographic run that continues into the venous phase. O′Kelly et al described two main components for their classification scheme: the amount of aneurysm filling and the phase in which the aneurysm clears ( Table 17.1).
The degree of aneurysm filling is classified from A to D after the deployment of the FDS. Aneurysms receive a grade of A if greater than 95% of the aneurysm fills, grade B for 5 to 95%, grade C for neck remnant (< 5%), and grade D for no filling of the aneurysm. The time to contrast clearance from the aneurysm is represented in the stasis grade and is measured on a three-point scale: grade 1, clearing in the arterial phase; grade 2, clearing in the capillary phase; and grade 3, clearing in the venous phase. Thus, aneurysms in the OKM scale are described with both a letter and a number grade ( Fig. 17.1, Fig. 17.2, Fig. 17.3). Grades may be given to both pre- and posttreatment angiograms of aneurysms.