In 2010, the O'Kelly-Marotta grading scale was proposed as a method of assessing the degree of angiographic filling and contrast stasis in the setting of intracranial aneurysms treated by endovascular flow diversion. Taking into account the dynamic nature of the contrast stasis, it is designed for use with cerebral angiography to predict aneurysm closure over time 1).
A digital subtraction angiogram involving arterial injection and extending completely into the venous phase is necessary for accurate grading.
Two variables are addressed, namely the degree of aneurysm filling and the timing of contrast clearance.
A: total filling (>95%)
B: subtotal filling (5-95%)
C: entry remnant (<5%)
D: no filling (0%)
1: no stasis (arterial phase clearance, before capillary phase)
2: moderate stasis (clearance before venous phase)
3: significant stasis (persistent contrast at venous phase)
ten possible scores exist (i.e. A1, A2, A3, B1, B2, B3, C1, C2, C3, and D) as the absence of filling by definition precludes the observation of different phases of stasis the OKM scale should be applied to both pre- and post-treatment cerebral angiography the scale has been shown since its inception to demonstrate a high degree of inter- and intraobserver agreement 2).