Introduction Onyx HD-500 embolization of intracranial aneurysms leads to high rates of complete and durable occlusion. However, little information exists as to what constitutes an optimal immediate angiographic result. We devised a simple grading scheme based on the pattern of parent artery and aneurysm neck reconstruction, and correlated it with long term outcome.

Methods All cases of Onyx embolization for unruptured aneurysms performed between September 2008 and April 2010 were retrospectively reviewed. Immediate angiographic results were categorized according to the pattern of extra-aneurysmal Onyx leakage: grade A, none; grade B, ‘hat brim’ lamination; and grade C, ‘ectopic’ Onyx (C1, non-flow limiting; C2, flow limiting). Results of follow-up vascular imaging were reviewed and correlated with the angiographic grade.

Results 24 embolization procedures were performed in 21 patients with 23 aneurysms. Aneurysm size ranged from 2.5 to 24 mm and neck width from 2 to 8 mm. Complete occlusion was achieved in 20 cases (83.3%) and subtotal occlusion in three (12.5%). Immediate angiographic results were: grade A in ten (41.7%), grade B in eight (33.3%), and grade C in six (25%). Stable angiographic results were seen in 85%, 94%, 94%, and 100% at 6, 12, 24, and 36 months, respectively. Angiographic recurrence was observed in four cases (16.7%), all grade A (p=0.006). Delayed parent vessel occlusion occurred in two cases (8.3%), both grade C2 (p=0.014).

Conclusions This simple grading system may help predict long term angiographic results. Hat brim Onyx lamination seems to provide an optimal balance between treatment durability and parent vessel patency. Prospective validation is warranted.