To report our experience with Onyx HD-500^® (Micro Therapeutics, Inc., Irvine, CA, USA) in the endovascular treatment of complex intracranial aneurysms as an alternative to treatment with platinum coils.

Between October 2003 and December 2007, 38 patients (20 female and 18 male) were selected for inclusion in the study based on aneurysm size and dome-to-neck ratio. Altogether, 37 (97.3%) aneurysms were located in the anterior circulation, and one (2.7%) was in the posterior circulation. Of these, 35 (92.1%) had wide necks (>4mm and/or a dome-to-neck ratio<2). Clinical and angiographic follow-ups were performed at six and 12months.

Successful embolization was achieved in 36 of the 38 patients. Complete occlusion was seen in 29 patients (80.5%), and seven (19.4%) had subtotal occlusion on the immediate angiographic control. After six months, 29 patients (80.5%) initially with total occlusion were stable, while four with subtotal occlusion had progressed to total occlusion and three showed recanalization. Of the latter, two were reembolized and the third patient did not return for retreatment. The one-year angiographic follow-up showed no changes. The morbidity rate was 8.3% (3/36) and procedural mortality was 0%.

The Onyx HD-500 liquid embolic system is a feasible and safe therapeutic option for patients presenting with complex aneurysms, but who are not candidates for other techniques or in whom previous treatment has failed.