Introduction Onyx HD-500 is an alternative endovascular treatment in selected cerebral aneurysms that offers advantages over standard coiling or stent assisted coiling in that complete occlusion of the aneurysm can be obtained without subsequent compaction. Widespread use of Onyx 500 HD is limited by technical demands of the procedure and by competing advances in flow diversion technologies. Parent vessel steno-occlusive progression is reported, however the etiology and management is controversial.

Methods The medical records of patients treated with Onyx HD-500 were retrospectively reviewed under IRB approval at the University of Illinois at Chicago for 2008–2011. Clinical and radiographic evaluations, both peri-procedural and in follow-up, were assessed.

Results 17 patients underwent treatment of unruptured ICA aneurysms with Onyx HD-500. Three patients (17.6%) developed visual symptoms post procedure: one delayed ophthalmic artery occlusion with development of monocular blindness, one right visual field deficit, and one transient monocular scotoma which resolved after 2 months. Four patients (23.5%) developed delayed ICA stenosis at 6–8 month follow-up angiography despite a standard regimen of antiplatelet medication with sensitivities to ASA and clopidogrel confirmed by Verify Now testing on 3/4 patients (% inhibition 55, 70, and 80). Quantitative MRI (Q-MRI) was obtained on all of these patients to guide treatment. One progressed to complete, but asymptomatic adjacent ICA occlusion with stable MCA flow and vascular reserve on Q-MRI. The second developed delayed asymptomatic 40% stenosis of the ICA segment adjacent to the aneurysm with normal Q-MRI flow values so no intervention was undertaken. The third patient with pre-existing mild carotid siphon stenosis proximal to the aneurysm neck had transient delayed worsening to 70% stenosis over a 4 mm segment, 3 mm proximal to the Onyx at the aneurysm neck. She had stable Q-MRI flow and vascular reserve, and the stenosis angiographically returned to near baseline by 27-month follow-up. The fourth patient developed critical stenosis of the supraclinoid ICA 5 mm distal to the aneurysm neck with possible TIA (transient ischemic attack) at 8 months post treatment. Q-MRI showed decrease MCA flow and angioplasty was performed with subsequent improvement in vessel caliber and increased flow. Repeat Q-MRI 11 months later demonstrated progressive reduction in MCA flow and a second angioplasty with stenting was performed, with the patient remaining asymptomatic at 27 months. Prolonged dual antiplatelet regimens were continued in 2/4 patients, one with progression of stenosis and one with improvement of stenosis.

Conclusions We observed a higher rate of delayed parent vessel steno-occlusive progression after aneurysm embolization with Onyx HD-500 than reported in the literature despite overall low morbidity. In two of the cases, the stenosis involved a carotid segment not immediately adjacent to the treated aneurysm neck, suggesting a pathophysiologic mechanism other than solely an effect of the Onyx cast. Two patients had a transient or mild stenosis while two others progressed with time. The role of prolonged dual antiplatelet therapy in these patients is not clear. Quantitative vessel flow imaging was useful in subsequent medical management and decision making to perform therapeutic angioplasty/stenting to preserve cerebral vascular flow.

Competing interests A Carlson: None. A Alaraj: Ev3, Cordis-Codman. S Amin-Hanjani: NIH, GE Healthcare, VasSol Inc. F Charbel: VasSol, Inc. V Aletich: Micrus Endovascular. Ev3, Cordis-Codman.