The Role of Collateral Circulation in Branch Vessel Occlusion After Flow Diversion.

OBJECTIVE: Flow diversion for treatment of intracranial aneurysms frequently necessitates covering adjacent branch vessels. Although branch vessel occlusion is common, associated clinical deficits are rare. We and others hypothesize that clinically silent branch vessel occlusion is due to underlying collateral circulation. To study the role of collateral circulation in covered branch vessel occlusion, we assessed collateral vessels and altered branch vessel flow on transfemoral catheter angiography in patients undergoing flow diversion of intracranial aneurysms.

METHODS: Pre-treatment, immediate post-treatment and interval follow-up angiograms were evaluated for branch vessel flow patterns and associated collateral circulation in a consecutive retrospective cohort of 84 patients from 2011-2017 with branch vessel coverage related to aneurysm flow diversion using the Pipeline Embolization Device (PED, Medtronic, Minneapolis, MN, USA).

RESULTS: We identified 142 branch vessels covered by the PED construct for treatment of 89 aneurysms, predominately in the anterior circulation (>90%). Collateral circulation was observed in roughly a third of these vessels and was associated with diminished (P < .001) or absent (P < .001) flow on follow-up angiography. Only 2 of 80 terminal branch vessels (no collaterals) were occluded, and those occurred in a patient with PED construct thrombosis. Altered branch vessel flow was not associated with vascular risk factors, treatment technique, or outcome measures, including new or worsening neurologic deficit.

CONCLUSIONS: Altered flow in branch vessels covered during flow diversion reflects underlying collateral circulation and is not associated with downstream ischemic deficits.