Collar Sign in Incompletely Occluded Aneurysms after Pipeline Embolization: Evaluation with Angiography and Optical Coherence Tomography

Abstract

The collar sign appears to be indicative of endothelialization, but continued blood flow into the aneurysm. This is unusual given the processes involved in aneurysm occlusion after placement of the Pipeline Embolization Device and has not been previously reported.

European Multicenter Study for the Evaluation of a Dual-Layer Flow-Diverting Stent for Treatment of Wide-Neck Intracranial Aneurysms: The European Flow-Redirection Intraluminal Device Study

“…The 2 main principles on which the concept was founded are diversion of blood flow away from the aneurysm inducing stasis and thrombosis within the aneurysm sac and endothelialization along the stent scaffold and restoration of the integrity of the arterial wall. 8 These devices have effectively addressed the issue of recanalization and the need for retreatment associated with other endovascular treatment modalities and are continuously gaining popularity among neurointerventionalists. 9 Whereas treatment of internal carotid artery aneurysms up to the superior hypophyseal segment provided an early experience with flow diverters, 1 use has since expanded to a number of different aneurysm locations.…”

Endothelialization following Flow Diversion for Intracranial Aneurysms: A Systematic Review

“…Following exclusion of duplicate and irrelevant references and after detailed abstract and title screening, 10 references directly relating to endothelialization were included per the search criteria (On-line Table). [5][6][7][8][9][10][11][12][13][14] Two of the included references studied endothelialization in human patients. 7,14 The remainder of the included articles used preclinical animal models, constituting pigs (n ϭ 1) and rabbits (n ϭ 7).…”

“…Recent work by our group has demonstrated the angiographic appearance of separation of the parent vessel from aneurysms following PED placement, termed the "collar sign," in incompletely occluded aneurysms. 7 We have hypothesized that this represents endothelialization along the stent surface in juxtaposition to the aneurysmal neck. Paradoxical incomplete aneurysm occlusion following PED placement at 6-month follow-up may be po- tentially explained via the existence of interspersed channels between regions of neointimal hyperplasia, still allowing blood flow, corroborated by a case report by Dai et al 30 Similarly, endothelialization has been shown to be a driving factor in determining aneurysmal exclusion in intracranial aneurysms treated by coil embolization.…”

Flow diversion for treatment of intracranial aneurysms: Mechanism and implications

“…44 The "collar sign" is visualized as an interval in opacification of contrast between the parent vessel and aneurysm sac on angiography and is thought to represent the endothelialization process across the neck of the aneurysm. Failure of proper endothelialization process can lead to unsecured aneurysms and ruptures.…”

“…Griessenauer et al coined the term "collar sign" to describe the radiographic pattern of incompletely occluded aneurysms of patients who underwent PED placement. 44 The "collar sign" is visualized as an interval in opacification of contrast between the parent vessel and aneurysm sac on angiography and is thought to represent the endothelialization process across the neck of the aneurysm. Here, they found that 50% of patients who had incompletely occluded aneurysms (10.5%) at their 6-month follow-up also had the "collar sign."…”