In vivo evaluation of the new PHIL low viscosity in a swine rete mirabile model

Abstract

Introduction: Few liquid embolic materials are available for treatment of arteriovenous malformations. We describe the in vivo experience with the new PHIL low viscosity (LV) liquid embolic agent in a swine rete mirabile model.

Methods: Eight swine were treated. Two animals underwent embolization of a rete with PHIL LV and the contralateral rete with Squid 12 (euthanized the same day). Six animals underwent embolization of the right rete: two with balloon flow arrest (euthanized at 14 d) and four with a microcatheter alone (euthanized at 14 and 90 d). Performance characteristics of the embolic agents were evaluated. Microscopic and histological analysis of the harvested retia was performed. Macroscopic examinations and high contrast digital-based radiographs of the central nervous system were obtained.

Results: We did not experience any technical complication during embolization of each rete. Overall occlusion ability, on/off injection and ease to retrieve the microcatheter/balloon with PHIL LV were optimal. Fluoroscopic visualization of the PHIL LV cast was adequate to optimal. Average embolization time with flow arrest was 9.5 min versus 19.5 min with microcatheter plugging. Embolizations with PHIL LV required less volume and were shorter when compared to Squid 12. Subacute (14 d) and chronic (90 d) microscopic and histological analysis demonstrated minimal inflammatory changes in the perivascular tissues and permanent occlusion of the embolized vasculature.

Conclusion: In this swine rete model, the new PHIL LV embolic agent had an excellent embolization performance. Vessels embolized remained occluded up to 90 d from the procedure with minimal inflammatory changes.

Keywords: AVM; dural arteriovenous fistula; embolic; rete.

Figure 1.

Unsubtracted fluoroscopy of Squid 12 (left) and PHIL LV (right) casts. Note the tip of the microcatheter (arrow) in the distal ascending pharyngeal artery (APA). Both liquid embolics were refluxed along the distal APA.

Figure 2.

Pre- (a) and post- (b) embolization unsubtracted fluoroscopy of the right swine rete (white circle). (a) Note the tip of the microcatheter (arrow). (b) Note the proximal marker of the microcatheter (arrow). (c) A 90-d follow-up unsubtracted fluoroscopy demonstrating stability of the PHIL LV cast as compared to the post-embolization cast (b). (d) The rete X-ray (arrow) showed dispersion of the embolic material throughout the rete confirming the angiographic appearance of the embolic cast (b and c).

Figure 3.

High power views (50 µm) of retia cross sections demonstrating luminal occlusion with embolic material and blood clot: top row (a–c) shows rete harvested at 14 d and bottom row (d–f) shows rete harvested at 90 d from the procedure. (a) Shows an intact internal elastic lamina (arrow). (b) With luminal embolic material (black arrow) and proteoglycan-rich neointimal ingrowth (white arrowhead). (c) Shows adventitial chronic inflammatory cell infiltration (arrow). (d) With marked medial attenuation of an occluded cross section (black arrow) in comparison to an adjacent patent cross section (white arrowhead). (e) Shows cross sectional occlusion with embolic material (black arrow) and eccentric fibrointimal tissue (white arrowhead). (f) Shows embolic material (arrows) with inflammatory and giant cell infiltration in the lumen. (a, b, d and e) with Movat pentachrome stain; (c and f) with hematoxylin-eosin stain.