Polymeric embolization coil of bilayered PVA strand for therapeutic vascular occlusion: a feasibility study in canine experimental vascular models

Abstract

PURPOSE The purpose of this study was to investigate the feasibility of PVA (polyvinyl alcohol) polymer coil as a new endovascular embolic agent and to gauge the related histologic response in a canine vascular model. METHODS PVA polymer coil was fabricated by cross-linking PVA and tantalum particles. Basic properties were then studied in vitro via swelling ratio and bending diameter. Normal renal segmental arteries and wide-necked aneurysms of carotid sidewalls served as canine vascular models. Endovascular PVA coil embolization of normal renal segmental arteries (n=20) and carotid aneurysms (n=8) was performed under fluoroscopic guidance in 10 dogs. Degree of occlusion was assessed immediately and at 4 weeks post-embolization by conventional and CT angiography. Histologic features were also graded at acute (Day 1: segmental arteries, 6

aneurysms, 4) and at chronic (Week 4: segmental arteries, 14

aneurysms, 4) phases post-embolization, assessing inflammation, organization of thrombus, and neointimal proliferation. RESULTS Swelling ratio declined as concentrations of cross-linking agent rose. Mean bending diameter was 2.05 mm (range, 0.86-6.25) in water at 37℃ and 2.29 mm (range, 0.94-6.38) in canine blood samples at 37℃. Occlusion of normal renal segmental arteries was sustained (Day 1: complete occlusion, 20

Week 4: complete occlusion, 14), whereas immediate outcomes in carotid aneurysms (Day 1: complete occlusion, 5

residual neck only, 3) were not sustained (Week 4: complete occlusion, 1

minor recanalization, 1

major recanalization, 2). At Week 4, chronic inflammatory cells predominated, with progressive organization of thrombus and fibrocellular ingrowth. All aneurysms bore full neointimal linings on the coil mass in chronic phase. CONCLUSION Vascular occlusion by PVA polymer coil proved superior in normal renal segmental arteries and feasible in surgically constructed carotid aneurysms (with packing densities ≥30%), constituting acceptable radiologic feasibility and histologic response.