Transsinusoidal Portal Vein Embolization with Ethylene Vinyl Alcohol Copolymer (Onyx): A Feasibility Study in Pigs Maarten L. J. SmitsPeter VanlangenhoveEmiel J. C. Sturm • Maurice A. A. J. van den BoschMonirath HavMarleen Praet • Maarten A. D. VenteFrederic R. SnapsLuc Defreyne

Purpose Portal vein embolization is performed to increase the future liver remnant before liver surgery in patients with liver malignancies. This study assesses the feasibility of a transsinusoidal approach for portal vein embolization (PVE) with the ethylene vinyl alcohol copolymer, Onyx. Methods Indirect portography through contrast injection in the cranial mesenteric artery was performed in eight healthy pigs. Onyx was slowly injected through a microcatheter from a wedged position in the hepatic vein and advanced through the liver lobules into the portal system. The progression of Onyx was followed under fluoroscopy, and the extent of embolization was monitored by indirect portography. The pigs were euthanized immediately (n = 2), at 7 days (n = 4), or at 21 days postprocedure (n = 2). All pigs underwent necropsy and the ex vivo livers were grossly and histopathologically analyzed. Results Transsinusoidal PVE was successfully performed in five of eight pigs (63%). In 14 of 21 injections (67%), a segmental portal vein could be filled completely. A mean of 1.6 liver lobes per pig was embolized (range 1‐2 lobes). There were no periprocedural adverse events. Focal capsular scarring was visible on the surface of two resected livers, yet the capsules remained intact. Histopathological examination showed no signs of recanalization or abscess formation. Mild inflammatory reaction to Onyx was observed in the perivascular parenchyma. Conclusions The porcine portal vein can be embolized through injection of Onyx from a wedged position in the hepatic vein. Possible complications of transsinusoidal PVE and the effect on contralateral hypertrophy need further study.