Percutaneous Extrahepatic Portacaval Shunt with Covered Prostheses: Feasibility Study

Evaluation of the rabbit liver by direct portography and contrast-enhanced computed tomography: anatomical variations of the portal system and hepatic volume quantification

Background

The study was aimed at: (1) describing the incidence of anatomic variations of the portal system in the rabbit using direct portography; and (2) estimating the liver volume and caudate lobe volume by using contrast-enhanced computed tomography (CECT) in the same animal model.

Methods

Forty-six New Zealand white rabbits were included. All of them underwent direct portography and unenhanced CECT. Conventional liver rabbit portal system anatomy (type 1) consisted of the bifurcation of the main portal vein (MPV) into the right portal vein (RPV) and left portal vein (LPV), which subsequently divided into medial left portal vein and lateral left portal vein. Trifurcation of the LPV was considered type 2. The LPV that divides into four smaller branches was classified as type 3. Other configurations of the portal system, including particular cases of MPV branching, were grouped as type 4. Liver lobes were manually segmented.

Results

The incidence of each type of portal system anatomy was: type 1, 67.4%; type 2, 15.2%; type 3, 13.0%); and type 4, 4.3%. The mean volume of the caudate lobe was 19.1 ml ± 5.7 ml and of the cranial lobes it was 66.7 ml ± 13.7 ml, and the total liver volume was 85.7 ml ± 16.7 ml.

Conclusions

In New Zealand white rabbits, type 1 is the prevalent type of portal system, liver volume is about 86 ml, and the caudate and cranial lobes are separated. This information could be important when planning experimental rabbit liver procedures.

Twenty-five years after the first TIPS in Spain

The incorporation, 25 years ago, of transjugular intrahepatic portosystemic shunting, better known by the acronym TIPS, represents an indisputable improvement in the treatment and management of patients with symptoms due to portal hypertension. This article discusses the origins of the technique and the technical innovations that have been progressively added through the years. The implantation of coated stents, which protect the stent from processes in the parenchymal track that can lead to stenosis, have helped ensure long-term patency, thus reducing the need for reintervention. Solid evidence from valuable publications has situated TIPS at the forefront of the treatment options in a wide variety of clinical situations associated with portal hypertension.

Evaluation of MR/Fluoroscopy–guided Portosystemic Shunt Creation in a Swine Model

PURPOSE

To evaluate three different percutaneous portosystemic shunts created with magnetic resonance (MR) imaging and fluoroscopy guidance in a swine model.

MATERIALS AND METHODS

In stage 1 of the experiment, an active MR intravascular needle system was created for needle tracking and extracaval punctures. Twenty inferior vena cava (IVC)/superior mesenteric vein (SMV)/portal vein (PV) punctures were performed in 10 swine (weight, 40-45 kg) in a 1.5-T short-bore interventional MR imager. With use of a real-time MR imaging sequence, the needle was guided through the IVC and into the SMV or PV (N = 20 punctures). After confirmation, a wire was advanced into the portal venous system under MR imaging guidance (N = 20). In stage 2, animals were transferred to the radiographic fluoroscopy suite for deployment of shunts. Three different shunts were evaluated in this study: (i) a commercial stent-graft, (ii) a prototype bridging stent, and (iii) a prototype nitinol vascular anastomotic device. Postprocedural necropsy was performed in all animals.

RESULTS

Successful MR-guided IVC/SMV punctures were performed in all 20 procedures (100%). All three shunts were deployed. Stent-grafts had the poorest mechanism for securing a shunt. The vascular anastomotic device and the bridging stent had more secure anchoring mechanisms but also had higher technical failure rates (50% and 40%, respectively). When deployed successfully, the vascular anastomotic device resulted in no bleeding at the sites of punctures at necropsy.

CONCLUSION

Percutaneous shunts and vascular anastomoses between the portal mesenteric venous system and IVC were successfully created with use of a combination of MR imaging and conventional fluoroscopy for guidance.

Intervascular Anastomoses Created by an Endovascular Approach: Technical Aspects and Initial Results in an Animal Study

PURPOSE

The current article describes the initial results after the creation of intervascular connections with use of an exclusively endovascular approach. Connections of two vessels were performed in the thoracic and abdominal areas with use of a kinematic needle without traversing a solid organ. The materials developed specifically for this technique are described.

MATERIALS AND METHODS

The procedure was carried out in 11 animals and consisted of bringing together two vascular structures with use of magnets, performing a puncture from the lumen of one vessel to that of the other, and inserting a prosthesis between the two. The prosthesis has a biconical morphology and is made with a 0.016-inch monofilament of nitinol. Its most outstanding feature is that, when it is dilated with a balloon, it shortens and "rolls up," flattening its ends. This allows good fixation to the vessel wall, avoiding the protrusion of metal into the lumen of the native vessel.

RESULTS

On four occasions, the aorta was connected to another nearby vessel: the abdominal aorta to the inferior vena cava (IVC; n = 1), the ascending aorta to the trunk of the pulmonary artery (n = 1), and the descending aorta to the left pulmonary artery (n = 2). On another four occasions, two veins were connected: the portal vein and the IVC. Finally, on three occasions, the right pulmonary artery was connected to the superior vena cava. The connection was safely and accurately performed with passage of a guide wire in all cases. In two experiments, the prosthesis was too short and leakage with massive bleeding was observed after a successful initial deployment of the prosthesis

CONCLUSION

Intervascular anastomoses created by an endovascular approach are feasible in the authors' experimental model for several different vessel pairings.

Percutaneous MR imaging-guided transvascular access of mesenteric venous system: study in swine model

PURPOSE

To determine if, with use of magnetic resonance (MR) imaging guidance alone, transcaval puncture of the superior mesenteric vein (SMV) and/or portal vein is feasible with a percutaneous femoral vein approach.

MATERIALS AND METHODS

The Institutional Animal Care and Use Committee approved the animal studies. Ten inferior vena cava (IVC)-SMV punctures were performed in six pigs. An active MR intravascular needle system was used for all transvascular punctures, and all procedures were performed with a 1.5-T MR unit. The needle was introduced via a 12-F femoral vein sheath and advanced into the IVC by using a real-time gradient-recalled-echo sequence (3.4/1.2 [repetition time msec/echo time msec], 45 degrees flip angle, and six to eight frames per second). Fast transverse spoiled gradient-recalled acquisition in the steady state (SPGR) (6.0/1.5, 60 degrees flip angle, one frame per second) was performed to confirm needle trajectory. The needle system was advanced under real-time MR imaging to puncture the SMV. The location of the needle tip was confirmed with a fast spin-echo sequence (1904/4.5, 36-cm field of view). A direct MR portogram was obtained after the administration of gadopentetate dimeglumine at a concentration of 25% with fast SPGR (6/1.3, 90 degrees flip angle, no section selection, three frames per second). Success was defined as entry into the mesenteric venous system without traversal of any retroperitoneal organs or adjacent vasculature.

RESULTS

Successful MR imaging-guided IVC-SMV punctures were performed in all 10 procedures (100%). The needle was fully visualized as it traversed the retroperitoneum and entered the SMV. MR portograms were successfully obtained following all punctures through the needle. Conventional transverse MR imaging helped confirm that the needle did not traverse any retroperitoneal organs or vessels.

CONCLUSION

With use of only MR imaging guidance and an active MR imaging intravascular needle system, the authors were able to successfully puncture the SMV from the IVC with direct visualization of the needle and all retroperitoneal structures.

Experimental Percutaneous Extrahepatic Portacaval Shunt Creation by Transjugular Approach in Swine

The purpose of the study was to evaluate the feasibility of the creation of a percutaneous extrahepatic portacaval shunt (PEPS) in swine by a transjugular approach and to find a suitable stent-graft to use in PEPS. In 12 swine, the extrahepatic portal vein (PV) was entered from the inferior vena cava (IVC) by a needle system introduced from the transjugular approach. A catheter introduced through the transhepatic approach served as a target. Five types of stent-graft consisting of homemade Z stents and a polytetrafluoethylene cover were explored for PEPS creation. Eight animals had follow-up venograms up to 6 weeks or until the shunt became severely stenotic. Gross and histologic examinations were performed after the final follow-up venography. The PV punctures and stent-graft placement were difficult, but the PEPS was established in all animals. In four animals, the stent-graft failed to adequately cover the tract, causing severe hemorrhage. Only two shunts remained patent up to 6 weeks. The other shunts exhibited severe stenosis or occlusion. At gross examination, all shunts traversed the liver parenchyma of the caudate lobe surrounding the IVC. The extravascular PEPS portion was 4 mm to 2 cm long. All shunts entered the PV close to the splenomesenteric junction and exhibited neointimal formation. Shunt stenoses were caused by neointimal hyperplasia and occlusions by a superimposed thrombus. PEPS can be created by the transjugular approach in swine, but only the PV shunt entrance is extrahepatic. None of the tested rigid stent-grafts were suitable for PEPS creation. A short flexible stent-graft with flanged ends is suggested for further exploration.

Transvenous Extrahepatic Portacaval Shunt with Use of a Modified Prototype Stent-Graft: Experimental Study in Animals

PURPOSE

To evaluate the safety and short-term patency of an experimental transvenous extrahepatic portacaval shunt (TEPS) in an animal model.

MATERIALS AND METHODS

With use of intravascular ultrasound (IVUS) guidance, the main portal vein (PV) was accessed from the inferior vena cava in six pigs and a TEPS was created with use of a prototype flanged stent-graft. Partial PV embolization was then performed to increase the post-TEPS PV pressure. Baseline and postprocedural hemoglobin and hematocrit measurements were obtained and liver function studies were conducted. Immediate postprocedural computed tomography (CT) of the abdomen was used to identify procedural complications. Follow-up venography was performed at 2, 4, and 12 weeks to assess short-term patency. Necropsy was performed at 3 months.

RESULTS

IVUS-guided PV access was accomplished with a mean of two punctures per animal (range, 1-4). TEPS creation was successful in five of six animals. One animal was killed immediately after unsuccessful shunt creation after stent-graft misdeployment and hemorrhage. A second animal required the insertion of a conventional stent coaxially because portions of the leading arms were inadvertently deployed in the portacaval space and the initial flow through the shunt was venographically suboptimal. CT images obtained after successful TEPS creation (n = 5) revealed no evidence of hemoperitoneum, and there was no decrease in hemoglobin or hematocrit levels from baseline values. All five TEPSs were widely patent at 2-week and 4-week venography with only mild pseudointimal hyperplasia (<50% diameter stenosis) identified in one shunt. Twelve-week venography and necropsy demonstrated no evidence of shunt stenosis in one animal, less than 50% diameter stenosis in one animal, 50%-75% diameter stenosis in two animals, and shunt occlusion in one animal.

CONCLUSION

Early results with TEPS with use of a modified prototype flanged stent-graft are promising as a potentially safe alternative means of portal decompression. Additional refinements of the stent-graft delivery process are needed to improve the accuracy of deployment.