Patients with documented PMS-VT need to be treated with intravenous or subcutaneous heparin to prevent propagation of the thrombus. First, even in the early postoperative period, the risks of clot propagation or complete superior mesenteric vein/portal vein occlusion far outweighs the risk of bleeding. Second, based on findings from observational studies, spontaneous recanalization of the portal vein is uncommon, and cavernous transformation develops in most patients without treatment [27]. However, randomized trials comparing patients under anticoagulation with patients without anticoagulation are lacking. Nonetheless, anticoagulant therapy has become standard of care for the treatment of acute PMS-VT. Both the American Association for the Study of Liver Diseases guidelines and American College of Chest Physicians Evidence-based Clinical Practice Guidelines recommend treatment with anticoagulants [28, 29]. Interestingly, the recanalization rates under anticoagulation differ between studies. In the one prospective multicenter trial with > 100 patients enrolled, anticoagulation resulted in a recanalization rate of the main portal vein and its left or right branch of 39 % [30]. Obstruction of the portal vein persisted in the rest of the patients, and portal cavernoma already had developed in 40 % of the patients by the end of follow-up, which put them at risk for permanent portal hypertension. In a study by Plessier et al. [31], anticoagulation treatment was less effectivwwe in inducing recanalization of complete PVT than in preventing extension of thrombosis to or from the portal vein. It seems that the thrombus burden also has an effect on response to anticoagulation therapy and should be taken into account when selecting patients for anticoagulation alone in the treatment of acute PMS-VT. In particular, complete recanalization was achieved more frequently in cases where the thrombosis involved only the portal vein or the superior mesenteric vein, rather than in patients with more extensive involvement of the portal venous system [32]. At the authors’ institution, unfractionated heparin is initially given IV with target-activated partial thromboplastin time between 1.5 and 2.5. Oral anticoagulant therapy with warfarin for 3–6 months should follow, targeting a prothrombin time–international normalized ratio (PT-INR) between 2 and 3.

The incidence of PMS-VT may be influenced by the lack of clear recommendation regarding anticoagulation following “high-risk” surgery procedures (i.e., major venous reconstruction, extended hepatic resection, pancreaticoduodenectomy). In particular, some surgeons delay or completely withhold routine venous thromboembolism prophylaxis following major hepatectomy, because it is believed that these patients are at risk for postoperative liver insufficiency, leading to the concern they are already anticoagulated. This belief is often supported by the resulting laboratory derangements in measurable liver function, including elevations in the prothombin time/international normalized ratio (PT/INR) and partial thromboplastin time (PTT), as well as occasional thrombocytopenia. Because of that, many surgeons carefully observe patients with portal vein thrombosis following hepatectomy and initiate anticoagulation therapy only when the thrombus extended to the superior mesenteric vein or reduced portal venous flow. In contrast with this practice, Ejaz et al. showed that despite having alterations in platelets, PT/INR, and PTT, patients with liver insufficiency actually often have significant increased risk for venous thrombosis, leading to the routine use of thromboprophylaxis in these patients [33].

Because anticoagulation only leads to a recanalization of the PMS-VT in nearly 40 % of patients, alternative and more aggressive treatment strategies are used by some centers. During the last decade, several treatment modalities have been used, including percutaneous transhepatic thrombolysis, mechanical thrombectomy, and percutaneous transhepatic balloon angioplasty and/or stent placement without thrombolysis or thrombectomy. Advancements in interventional radiologic techniques have made it possible to administer thrombolytic agents in the proximity of the clot. Local infusion of thrombolytic agents (urokinase 15,000–30,000 IU/h or recombinant tissue plasminogen activator 1.8 mg/h, for 4–5 days.) has been reported to achieve recanalization in 60 %, up to 100 %, of patients [34–36]. The effect of thrombolysis can be visualized with angiographies via the catheter on a regular basis or, if clinically indicated, until the catheter is removed. Removal is conducted under fluoroscopy. However, positioning a radiologic catheter adjacent to clot might be technically problematic (especially in patients with complete intra- and extrahepatic thrombosis), and thrombolysis might be prohibitively hazardous in the early postoperative period after major HPB procedures, due to the risk of major bleeding [36]. Most clinicians therefore consider pharmacologic thrombolysis as therapy reserved for patients with severe disease with propagation of thrombus or without improvement of symptoms. Furthermore, catheter-directed thrombolytic therapy may fail, especially in the setting of acute thrombus superimposed on chronic thrombus [35, 36]. To avoid the drawbacks of thrombolysis, several investigators have successfully treated the cases of postoperative PMS-VT by mechanical percutaneous thrombectomy [37]. Venous thrombectomy is generally considered to be less successful than arterial thrombectomy because of difficulties in removing adherent clot from the thin, delicate vein wall. In the acute setting, however, percutaneous venous thrombectomy may be technically easier, because the clot has not yet become adherent to the vein wall [38].

By debulking the thrombus burden, mechanical percutaneous thrombectomy may reduce the duration and the total dose of thrombolytic agents, thereby reducing the bleeding risk for the patient. However, thrombectomy has potential risks of embolism, intimal trauma, and re-thrombosis [39]. Balloon angioplasty and/or stent placement for treating postoperative PMS-VT has several advantages. The procedure can restore the patency of the portal vein-superior mesenteric vein (if there is no thrombosis in the intrahepatic portal vein) without the need for prolonged thrombolysis, reducing the bleeding risk in this group of postoperative patients [40]. When balloon angioplasty and/or stent placement without thrombolysis or thrombectomy are used to treat thrombotic vessels, there is a risk that the thrombus will prolapse through the stent mesh, causing re-occlusion or distal embolism. Balloon angioplasty or stent placement also has several potential limitations. First, there is a risk of suture dehiscence during balloon angioplasty if the patient has thrombosis in the early postoperative period and has undergone venorraphy during the surgical treatment. The use of a balloon catheter with a smaller diameter relative to that of the patent portal vein or superior mesenteric vein and careful under-inflation of a balloon catheter relative to the diameter of the deployed stent may prevent this complication. Second, the long-term patency rate is not excellent, although these results are limited to small case series [40–42].

Surgical exploration must be undertaken when clinical, biochemical, and radiologic signs of bowel infarction are detected, in order to eradicate the source of septic shock. The first report of a successful portal vein/superior mesenteric vein thrombectomy for acute PMS-VT was provided in 1968 by Mergenthaler and Harris [43]. However, surgeons have been historically hesitant to embrace this approach. The surgical principles are simple: the superior mesenteric vein can be accessed at the inferior border of the pancreas, whereas the portal vein is accessed and controlled dissecting the hepatoduodenal ligament. Once the involved vessel has been isolated and taped proximally and distally to the thrombosis site, a venotomy is performed, and thrombotic material is mechanically removed with forceps and a surgical suction device [24]. Recently, a combined surgical/interventional approach has been described. After conventional surgical thrombectomy, a guiding sheath is inserted into the superior mesenteric vein or in the portal vein via the venotomy, and radiologic interventional mechanical thrombectomy is performed. An important advantage of the combined approach is the possibility to remove thrombi in both directions (antegrade and retrograde) and in formerly inaccessible areas as the intrahepatic portal vein branches. To keep the portal vein patent after successful thrombectomy, it seems to be essential to have sufficient blood inflow from the mesenteric and splenic veins and downstream into the liver parenchyma [24].