Portal vein embolization (PVE) is a preoperative procedure performed in interventional radiology to initiate hypertrophy of the anticipated future liver remnant a couple weeks prior to a major liver resection procedure. The procedure involves injecting the right or left portal vein with embolic material to occlude portal blood flow. By occluding the blood flow to areas of the liver that will be resected away, the blood is diverted to healthy parts of the liver and induces hyperplasia. This may allow for a more extensive resection or stage bilateral resections that would otherwise be contraindicated resulting in better oncological treatment outcomes.
Medical uses Indications for PVE depend on the ratio of future liver remnant (FLR) to total estimated liver volume (TELV) and liver condition. Although there is no consensus to the absolute minimum liver volume required for adequate post-resection liver function, a FLR/TELV ratio of at least 25% is recommended in patients with otherwise normal livers. The recommendation for those with chronic liver disease such as cirrhosis is a FLR/TELV ratio of at least 40%. In these patients a PVE may be indicated to increase the FLR and the FLR/TELV ratio. Preoperative patients receiving extensive chemotherapy with a FLR/TELV less than 30% should also receive PVE prior to resection; conversely, chemotherapy does not preclude subsequent PVE. Other important considerations before a PVE include co-morbidities such as diabetes, procedure type and the extent of planned resection. Insulin resistance has been associated with slower rates of regeneration and higher likelihood of inadequate FLR growth after PVE. Additionally, if the resection requires more extensive surgery such as a resections of the pancreas or small bowel, a greater FLR/TELV ratio may be needed for safe recovery.
Outcomes Preoperative PVE is a very well tolerated procedure with extremely low mortality rates (0.1 percent) and technical failure rates (0.4 percent). Complication rates from the procedure are low as well (2–3 percent) and include portal vein thrombosis, liver infarction, necrosis, infection, pneumothorax, and other risks as listed above. Success of PVE is determined by degree of regenerative response, which again depends on factors such as baseline liver condition, technical approach and pre-existing co-morbidities. Five-year survival in patients with originally unresectable tumors as a result of inadequate future liver remnant and received PVE with subsequent resection was found in one study to be 29%. Originally, there was concern that PVE could promote tumor growth and increase recurrence rates, however a systematic review has found that there was no significant difference observed in postoperative hepatic recurrence or 3 and 5 year overall survival rates. This suggests that PVE does not have any significant adverse effects on the risk of oncogenesis. Overall, PVE is an important technique that can allow for patients with inadequate predicted FLR/TELV ratios an opportunity for resection and potential cure of their liver conditions.
Contraindications Portal hypertension is an absolute contraindication, as these patients are not surgical candidates and are at higher risk of significant complications from PVE. Additionally, complete lobar portal vein occlusion of either lobe would preclude expected increases in FLR from PVE due to already existing diversion of portal flow. Patients with extrahepatic metastatic disease are also not candidates for resection, and therefore PVE is contraindicated. In the past patients with bi-lobar disease were not considered for PVE, however now there may be a role of PVE in combination with a two-stage hepatectomy. Additionally, patients who have an inadequate predicted FLR post PVE should not be considered. Other contraindications include any conditions that make a patient unfit for surgery or intervention (poor cardiopulmonary status, sepsis, kidney failure, etc.).
Risks and Benefits PVE has been shown to have the following risks:
Portal vein thrombosis, liver infarction, necrosis and portal hypertension. Risks related to any percutaneous transhepatic procedures such as bleeding and infection. Accelerated tumor growth due to compensatory hepatic arterial flow and in cases when all of the tumor-bearing areas are not properly embolized. PVE has been shown to have the following benefits:
Decrease post-resection morbidity by decreasing number of complication and length of hospital stay. Patients initially with unresectable tumors due to inadequate FLR/TELV are able to have resections. Decrease post-resection mortality by increasing the volume of functional liver parenchyma. Poor regenerative response to PVE predicts poor compensatory regeneration following liver resection and can help identify patients unsuitable for resection.
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