الفهرس 
Anatomy of the Portal VeinOnly 14 pages are availabe for public view
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Abstract
The liver tumors represent a major pathology in medical practice, considering their high incidence, the diagnostic difficulties and the high rate of morbidity and mortality.
Liver resection is considered to be the best treatment option for patients with malignant liver tumors and metastases. The loss of functional liver mass after hepatectomy is compensated by the regenerative capacity of the liver to regain the initial volume and function. Extensive hepatic resections beyond 75% of the liver mass, however, are associated with an inadequate regenerative reserve of the remaining parenchyma. This results in parenchymal dysfunction and liver failure, which is associated with a high mortality rate.
To reduce the risk of liver failure and to increase the number of resectable patients requiring extensive hepatectomy, portal vein occlusion has been introduced. Four to eight weeks before the planned hepatectomy, the individual portal vein branches that supply the tumor-bearing liver lobe are occluded by ligation or embolization. This procedure has been demonstrated to induce atrophy of the portal blood-deprived lobe, whereas the non-ligated contralateral tissue, which represents the remnant liver after later hepatectomy, undergoes compensatory hypertrophy.
Reporting of the median hospital stay is important, particularly after hepatic resection, as it directly relates to postoperative morbidity (eg, cholestasis, impaired synthetic function, fluid retention) and mortality. In addition, many patients who were initially not considered for resection because of a lack of sufficient remaining normal hepatic parenchyma can be added to the pool of candidates for surgical treatment after induction of selective liver hypertrophy to produce sufficient normal liver tissue left after resection either by PVE or PVL.
The minimum absolute liver volume necessary to support post-resection hepatic function has not been clearly defined. However, a FLR/TELV ratio of at least 25% is recommended in patients with otherwise normal livers, with a ratio of at least 40% in patients in whom the liver is considered compromised (eg, from chronic liver disease or high-dose chemotherapy).
The aim of portal vein embolization is to intentionally occlude the portal vein of the hepatic lobe to be resected and to induce selective enlargement of the future liver remnant. As a result, the volume of future liver remnant is increased after portal vein embolization and the operative morbidity is expected to be decreased by minimize the abrupt rise in portal pressure at resection that can lead to hepatocellular damage to the FLR and to improve overall tolerance to major resection by increasing hepatic mass prior to resection in order to reduce the risk of post-resection metabolic changes.
A thorough knowledge of hepatic segmentation, portal venous anatomy, branching variants of the portal vein and congenital anomalies of portal vein is essential before doing PVE.
In addition, the indications, contraindications, methods for evaluating for hepatic lobar hypertrophy, timing of surgery, and possible complications need to be fully understood before performing PVE or PVL.
Technique of PVE may vary among operators, and further research is necessary to determine the best embolic agents available and the expected rates of liver regeneration.
PVE is performed by two standard approaches: the transhepatic contralateral (ie, via the FLR), transhepatic ipsilateral (ie, via the liver to be resected) using seldinger technique. These approaches are chosen on the basis of operator preference, type of hepatic resection planned, extent of embolization, and type of embolic agent used.
Nevertheless, as hepatobiliary surgeons become more experienced at performing extended hepatic resections, PVE may be requested more frequently.
Portal vein occlusion has become an integral component in the treatment algorithm of patients with inadequate FLR. Portal vein occlusion redirects blood to the FLR and has been shown to reduce the risk of complications due to peri operative liver failure.
Although PVE is the preferred choice by many, a role for PVL has also been demonstrated by some authors.
Portal Vein Ligation (PVL) is a safe and efficient method of increasing the Future Liver Remnant Volume in patients with synchronous colorectal cancer and multiple, bilateral liver metastases, in the presence of a small remnant liver volume.
Ligation of the portal branch was performed during resection of the colorectal primary tumor with or without clearance of the FLR.
The most common complication after PVE or PVL is the Post embolization syndrome in the form of pain, fever, nausea, vomiting, and leukocytosis but there are other uncommon complication such as transient bleeding into the biliary tree or bleeding elsewhere, migration of embolic material to the portal vein of the future remnant liver and main portal vein thrombosis should be in mind.
Assessment of post embolization or Ligation complications is important to avoid the risks associated with the procedure by color Doppler ultrasonography (CDUS), helical computed tomography (CT), Multi-detector CT.
Color Doppler ultrasonography (CDUS) provides rapid, comprehensive, and accurate evaluation of the portal vein and flow direction. This technique can be performed before PVE under sterile conditions at the patient’s bedside, intraoperatively, or immediately postoperatively to determine early complication.
Helical dynamic computed tomography (CT) is performed immediately prior to PVE to document the extent of disease (ie, extrahepatic disease or involvement of the planned FLR), FLR size, and portal venous anatomy and 2 weeks after PVE to improve visualization of patency of one of portal venous branches and complete occlusion of the other branch.
Multi-detector CT with volumetry is performed immediately before PVE to asses FLR volume and the virtual hepatectomy plane for Virtual hepatectomy then performed approximately 3 to 4 weeks after PVE to assess the degree of FLR hypertrophy.
If liver regeneration occurs and there is no spread of disease that would contraindicate the procedure, resection is performed. Otherwise, follow-up CT is performed at monthly intervals.