Portal vein thrombosis overview

# Overview
Portal vein thrombosis is the formation of thrombus in the portal venous system of liver. Portal vein thrombosis was first discovered by Balfour and Stewart in 1868. Portal vein thrombosis may be classified according to the extension into 4 groups. It is thought that portal vein thrombosis is caused by Virchow's triad which includes reduced portal blood flow, hypercoagulable state, vascular endothelial injury. Portal vein thrombosis may be caused by inherited prothrombotic disorders and acquired thrombophilic disorders. Portal vein thrombosis must be differentiated from other diseases that cause abdominal pain, diarrhea, nausea and vomiting. The prevalence of portal vein thrombosis is approximately 5000-10,000 per 100,000 in overall cases of portal hypertension in developed counties and 40,000 per 100,000 in developing countries. Common risk factors in the development of portal vein thrombosis include cirrhosis, pancreatitis, duodenal ulcer, cholecystitis, Crohns disease, ulcerative colitis and cholecystectomy, diverticulitis and appendicitis. If left untreated, patients with portal vein thrombosis may progress to develop portal cavernoma, gastric or esophageal varices/bleeding, hepatic encephalopathy, splenomegaly, portal biliopathy or cholangiopathy. Common symptoms of portal vein thrombosis include abdominal pain or distention, diarrhea, nausea and vomiting, and anorexia. Less common symptoms of portal vein thrombosis include weight loss, fever, ascites, jaundice, and bloody stools. Common physical examination findings of portal vein thrombosis include abdominal pain or distention, splenomegaly and signs of ascites. Laboratory findings is usually normal among patients with portal vein thrombosis. In patients with cirrhosis, laboratory findings may demonstrate an elevated bilirubin, low platelet count, prolonged international normalized ratio (INR), or renal insufficiency. Ultrasonography is the gold standard test for the diagnosis of portal vein thrombosis. The following result of ultrasonography is confirmatory of portal vein thrombosis is portal cavernoma (multiple tortuous small vessels replacing the portal vein) and absence or reduced flow in portal vein. Medical therapy for portal vein thrombosis include anticoagulation to maintain INR between 2 to 3. The goal of anticoagulation is to prevent extension of the clot and to allow for recanalization so that intestinal infarction and portal hypertension do not develop. Surgery is not the first-line treatment option for patients with portal vein thrombosis. Surgery is usually reserved for patients with either failed medical therapy, liver failure, and cirrhosis.

# Historical Perspective
Portal vein thrombosis was first discovered by Balfour and Stewart in 1868. In 1868,  G201210A mutations were first implicated in the pathogenesis of portal vein thrombosis.  In 1945, Allan Whipple, an american surgeon, reported treatment of the portal hypertension with shunts. He eventually tried shunts between different mesenteric veins. Finally, he found portocaval shunt as the best choice. In 1980's, researchers have observed that endoscopic sclerotherapy is more efficient than surgical shunting in preventing recurrent variceal bleeding.

# Classification
Portal vein thrombosis may be classified according to the extension into 4 groups including confined to the portal vein beyond the confluence of the splenic vein, extended to the superior mesenteric vein, but with patent mesenteric vessels, extended to the whole splanchnic venous system, but with large collaterals, and extended to the whole splanchnic venous system with only fine collaterals. Based on the duration of symptoms, portal vein thrombosis may be classified as either acute or chronic.

# Pathophysiology
It is thought that vein thrombosis is caused by Virchow's triad which includes reduced portal blood flow, hypercoagulable state, vascular endothelial injury. There are two mechanisms that contribute to loss of portal vein blood flow to liver, arterial rescue and venous rescue. It is a rapid process and takes a few days to start and 3-5 weeks to complete after portal vein obstruction. Collateral vessel joins to form cavernoma which connects the proximal and distal part of thrombosed portal vein. Finally, the portal vein becomes fibrosed, thin cord. All these events leads to low systemic vascular resistance and high cardiac output. These are the characteristic findings of hyper-kinetic circulation.

# Causes
Portal vein thrombosis may be caused by inherited prothrombotic disorders and acquired thrombophilic disorders. Less common causes of portal vein thrombosis include acquired conditions such as cirrhosis and hepatocellular carcinoma and procedures such as abdominal surgery or surgical injury of the portal vein axis and splenectomy.

# Differentiating portal vein thrombosis from Other Diseases
Portal vein thrombosis must be differentiated from other diseases that cause abdominal pain, diarrhea, nausea and vomiting, such as chronic pancreatitis, Pancreatic carcinoma, Dumping syndrome, Acute appendicitis, acute diverticulitis, Infective colitis, viral hepatitis, Liver abscess, Mesenteric ischemia, Acute ischemic colitis.

# Epidemiology and Demographics
The incidence of portal vein thrombosis in cirrhotic patients is unknown. The prevalence of portal vein thrombosis is approximately 5000-10,000 per 100,000 in overall cases of portal hypertension in developed counties and 40,000 per 100,000 in developing countries. The overall mortality rate of portal vein thrombosis is less than 10% except for patients with malignancy or cirrhosis. Patients of all age groups may develop portal vein thrombosis. There is no racial predilection to portal vein thrombosis. Portal vein thrombosis affects men and women equally.

# Risk Factors
Common risk factors in the development of portal vein thrombosis include cirrhosis, pancreatitis, duodenal ulcer, cholecystitis, Crohns disease, ulcerative colitis and cholecystectomy, diverticulitis and appendicitis. Less common risk factors in the development of portal vein thrombosis include oral contraceptives, pregnancy or puerperium, and hyperhomocysteinemia.

# Screening
There is insufficient evidence to recommend routine screening for portal vein thrombosis.

# Natural History, Complications, and Prognosis
If left untreated, patients with portal vein thrombosis may progress to develop portal cavernoma, gastric or esophageal varices/bleeding, hepatic encephalopathy, splenomegaly, portal biliopathy or cholangiopathy. Depending on the extent of the model for end-stage liver disease score at the time of diagnosis, the prognosis may vary. However, the prognosis is generally regarded as good.

# Diagnosis

## Diagnostic Criteria
Ultrasonography is the gold standard test for the diagnosis of portal vein thrombosis. The following result of ultrasonography is confirmatory of portal vein thrombosis is portal cavernoma (multiple tortuous small vessels replacing the portal vein) and absence or reduced flow in portal vein.

## History and Symptoms
Common symptoms of portal vein thrombosis include abdominal pain or distention, diarrhea, nausea and vomiting, and anorexia. Less common symptoms of portal vein thrombosis include weight loss, fever, ascites, jaundice, and bloody stools.

## Physical Examination
Patients with portal vein thrombosis usually appear ill. Common physical examination findings of portal vein thrombosis include abdominal pain or distention, splenomegaly and signs of ascites.

## Laboratory Findings
Laboratory findings is usually normal among patients with portal vein thrombosis. In patients with cirrhosis, laboratory findings may demonstrate an elevated bilirubin, low platelet count, prolonged international normalized ratio (INR), or renal insufficiency.

## Electrocardiogram
There are no ECG findings associated with portal vein thrombosis.

## X-ray
There are no x-ray findings associated with portal vein thrombosis.

## Ultrasound
Findings on an ultrasound diagnostic of portal vein thrombosis include echogenic material obstructing lumen of vessel, complete or partial absence of flow in portal vein, and collateral circuits by-passing the obstructed vessel.

## CT scan
Abdominal CT scan is used for the diagnosis of portal vein thrombosis. Findings on CT scan suggestive of hyperattenuating material in the portal vein lumen, nonenhanced intraluminal-filling defect, Lack of luminal enhancement, increased hepatic enhancement in the arterial phase and decreased hepatic enhancement in the portal phase.

## MRI
Abdominal MRI is used for the diagnosis of portal vein thrombosis. Findings of MRI diagnostic for portal vein thrombosis include filling defect that partially or completely occludes the vessel lumen in the portal venous phase, clot appears iso-intense on T-1 weighted images, and usually has a more intense signal on T-2 images, and the presence of varices.

## Other Imaging Findings
Contrast enhanced ultrasonography (CEUS) is helpful in the diagnosis of portal vein thrombosis. Findings on CEUS suggestive of portal vein thrombosis include pulsatile flow in a portal vein thrombus, absence of enhancement of the portal vein thrombus in the arterial phase.

## Other Diagnostic Studies
There are no other diagnostic studies associated with portal vein thrombosis.

# Treatment

## Medical Therapy
Medical therapy for portal vein thrombosis include anticoagulation to maintain INR between 2 to 3. The goal of anticoagulation is to prevent extension of the clot and to allow for recanalization so that intestinal infarction and portal hypertension do not develop.

## Surgery
Surgery is not the first-line treatment option for patients with portal vein thrombosis. Surgery is usually reserved for patients with either medical failed therapy, liver failure, and cirrhosis.

## Primary Prevention
There are no established measures for the primary prevention of portal vein thrombosis.

## Secondary Prevention
There are no established measures for the secondary prevention of portal vein thrombosis.