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What is Portal vein thrombosis and explain in detail?
Portal vein thrombosis (PVT) is a vascular disease of the liver that occurs when a blood clot occurs in the hepatic portal vein, which can lead to increased pressure in the portal vein system and reduced blood supply to the liver. The mortality rate is approximately 1 in 10.An equivalent clot in the vasculature that exits the liver carrying deoxygenated blood to the right atrium via the inferior vena cava, is known as hepatic vein thrombosis or Budd-Chiari syndrome.

Signs and symptoms
Portal vein thrombosis causes upper abdominal pain, possibly accompanied by nausea and an enlarged liver and/or spleen; the abdomen may be filled with fluid (ascites). A persistent fever may result from the generalized inflammation. While abdominal pain may come and go if the thrombus forms suddenly, long-standing clot build-up can also develop without causing symptoms, leading to portal hypertension before it is diagnosed.Other symptoms can develop based on the cause. For example, if portal vein thrombosis develops due to liver cirrhosis, bleeding or other signs of liver disease may be present. If portal vein thrombosis develops due to pylephlebitis, signs of infection such as fever, chills, or night sweats may be present.

Causes
Slowed blood flow due to underlying cirrhosis or congestive heart failure is often implicated. The prevalence of PVT in patients with cirrhosis is unclear, with a wide variety of incidence claimed by various researchers (estimated to be 1 in 100 by some while others believe it affects nearly 1 in 4).Thrombophilia (including inherited conditions such as factor V Leiden deficiency, protein C or S deficiency, or antiphospholipid antibody syndrome) is another common cause. Nearly one-third of patients have a myeloproliferative disorder (e.g. polycythemia vera or primary thrombocytosis), most commonly due to a Janus kinase 2 (JAK2) gene mutation. Oral contraceptive use or pregnancy are other non-inherited tendencies for thrombosis.Alternatively, the portal vein may be injured as a result of pancreatitis, diverticulitis, cholangiocarcinoma, hepatocellular carcinoma (HCC), or abdominal surgery/trauma. Red flags for cancerous growth as a cause are elevated alpha fetoprotein levels, portal vein diameter greater than 2.3 cm, pulsatility on Doppler ultrasound imaging, or hyperintense hepatic arterial phase (HAP) on CT scan with contrast.PVT is also a known complication of surgical removal of the spleen. During the last several years, myeloproliferative neoplasms (MPNs) have emerged as a leading systemic cause of splanchnic vein thromboses (which include PVT).

Mechanism
The main portal vein is formed by the union of the splenic vein and superior mesenteric vein (SMV). It is responsible for approximately three-fourths of the liver’s blood flow, transported from much of the gastrointestinal system as well as the pancreas, gallbladder, and spleen. Cirrhosis alters bleeding pathways thus patients are simultaneously at risk of uncontrolled bleeding and forming clots. A long-standing hindrance in flow as in chronic PVT, also known as portal cavernoma, can cause an increase in the hepatic venous pressure gradient (portal hypertension) and increased blood flow through subsidiary veins. This may lead to ascites or bleeding from varices.An infected thrombus may become septic, known as pylephlebitis; if blood cultures are positive for growth at this time, the most common organism is Bacteroides.

Diagnosis
The diagnosis of portal vein thrombosis is usually made with imaging confirming a clot in the portal vein; ultrasound is the least invasive method and the addition of Doppler technique shows a filling defect in blood flow