Other causes include:Prehepatic causes

Portal vein thrombosis
Splenic vein thrombosis
Arteriovenous fistula (increased portal blood flow)
Splenomegaly and/or hypersplenism (increased portal blood flow)Hepatic causes

Cirrhosis of any cause. alcohol use disorder
chronic viral hepatitis
biliary atresia
Primary biliary cirrhosis
Primary sclerosing cholangitis
Chronic pancreatitis
Hereditary haemorrhagic telangiectasia
Schistosomiasis
Congenital hepatic fibrosis
Nodular regenerative hyperplasia
Fibrosis of space of Disse
Granulomatous or infiltrative liver diseases (Gaucher disease, mucopolysaccharidosis, sarcoidosis, lymphoproliferative malignancies, amyloidosis, etc.) Toxicity (from arsenic, copper, vinyl chloride monomers, mineral oil, vitamin A, azathioprine, dacarbazine, methotrexate, amiodarone, etc.) Viral hepatitis
Fatty liver disease
Veno-occlusive diseasePosthepatic causes

Inferior vena cava obstruction
Right-sided heart failure, e.g. from constrictive pericarditis
Budd–Chiari syndrome also known as hepatic vein thrombosis

Pathophysiology
The pathophysiology of portal hypertension is indicated by increased vascular resistance via different causes; additionally, hepatic stellate cells and myofibroblasts are activated. Increased endogenous vasodilators in turn promote more blood flow in the portal veins.Nitric oxide is an endogenous vasodilator and it regulates intrahepatic vascular tone (it is produced from L-arginine). Nitric oxide inhibition has been shown in some studies to increase portal hypertension and hepatic response to norepinephrine. Diagnosis
Ultrasonography (US) is the first-line imaging technique for the diagnosis and follow-up of portal hypertension because it is non-invasive, low-cost and can be performed on-site.A dilated portal vein (diameter of greater than 13 or 15 mm) is a sign of portal hypertension, with a sensitivity estimated at 12.5% or 40%. On Doppler ultrasonography, a slow velocity of <16 cm/s in addition to dilatation in the main portal vein are diagnostic of portal hypertension.
Portal hypertension is abnormally increased portal venous pressure – blood pressure in the portal vein and its branches, that drain from most of the intestine to the liver. Portal hypertension is defined as a hepatic venous pressure gradient greater than 5 mmHg. Cirrhosis (a form of chronic liver failure) is the most common cause of portal hypertension; other, less frequent causes are therefore grouped as non-cirrhotic portal hypertension. When it becomes severe enough to cause symptoms or complications, treatment may be given to decrease portal hypertension itself or to manage its complications. Signs and symptoms
Signs and symptoms of portal hypertension include:

Ascites (free fluid in the peritoneal cavity),Abdominal pain or tenderness  (when bacteria infect the ascites, as in spontaneous bacterial peritonitis). Increased spleen size (splenomegaly), which may lead to lower platelet counts (thrombocytopenia)
Anorectal varices
Swollen veins on the anterior abdominal wall (sometimes referred to as caput medusae) In addition, a widened (dilated) portal vein as seen on a CT scan or MRI may raise the suspicion about portal hypertension. A cutoff value of 13 mm is widely used in this regard, but the diameter is often larger than this is in normal individuals as well. Causes
The causes for portal hypertension are classified as originating in the portal venous system before it reaches the liver (prehepatic causes), within the liver (intrahepatic) or between the liver and the heart (post-hepatic). The most common cause is cirrhosis (chronic liver failure).