The intrahepatic shunts found in large dog breeds are passed on in a simple autosomal recessive way, while the extrahepatic shunts of the small breeds are inherited on a polygenic basis.

Several studies have attempted to predict the survival of patients with Budd–Chiari syndrome. In general, nearly 2/3 of patients with Budd–Chiari are alive at 10 years. Important negative prognostic indicators include ascites, encephalopathy, elevated Child-Pugh scores, elevated prothrombin time, and altered serum levels of various substances (sodium, creatinine, albumin, and bilirubin). Survival is also highly dependent on the underlying cause of the Budd–Chiari syndrome. For example, a patient with an underlying myeloproliferative disorder may progress to acute leukemia, independently of Budd–Chiari syndrome.

Congestion of the mucosa in other parts of the gastrointestinal tract can also be seen in portal hypertension. When the condition involves the colon, it is termed "portal hypertensive colopathy".

The cause can be found in more than 80% of patients.

- Primary Budd–Chiari syndrome (75%): thrombosis of the hepatic vein

- Hepatic vein thrombosis is associated with the following in decreasing order of frequency:

2. Polycythemia vera

1. Pregnancy

2. Postpartum state

3. Use of oral contraceptives

4. Paroxysmal nocturnal hemoglobinuria

5. Hepatocellular carcinoma

6. Lupus anticoagulants

- Secondary Budd–Chiari syndrome (25%): compression of the hepatic vein by an outside structure (e.g. a tumor)

Budd–Chiari syndrome is also seen in infections such as tuberculosis, congenital venous webs and occasionally in inferior vena caval stenosis.

Often, the patient is known to have a tendency towards thrombosis, although Budd–Chiari syndrome can also be the first symptom of such a tendency. Examples of genetic tendencies include protein C deficiency, protein S deficiency, the Factor V Leiden mutation, hereditary anti-thrombin deficiency and prothrombin mutation G20210A. An important non-genetic risk factor is the use of estrogen-containing (combined) forms of hormonal contraception. Other risk factors include the antiphospholipid syndrome, aspergillosis, Behçet's disease, dacarbazine, pregnancy, and trauma.

Many patients have Budd–Chiari syndrome as a complication of polycythemia vera (myeloproliferative disease of red blood cells). Patients suffering from paroxysmal nocturnal hemoglobinuria (PNH) appear to be especially at risk for Budd–Chiari syndrome, more than other forms of thrombophilia: up to 39% develop venous thromboses and 12% may acquire Budd-Chiari.

A related condition is veno-occlusive disease, which occurs in recipients of bone marrow transplants as a complication of their medication. Although its mechanism is similar, it is not considered a form of Budd–Chiari syndrome.

Other toxicologic causes of veno-occlusive disease include plant & herbal sources of pyrrolizidine alkaloids such as Borage, Boneset, Coltsfoot, T'u-san-chi, Comfrey, Heliotrope (sunflower seeds), Gordolobo, Germander, and Chaparral.

Dilated submucosal veins are the most prominent histologic feature of esophageal varices. The expansion of the submucosa leads to elevation of the mucosa above the surrounding tissue, which is apparent during endoscopy and is a key diagnostic feature. Evidence of recent variceal hemorrhage includes necrosis and ulceration of the mucosa. Evidence of past variceal hemorrhage includes inflammation and venous thrombosis.

Several studies have found that patients with portal hypertension develop increased blood flow to the stomach. The physiological findings that correlate with worsening portal hypertensive gastropathy include an increased portal venous pressure gradient and decreased hepatic blood flow. Biopsies of the stomach in patients with portal hypertensive gastropathy show ectatic (or dilated) blood vessels, evidence of bleeding by means of red blood cells in the lamina propria, and edema in the stomach wall.

A treatment plan may involve lactulose, enemas, and use of antibiotics such as rifaximin, neomycin, vancomycin, and the quinolones. Restriction of dietary protein was recommended but this is now refuted by a clinical trial which shows no benefit. Instead, the maintenance of adequate nutrition is now advocated.

The management of ascites needs to be gradual to avoid sudden changes in systemic volume status which can precipitate hepatic encephalopathy, renal failure and death. The management includes salt restriction, diuretics (spironolactone), paracentesis, and transjugular intrahepatic portosystemic shunt.

Unlike oesophageal varices, rectal varices are less prone to bleeding, are less serious when a bleed does occur, and are easier to treat because of the more accessible location.

Typically, treatment consists of addressing the underlying portal hypertension. Some treatments include portosystemic shunting, ligation, and under-running suturing. Insertion of a transjugular intrahepatic portosystemic shunt (TIPS) has been shown to alleviate varices caused by portal hypertension. Successful treatment of portal hypertension that subsequently reduces anorectal varices provides a confirmation of the initial diagnosis, allowing for a distinction between varices and hemorrhoids, which would not have been alleviated by reduction of portal hypertension.

The terms rectal varices and haemorrhoids are often used interchangeably, but this is not correct. Haemorrhoids occur due to prolapse of the rectal venous plexus and are no more common in patients with portal hypertension than those without. Rectal varices, however, are only found in patients with portal hypertension and are common in conditions such as cirrhosis.

Causes can include pancreatitis, cirrhosis, diverticulitis, and cholangiocarcinoma. It is also a known complication of splenectomy.

It is a serious medical disorder and the mortality rate can be as high as 30%. The high mortality rate is likely a measure that this syndrome is seen in critically ill patients, rather than this syndrome being in itself lethal, although it can also present in otherwise healthy individuals (especially if the disorder was induced by pharmacologic agents). Drug induced megacolon (i.e. from Clozapine) has been associated with mortality as high as 27.5%.

In ideal circumstances, patients with known varices should receive treatment to reduce their risk of bleeding. The non-selective β-blockers (e.g., propranolol, timolol or nadolol) and nitrates (e.g., isosorbide mononitrate (IMN) have been evaluated for secondary prophylaxis. Non-selective β-blockers (but not cardioselective β-blockers like atenolol) are preferred because they decrease both cardiac output by β blockade and splanchnic blood flow by blocking vasodilating β receptors at splanchnic vasculature. The effectiveness of this treatment has been shown by a number of different studies.

However, non-selective β-blockers do not prevent the "formation" of esophageal varices.

When medical contraindications to beta-blockers exist, such as significant reactive airway disease, then treatment with prophylactic endoscopic variceal ligation is often performed.

The average age of diagnosis for GAVE is 73 years of age for females, and 68 for males. Women are about twice as often diagnosed with gastric antral vascular ectasia than men. 71% of all cases of GAVE are diagnosed in females. Patients in their thirties have been found to have GAVE. It becomes more common in women in their eighties, rising to 4% of all such gastrointestinal conditions.

5.7% of all sclerosis patients (and 25% of those who had a certain anti-RNA marker) have GAVE.

GAVE is associated with a number of conditions, including portal hypertension, chronic kidney failure, and collagen vascular diseases.

Watermelon stomach also occurs particularly with scleroderma, and especially the subtype known as systemic sclerosis. A full 5.7% of persons with sclerosis have GAVE, and 25% of all sclerosis patients who had a certain anti-RNA marker have GAVE. In fact:

The endoscopic appearance of GAVE is similar to portal hypertensive gastropathy, but is not the same condition, and may be concurrent with cirrhosis of the liver. 30% of all patients have cirrhosis associated with GAVE.

Sjögren's syndrome has been associated with at least one patient.

The first case of ectopic pancreas associated with watermelon stomach was reported in 2010.

Patients with GAVE may have elevated gastrin levels.

The Genetic and Rare Diseases Information Center (GARD) states that pernicious anemia is one of the conditions associated with GAVE's, and one separate study showed that over three-fourths of the patients in the study with GAVE's had some kind of Vitamin B12 deficiency including the associated condition pernicious anemia.

Intestinal permeability and diverticulitis may occur in some patients with GAVE.

Non-cirrhotic portal fibrosis (NCPF) is a chronic liver disease and type of non-cirrhotic portal hypertension (NCPH).

It is characterized by 'obliterative portovenopathy', which leads to various problems such as portal hypertension, massive splenomegaly, and variceal bleeding. It is estimated that about 85% of people with NCPF have repeated episodes of variceal bleeding.

Treatments include anticoagulants, shunts, bypass surgery, and transplants.

Surgical treatment is best, when it can be performed. Pressure within the portal vein is measured as the shunt is closed, and it must be kept below 20 cm HO or else portal hypertension will ensue. Methods of shunt attenuation should aim to slowly occlude the vessel over several weeks to months in order to avoid complications associated with portal hypertension. These methods include ameroid ring constrictors, cellophane banding, intravascular or percutaneous silicone hydraulic occluders. The most common methods of attenuation used by veterinarians are ameroid ring constrictors and cellophane banding. Both methods have reportedly good outcomes in both cats and dogs, although the true composition of readily sourced cellophane has been found to be made from plastics (inert) and not cellulose (stimulates a fibrous reaction). Recently, a commercial supplier of regenerated cellulose based cellophane for veterinarians has been established for use of cellophane banding for portosystemic shunts in dogs and cats. Complete closure of extrahepatic shunts results in a very low recurrence rate, while incomplete closure results in a recurrence rate of about 50 percent. However, not all dogs with extrahepatic shunts tolerate complete closure (16 to 68 percent). Intrahepatic shunts are much more difficult to surgically correct than extrahepatic shunts due to their hidden nature, large vessel size, and greater tendency toward portal hypertension when completely closed. When surgery is not an option, PSS is treated as are other forms of liver failure. Dietary protein restriction is helpful to lessen signs of hepatic encephalopathy, and antibiotics such as neomycin or metronidazole and other medicines such as lactulose can reduce ammonia production and absorption in the intestines. The prognosis is guarded for any form of PSS.

Population studies from numerous areas in the world have shown that HHT occurs at roughly the same rate in almost all populations: somewhere around 1 in 5000. In some areas, it is much more common; for instance, in the French region of Haut Jura the rate is 1:2351 - twice as common as in other populations. This has been attributed to a founder effect, in which a population descending from a small number of ancestors has a high rate of a particular genetic trait because one of these ancestors harbored this trait. In Haut Jura, this has been shown to be the result of a particular "ACVRL1" mutation (named c.1112dupG or c.1112_1113insG). The highest rate of HHT is 1:1331, reported in Bonaire and Curaçao, two islands in the Caribbean belonging to the Netherlands Antilles.

Most people with HHT have a normal lifespan. The skin lesions and nosebleeds tend to develop during childhood. AVMs are probably present from birth, but don't necessarily cause any symptoms. Frequent nosebleeds are the most common symptom and can significantly affect quality of life.

A very small proportion (those affected by "SMAD4" (MADH4) mutations, see below) have multiple benign polyps in the large intestine, which may bleed or transform into colorectal cancer. A similarly small proportion experiences pulmonary hypertension, a state in which the pressure in the lung arteries is increased, exerting pressure on the right side of the heart and causing peripheral edema (swelling of the legs), fainting and attacks of chest pain. It has been observed that the risk of thrombosis (particularly venous thrombosis, in the form of deep vein thrombosis or pulmonary embolism) may be increased. There is a suspicion that those with HHT may have a mild immunodeficiency and are therefore at a slightly increased risk from infections.

Cruveilhier–Baumgarten disease or Pégot-Cruveilhier–Baumgarten disease is a rare medical condition in which the umbilical or paraumbilical veins are distended, with an abdominal wall bruit (the Cruveilhier-Baumgarten bruit) and palpable thrill, portal hypertension with splenomegaly, hypersplenism and oesophageal varices, with a normal or small liver.

It was first described by Pégot in 1833, and then by Jean Cruveilhier (1835) and Paul Clemens von Baumgarten (1907).

Armstrong "et al." (1942) and Steinburg and Galambos (1967) described two different types of the condition:

- Cruveilhier-Baumgarten syndrome: liver cirrhosis or portal hypertension is the cause of the distension of the paraumbilical veins (i.e. an "acquired" condition in which the veins reopen due to high portal pressure).

- Cruveilhier–Baumgarten disease: the distension of the paraumbilical veins is due to failure of umbilical vein closure, with little or no evidence of liver disease found on liver biopsy (i.e. a "congenital" patency of the umbilical vein leading to portal hypertension).

Following diagnosis, mean survival of patients with PPH is 15 months. The survival of those with cirrhosis is sharply curtailed by PPH but can be significantly extended by both medical therapy and liver transplantation, provided the patient remains eligible.

Eligibility for transplantation is generally related to mean pulmonary artery pressure (PAP). Given the fear that those PPH patients with high PAP will suffer right heart failure following the stress of post-transplant reperfusion or in the immediate perioperative period, patients are typically risk-stratified based on mean PAP. Indeed, the operation-related mortality rate is greater than 50% when pre-operative mean PAP values lie between 35 and 50 mm Hg; if mean PAP exceeds 40-45, transplantation is associated with a perioperative mortality of 70-80% (in those cases without preoperative medical therapy). Patients, then, are considered to have a high risk of perioperative death once their mean PAP exceeds 35 mm_Hg.

Survival is best inferred from published institutional experiences. At one institution, without treatment, 1-year survival was 46% and 5-year survival was 14%. With medical therapy, 1-year survival was 88% and 5-year survival was 55%. Survival at 5 years with medical therapy followed by liver transplantation was 67%. At another institution, of the 67 patients with PPH from 1652 total cirrhotics evaluated for transplant, half (34) were placed on the waiting list. Of these, 16 (48%) were transplanted at a time when 25% of all patients who underwent full evaluation received new livers, meaning the diagnosis of PPH made a patient twice as likely to be transplanted, once on the waiting list. Of those listed for transplant with PPH, 11 (33%) were eventually removed because of PPH, and 5 (15%) died on the waitlist. Of the 16 transplanted patients with PPH, 11 (69%) survived for more than a year after transplant, at a time when overall one-year survival in that center was 86.4%. The three year post-transplant survival for patients with PPH was 62.5% when it was 81.02% overall at this institution.

Intestinal varices are dilated submucosal veins in the intestine.

One treatment includes a transjugular intrahepatic portosystemic shunt.

Gastric varices are dilated submucosal veins in the stomach, which can be a life-threatening cause of bleeding in the upper gastrointestinal tract. They are most commonly found in patients with portal hypertension, or elevated pressure in the portal vein system, which may be a complication of cirrhosis. Gastric varices may also be found in patients with thrombosis of the splenic vein, into which the short gastric veins which drain the fundus of the stomach flow. The latter may be a complication of acute pancreatitis, pancreatic cancer, or other abdominal tumours, as well as hepatitis C. Gastric varices and associated bleeding are a potential complication of schistosomiasis resulting from portal hypertension.

Patients with bleeding gastric varices can present with bloody vomiting (hematemesis), dark, tarry stools (melena), or rectal bleeding. The bleeding may be brisk, and patients may soon develop shock. Treatment of gastric varices can include injection of the varices with cyanoacrylate glue, or a radiological procedure to decrease the pressure in the portal vein, termed transjugular intrahepatic portosystemic shunt or TIPS. Treatment with intravenous octreotide is also useful to shunt blood flow away from the stomach's circulation. More aggressive treatment including splenectomy (or surgical removal of the spleen) or liver transplantation may be required in some cases.