Portal hypertension

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Cholestatic liver disease in a dog, showing characteristic nutmeg appearance due to chronic portal hypertension[1]

Portal hypertension, defined as portal vein intravascular pressure > 10 mmHg, is the result of increased vascular resistance in the portal circulation, increased portal venous blood flow, or both[2].

In veterinary medicine, where portal pressure is seldom measured directly, the diagnosis of portal hypertension often is inferred from identification of associated complications including multiple acquired portosystemic shunts, ascites and hepatic encephalopathy.

The portal vein, which receives blood from the intestines, spleen and stomach, can be compromised vascularly by a number of conditions such as:

Portal hypertension in dogs can lead to arteriovenous shunts either prehepatic, intraheptic or posthepatic (vena caval). Additional complications such as hepatic fibrosis and cirrhosis, ascites and hypersplenism can also develop[6]. Alterations in pancreatic perfusion, usually marked pancreatic vein distension, may result predispose to development of pancreatitis[7].

Clinical symptoms are often absent, but mental depression, lethargy, ascites and abdominal distension may be evident. The ascites, which is formed due to accumulation of a pure transudate abdominal effusion in the absence of significant hypoalbuminaemia is uncommon in dogs and characteristic of pre-sinusoidal portal hypertension[8].

Sublingual vein distension may be apparent on close inspection of the tongue[9].

Blood tests often reveal elevated levels of ammonia and other encephalotoxins related to hepatic encephalopathy.

Diagnosis usually requires ultrasonographic imaging or radiographic dye imaging (computed tomography angiography) to confirm the suspicion[10].

Treatment of portal hypertension primarily is aimed at controlling the complications of portal hypertension, especially ascites and hepatic encephalopathy and addressing the initiating cause[11].

References

  1. Nedredal GI et al (2011) Portal hypertension correlates with splenic stiffness as measured with MR elastography. J Magn Reson Imaging 34(1):79-87
  2. Sakamoto Y et al (2012) Three minimally invasive methods of measuring of portal vein pressure in healthy dogs. J Vet Med Sci 74(10):1299-1302
  3. Zwingenberger A (2009) CT diagnosis of portosystemic shunts. Vet Clin North Am Small Anim Pract 39(4):783-792
  4. Brown DL et al (2010) Congenital hepatic fibrosis in 5 dogs. Vet Pathol 47(1):102-107
  5. Izawa T et al (2011) Encapsulating peritoneal sclerosis associated with abnormal liver development in a young dog. J Vet Med Sci 73(5):697-700
  6. Lin D et al (2012) A novel canine model of portal vein stenosis plus thioacetamide administration-induced cirrhotic portal hypertension with hypersplenism. Cell Biochem Biophys 62(1):245-255
  7. Chen Y et al (2007) A sharp rise in portal vein pressure, not arterial constriction, initiates bile salt-induced pancreatic microcirculatory disturbance. Sheng Wu Yi Xue Gong Cheng Xue Za Zhi 24(6):1280-1285
  8. James FE et al (2008) Ascites due to pre-sinusoidal portal hypertension in dogs: a retrospective analysis of 17 cases. Aust Vet J 86(5):180-186
  9. Li BY et al (2009) Characteristics of sublingual vein and expressions of vascular endothelial growth factor and hypoxia-inducible factor 1alpha proteins in sublingual tissues of Beagle dogs with portal hypertension. Zhong Xi Yi Jie He Xue Bao 7(5):463-467
  10. Yoon H et al (2011) Contrast-enhanced computed tomography angiography and volume-rendered imaging for evaluation of cellophane banding in a dog with extrahepatic portosystemic shunt. J S Afr Vet Assoc 82(2):125-128
  11. Buob S et al (2011) Portal hypertension: pathophysiology, diagnosis, and treatment. J Vet Intern Med 25(2):169-186