Li-10-5PORTAL HYPERTENSION by Dr. E. ORFEI
It is: "increase of portal vein pressure". No less than one and a half liter of blood circulates through the liver per minute, 100 liters per hour and an astounding volume of 2000 liters (2 tons) per day. Two thirds of this blood are supplied by the portal vein and one third by the hepatic artery. The normal portal vein pressure is 5-10mm of mercury. During surgery, manometric pressures above 30 mm of saline in the portal vein and above 17mm of Hg in the splenic vein, indicate portal hypertension.
2- Anatomy of portal venous system.
The portal vein system drains blood from the absorptive segment of the gastro- intestinal tract, namely from the lower esophagus to the rectum for the purpose of subjecting to the liver every compound that has been ingested with the diet and having it chemically manipulated and properly transformed by the liver to be utilized by all other organs. One of the main functions of the liver is that of neutralizing toxic compounds that we normally take up with our foods. Various groups of veins from the lower esophagus, stomach, small intestine, spleen, pancreas, large intestine and rectum merge together to form the big portal vein at the hilus of the liver.
From the lower esophagus and upper stomach the submucosal veins (the intrinsic circulation) perforate the muscularis propria, reach the external surface (extrinsic circulation) and form a periesophageal plexus which drains into the left gastric and splenic veins via short gastro-splenic veins (vasa breviora). In portal hypertension the portal blood flows back to the splenic vein, spleen, gastro-splenic veins, extrinsic gastro-esophageal veins, intrinsic esophageal veins which become varicose and drain upward through the thoracic and cervical esophagus into the azygos and inferior thyroid veins and into the systemic veins.
From the spleen the blood drains into the splenic vein which meets with the superior mesenteric vein to form the main portal vein. The blood from the small intestine and from the right and transverse colon drains into the superior mesenteric vein. The blood from pancreas drains into the splenic vein. The blood from left colon and rectum drains into the inferior mesenteric vein which enters the middle third of the splenic vein. Back flow in this vein produces hemorrhoids.
3-Causes of portal hypertension.
The site of vascular resistance determines the cause of portal hypertension.
1- Supra-hepatic block: Budd- Chiari syndrome. Thrombosis of suprahepatic segment of inferior vena cava. Veno-occlusive disease.
2- Intra-hepatic block: Perisinusoidal block: lesions of portal venules: cirrhosis ,schistosomiasis etc. Sinusoidal block at the level of lobular sinusoids. Mixed sinusoidal and perisinusoidal blocks.
3- Infra-hepatic block: Occlusion of portal vein or splenic vein or both. It is especially frequent in children due to portal vein thrombosis following umbilical sepsis.
1- Idiopathic. Rare in United States but more frequent in England, India and Japan. It corresponds to the" Banti Syndrome" of Italy and" non cirrhotic portal fibrosis", "portal vein sclerosis" of Great Britain," tropical splenomegaly" and "Bengal splenomegaly" of India," obliterative portal venopathy" of other authors. In this condition there is no evident anatomical cause for the portal hypertension, which nonetheless produces serious complications such as splenomegaly, hypersplenism and ruptured esophageal varices. Histologically one might see fibrosis of some portal tracts; replacement of portal veins with small multiple venous channels and sometimes perisinusoidal fibrosis under electron microscopy. It is treated with porto-systemic shunting and it has better course than portal hypertension due to cirrhosis.
4-Clinical manifestations of portal hypertension.
Variceal bleeding. It occurs frequently in cirrhotics mostly from their esophageal varices. This is a serious complication. The bleeding will cause acute deterioration of liver functions and mortality. Also rebleeding within few days aggravates the prognosis. Bleeding in chronic liver diseases will cause:
-aspiration pneumonia due to impaired consciousness and episodes of hematemesis and endoscopy. It could be prevented with a nasogastric tube and orotracheal intubation.
-hepatic encephalopathy due to resorption of gastric blood which should be evacuated.
-infections by enteric organisms which may cause peritonitis.
-renal /electrolyte imbalance with renal failure.
-portal hypertensive gastropathy causing petechial hemorrhages , gastric erosions and gastric bleeding.
-liver failure and death.
Ascites develops in conditions blocking the supra-hepatic (hepatic veins) and intra-hepatic portal circulation (hepatic sinusoids) and very rarely or not at all in those conditions blocking the infra-hepatic circulation (portal vein). It will therefore develop in Budd- Chiari syndrome, in veno-occlusive disease, right heart failure, cirrhosis, acute hepatitis, perisinusoidal fibrosis but not in portal or splenic vein thrombosis. The reason for this difference is in the different structure of the hepatic sinusoids compared with other capillaries. The hepatic sinusoids at difference with capillaries do not have basement membranes but are lined by endothelial cell which have a very wide flat cytoplasm which is perforated by numerous "fenestrae"measuring 100-500nm in diameter which admit the passage of plasma with its macromolecules including plasma proteins into the space of Disse. Most of the he fluid in the Disseís space enters the lymph vessels of the portal fields and goes to the hilus of the liver and from there to the capsule of the liver and to the thoracic duct via periaortic plexus. A small quantity goes to the chest with the lymphatic vessels surrounding the hepatic veins. Lymph produced by the liver represents the major part, 95 %, of thoracic duct lymph and it is very reach in proteins, 40-50 grams per liter. The thoracic duct that drains lymph from liver, stomach, pancreas , intestine, originates from the upper pole of the cisterna chyli at the level of the inferior border of the 12th thoracic vertebra. It ascends into the posterior mediastinum close to the aorta and azygos vein and beyond the arch of the aorta curves toward left and drains into the veins of the left side of the neck, most frequently into the left subclavian or left internal jugular vein. The lymph flow is about one liter per day.
An increase of sinusoidal pressure causes an increase of lymph flow into the Disse spaces and lymphatics of the liver. Moreover the sinusoidal blood has the same oncotic pressure as the lymph fluid and cannot
counteract the mechanical pressure. More lymph circulates in the glissonian capsule. Some is released into the abdominal cavity. Thatís the source of the ascites. Every millimeter of increase of portal pressure will cause 60 % more lymph exudation from the liver capsule. If one encloses the liver in a plastic bag and produces portal hypertension, ascitic fluid will collect only in the bag and not in the abdominal cavity. Ascitic fluid appears to be continuously reabsorbed by the lymphatics of the undersurface of the diaphragm.
Renal failure without anatomical alteration of the kidneys is seen frequently in severe liver diseases such as alcoholic cirrhosis with ascites. The clinical signs consist of oliguria, sodium retention, potassium loss followed by progressive azotemia and coma. The prognosis is very grave. The disturbance is purely functional. The kidneys are anatomically intact and can be used for transplantation. The causes are unknown. Renin-angiotensin-aldosterone system, sympathetic nervous system, antidiuretic hormone , arachidonic acid, natriuretic factor synthesized by atrial myocytes and natriuretic hormone probably synthesized in the hypothalamus have been taken into consideration.
Atrial Natriuretic Factor (ANF) is stored as peptide precursor by atrial myocytes in specific granules and is released into the circulation under atrial distension. It causes acute fall of blood pressure, increase of glomerular filtration rate, increase of urine volume and sodium excretion and suppression of renin aldosterone level. There is inhibition of sodium reabsorption in the medullary collecting tubules. ANF is increased in cirrhotics.
Natriuretic Hormone is a digitalis -like compound. It increases sodium excretion and arterial pressure.
Definition:" slenomegaly with reduction of one or more cellular elements of the blood, with normal or hypercellular bone marrow and correction of the blood cytopenia with splenectomy".
Besides the filtering and immunologic functions, the spleen is a reservoir for blood cells. It stores about 30% platelets, about 30% of granulocytes and only 3-5 % of red cells. These elements can be released under adrenaline stimulation.
Causes of hypersplenism
1)Congestive splenomegaly. Right heart failure, 11-50% of portal hypertension cases.
2) Infections involving the spleen. Viral, bacterial, fungal, protozoal
3)Splenomegaly due to storage disorders, or cellular infiltrations such as lympfoma, sarcoidosis extramedullary hematopoiesis, or depostion of other material such as amyloidosis.
Symptoms of hypersplenism.
1) Anemia is mild and mostly due to increased sequestration of red cell in the spleen.
2) Tthrombocytopenia due to increased storage of platelet pool in the enlarged spleen. The platelet count is inversely related to the size of the spleen.
3) Granulocytopenia is usually mild. It is again due to sequestered white cells in the enlarged spleen, more than 30%. Granulocytopenia in hypersplenism seldom represents a problem for the patients in fighting infections because they are able to mobilize more required white cells from the bone marrow.
5-Treatment of portal hypertension.
Beta blockers-Sclerotherapy-Shunt surgery-Liver transplantation.