Portal hypertension develops secondarily to partial or complete obstruction of the portal blood flow. The obstruction may be one of two types, intrahepatic or extrahepatic, or a combination of both. The site of the portal block, whether intrahepatic or extrahepatic, can usually be determined by certain tests of hepatic function. According to Whipple,1 a high retention of sulfobromophthalein sodium in the blood thirty minutes after intravenous injection, a positive reaction to the hippuric acid test, a reversal of the albumin-globulin ratio, a positive reaction to the cephalin flocculation test, all point to the diagnosis of cirrhosis of the liver with intrahepatic portal block. If these reactions are negative, one can assume that the block is extrahepatic.
Intrahepatic block may be caused by portal cirrhosis of the Laennec type or by thrombosis of the hepatic veins, the so-called Chiari syndrome. The extrahepatic block may be congenital, the result of thrombosis