A 8 year old girl from Bihar presented with three episodes of massive hematemesis and melena. There is no history of jaundice. On examination, she had a large spleen, non-palpable liver and mild ascites. Poal vein was not visualised on ultrasonography. Liver function tests were normal and endoscopy revealed esophageal varices. The most likely diagnosis is:

This is the classical presentation of exahepatic poal vein obstruction (EHPVO). The patient is usually a child presenting with variceal bleed, without any liver dysfunction and significant ascites. Poal vein is not visualised in ultrasonography and is replaced by collaterals. There will be significant splenomegly. Absence of fever and hepatomegaly rules out kala azar. Ref: Sleisenger and Fordtran's Gastrointestinal and Liver Disease 9th edition: chapter 83.