A 7 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. Portal vein was not visualized on ultrasonography. Liver function tests were normal and endoscopy revealed esophageal varices. The most likely diagnosis is –
Differentiation between Extrahepatic and Hepatic / Post hepatic portal hypertension 

Post sinusoidal and hepatic causes of portal hypertension will have
evidence of Liver parenchymal damage / deranged LFT (jaundice)
a dilated portal vein on ultrasonography
Extrahepatic presinusoidal obstruction will not have any effect on the Liver and hence there will be no evidence of hepatocellular damage.
No jaundice / No raised deranged LFT

Also non visualization of portal vein is a characteristic of portal vein thrombosis, an Extrahepatic cause.

Esophageal varices and splenomegaly are a manifestation of portal hypertension and will be present in all the above sites of obstruction.
Kala azar with portal hypertension
Portal hypertension of unknown etiology
Chronic liver disease with portal hypertension
Portal hypertension due to extrahepatic obstruction