Budd-Chiari syndrome (BCS) is a rare disorder caused by obstruction of hepatic venous outflow. Symptoms depend on the speed and extent of blockage; they range from none to fulminant hepatic failure. Three clinical patterns are recognised:

1. Acute (days–weeks)
   Sudden, severe right-upper-quadrant pain, rapidly accumulating ascites, tender hepatomegaly, nausea and vomiting. Jaundice, high fever and early hepatic encephalopathy may appear if massive necrosis develops.
2. Sub-acute (weeks–3 months)
   Moderate ascites, gradual abdominal distension, low-grade fever, fatigue and dull hepatic pain; collaterals begin to form so jaundice is often mild or absent.
3. Chronic (>3 months)
   Persistent ascites, non-tender hepatomegaly, splenomegaly, lower-limb oedema and visible abdominal wall collaterals. Portal hypertension leads to oesophageal varices that can bleed massively. About half of patients develop renal impairment; 15–20 % are virtually asymptomatic owing to extensive venous collaterals.

Alarm features that suggest advanced disease or acute decompensation include confusion (hepatic encephalopathy), rapid liver enlargement with intractable ascites, haematemesis from variceal rupture, and oliguria indicating hepatorenal syndrome. Early recognition is essential because untreated BCS has a 3-year mortality >90 %.