3 causes: 

• presinusoidal (PV/Splenic V thrombosis)

• sinusoidal (cirrhosis, tumor, etc)

• post-sinusoidal (RHF, constrictive pericarditis, Budd-Chiari)

Imaging manifestations:

• Ascites

• Splenomegaly (>13 cm length,  >6 cm width)

• Varices (paraumbilical, paraesophageal, abdominal wall, perisplenic, perigastric, omental)

• Mesenteric edema (increased fat attenuation)

• Dilated mesenteric veins (PV > 13 mm)

• Slow/reverse flow in PV on US (<15 cm/sec; biphasic/completely reversed)

• Portal gastropathy, enteropathy, colopathy

• GB wall thickening

• Enlarged tortuous hepatic artery

• Portosystemic shunts