What can cause an enlarged superior mesenteric vein in a 7 yr old child?

Need investigation: Enlarged superior mesenteric vein ( possibly other veins of portal system ) need investigation what is causing obstruction to inflow of blood into liver , from cirrhosis , congenital vascular webs , to budd chiari syn. Where hepatic veins obstructed , please discuss with your doctor for early intervention and cure..

Enlarged SMV: Blockage upstream can cause enlargement like an issues at the level of the liver or portal vein.