Portal hypertension secondary to a right atrial tumor in a dog.

A German Shepherd Dog was examined because of ascites and hepatomegaly. The finding of proteinaceous ascitic fluid and hepatic histologic features of centrizonal sinusoidal congestion suggested hepatic venous outflow obstruction. Diagnostic tests eliminated heart failure from the differential diagnosis and thus indicated an obstruction between the right atrium and hepatic sinusoids. Vascular manometry and angiography established the site of the lesion in the right atrium and confirmed portal vein hypertension. Surgical exploration revealed an unresectable right atrial tumor occluding the caudal vena cava.