Gastric adenocarcinoma in a horse with portal vein metastasis and thrombosis: a novel cause of hepatic encephalopathy.

A 17-year-old Quarter horse mare was referred to Cornell University for postmortem examination after 72 hours of encephalopathy that consisted of depression, mania, and blindness. A plasma sample and cerebral spinal fluid demonstrated hyperammonemia. Gross necropsy examination findings included the following: mild icterus, a transmural mass in the glandular portion of the gastric fundus, multiple masses throughout the liver, and a large tumor thrombus in the portal vein. Microscopically, the gastric mass, hepatic masses, and portal vein thrombus were composed of similar neoplastic epithelial cells that formed variably sized acini and branching cords separated by a dense desmoplastic stroma. Throughout the cerebral frontal cortex were numerous Alzheimer type II astrocytes. Hepatic encephalopathy was caused by gastric adenocarcinoma, with metastasis to the liver and the portal vein. The clinical and pathologic lesions from this unique case, as well as hyperammonemia and portal vein thrombosis in the pathogenesis of hepatic encephalopathy, are discussed.