Pleural effusion resulting from malignant hepatoblastoma in a horse.

Pleural effusion, secondary to a metastasis from a malignant hepatoblastoma, was diagnosed in a 3-year-old Appaloosa gelding. Severe hemorrhagic transudate in both pleural cavities resulted in acute onset of labored breathing, tachypnea, tachycardia, and jugular vein pulsation. Results of ultrasonography and radiography of the ventral lung field and cranial portion of the abdomen initially were nondiagnostic, as were results of cytologic examination of peritoneal fluid and tracheal wash specimens. Moderately high serum gamma-glutamyl transferase and alkaline phosphatase activities, despite normal hepatocyte-specific enzyme (sorbital dehydrogenase) activity, were indicative of biliary stasis without hepatocyte destruction. The horse was euthanatized. Necropsy revealed a 47-kg hepatoblastoma, with metastases in the lungs and intestines.