This paper describes the clinical, ultrasonographic, radiographic and postmortem findings in 12 cows with thrombosis of the caudal vena cava. The principal clinical signs were chronic bronchopneumonia and fever in 11 cows; one cow had epistaxis and one cow bled from the mouth; eight cows had anaemia and leucocytosis, and the clotting time for the glutaraldehyde test was markedly decreased in all the cows; in nine of the cows the activity of γ-glutamyltransferase was high, suggesting chronic hepatic congestion. The most important ultrasonographic finding was congestion of the caudal vena cava attributable to thrombosis of the vein. In all the cows the caudal vena cava was round to oval on cross-section, rather than the normal triangular shape. The hepatic, splenic and portal veins were dilated in five, three and one cow, respectively. The results of radiography and endoscopy supported a diagnosis of bronchopneumonia, but there were radiographic changes in the diaphragmatic lung lobes that supported a diagnosis of vena caval disease in only four cows. Postmortem there was a thrombosis of the caudal vena cava in all the cows, and the thrombi were located in the thoracic, subphrenic and abdominal part of the caudal vena cava at the level of the liver in four, one and seven cows, respectively. In three cows, the thrombus was situated where a hepatic abscess had broken into the caudal vena cava, and in one cow it was at the site of a diaphragmatic abscess. In another cow, there was a fistula between the major bronchus of the right diaphragmatic lung lobe and the caudal vena cava where the thrombus was situated. Three cows had liver abscesses that had not broken into the caudal vena cava. There was severe bronchopneumonia in 11 of the cows, some of which also had multiple pulmonary abscesses.
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