This report describes the case of an 11-year-old castrated male Shih Tzu who developed chylothorax three years following implantation of a transvenous pacemaker. Imaging demonstrated one definitive obstruction in the cranial vena cava and 3 additional suspected filling abnormalities within both external jugular veins, brachiocephalic veins and cranial vena cava. A thrombus was visualized in the cranial vena cava via transesophageal echocardiography. Thoracic duct ligation and cisterna chyli ablation were performed, with a resultant change in the nature of the fluid from chylous to a modified transudate. Repeat angiography and computed tomography three months later demonstrated a stenosis within the cranial vena cava. Balloon angioplasty was attempted, however it was unsuccessful in decreasing pleural effusion. Palliative thoracocentesis was continued until the patient developed a lung lobe torsion, at which time euthanasia was elected. Necropsy confirmed cranial vena caval syndrome secondary to transvenous pacemaker implantation induced fibrous proliferation within the vessel lumen.
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