Veterinary Medicine - September 2008 - (Page 500)

A challenging case PEER-REVIEWED 3A & 3B. Lateral and ventrodorsal thoracic radiographs obtained 20 months after the cat’s thoracic duct ligation and partial pericardiectomy. Possible scant effusion is seen on the lateral view; no abnormalities were identiﬁed on the ventrodorsal view. DISCUSSION Chylothorax is caused by abnormal ow or pressure in the thoracic duct that leads to thoracic lymphangiectasia—a condition involving exudation of chyle from intact but dilated thoracic lymphatic vessels. Lymphatic vessel dilatation may occur in response to increased lymphatic ow caused by increased hepatic lymph production, decreased lymphatic drainage into the venous system as a result of high venous pressures, or both factors acting simultaneously. Possible underlying causes of chylothorax include heart disease (cardiomyopathy, pericardial effusion, heartworm disease, tetralogy of Fallot, tricuspid dysplasia, or cor triatriatum dexter [triatrial heart, or two-chambered right atrium]), cranial mediastinal masses (lymphoma or thymoma), venous thrombi, fungal granulomas, and congenital thoracic duct abnormalities.1-3 In this case, our primary differential diagnoses were idiopathic chylothorax and thoracic lymphangiectasia secondary to cranial vena cava compression by the thymic cyst. is unknown, but it can occur subsequent to prolonged contact of the pleura with an exudative effusion, such as chyle or hemorrhage. Fibrosing pleuritis can be dif cult to diagnose without a thoracotomy. It should be suspected if, after removing the pleural effusion, thoracic radiographs reveal that the lungs do not appear to be completely expanded or if dyspnea remains even though a patient’s effusion is minimal.1-3 Thickened pericardium. Cats with chylothorax often have either a thickened pericardium or tissue overlying the pericardium, likely due to chronic irritation by chyle. This thickening may raise systemic venous pressure, which might impede chyle drainage into the cranial vena cava and increase lymphatic ow in the thoracic duct. A pericardiectomy may be indicated to decrease right-sided venous pressures in a cat with a thickened or abnormal pericardium or overlying tissue. Normal venous pressures should permit normal routing of lymphatic ow. In a recent report, one dog and one cat had resolution of chylothorax with pericardiectomy alone.1,2 management, which includes feeding a low-fat diet, performing thoracentesis as needed, and administering a benzopyrone, is often unsuccessful. A low-fat diet potentially lowers the amount of fat in the effusion, which allows the uid to be resorbed more effectively from the thoracic cavity. Benzopyrone drugs, such as rutin, have been used to treat lymphedema in people for years.1-3 The exact mechanism of action of rutin, which is a bio avonoid extract from plants, is unknown; however, rutin may reduce leakage from blood vessels, increase proteolysis and removal of protein from tissues, and enhance macrophage phagocytosis of chyle.4 Unfortunately, evaluating the ef cacy of rutin in cats has been dif cult because cats can experience spontaneous resolution of idiopathic chylothorax.5 Rutin can be obtained at a vitamin store, and the dosage is 50 to 100 mg/kg orally every eight hours. Complications of chylothorax Fibrosing pleuritis. When evaluating cats with chylothorax, it is important to consider whether brosing pleuritis is present. The underlying cause of brosing pleuritis Surgical treatment of chylothorax Surgery is an alternative treatment for chylothorax. Thoracic duct ligation and partial pericardiectomy are recommended. In a recent report of cats with idiopathic chylothorax, eight of 10 cats had resolution of chylothorax Medical treatment of idiopathic chylothorax Idiopathic chylothorax is a serious condition that is dif cult to treat. Medical 500 September 2008 VETERINARY MEDICINE

Table of Contents Feed for the Digital Edition of Veterinary Medicine - September 2008

Veterinary Medicine - September 2008 Contents Leading Off Practical Matters Idea Exchange A Challengin Case: Thymic Cyst and Recurrent Chylothorax in a Cat 10 Life-Threatening Behavior Myths CE Form Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - September 2008

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