Chylothorax is the accumulation of lymph fluid, or chyle, within the pleural space. Chyle consists of lipids, proteins, and triglycerides. The list of possible underlying causes for chylothorax is long and includes: neoplasia (mediastinal or heart based masses), congenital abnormalities (tetraology of Fallot, tricuspid valve dysplasia, cor triatriatum dexter, double-chambered right ventricle, pericardioperitoneal diaphragmatic hernia, and thoracic duct anomalies), infectious diseases (heartworm disease, fungal disease), jugular vein or vena cava thrombosis, diaphragmatic hernia, and traumatic rupture of the thoracic duct.1 However, most commonly in dogs chylothorax is idiopathic, also known as thoracic lymphangectasia. Predisposed breeds include theAfghan hound and oriental cat breeds. Clinical signs are consistent with those resulting from any thoracic effusion and may include tachypnea, increased respiratory effort, cough or a restrictive breathing pattern. Less specific signs can include lethargy, anorexia, and weight loss, particularly in chronic cases. Although bloodwork changes are typically non-specific, lymphopenia, hyponatremia, and hyperkalemia can occur in chronic cases that have undergone multiple thoracocentesis.
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