TREATMENT :  A right flank laparotomy was performed in order to exteriorize the cecum and allow injection of new methylene blue into the ileocecal lymph node for identification of the thoracic duct. A right thoracotomy was performed at T10-11 for ligation of the thoracic duct. Histopathologic analysis of pleural tissue revealed mild proliferative fibrinosuppurative pleuritis with no infectious agents detected.

OUTCOME:  Resolution of dyspnea and exercise intolerance occurred postoperatively. Postoperative radiographs are shown above. The patient was maintained on a low fat diet and low dose furosemide.

DISCUSSION:  Chylothorax is a result of increased lymphatic flow due to increased formation and/or decreased lymphatic drainage into the venous system secondary to high venous pressures. In most animals, an etiology is not identified, however conditions such as mediastinal masses, cardiac disease, thrombi, or congenital thoracic duct abnormalities can cause chylothorax. True chylous fluid has a higher triglyceride concentration than serum.

Medical management involves fluid drainage via repetitive thoracocentesis or thoracostomy tubes, combined with a low fat diet that may improve the ability to resorb thoracic cavity fluid. Medium chain triglycerides actually do not bypass the thoracic duct in dogs, therefore they may not improve medical management. Benzopyrone drugs (Rutin) decrease pleural effusion in 25% of chylothorax cases.

Surgery is indicated if medical management is not successful. If fibrosing pleuritis has developed, prognosis is grave. The surgical procedure entails mesenteric lymphangiography for thoracic duct identification, followed by duct ligation. Thoracostomy tubes are placed temporarily postoperatively. If successful, surgery will result in complete resolution of pleural effusion.