Abstract/Introduction
Chylothorax is a rare and serious condition reported in small animal and human medicine resulting from the accumulation of chyle within the thoracic cavity. Chyle is a triglyceride and chylomicron rich lymphatic fluid derived from the emulsification of dietary long chain fatty acids and secreted into the lymphatic system from the intestinal mucosal cells.3 It is typically opaque with a total protein of 2.5–4.5 g/dl and has a predominantly lymphocytic nucleated cell count of 400–10,000 cells/dl. Biochemically, chyle has a triglyceride level greater than that of the serum, has a cholesterol level less than the serum, and generally has an alkaline pH.3
Chylothorax is thought to be due to either direct trauma resulting in rupture of the thoracic duct or disease processes that results in obstruction of the thoracic duct or prevents lymph flow to the venous circulation.1 Identified disease processes include neoplasia, granulomas, thrombosis/obstruction of the vena cava, right-sided heart failure, mediastinal masses, lung lobe torsion, foreign bodies, lymphatic abnormalities, congenital thoracic duct abnormalities, constrictive pericarditis and heartworm infection.1 Diagnostic evaluation to determine the underlying cause of the chylous effusion includes radiography, ultrasonography, fluid analysis, echocardiography and serologic testing. If an underlying disease process is identified, then treatment is directed toward resolving it. However, an underlying disease process is often not identified, and the condition is considered idiopathic.1
Medical management of idiopathic chylothorax, including palliative thoracocentesis, dietary manipulation, and pharmaceutical control, has met with mixed results. Resolution rates in medically managed cases has ranged from 20–75%.1,4,12 Thoracocentesis may alleviate acute episodes of respiratory distress associated with accumulation of pleural fluid, however, frequent or long term use of thoracocentesis has been shown to result in hypoproteinemia, hyponatremia, hyperkalemia, lymphopenia and malnutrition.12,13 Additionally, chylous effusions are irritating to the pleura and can result in a fibrosing pleuritis resulting in fluid pockets.1,3,12 Low fat diets and diets rich in medium chain triglycerides have also been recommended in order to decrease production of chyle.1 Rutin, a bioflavenol benzopyrone compound extracted from the Brazilian Fava tree, has been used in both human and veterinary medicine for the treatment of chylothorax with some success.6,10,12 Rutin is thought to have anti-oxidant, anti-inflammatory, antithrombotic, cytoprotective, vasoprotective, and immune modulatory properties.10,12 Orlistat and octreotide have each been reported in human medicine for the treatment of chylous effusion.2,8 Orlistat is a reversible inhibitor of gastric and pancreatic lipases which is thought to decrease the amount of triglycerides available for intestinal uptake and therefore decrease the production of chyle.2 Octreotide is a long-acting somatostatin analog that acts to decrease lymph fluid excretion and reduce lymphatic flow, thereby reducing chyle production.8
Surgical management of chylothorax may include pleurodesis, thoracic duct ligation, cisterna chyli ablation with thoracic duct ligation, pleuroperitoneal shunt, thoracic omentalization and pericardectomy.1,7 Various chemical sclerosing agents, such as tetracycline and talc, have been used to induce pleurodesis. Caudal thoracic duct ligation (TDL) has been the surgical method of choice, however up to a 60% recurrence rate has been seen in some studies. More recent studies have achieved better results by combining TDL with either cisterna chyli ablation or pericardectomy.5,7,11 One other technique described uses an active pleuroperitoneal shunt device. This device has an afferent end placed in the thoracic cavity, a pump mechanism that is placed under the thoracic musculature, and an efferent end placed in the abdominal cavity.3 This technique has size limitations and has been reported to fail due to obstruction.3
The incidence of chylothorax in non-domestic species is unknown. There is one case report of idiopathic chylothorax in a black and white ruffed lemur that responded favorably to medical treatment with rutin.9 As described above, both medical and surgical treatments of chylothorax are available, but the results are often disappointing and the outcome can be poor. Two cases that were seen recently at the University of Florida Veterinary Medical Center (UFVMC) are discussed below.
Case Reports
Case 1
A 1.5-year-old intact male clouded leopard (Neofelis nebulosa) was referred to the UFVMC for treatment of chylothorax. The leopard had a 2-week history of progressive dyspnea and had been placed on oral antibiotics (cephalexin 500 mg PO BID) and rutin (1000 mg PO BID) by the referring veterinarian prior to admission. Whole body radiographs, abdominal and thoracic ultrasonography, echocardiography, thoracocentesis with fluid cytology, CBC and blood chemistry profile were performed upon admission. Radiographic, ultrasonographic and serologic testing were consistent with a diagnosis of idiopathic chylothorax. Due to the severity of his clinical signs, thoracic duct ligation with cisterna chyli ablation was performed. Follow-up radiographs over the next 10 days revealed recurrence of pleural effusion and progression of restrictive pleuritis. Thoracocentesis was performed as needed for management of dyspnea. Due to the lack of clinical response to the initial surgery and severe nature of his clinical signs, a second surgery was performed 7 days following the initial surgery. At this time, the initial ablation and ligation was evaluated and underwent revision. The pericardium was found to be thickened and a pericardiectomy was performed. Multiple fibrous adhesions were noted throughout the thoracic cavity and the right cranial and middle lung lobes were observed to be atelectic and fibrosed and were subsequently removed. Chest tubes were placed for management of the effusion. Over the next few days, repeated thoracocentesis contributed to the development of hypoproteinemia which did not resolve despite treatment with intravenous human albumin. The animal was euthanatized 7 days after the second surgery due to its declining condition and development of neurologic signs consistent with hypoxia. Gross postmortem and histologic examination did not identify an underlying or inciting cause for his disease.
Case 2
A 6-year-old intact male, privately-owned ring-tailed lemur (Lemur catta) presented for evaluation of a 4-day history of respiratory distress and progressive anorexia. Radiographs, thoracocentesis with fluid cytology, CBC, blood chemistry, thoracic and abdominal ultrasound, echocardiography and serology for heartworm and toxoplasmosis were performed. Test results were consistent with a diagnosis of idiopathic chylothorax. Medical and surgical options were discussed with the owner but were declined and the animal was discharged. He returned 1 month later for recurrence of dyspnea and weakness. Palliative thoracocentesis was performed and treatment options were again discussed with the owner but were declined. He returned again in 3 months with recurrent signs. Survey radiographs and thoracocentesis were performed and findings were consistent with his previous visits. At this time, he was started on 250 mg of rutin (GNC Rutin 500 mg PO TID). At the time of this report, 3 months from his last visit, his condition remains unchanged according to his owner.
Literature Cited
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