Managing canine chylothorax

Chylothorax is the accumulation of lymphatic fluid (also known as chyle) within the thoracic cavity.1 Because of the rib cage's rigid confines, fluid accumulation within the thoracic cavity is not well tolerated and results in respiratory signs, such as increased respiratory rate and effort, after reaching a critical volume. This volume depends on the rate at which it accumulates, the individual dog’s size, respiratory adherence, and overall respiratory function.2

While fluid gradually builds up in the thoracic cavity over time, dogs are often presented on an emergency basis, as the fluid hits the critical volume that results in a respiratory crisis. Once the respiratory system is affected, fluid removal via thoracocentesis is required to improve respiratory function.

To make a chylothorax diagnosis, a diagnostic thoracocentesis is required. This is often performed in conjunction with a therapeutic thoracocentesis to improve the dog’s respiratory function. Thoracic fluid triglycerides will be increased relative to the dog’s serum levels, whereas fluid cholesterol will be reduced relative to the dog’s serum levels.1 It is important that the pleural fluid values are compared to a concurrently collected serum sample and not historical data. Cytological evaluation is important to rule out other sources of pleural effusion, but it can have various cell types present with a chylothorax diagnosis.1

Canine chylothorax is most commonly considered to be idiopathic in nature, but it can also be caused by any disease process that results in a disruption of normal lymphatic flow.1 Primary causes resulting in secondary chylothorax have included cranial mediastinal mass effects, primary cardiac disease, pericardial effusion, trauma, and lung lobe torsions.1-3 When investigating chylothorax, it is important that all possible causes are ruled out before making the presumptive diagnosis of idiopathic chylothorax, as treatments will differ based on the primary cause. When chylothorax is the secondary result of another disease process, the primary disease process must first be addressed before considering direct interventions for treating the chylothorax itself.

Diagnostic evaluation may include thoracic and abdominal imaging to evaluate intrathoracic and intra-abdominal structures, echocardiography to evaluate for primary cardiac disease and pericardial effusion, and a CT lymphangiogram (CTLA) to rule out compressive lesions of the lymphatic and venous systems.1,2,4-7 If advanced imaging is not immediately available, thoracic and abdominal radiography and/or ultrasonography may be used to rule out space-occupying lesions, with CT imaging being reserved for dogs more likely to have idiopathic chylothorax and a desire for surgical interventions.2

Following the diagnosis of idiopathic canine chylothorax, treatment options may include medical or surgical therapies.

Medical management may include the following8:

• Intermittent therapeutic thoracocenteses
• Low-fat diets
• Medications such as octreotide

Therapeutic thoracocenteses are used as needed to remove the buildup of chylous effusion within the thorax to improve clinical respiratory signs. Overall success has been reported in only 26% of animals with idiopathic chylothorax, likely because of the progressive inflammatory changes within the thoracic cavity resulting in difficulty with complete pleural evacuation over time, as well as the development of pleural fibrosis.2,8

Low-fat diets have been used to reduce the overall production of chyle, thus reducing the flow of chyle through the lymphatic system, which may reduce the volume of chylous effusion buildup and allow time for defects in the thoracic duct to heal. Evidence in dogs suggests that the lipid content of chyle can be reduced with this treatment, but the flow through the thoracic duct is not directly reduced.8

Octreotide, a somatostatin analog, has been used to reduce the flow of chyle through the thoracic duct. This has been used with success in human patients who have chylous effusion secondary to trauma to the thoracic duct but has been less successful in dogs with idiopathic chylothorax.8

Surgical interventions may include the following1-3:

1. Thoracic duct ligation
2. Subtotal pericardiectomy
3. Cisterna chyli ablation
4. PleuralPort placement

Thoracic duct ligation is ideally planned based on CTLA, as this imaging can best identify the anatomic variations of an individual thoracic duct.4-7 The duct can be accessed through open or minimally invasive approaches and is ligated with suture or hemoclips as far caudally in the thoracic cavity as possible to ensure all contributing branches are obstructed. The forward flow of chyle is prevented in the short term while the body develops new lymphaticovenous connections to restore chyle flow.9,10 Intraoperative use of near-infrared fluorescence (NIRF) imaging can be used to confirm complete occlusion of the thoracic duct.11

Subtotal pericardiectomy can also be performed via open or minimally invasive approaches. Removal of the pericardium is aimed at reducing the systemic venous pressure as chyle is being returned to the heart via the cranial vena cava. Increased pressure from primary cardiac disease and/or a constrictive pericardium can result in back pressures within the vena cava and lymphatic extravasation into the thoracic cavity. Determining whether constrictive pericarditis is present can be challenging and invasive;12,13 thus, combining a subtotal pericardiectomy with a thoracic duct ligation has been reported without a definitive diagnosis of constrictive pericarditis.4,10,14-16

Cisterna chyli ablation can be performed through an open or minimally invasive approach. This procedure aims to reduce the forward flow of lymphatic fluid into the thoracic duct by opening the cisterna chyli and allowing lymphatic fluid to drain into the abdominal cavity.9 When combined with thoracic duct ligation, this can reduce the pressure of any forward flow of chyle on the thoracic duct ligation and allow time for the new lymphaticovenous connections to be developed. These new connections may be made within the abdominal cavity, reducing the risk of further chyle leakage within the thoracic cavity.9

PleuralPort placement is a long-term solution for thoracic drainage of chylous (or other) effusion.2,17,18 A fenestrated catheter is surgically placed within a hemithorax and is connected to a drainage port that is placed within the subcutaneous space on the dorsolateral aspect of the ipsilateral hemithorax. The port can be palpated externally and accessed percutaneously with a Huber needle to intermittently drain the thoracic cavity without requiring repeated puncturing of the pleura for thoracocentesis.2,17 Unilateral or bilateral PleuralPorts can be placed based on the volume of effusion and accessibility of the fluid. A PleuralPort is often considered when surgical management has failed, but it can also be considered in place of surgical intervention.

Many combinations of surgical procedures have been reported.3 The most reported combinations include thoracic duct ligation with concurrent subtotal pericardiectomy and thoracic duct ligation with concurrent cisterna chyli ablation.3,4,9,10,12,14-16 A combination of thoracic duct ligation, subtotal pericardiectomy, and cisterna chyli ablation has also been reported in veterinary literature.19

Takeaway

Medical management has a limited success rate for idiopathic chylothorax overall.8 Surgical interventions have a variety of reported success rates, with marked improvement in success being noted with the more recent use of preoperative (CTLA) and intraoperative (NIRF) imaging techniques.3,4,9,10,12,14-16 With these improved imaging techniques, the previously reported need to combine surgical techniques has recently been challenged.12 Although there are many approaches to surgically managing idiopathic canine chylothorax, the specific approach will be made based on the diagnostic information collected from an individual dog, along with the skill set, knowledge, and preference of the surgical care team.

Katie Hoddinott, DVM, DVSc, BSc, DACVS-SA, is a native of Nova Scotia, Canada. She graduated with her DVM from the Atlantic Veterinary College, University of Prince Edward Island, in 2012. She then completed 2 internships and a surgery residency at the Ontario Veterinary College, University of Guelph. She became a diplomat of the American College of Veterinary Surgeons – Small Animal in 2019. Hoddinott is currently working at the Atlantic Veterinary College as an assistant professor in small-animal surgery, where she enjoys teaching undergraduate veterinary students, interns, and residents. Her professional interests lie mainly in surgical oncology and minimally invasive soft tissue surgery. Her current research focuses on advances in clinical teaching for surgery residents and surgical site infections.

REFERENCES

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