Comparison of Thoracic Duct Embolization versus Thoracic Duct Ligation for Treatment of Idiopathic Chylothorax in Dogs

Enrollment Status: Currently Enrolling

Inclusion criteria: Dogs greater than 10 kilograms (22.2 lbs) and less than 5 years of age diagnosed with idiopathic chylothorax.

Exclusion criteria: Dogs with an identified cause for chylothorax (e.g. cardiac disease, lung lobe torsion, neoplasia) or that have had prior surgery for treatment of chylothorax are not eligible. Each dog will undergo a complete physical exam, screening blood work, analysis of the fluid in the chest, ultrasound evaluation of the heart, and CT lymphangiogram (under general anesthesia), prior to inclusion in this study to determine a diagnosis of idiopathic chylothorax. This is the standard diagnostic work-up performed prior to surgery.

Treatment: Following inclusion, your dog will be randomly assigned to one of two groups. One group will undergo thoracoscopic thoracic duct ligation (TDL) and the other group will undergo thoracic duct embolization (TDE). The primary investigator (Dr. Brad Case) has worked with chylothorax in several prior clinical trials, and has vast experience with treatment of chylothorax including both embolization and ligation techniques

Your pet will be placed under general anesthesia for their procedure. For dogs in the TDL group, three very small (5-10mm) incisions will be made near the ribs for insertion of special surgical instruments (thoracoscopic instruments) to allow the surgeon to see inside the chest cavity and ligate the thoracic duct branches. The thoracic duct will be visualized using a dye (indocyanine green and/or methylene blue) injected prior to surgery. For dogs in the TDE group, a single small (2-3 cm) incision will be made in the abdomen to locate a lymph node and inject contrast agent to help visualize the lymphatic vessels. The lymphatic vessel will be catheterized and a false clot (glue embolus) will be injected to block the thoracic duct. A thoracostomy (chest) tube will be placed to monitor post-operative fluid production in all patients, as is standard of care for chylothorax patients.

All enrolled dogs will be hospitalized post-operatively in the intensive care unit for a minimum of 48 hours for monitoring. The thoracostomy tube will remain in place for a minimum of 48 hours, and post-operative fluid analysis and triglyceride levels will be measured at 24 and 48 hours post-operatively. Your pet will be discharged once they are voluntarily eating and drinking, and their pain is deemed appropriately controlled with oral medications based on the Colorado State University pain score. As part of your agreement to enter this study, all dogs must be re-evaluated at the UF Small Animal hospital at 1-, 3-, and 6 months post-operatively for physical exam and chest x-rays to confirm occlusion of the thoracic duct and resolution of chylothorax.

This study is a randomized study.  Your pet has a 50% chance of receiving thoracic duct ligation or thoracic duct embolization.

Cost: The study will cover a maximum of $1,200 towards the cost of anesthesia, surgical procedures, and required medications and post-operative hospitalization. All other costs will be the responsibility of the client. On average chylothorax patients are treated surgically for $4,500-5,500. For inclusion in the study, all dogs must have undergone a complete diagnostic work-up for chylothorax previously (described above) – the estimated cost of the diagnostic work up for chylothorax is $2,000-2,500, which is not included in the cost of surgery. 

The client will be responsible for all fees associated with follow-up, as is standard for chylothorax patients. If recurrence of fluid build-up occurs, you will be responsible for the cost of repeat CT scan to determine the cause. The study will cover the cost of repeat surgery if determined necessary based on repeat CT scan.

Contact information: If you have questions regarding this study or would like see if your dog is a good candidate, please contact Dr. Francesca Solari at fsolari@ufl.edu.

PIs: J Brad Case, DVM, MS, Diplomate ACVS-SA, ACVS Founding Fellow Minimally Invasive Surgery

Background information:

Some dogs are at risk of developing a condition called chylothorax. Chylothorax can occur because of a “leaky vessel” (known as the thoracic duct) which can cause accumulation of fluid (chyle) in the chest cavity. This excess of fluid within the chest cavity can impair the lungs during breathing and result in potentially life-threatening situations. Treatment of chylothorax in dogs typically requires surgical intervention to occlude the thoracic duct, preventing fluid from leaking from the thoracic duct into the pleural cavity. Traditionally, surgical intervention of chylothorax requires the abdominal and chest cavities to be opened to allow access for ligation of the thoracic duct, causing a considerable amount of discomfort and even pain after surgery. Minimally invasive approaches have been developed, like thoracoscopic thoracic duct ligation where ligation is performed through small incisions with the use of a camera and specialized instruments. 

The addition of another technique, known as pericardectomy (removal of the pericardium, which is a sac-like organ surrounding the heart) along with thoracic duct repair is often performed to reduce the chance of recurrence. Even with these techniques in combination, recurrence rates of up to 20% have been reported. Pericardiectomy is associated with operative death in some cases and adds significant time and risk to the patient. Additionally, more recent studies suggest that pericardiectomy may not be necessary in all patients and report similar recurrence rates between patients undergoing ligation alone versus ligation with pericardiectomy. Therefore, pericardiectomy may not be indicated in all patients with chylothorax. 

In people with chylothorax, non-invasive embolization of the thoracic duct alone is performed routinely. During this procedure, a small catheter is placed through the skin within a lymphatic vessel inside the abdomen. This lymphatic vessel connects to the thoracic duct in the chest. The catheter is advanced into the thoracic duct, and an artificial clot (embolus) is created to seal off the leaky vessel. Since the chest cavity remains closed during this entire procedure, it is much less invasive than traditional approaches, resulting in less discomfort/pain after surgery and a quicker recovery to normal. Additionally, this technique allows for occlusion of the vessel over a larger area than the ligation method, and may therefore decrease the risk of recurrence. A prior study in dogs described a technique for embolization of the thoracic duct where a small incision is made into the abdominal cavity to locate and catheterize the lymphatic vessel. This was found to be successful in all but one dog, who had recurrence due to undiagnosed cancer. However, embolization was performed along with pericardiectomy and thoracic duct ligation, so it remains unknown if embolization alone is sufficient to treat chylothorax in dogs. 

The aim of this project is to compare minimally invasive embolization of the thoracic duct to minimally invasive ligation of the thoracic duct to determine if clinical outcome is comparable, and if this technique alone is sufficient to treat idiopathic chylothorax in dogs.