Description of a Novel Approach for Thoracic Duct Ligation and Embolization in Dogs with Idiopathic Chylothorax

• Inclusion Criteria: Dogs greater than 10 kilograms (22.2 lbs) diagnosed with idiopathic chylothorax.
• Exclusion Criteria: Dogs with an identified cause for chylothorax (e.g. cardiac disease, lung lobe torsion, neoplasia) are not eligible. The final diagnosis of idiopathic chylothorax will be based on a special type of imaging/scan called a CT lymphangiogram that is standard of care for this condition.
• Procedures: Each dog will undergo a complete physical exam, screening blood work, ultrasound evaluation of the heart, and CT lymphangiogram (under general anesthesia) prior to inclusion in this study. For the surgery, a small incision (3-5 cm) is made in the abdomen to locate a lymph node and inject contrast agent to help visualize and embolize the lymphatic vessels. Three very small incisions along the ribs (5-10 mm) will allow insertion of special surgical instruments (thoracoscopic instruments) to allow the surgeon to see inside the chest cavity and clip off the thoracic duct branches. A lymphangiogram (real-time x-ray) will be performed to confirm the occlusion of the thoracic duct. Each dog will be monitored at the UF Small Animal Hospital for at least 48 hours following the procedure. They will be returned to the owner once they are eating and drinking voluntarily and are comfortable based on Melbourne Pain Scale Assessment. All dogs admitted to this study must be re-evaluated via CT lymphangiogram (under anesthesia) between 10-12 weeks after surgery to confirm occlusion of the thoracic duct and resolution of chylothorax.
• Cost: The study will cover a maximum of $1,500 towards the cost of initial diagnostics, anesthesia, surgical procedures, and required medications and post-operative hospitalization. Additionally, the study will cover a total of $1,500 towards recheck appointments including the post-operative CT lymphangiogram 10-12 weeks following surgery. All other costs will be the responsibility of the client.
• Study Contact: If you would like to be considered for the study, please call the UF Small Animal Hospital to schedule an appointment for your dog with the Surgery Service at (352) 392-2235. For other questions regarding the study, please complete the Study Interest Form.
• Principal Investigator: J Brad Case, DVM, MS, Diplomate ACVS-SA, ACVS Founding Fellow, Minimally Invasive Surgery

Background:

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 the accumulation of fluid into the chest cavity. This excess of fluid within the chest cavity can therefore impair the lungs during breathing, and can result in potentially life-threatening situations. Chylothorax will often require surgical treatment to repair the thoracic duct, which prevents more fluid from leaking into the chest cavity. Traditionally, surgical treatment of chylothorax requires the abdominal and chest cavities to be opened to allow access, causing a considerable amount of discomfort and even pain after surgery. Even after traditional surgical treatment, in approximately 50% of dogs, the thoracic duct will continue to leak fluid. 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 improves outcome to approximately 80% success. However, pericardectomy is associated with surgery related death in some cases and adds significant time and risk to the patient’s recovery.

In people with chylothorax, non-invasive embolization (blockage) of the thoracic duct is now being performed routinely. During this procedure in people, a small catheter is placed through the skin within a vessel inside the abdomen. This 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. Additionally, this technique allows for blocking of the vessel over a larger area than the traditional methods, and may therefore decrease the risk of recurrence.

The purpose of this study is to modify the procedure used in people to develop a minimally-invasive (small abdominal incision) approach for thoracic duct ligation and embolization in dogs. We will evaluate our new approach in three dogs with idiopathic chylothorax. The dogs will benefit from the procedure as currently accepted standard of care treatments will be provided but with a minimally invasive approach in contrast to open surgery. Our ultimate goals are to expand this to a larger study in client-owned dogs and to continue the development of the minimally-invasive and interventional radiology program at UF Veterinary Medicine.