Chylothorax Trial

Clinical Trial for the Treatment of Chylothorax in the Dog

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Introduction to and current treatments for chylothorax in the dog

Rationale and basis for new surgical treatments for chylothorax in the dog

Study Design for Evaluation of Cisterna Chyli Ablation or Pericardectomy for Treatment of Chylothorax

Sample Consent Form for Enrollment in the Trial (pdf)

Current Status of the Trial-Results Update

What is idiopathic chylothorax?

Chylothorax is a disease where fatty fluid accumulates within the chest cavity. This fatty fluid, which is called chyle, is the fluid which drains from the abdominal lymphatic channels. From these channels, chyle drains into a structure called the cisterna chyli within the abdomen. The cisterna chyli is a reservoir that then funnels chyle into the thoracic duct, which traverses the thoracic cavity along the aorta and empties into the venous circulation near the heart. Chylothorax is considered to be idiopathic when there is no obvious cause such as trauma, surgery, cancer or other notable disease of the chest, circulatory system or thoracic organs.

How is chylothorax treated?

The cause of idiopathic chylothorax is poorly understood and treatment of this disease can frequently be unsatisfactory. Conservative treatments such as periodic drainage or medical therapies often constitute a "holding pattern" for many dogs, failing to provide permanent relief. In the dog, surgical treatment of chylothorax is most commonly done by ligation of the thoracic duct, a procedure best performed when combined with imaging studies (contrast lymphangiography) to outline the duct and all of its channels. This was first described in 1982 and subsequent case series have established that success in resolving chylothorax in dogs is about 50-60% with this method.

Since that time, a wide variety of treatments have been proposed to try to improve upon these results. These methods have often been tested in limited case series and most have generally been abandoned when the success rates were shown to be no better or even worse than that of thoracic duct ligation alone. These treatments have included medical therapy such as with rutin or octreotide (a somatostatin analogue), sclerotherapy (pleurodesis), thoracic duct embolization with cyanoacrylic adhesives, pleural shunting or pumping, diaphragmatic fenestration and omental draping into the pleural space. In our clinical experience at the University of Wisconsin, all of these therapies (with the exception of omental draping) have not provided any improvement in results over surgical ligation of the thoracic duct. Omental draping, for which a single case report has been published, has not been performed at the UW-VMTH. This is because the omental lymphatic drainage empties into the cisterna chyli and hence the thoracic duct, creating the physiological equivalent of a perpetual motion machine. Thus, the rationale behind trans-diaphragmatic draping of the omentum into the chest as an absorptive drain remains obscure. In the absence of compelling clinical data to show its efficacy, we do not see a basis for use of this procedure. Sporadic use of many of these different treatments, alone or in combination with thoracic duct ligation, continues at referral centers based on various rationales which weigh the costs, impacts of surgical trauma and likelihood of a positive long term outcome. No single treatment is universally accepted because the overall prognosis with all methods for treating chylothorax is guarded at best.

There has been a significant lack of improvement in the treatment of chylothorax since 1990. Strategies for treatment of chylothorax up to that time were focused on several principles, 1) obstruction of chyle flow into the chest (thoracic duct ligation or thoracic duct embolization), 2) reduction of chyle volume (dietary or drug treatments such as MCT oil and low fat diets), 3) transport of chyle elsewhere to relieve respiratory distress, such as to the peritoneum for absorption or to the venous system by mechanical aids (shunts, pumps and diaphragmatic fenestration), 4) obliteration of the pleural space to eliminate a place for chyle to accumulate (pleurodesis). In the last decade, new treatments have been limited to several drug treatments introduced to reduce the volume of chyle formation (rutin and octreotide), which have not proven to be uniformly effective in resolving chylothorax in dogs. The only other innovation in the last decade has been the attempt to use the omentum as a physiologic drain, reported in a single dog. However, as noted above, the rationale behind that approach is difficult to ascertain and no further reports on its efficacy have been forthcoming. Recently, two new approaches to this disease have been presented with encouraging preliminary results. These methods, cisterna chyli ablation and pericardectomy, are the focus of this prospective randomized trial.