Let us consider the chest cavity for a moment. The chest can also be called the “thorax” and the chest cavity is sometimes called the “thoracic cavity.” The thorax houses the lungs and heart. There are some other structures present as well such as nerves, large blood vessels, and other conduits (such as the esophagus transporting food through the chest and into the stomach on the abdominal side of the diaphgragm) but the main residents of the chest are the heart and lungs.
The lungs are the focus of this topic. The diaphragm and rib muscles extend and contract to draw breath into the lungs and expel it again. The lungs are like sponges filled with air instead of fluid and life depends on their ability to expand and contract normally. There is not a lot of extra room inside the chest so when something starts taking up space in the chest, the lungs cannot inflate to their natural extent. It becomes hard work to breathe and the patient’s focus becomes expanding the lung against limited space, sort of like trying to blow up a balloon that is too tight.
Fluid can accumulate in the chest. This is totally different from fluid accumulating in the lungs. Fluid in the lungs is more like drowning, with coughing and sputtering. Fluid in the chest cavity is just taking up space and keeping the lung from expanding. The problem is not so much coughing as working hard with all the muscles available to get enough air.
TYPES OF FLUIDS
There are many types of fluids that can accumulate in a body cavity. When the fluid is blood, the problem is called “hemothorax.” When the fluid is pus, the problem is called “pyothorax.” When the fluid is actually air, the problem is “pneumothorax.” When the fluid is lymph, the problem is called “chylothorax.” With chylothorax, the fluid is milky when it is drained from the chest, its whiteness being from fat. Chylothorax respresents a special problem and requires special therapy.
The effort the patient is making to breathe will probably be the first sign of trouble and upon seeing this, your veterinarian is likely to recommend radiographs. Fluid in the chest will be obvious. From there, the chest will need to be tapped with a needle and the fluid drained. This will create some relief for the patient as the lung will once again be able to expand. The fluid will most likely need to be sent to the lab for testing to determine the fluid type.
WHAT IS LYMPH?
We all know what blood is. We all know that blood circulates in veins and arteries and is moved by the pumping action of the heart. In fact there is another circulatory system in the body: the lymphatic system. Lymph fluid represents extra fluid draining from between the cells of the body, gradually channeling into lymph vessels. The fluid is moved by the natural movement of the body and its muscles. Lymph circulates through lymph nodes where cells of the immune system are exposed to the “drift wood” of debris that the lymph fluid has picked up. In this way, the immune system “sees” infection, tumor cells, foreign organisms etc. Cells that circulate in the lymph fluid help fight infection and eventually the lymph fluid circulation ends by merging into the bloodstream. Lymph fluid is full of fat because fat is absorbed into the lymphatic system (the “lacteals”) of the intestine after digestion. Lymphatic fluid (also called “chyle”) contains fat, water, and lymphocytes (cells of the immune system).
When something goes wrong with the circulation of the lymph fluid, lymph fluid can accumulate in the chest.
If there is a reason for the chyle build up, it is important to find that reason. Often (especially in the cat), the reason is heart disease. Heart disease generally interferes with lymphatic drainage and poor drainage leads to the chyle build up but there can be other reasons for chyle build up besides heart disease. Any sort of mass or growth in the chest could also be responsible. If a cause can be found, then it should be addressed if possible. If no cause can be found then the condition is termed “idiopathic” and is simply managed either medically or surgically.
Cats are diagnosed with chylothorax approximately four times as often as dogs.
DIAGNOSIS: IDIOPATHIC CHYLOTHORAX
There are several options for treatment though they have pros and cons. The most conservative method is “medical management.” This means that whenever the patient seems to be having some distress, the chest fluid is drained. How often this is necessary is highly individual but every few weeks is a common interval. In time, after many taps, scarring can build up to cause the fluid to “loculate” which means that small pockets of fluid form rather than one drainable area. This makes tapping more difficult over time.
Another treatment involves the use of "somatostatin," a chemical normally produced in the brain to regulate intestinal hormone and enzyme secretion. One of its effects is to reduce chyle flow through the thoracic duct. A commercial product is available and can be used in pets but its use should be considered somewhat experimental.
More permanent solutions require surgery. Here are some procedures that have been recommended in the past:
THORACIC DUCT LIGATION
The thoracic duct is the largest lymph vessel and is present in the chest. In older times it was thought that chylothorax resulted from a tear in the duct, spilling lymph into the chest. This turns out generally not to be the case but ligation of the duct is successful in permanently resolving chylothorax in 50% of dogs undergoing surgery. Less than 40% of cats achieved resolution. In patients where surgery was not successful, fluid build up continued (though not always chyle, sometimes just watery fluid would return).
This technique involves placement of a sort of a drain in the diaphragm so that fluid from the chest could drain into the belly where causes no harm. Shunts can be active (where there is a pump that can be manually compressed) or passive where normal breathing and motion moves the fluid. Complication rate is fairly high with this procedure (nearly 50%) and it has not been recommended for cats. It does yield an average of 20 months of symptom-free living in dogs.
THORACIC DUCT LIGATION WITH PERICARDECTOMY
This method appears to be the current treatment of choice. The pericardium is the fibrous sac containing the heart. When it is bathed in chyle, it becomes thickened and may be slightly constricting the low pressure right side of the heart. When the pericardium is stripped away, lymph may be able to circulate in more normal channels that it previously could not. When this procedure was combined with thoracic duct ligation, chylothorax permanently resolved in 100% of dogs and 80% of cats. The surgery is difficult and highly invasive (as one might imagine since it involves manipulation of the heart) and should be performed by a surgery specialist only.
BEWARE OF FIBROSING PLEURITIS
Chyle in the chest is irritating to the local tissue; the lungs can actually develop scarring from being in contact with chyle. Scarring prevents the lungs from expanding normally even after the chyle is removed. The only treatment is to surgically remove the scar tissue using a procedure called "decortication", a process fraught with complications if the lungs are diffusely affected. If both lungs must be decorticated, it is common for a life-threatening pulmonary edema to occur as the lungs try to re-expand. Sometimes air leaks out of the lung and fills the chest with air ("pneumothorax"). Before opting for any surgical treatment of idiopathic chylothorax, this potential complicating factor should be discussed with the surgeon.
Page last updated: 4/15/2014