Chyle is a term used to describe lymph fluid that arises from the intestine and, therefore, contains a high percentage of fat.  Chylothorax is a collection of this fluid in the pleural space (chest cavity).  Normally, chyle is transported from the intestine to the heart and circulation through the thoracic duct.  The thoracic duct is a small vessel that runs from the abdomen and intestine, through the chest cavity, and empties in a major vein at or near the heart.  If the thoracic duct, which carries all the chyle, ruptures or leaks, the chyle will be spilled into the chest cavity and chylothorax is the result.

There are several causes of chylothorax, and they range from benign processes to malignant cancers.  Masses that can form in the chest and obstruct the thoracic duct may potentially cause chylothorax.  Usually, these masses are malignant cancers.  Heart disease, resulting in elevated pressures in the heart prevent normal drainage of the thoracic duct, may also cause chylothorax.  Trauma (hit by a car or falling from a window for example) may be severe enough to cause the thoracic duct to rupture.  In some cases, a specific reason for the chyle leakage can not be determined, and we term this idiopathic or spontaneous chylothorax.  Several tests will need to be done to try and determine the underlying cause. Common tests include a laboratory analysis of the fluid, including cultures, to make sure a bacterial infection is not present.  Ultrasound examinations of the chest to evaluate heart function and to screen for any masses or growths are usually indicated as well.  Radiographs (X-rays) of the lung field are usually obtained also.  These can be especially helpful after the majority of the chylous fluid is removed.  CT imaging of the thorax can further define problems not detected by other modalities.

Clinical signs of chylothorax may be limited to the respiratory system (difficulty breathing) as the chest cavity fills up with fluid.  Potential underlying causes, such as cancer or trauma, may also predominate the clinical picture.  The severity of signs depends in large part on how much chyle is present, and how rapidly it developed.  The larger amount of fluid, and the more rapid its accumulation, the worse the clinical signs will be.  This disease is potentially life threatening as the ability to breath is compromised.

Treatment of this condition is broken down into two phases.  The initial step is the removal of accumulated fluid.  This may need to be done on an emergency, life saving basis.  A small needle may be used to initially aspirate the fluid and give enough relief that more aggressive measures can be taken.  The placement of chest tubes to continuously drain the chest cavity of the chyle gives much better short term control of the disease and is frequently done after initial stabilization.  The long term treatment will depend upon the underlying cause, if one is identified.  Any predisposing conditions, such as cancer or heart disease, need to be treated specifically to help control the chylous fluid build up.  Idiopathic chylothorax, where no underlying cause is found, presents a unique treatment challenge.  In cases like this, the treatment is mainly supportive and symptomatic.  Some cases will resolve spontaneously if the chest is kept “dry” long enough.  This is one reason for leaving the chest tubes in (if any were placed) for at least several days.  Some medications have occasionally been shown to be beneficial as well.  Lasix or other diuretics (water pills) may help the body get rid of excessive fluid, but they also dehydrate the animal and need to be used cautiously.  Steroids, such as prednisone, have also occasionally been used with varying degrees of success.  Another medication, Rutin, may help stabilize the membranes of the thoracic duct and decrease chylous leakage.  Rutin is available at most health food stores.  Since chyle is a product of intestinal absorption, and mainly contains fat, dietary changes may also help to control the condition.  Low fat diets are frequently employed to treat this disease.  If medical therapy is not successful in reducing and controlling the fluid accumulation, surgery may be an option.  The surgery involves identifying and ligating (tying off) the thoracic duct.  Some animals require 2 or more surgeries before improvement is seen.  Other animals show marked improvement after the first procedure.  Still others never seem to be controlled in spite of medical treatment and multiple surgical procedures.