Chylothorax in Cats
Dr. Theresa Welch Fossum
A complete medical history and thorough physical examination
Diagnostic tests will be performed to determine that fluid is present in the chest cavity, verify that the fluid is chyle and determine if there is an underlying disease such as heart disease or tumor that might have caused the effusion.
Diagnostic tests to determine that fluid is present in the thoracic cavity include:
Careful auscultation of the chest (using a stethoscope) to determine whether the heart and lung sounds are normal. When fluid is present the heart sounds may appear muffled. If heart disease is present, a murmur may be heard.
Thoracic radiographs (chest X-rays) to identify fluid in the chest and determine how much is present and where it is located. The radiographs will also be evaluated to determine whether other causes of difficult breathing like pneumonia, asthma, or tumor, or fluid formation might be present.
Diagnostic tests are needed to confirm that the fluid is chyle. Some of these tests include:
Analysis of fluid removed from the chest by needle thoracentesis (chest tap) for physical characteristics (color, clarity), the type and number of cells, amount of protein and the amount of triglyceride (fat) in the fluid
Measurement of triglyceride content. Chylous fluid has a higher triglyceride content than serum. To make this comparison, blood may be drawn from your pet and also measured for triglyceride content.
Chylous fluid typically is composed primarily of lymphocytes and neutrophils. These are normal cells that are also present in the bloodstream. The fluid is usually carefully analyzed for the presence of cells that might indicate a tumor is present in the chest cavity.
The fluid is usually checked for bacteria or the presence of cells that might indicate that an infection is present.
Diagnostic tests to determine if there is an underlying disease present include:
Before removing the fluid, your veterinarian may wish to perform an ultrasound on the chest to determine whether a tumor might be present in the area in front of the heart (mediastinal mass). When fluid is present in the chest cavity, ultrasonography is very helpful in evaluating the chest cavity for masses or other abnormalities. It may also be used to guide the chest tap if the fluid is pocketed.
An echocardiogram may be performed to determine if heart function is normal, whether there are cardiac lesions, such as acquired valvular abnormalities, or congenital cardiac defects, whether the pericardium (the sac around the heart) is thickened or contains fluid (pericardial effusion) or whether a heart base tumor is present.
A heartworm test is usually performed.
Repeat radiographs may be taken, after the fluid has been removed, to determine whether the lungs re-inflate. Fibrosing pleuritis – thickening and scarring of the lining of the lungs and the inside of the chest cavity – may be associated with chronic chylothorax and result in the lungs not re-inflating normally.
Routine blood work, including a complete blood count (CBC) and serum biochemical panel, will often be done to help assess organ function and overall health of your pet.
Your veterinarian may recommend other tests to help further identify potential diseases that may have caused the chylothorax or to identify concurrent diseases that might be present.
Treatment of chylothorax may be divided into either medical management or surgical treatment. Note that some animals do resolve the condition on their own, probably because they reroute the chyle into alternate lymphatics and blood vessels in their abdomen.
The initial concern in treating your pet will be to improve his ability to breathe. Your veterinarian will generally remove the fluid in your pet's chest cavity using a needle. Occasionally, sedation or anesthesia will be required but a chest tap can often be performed with the animal awake. Depending on the degree of difficulty that your animal is experiencing breathing, oxygen therapy may be required. Further treatment will depend on whether an underlying disease was identified or whether the condition is thought to be idiopathic (no underlying disease found).
Medical management is usually considered first for the treatment of idiopathic chylothorax. It usually consists of intermittent chest taps to allow your pet to breathe more easily, dietary modification and drug therapy. If medical management is unsuccessful, surgery may be considered.
Intermittent thoracentesis (chest taps) usually are performed whenever your pet begins to have increased difficulty breathing. When medical therapy is successful, the intervals between taps usually increases because the fluid accumulates more slowly or is more effectively absorbed from the chest cavity into the bloodstream.
A commercial low-fat diet may be helpful. If your pet will not eat these diets, ask your veterinarian for a recipe for a homemade low-fat diet. Homemade diets are often more palatable than the commercial diets, but care must be taken to ensure that they are nutritionally complete.
Benzopyrone drugs such as Rutin may be recommended. These drugs are experimental, but may help your pet absorb the chyle until it resolves spontaneously. Rutin is generally given three times a day by mouth. The tablets may be crushed and put in the food, but care must be taken to ensure that your pet actually ingests the medication.
Thoracic duct ligation is the most successful surgical therapy for idiopathic chylothorax. This surgery is most likely to be successful if mesenteric lymphangiography, which is a dye study that shows the thoracic duct and its branches, is performed in conjunction with the duct ligation. When these procedures are performed, your pet will have two incisions – one behind the last rib and one in between several of the last ribs. A chest tube is placed after surgery to monitor the amount of fluid that is produced. This surgery is not always successful; some animals continue to produce chyle and others continue to produce a clear fluid after surgery. The surgery is most likely to be successful if it is performed by someone experienced with this procedure. Your veterinarian will likely refer you to a specialist for the surgery.
If thoracic duct ligation is not successful, a pleuroperitoneal shunt may be placed. The pump lies under the skin and requires that you compress it in order to empty the chest fluid into the abdomen or the bloodstream. These pumps are expensive and are usually considered only as a last resort.
If an underlying condition is found that is surgically treatable such as fluid within the pericardial sac, then that surgery may be performed to see if the chylothorax will resolve.
Occasionally, when the lungs are floating in fluid, they twist on themselves. When this happens, even more fluid is produced and the situation can become very quickly life-threatening. If you notice a sudden worsening of your pet's condition you should see your veterinarian as soon as possible.
When chylothorax has been present for a long time, the lining of the lungs becomes scarred and thickened (fibrosing pleuritis). This may prevent the lungs from expanding normally. Treatment of this condition is difficult. The thickened lining can be removed surgically, but this often results in air leakage from the lungs. When fibrosing pleuritis is present, the prognosis is very guarded.