Overview of Canine Chylothorax
Chylothorax is a condition in which a characteristic type of lymph fluid called chyle accumulates in the chest cavity and causes difficulty breathing. Lymph is the fluid that is drained from tissues and functions to carry protein and cells from the tissues to the bloodstream via small vessels, known as lymphatics. When the lymph is drained from the intestines, it contains a high quantity of fat and is known as chyle. Thus, chylothorax is a collection of chyle in the chest cavity. The accumulation of chyle in the chest cavity leads to difficulty breathing because the lungs cannot expand normally to take in oxygen.
This condition may occur in any breed of dog, but some breeds appear to have a higher than expected incidence, including Afghan hounds and shiba inu dogs. Afghan dogs appear to develop signs related to this disease when they are middle-aged, whereas the shiba inu is often less than a year of age when the condition is diagnosed.
Chylothorax is most common in middle-aged and older animals, but can occur in very young animals as well.
The cause of the chylothorax in many animals idiopathic, which means the cause is not determined. However, some animals are determined to have tumors, heart disease or blood clots that elevate pressures in the bloodstream and cause the chyle to leak from the lymphatic vessels in the chest. It is important that underlying causes be identified and treated whenever chylothorax is diagnosed.
What to Watch For
Signs of chylothorax in dogs may include:
Diagnosis of Chylothorax in Dogs
If your pet is diagnosed with chylothorax, he will require veterinary care. Your veterinarian’s efforts will be directed at two things: making your pet more comfortable by removing as much of the fluid from the chest cavity as possible, and performing tests to determine whether there is an identifiable cause for the chylothorax. Diagnostic tests that your veterinarian may wish to perform include:
Chest radiograph. Chest radiographs or X-rays are done to confirm the presence of fluid in the chest cavity and to help determine how much fluid is present. After some of the fluid has been removed, a repeat X-ray is often done to evaluate the lungs to see if they can re-expand normally and to look for masses or other abnormalities in the chest cavity. Chest radiographs are also used to evaluate the size of the heart and blood vessels.
Chest tap. A chest tap (needle thoracentesis) is done to remove some fluid to allow your pet to breathe easier and also to obtain some fluid for analysis. A chest tap is done by inserting a small needle between the ribs and withdrawing the fluid into a syringe. Most animals tolerate chest taps and the procedure can be done without any sedation. However, occasionally, your veterinarian may need to give your pet some sedation or even general anesthesia in order to remove the fluid.
Fluid analysis. Chyle is a milky white fluid that contains a high concentration of triglyceride. Your veterinarian will run a triglyceride on the fluid removed from the chest cavity and compare it to the triglyceride content in a blood sample. If the chest fluid is chyle, the triglyceride level will be higher than the triglyceride in the blood sample.
Cytology (examination of the fluid under a microscope). Your veterinarian will also examine the fluid to determine whether there are abnormal cells, such as those that might indicate that a cancer is present, or whether infection is present.
Additional tests may be done to help determine the cause of the chylothorax and the overall condition of your pet. These tests might include ultrasonography of the chest, an echocardiogram (ultrasound of the heart) to evaluate heart function and various blood tests such as a heartworm test.
Treatment of Chylothorax in Dogs
If an underlying disease is found, your veterinarian will help you decide whether further treatment is warranted. The specific treatment depends on the underlying condition. If you elect to treat the underlying disease, your veterinarian will try to keep your pet comfortable by periodically removing the fluid to allow him to breathe more easily. Your pet may also be placed on various medications and a low-fat diet.
If an underlying disease is not found, your veterinarian may recommend that conservative treatment be tried to see if the chylothorax will resolve. This will usually include periodic removal of the fluid from the chest cavity and placing your pet on a low-fat diet. If the fluid accumulation does not decrease or resolve in two to three months, your veterinarian may suggest that surgery be performed.
An experimental drug that may help animals with chylothorax is Rutin. This drug is being evaluated to determine if it will help animals reabsorb the chyle from their chest cavity and decrease the severity of the scarring of the lining of the lung.
Home Care and Prevention
In addition to observing your pet closely for evidence of difficult breathing, you may also be asked to administer various medications. Be sure that your veterinarian shows you how to determine if your pet is having difficulty breathing and how to administer any prescribed medications.
If your pet is unwilling to eat commercial low-fat diets, your veterinarian should be able to provide you with recipes for homemade low-fat diets.
There is very little that you can do to prevent your animal from developing chylothorax. In many animals the underlying cause of the chylothorax is never determined.
Chylothorax can occur secondary to heart failure associated with heartworm disease; therefore, be certain to discuss your pet’s need for heartworm prevention with your veterinarian.
In-depth Information on Chylothorax in Dogs
The thoracic duct is a lymphatic vessel that carries chyle from the intestines and into the chest where it empties into the bloodstream. Many of the conditions that cause chylothorax do so because they increase pressure in the blood vessels into which the thoracic duct empties. This increased pressure causes the chyle to “back up” in the duct and many new lymphatics are formed trying to bypass this obstruction. Because these lymphatics are very thin walled, they leak when there is pressure on them. Thus, the chyle seeps from the vessels and accumulates in the chest cavity.
One of the most important aspects of treating chylothorax is to determine the underlying cause so that the treatment can be tailored to the cause. Unfortunately, in many animals the underlying cause is not determined and the condition is termed idiopathic. Some of the causes of chylothorax that have been recognized in dogs include:
Mediastinal masses (lymphosarcoma, thymoma). These masses grow in the mediastinum or space between the left and right sides of the lungs. As they grow, they may partially occlude the blood vessels that the thoracic duct empties into.
Congenital heart disease (tetralogy of Fallot, tricuspid dysplasia). Because these diseases increase pressure in the heart and the blood vessels that the thoracic duct empties into, they also cause lymph to back-up in the thoracic duct. As with mediastinal masses, new lymphatics form and these new vessels simply leak chyle into the chest cavity.
Cardiomyopathy. This is an acquired heart disease where the heart does not contract normally. Similar to congenital heart disease, this leads to an increase in pressure in the blood vessels and subsequent leakage of chyle into the chest cavity.
Pericardial effusion. This is an accumulation of fluid within the sac that surrounds the heart. When fluid accumulates here, it causes an increase in pressure in the blood vessels that the thoracic duct normally empties into.
Heartworm infection. Heartworm infection may cause heart failure that increases pressures in the vessels that the thoracic duct empties into.
Fungal granulomas. These abnormal collections of cells and fungal organisms may block the vessels that they thoracic duct empties into.
Venous thrombi. Blood clots may block the vessels that the thoracic duct empties into. This can occur after catheters have been placed in the jugular vein. It has particularly been noted when liquid diets are placed into the vein.
Congenital abnormalities of the thoracic duct. Abnormalities of the thoracic duct have been described in Afghan hounds and may account for their developing this disease more commonly than most other breeds.
Trauma is an uncommon cause of chylothorax in dogs; however, it has been recognized after automobile accidents or severe vomiting. Chylothorax associated with trauma usually has a good prognosis as the thoracic duct heals fairly quickly on its own without surgery.
In-depth Information on Diagnosis
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:
A complete medical history and thorough physical examination
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.
In-depth Information on Treatment
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.
Medical Management of Chylothorax in Dogs
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.
Surgical Therapy of Chylothorax in Dogs
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.
Follow-up Care of Dogs with Chylothorax
Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your dog does not rapidly improve.
Administer all prescribed medication as directed. Alert your veterinarian if you are experiencing problems treating your dog.
The frequency and nature of follow-up evaluations of your pet will be largely determined by the nature of any underlying diseases found and by the type of treatment chosen. If your pet has idiopathic chylothorax and medical management is chosen, your veterinarian may request that you return for periodic evaluations or may simply suggest that you return when you believe that your pet is having increased difficulty breathing.
If you notice that your pet is having difficulty breathing, do not wait until your next scheduled visit to see your veterinarian. Take your dog in immediately. Chylothorax can be life-threatening because the fluid can accumulate to such a point that the lungs cannot expand. When this happens, your pet will not be able to get enough oxygen to survive. Discuss with your veterinarian how to tell if your pet is in distress so that you will be better able to judge when you need to have your pet evaluated.
If surgery is performed, you will be asked to return for periodic evaluations. These evaluations will often include taking thoracic radiographs to determine whether the chylothorax has resolved.
When fluid is present, your veterinarian will periodically analyze it to determine its character as to whether it is chylous or not.