CHYLOTHORAX – Thoracotomy

Chylothorax is a fairly uncommon disease contracted by dogs and cats. It is identified by the abundance of chyle in the thoracic cavity. Chyle is a milky substance containing small fat molecules. During the process of digestion, fats from the meal are broken down and become small molecules known as chylomicrons. These molecules are absorbed by a structure known as the cisterna chyli (CC). It is located close to the kidneys, in the abdomen area. The CC acts as a lymphatic reservoir, not only does it receive intestinal chyle, but also lymphatic fluid which comes from the pelvic limbs and the rest of the abdomen. Chyle travels through the thoracic duct (TD) which is an extension of the cisterna chyli into the chest. And then in to the thoracic cavity. Eventually the contents of the TD are emptied into the CrVC (cranial vena cava) which is located near the heart. Chylothorax is caused by an abnormality in the thoracic duct which results in chyle being leaked into the thoracic cavity.

A common symptom of this disease is a pet’s struggle to breathe, caused by the chyle build-up and the inability of the lungs to fully inflate with air. A pet’s immune system is also largely impacted by this disease. This is due to the loss chyle (containing lymphatic fluid which is made up of proteins, vitamins and white blood cells) in the thorax. A result of this would be extreme metabolic disorders. Chyle also acts as an irritant to the lining of the pet’s lungs and heart, resulting in inflammation and further consequences.

Chylothorax can potentially be a result of any issue regarding the flow of chyle between the TD and CrVC. Common diseases causing chylothorax include: cancer, heart disease, fungal disease CrVC blood clots. Often, the underlying cause of chylothorax is not found and it is labelled as idiopathic which means the origin is unknown.

The common signs displayed by a pet which has chylothorax are not always associated with the buildup of chyle in their thorax. Any substances including, pus, blood and air, can result in breathing difficulties if they create a disturbance in lung expansion. Your pet may develop breathing difficulties or cough which does not result in phlegm being expelled indicating that they possibly have chylothorax. Your pet may seem lethargic and unwilling to eat, this is a result of losing vital nutrients when chyle does not reach the CrVC. Weight loss is also common in prolonged cases. If your pet experiences symptoms such as these please ensure that you take your pet to a veterinarian for evaluation.

You can expect your veterinarian to begin with a full physical examination. They may detect lung and heart sounds that are reduced or muffled which could indicate that there may be fluid build-up in the thoracic cavity. Another important sign that they will look out for is the presence of a heart murmur as heart disease is often caused my chylothorax.

If the veterinarian suspects that there is fluid in your pet’s lungs (pleural effusion), they often start by performing a radiograph. This will assist them in confirming the presence of fluid in the lungs. However, it does not diagnose your pet with chylothorax.

Next, a sample would be taken of the fluid in order to get more of an understanding of the disease your pet may have. This process, known as thoracentesis, is fairly uncomplicated. It requires a small gauge needle to suction fluid out of the thoracic cavity. It is often necessary to have your pet sedated during this procedure. If the fluid is milky, chylothorax is suspected. However, a sample will still be sent to the laboratory for testing.

Once there is confirmation that your pet has chylothorax, more procedures should take place in order to investigate the potential cause of the disease. These tests will likely be more sensitive than the radiographs.

Managing chylothorax requires the evacuation of fluid from the thorax. This can be done through intermittent thoracentesis or with a tube which is placed in your pet’s chest area. The tube method means your pet will need to be kept in hospital. The purpose of removing the chyle is to improve the expansion of the lungs which will result in improved breathing and less coughing. Thus, your pet will be more comfortable. It will be recommended that your pet is put on a low-fat diet which aims to reduce the number of chyle flowing through the thoracic duct. However, research has showed that the diet alone is not enough to reduce the chyle running through the thoracic duct. The over-the-counter medication called rutin is sometimes helpful in cases of idiopathic chylothorax. The medication is believed to stimulate protein break down and removal through the lymphatic vessels. How effective rutin is, has not yet been effectively proven.

Medical management of idiopathic chylothorax is rarely successful. The next option is then surgical intervention. As mentioned before, your pet can potentially have a compromised metabolism if the lack of chyle in the thoracic cavity is prolonged. If there is inflammation in the lungs caused by chronic chyle exposure, there is less of a chance that your pet will recover. If the treatment required for your pet’s case of chylothorax is surgery, it is recommended that you ask to be referred to a board-certified veterinarian.

The most common surgical process for treating chylothorax is called thoracic duct ligation (TDL). This procedure aims to promote abdominal lymphatic connections through the prevention of chyle into the TD. Ultimately, the goal will be to prevent chyle leakage through the TD into the thoracic cavity. The success rates have recently been improved by combining TDL with removing the heart lining, known as pericardiectomy. There will also be a tube placed in the chest which will allow aspiration post-operation. Some vets will opt to also perform abdominal surgery. This will allow vets to confirm the success of TDL after surgery.

Another promising treatment of chylothorax is the cisterna chyli removal (CCA). Cisterna chyli is found in the abdomen and it acts as a lymphatic fluid reservoir. CCA will destroy the reservoir in order to promote the creation of new pathways for the lymphatic fluid, essentially relieving the TD of pressure.
Another option, instead of surgery, is a less invasive alternative called video-assisted thoracoscopy. It is often used to perform TDL, CCA and pericardiectomy on dogs. It can be a better option as it is said to be significantly less invasive, reduce the time taken for lymphangiography to be completed and also remove the need of abdominal surgery.

Having your pet go for surgery has potential risks. It is also time consuming. Some of the complications associated with surgery are haemorrhage, nerve damage of the diaphragm, infection and continuous fluid accumulation in the chest.

Your pet will probably be put into the ICU (intensive care unit) in order for pain medication to be administered and allow for the chest tube aspiration to be done intermittently. In some cases, oxygen will also be supplied post-operation. Once the chest tube is removed, your pet will be discharged. If the surgery was successful, it usually takes from a few days to a week or two for the chylous effusion to resolve.

The success of TDL is between 40-60% and 80-100% if it is done in conjunction with a pericardiectomy. In the case where the surgical procedure fails to solve chylothorax, you should discuss other options with your veterinarian.