Chylothorax can occur at any age and is usually idiopathic. Large chylous effusions can cause symptoms such as dyspnea and chest pain, while small chylothoraces may be asymptomatic and are detected incidentally or during thoracentesis for other reasons.
Effective management requires a skilled interprofessional team, including pulmonologists, thoracic surgeons, nurses and dietitians. All should excel in monitoring symptoms and implementing pleural drainage systems.
Causes
Non-traumatic chylothorax can be caused by obstruction of the thoracic duct or by lymphatic dysfunction. In addition, increased hydrostatic pressure or direct invasion of malignant cells can also cause chylothorax.
Chylothorax is a milky fluid that originates in the thoracic duct and is transported to the systemic circulation via the pulmonary circulation. This fluid is secreted at a rate proportional to the amount of lipids in the diet. Chylothorax may occur when the thoracic duct is blocked or when lymphatic dysfunction causes an increase in the flow of chyle from the thoracic duct into the pleural cavity.
Conditions that can block the thoracic duct include:
sarcoidosis, goiter and blood clots. The thoracic duct is a tube that connects the thoracic aorta and thoracic duct to the superior vena cava. The thoracic duct is located in the rib cage on the right side between the sternum and the diaphragm.
Trauma to the chest or thoracic duct can be caused by blunt trauma or sudden decompression from a hernia or pneumothorax. Injuries can also occur from sneezing, spitting, coughing, vomiting and seat belts.
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The diagnosis of chylothorax is usually made based on physical examination and the results of tests performed to determine the cause of the chylothorax. Your veterinarian will listen to your pet’s heart and lungs during the physical exam. They will be able to hear reduced or muffled heart and lung sounds which are characteristic of fluid in the thoracic cavity (pneumothorax).
Chylothorax can sometimes be diagnosed by radiographs, but a more definitive diagnosis is made when a sample of pleural fluid is collected and tested. Centrifugation of pleural fluid can help to differentiate chyle from other effusions that have a milky appearance including pseudochylothorax and empyema. The addition of ethyl ether to the pleural fluid can help to distinguish pseudochylothorax from chyle as it dissolves the fatty components of the chylous effusion and clears the milky appearance. The ether test can also be helpful in identifying empyema as it separates the cell debris and clear supernatant characteristic of a pleural space infection or hemothorax.
Symptoms
Chylothorax, an accumulation of lymphatic fluid in the pleural space, is a serious medical condition associated with significant morbidity and mortality, increased hospital stays, and health care costs. This condition can occur in patients who have undergone surgical procedures, cancer treatments, or traumas; it also develops spontaneously. Patients with chylothorax experience significant negative impacts on respiratory function, nutritional status, and quality of life. A comprehensive understanding of this disorder, including the anatomy, pathophysiology, diagnosis, and management strategies is essential to optimize patient outcomes.
In most cases, chylothorax is unilateral. The chyle-producing duct, the thoracic duct, originates in the cisterna chyli of the abdomen and passes through the diaphragmatic hiatus to enter the thoracic cavity on the right side at the costophrenic and cardiophrenic angles (5).
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Depending on the volume and location of the effusion, symptoms may vary from mild to severe. Common symptoms include chest discomfort or pain, difficulty breathing (dyspnea), and a cough (chyloptysis) caused by reflux of the milky fluid into the bronchial airways.
Other less common symptoms include a low appetite, weight loss, asthenia, and night sweats due to the immunosuppression induced by the chylous fluid (12). In advanced cases, chylothorax can lead to significant nutritional deficits, muscle wasting, opportunistic infections, and death (13) (12) (14).
Chylothorax is easily diagnosed using thoracentesis and laboratory analysis of a pleural fluid sample (Figure 3). A pleural fluid sample typically contains a cloudy, milky-white fluid with normal protein content and an elevated PLA2R level.
An organized stepwise approach to managing chylothorax is critical to support optimal patient outcomes. This includes a detailed evaluation of the patient’s underlying condition, including a thorough physical examination and diagnostic tests such as thoracentesis, CT scan, or chest radiograph. Once the diagnosis is confirmed, the chylous effusion can be drained by thoracentesis. The procedure is quick, simple, and relatively painless, and the results are immediately available. Depending on the underlying cause, patients may require long-term monitoring or invasive interventions, such as thoracic duct ligation or embolization. An interprofessional healthcare team should be involved to facilitate the implementation of this effective care plan.
Diagnosis
Diagnosing a chylothorax involves physical exam and laboratory work. Chylothorax typically affects the right side of the chest more than the left due to the anatomy of the thoracic duct. Patients may have decreased breath sounds or dullness to percussion. Chylothorax is a transudative effusion, meaning the fluid leaks out of the pleural space rather than into it (see the image below). A chylous pleural effusion is milky and has a higher pleural lipid concentration than the serum. In addition, a pleural fluid analysis may show a lymphocyte-predominant protein-discordant exudate and a high ratio of triglyceride to cholesterol (see the image below). The diagnosis can be confirmed by repeated thoracocentesis and the Sudan III or IV stain on a pleural fluid sample. Lipoprotein electrophoresis of pleural fluid can also confirm the diagnosis, but is less widely available and is expensive.
The etiology of non-traumatic chylous effusions can be divided into surgical and nonsurgical causes. Surgical etiologies include thoracic duct injury and compressive mediastinum or abdominal lymphadenopathy. Nonsurgical etiologies include malignant disease, rheumatoid arthritis, tuberculosis, and inflammatory diseases. Surgically induced chylous effusions include a hepatobiliary resection for cirrhosis and scleroderma, and a thyroplasty for congenital heart disease.
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Non-traumatic chylous effusions are also more likely to be non-exudative than transudative. This is due to the fact that chylomicrons are smaller than plasma proteins and are more readily filtered by the lymphatic system. In addition, a comparatively high concentration of LDH in chylous effusion is due to the lysis of the chylomicrons within the pleural cavity (see the image below).
Imaging studies can assist with diagnosis by identifying traumatic injuries or compression of the thoracic duct. CT of the chest, abdomen, and pelvis can narrow the differential by identifying sites of traumatic injury to the lymphatic system, compressive mediastinal or abdominal lymphadenopathy, or ascites. Magnetic resonance (MR) lymphangiography, positron emission tomography/computed tomography (PET), and lymphoscintigraphy are alternative imaging modalities to visualize the lymphatic system.
A collaborative approach involving multiple healthcare professionals can aid in the management of chylothorax and prevent debilitating complications. Successful outcomes are associated with early detection, conservative treatment with dietary modifications and pharmacological therapies (such as medium-chain triglycerides and somatostatin analogs) and surgical interventions (including thoracic duct ligation, chemical pleurodesis, or embolization). Patients who do not respond to medical management are candidates for a staged care plan that progresses to more aggressive operative treatments.
Treatment
Chylothorax is a life-threatening condition if untreated. It can lead to respiratory compromise, fluid imbalance and electrolyte abnormalities. Complications include malnutrition, decreased immune function, and progression of the chylothorax to pneumothorax (a life-threatening pneumonic effusion). Effective treatment is crucial for optimal outcomes. A multidisciplinary approach with pulmonologists, surgeons, dietitians and other healthcare professionals is essential for patient care and improved outcomes.
Diagnosis is based on evaluating pleural fluid obtained by thoracentesis or chest tube drainage. The milky-looking chyle typically contains triglycerides and cholesterol in addition to proteins, electrolytes and cellular elements. Lipoprotein electrophoresis can confirm chyle composition, but is not widely available. The triglyceride content is diagnostic for chylothorax, while the presence of chylomicrons confirms that the chyle has entered the pleural space.
Treatment options depend on the underlying cause of the chylothorax. Small chylothoraces can often be managed conservatively with dietary modification and chest tube drainage, but may require surgery for recurrent effusions. Large chylothoraces are more difficult to manage, as they are associated with progressive symptoms and signs such as respiratory distress, thrombosis of the pulmonary vascular bed and obstructive pneumonia. Patients with refractory chylothorax may be treated by thoracic duct ligation or chemical pleurodesis, which reduces chyle flow and obliterates the chylous cavity in up to 90% of cases.
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Percutaneous catheterization and embolization of the thoracic duct and cisterna chyli has become the preferred method of treatment for both traumatic and nontraumatic chylous effusions. This procedure involves needle disruption of the thoracic duct and surrounding lymphatic vessels using ultrasound guidance to visualize the retroperitoneal lymphatics. The thoracic duct and cisterna are then injected with thrombolytic agents such as heparins or saline to seal the leak and prevent further chyle leakage.
Medical management with dietary modification and chest tube drainage is highly successful in up to 90% of patients with chylous pleural effusions. However, complications can occur in up to 40% of these patients, including malnutrition, hypovolemia and hyponatremia, hematologic disorders and immunosuppression. In addition, a patient who is receiving heparin-based therapy for another condition is at increased risk of developing chylothorax.
