bubble_chart Overview

The accumulation of chyle or lymph fluid in the pleural cavity due to leakage from the thoracic duct or fistula disease is called chylothorax.

bubble_chart Etiology

Under normal circumstances, except for the right upper limb and head and neck, the lymph fluid from the entire body drains into the thoracic duct, which then empties into the junction of the left internal jugular vein and left subclavian vein in the left neck, flowing into the systemic venous system. The thoracic duct originates from the cisterna chyli in the abdomen between the 12th thoracic vertebra and the 2nd lumbar vertebra, ascends along the course of the abdominal aorta, and travels upward behind and to the right of the abdominal aorta. It passes through the aortic hiatus of the diaphragm into the mediastinum. Within the posterior mediastinum, the thoracic duct ascends between the descending aorta and the azygos vein until it reaches the level of the 5th and 6th thoracic vertebrae, where it turns left and continues upward behind the descending aorta and esophagus. Finally, it reaches the neck posterior and medial to the left subclavian artery and enters the systemic venous system. Given these anatomical features of the thoracic duct, injuries or obstructions below the 6th thoracic vertebra (or below the level of the azygos vein) often cause right-sided chylothorax, while injuries or obstructions above the 5th thoracic vertebra (above the aortic arch) typically result in left-sided chylothorax.

The causes of chylothorax are diverse but can generally be divided into two major categories:

(1) Traumatic: Chest trauma or thoracic surgeries such as esophageal, aortic, mediastinal, or cardiac procedures may injure the thoracic duct or its branches, leading to leakage of chyle into the pleural cavity. Occasionally, hyperextension of the spine can also rupture the thoracic duct.

(2) Obstructive: Intrathoracic tumors such as lymphoma, lung cancer, or esophageal cancer can compress the thoracic duct, causing obstruction. The proximal segment of the obstructed duct may become overly dilated, increasing pressure and leading to rupture of the thoracic duct or its collateral systems. Filariasis-induced obstruction of the thoracic duct is now extremely rare.

Other causes of chylothorax are uncommon. Congenital abnormalities of the mediastinal or pulmonary lymphatic vessels are occasionally seen in neonatal cases of chylothorax. In rare cases of cirrhosis with portal hypertension, thrombosis or other factors causing obstruction of the major upper body veins or pulmonary lymphangioma may lead to leakage of subpleural lymphatic fluid, resulting in unilateral or bilateral chylothorax.

bubble_chart Pathological Changes

Chylothorax contains more fat substances than plasma, abundant lymphocytes, and a considerable amount of proteins, sugars, enzymes, and electrolytes. Once the thoracic duct ruptures, a large amount of chylous fluid leaks into the pleural cavity, inevitably leading to two serious consequences: First, the massive loss of nutrient-rich chylous fluid inevitably causes severe dehydration, electrolyte imbalance, nutritional disorders, and the depletion of large amounts of antibodies and lymphocytes, weakening the body's resistance. Second, the accumulation of a large amount of chylous fluid in the pleural cavity inevitably compresses the lung tissue, displaces the mediastinum to the opposite side, and partially obstructs the large veins returning blood to the heart, impeding blood flow and further exacerbating the insufficiency of systemic blood volume and the failure of cardiopulmonary function.

The amount of chylous fluid leaking into the pleural cavity varies widely, ranging from as little as 100–200 ml per day to as much as 3,000–4,000 ml per day, depending mainly on the size of the thoracic duct rupture, the negative pressure in the pleural cavity, the volume and rate of intravenous fluid administration, and the nature of the ingested food.

bubble_chart Clinical Manifestations

Traumatic thoracic duct injury often presents symptoms early and is easily misdiagnosed as hemothorax in the initial stages. After controlling the bleeding, the pleural drainage fluid changes from clear to turbid and from pale red to milky white, increasing with food intake (especially high-fat foods). Patients exhibit symptoms of severe dehydration, emaciation, and other signs of malnutrition. The accumulation of chylous fluid in the pleural cavity compresses the lung tissue, displacing the mediastinum to the opposite side and obstructing the return of major venous blood to the heart, leading to symptoms such as chest tightness, shortness of breath, and dyspnea. Reduced circulating blood volume and impaired venous return decrease cardiac output, resulting in tachycardia, low blood pressure, and complaints of palpitations, shortness of breath, dizziness, and weakness. Chylous fluid inhibits bacterial growth, making pleural cavity infections rare in chylothorax.

bubble_chart Diagnosis

Traumatic thoracic duct injury often presents symptoms early and is easily misdiagnosed as hemothorax in the initial stages. After controlling the bleeding, the pleural drainage fluid changes from clear to turbid and from pale red to milky white, increasing with food intake (especially high-fat foods). Patients exhibit symptoms of severe dehydration, weight loss, and other signs of malnutrition. The accumulation of chylous fluid in the pleural cavity compresses the lung tissue, displacing the mediastinum to the opposite side and obstructing the return of major venous blood to the heart, leading to symptoms such as chest tightness, shortness of breath, and dyspnea. Reduced circulating blood volume and impaired venous return decrease cardiac output, resulting in tachycardia, low blood pressure, and complaints of palpitations, shortness of breath, dizziness, and weakness. Since chylous fluid inhibits bacterial growth, chylothorax is rarely accompanied by pleural cavity infection.

bubble_chart Treatment Measures

(1) Conservative Treatment By means of closed thoracic drainage or repeated thoracentesis, the pleural effusion is completely drained to promote lung expansion, eliminate residual pleural space, and facilitate adhesion between the visceral and parietal pleura. This helps the ruptured thoracic duct or its branches heal sooner. Additionally, a high-protein, high-calorie, low-fat diet, along with parenteral nutrition, blood transfusion, and fluid replacement, reduces chylous leakage and aids recovery. Conservative treatment is generally suitable for patients in relatively stable condition with daily chylous effusion below 300–500 ml. Continuous treatment for about 1 week is administered to observe any signs of improvement. If conservative treatment fails, surgical intervention should be considered.

(2) Surgical Treatment The ruptured thoracic duct or its branches are ligated through surgical methods. The thoracic duct has abundant collateral circulation, so ligation does not cause obstruction of lymphatic flow. To ensure optimal surgical outcomes, preoperative preparation is crucial. First, the patient's malnutrition and water-electrolyte imbalances must be corrected. If necessary, lymphangiography can be performed to identify the location and extent of the thoracic duct injury, guiding the appropriate surgical approach. The surgical approach typically involves an incision on the affected side. For bilateral chylothorax, a right-sided approach is preferred. Two to three hours before surgery, a high-fat solution mixed with methylene blue is injected through a nasogastric tube to aid in locating the rupture site during the procedure. The thoracic duct is then doubly ligated or sutured above and below the rupture. If the rupture site cannot be identified intraoperatively, the thoracic duct can be exposed and doubly ligated at its anatomical location—below the azygos vein, anterior to the thoracic vertebrae, and posterior to the esophagus. A low-fat diet should be maintained for 2–4 weeks postoperatively.