Background
Chylothorax refers to the the formation of a pleural effusion consisting of chyle, often from a leak of the thoracic duct or one of its main tributaries. [1, 2, 3, 4] The exudative pleural fluid of a chylothorax will contain chylomicrons, and have a concentration of triglycerides over 110 mg/dL and cholesterol below 200 mg/dL. [5] It is a relatively rare condition that may develop as an iatrogenic complication of surgery (thoracic, lung, esophageal, bariatric), [6, 7, 8, 9, 10] or from nontraumatic causes, often as the result of hematologic malignancies. [2]
Chylothorax has no predilection for age or either sex. The incidence of chylothorax ranges from 0.4-4% in esophageal surgery, to 2.5-4.7% in congenital cardiac surgery. [11, 12] Chylothorax has also been reported after coronary artery bypass grafting in adults. Mortality and morbidity rates for cases of chylothorax are approximately 10% in major clinical medical centers [13] ; rates vary by patient characteristics (age and comorbidities) and etiology. Early complications include severe cardiorespiratory and fluid volume disturbances; over time, malnutrition and immunosuppression can occur. [2]
In 1875, H Quinke described the first traumatic chylothorax. In 1948, RS Lampson performed the first thoracic duct ligation.
Chylothorax. This anteroposterior upright chest radiograph shows a massive left-sided pleural effusion with contralateral mediastinal shift. Image courtesy of Allen R Thomas, MD.
Chylothorax. This computed tomography scan of the chest of a 3-year old child reveals a left-sided effusion and underlying parenchymal infiltrate and atelectasis. Image courtesy of Ibrahim Abdulhamid, MD.
Etiopathophysiology
A tear or leak in the thoracic duct causes chylous fluid to collect in the pleural cavity, which can cause acute or chronic alterations in the pulmonary mechanics. In a normal adult, the thoracic duct transports up to 4 L of chyle per day, allowing a rapid and large accumulation of fluid in the chest.
Nontraumatic
Malignant etiologies account for more than 50% of chylothorax diagnoses and are separated into lymphomatous and nonlymphomatous causes. Lymphoma is the most common etiology, representing about 60% of all cases, with non-Hodgkin lymphoma more likely than Hodgkin lymphoma to cause chylothorax. [14] By comparison, nonlymphomatous causes of malignant chylothorax are rare.
Nonmalignant etiologies are separated into idiopathic, congenital, autoimmune, and miscellaneous. These may include lymphangioleiomyomatosis (LAM), congenital conditions (lymphangiectasias, Down syndrome, Noonan syndrome, Gorham-Stout disease), sarcoidosis, lupus, Bechet disease, amyloidosis, nephrotic syndrome, and hepatic cirrhosis. [5, 15] Congenital chylothorax, involving multiple lymphatic vessel anomalies or thoracic cavity defects and potentially associated with other congenital anomalies, is the leading cause of pleural effusion in neonates. [16, 17] Clinicians must rule out all possible malignant causes before designating the chylothorax as idiopathic.
Traumatic
Trauma is the second leading cause of chylothorax (25%). [14]
Iatrogenic injury to the thoracic duct has been reported with most thoracic procedures. In particular, cardiothoracic surgery has been associated with 69-85% of cases of chylothorax in children. [18]
Milonakis et al looked at their experience in managing chylothorax following congenital heart surgery. [18] Of the 1341 children who underwent correction of congenital heart disease, 18 (1.3%) developed postoperative chylothorax, which was managed with a therapeutic protocol that included complete drainage of chyle collection and controlled nutrition. Six children received adjunctive somatostatin. When lymph leakage persisted (range, 2.5-14.7 mL/kg/d for 8-42 days) despite conservative management, surgical intervention was implemented. Once chylothorax resolved, a 6-week trial of low fat diet with supplemental medium-chain triglycerides was given. [18]
No deaths occurred. Conservative therapy was effective in 15 patients (83.3%); 3 patients with persistent drainage required thoracotomy with pleurodesis to achieve resolution, 2 of whom had not had an effective response with previously attempted chemical pleurodesis with doxycycline (range of duration leakage, 5.1-7.4 mL/kg/d for 15-47 days). [18]
In a retrospective study involving 392 pediatric patients (mean age, 97 days) who underwent surgical treatment of congenital heart disease to determine whether the site of insertion of central venous lines was associated with the occurrence of chylothorax after cardiac surgery, Borasino et al reported that the insertion of central venous lines in the upper body had an increased association with postsurgical chylothorax. [19] Overall, 62 of 392 patients (15.8%) developed postsurgical chylothorax; affected patients more frequently had central venous line sites in the upper body (P = 0.03), had higher RACHS-1 scores (risk assessment for congenital heart surgery) (P = 0.03), had longer bypass times (P = 0.02); and had longer cross-clamp times (P = 0.03). The investigators indicated that by avoiding the use of central venous lines in the internal jugular and subclavian veins, the incidence of chylothorax may be reduced in this setting. [19]
Yeh et al implemented a clinical practice guideline for the postoperative management of chylothorax in the pediatric cardiothoracic intensive care unit at their institution. [20] They analyzed two cohorts of patients: those treated before (early cohort; n = 118) and after (late cohort; n = 45) implementation of the guidelines. Patients treated after the guidelines were instituted had shorter duration of mechanical ventilation, reduced use of chest tubes and central venous lines, shorter NPO status, and shorter length of hospital stay. Implementation of clinical practice guidelines at their institution resulted in earlier diagnosis and improved outcomes. [20]
Nonsurgical traumatic injury is a rare cause, usually secondary to penetrating trauma but has also been reported as a result of blunt trauma. [21]
Pseudochylothorax: Chylothorax must be distinguished from pseudochylothorax, or cholesterol pleurisy, which results from accumulation of cholesterol crystals in a chronic existing effusion. Generally, the exudative effusion contains a cholesteraol level above 200 mg/dL, with triglycerides below 50 mg/dL. [5] The most common cause of pseudochylothorax is chronic rheumatoid pleurisy, followed by tuberculosis and poorly treated empyema.
Prognosis
In the short term, a chylothorax may result in acute respiratory failure, similar to that of an accumulating pleural effusion. Long term complications associated with a draining chylothorax can include: [5, 22, 23]
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Hypovolemia, particularly with a chylothorax of high output (>1000 mL/day)
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Protein calorie malnutrition: Draining chyle contains approximately 30g albumin/L and 2.2-6 g/dL of protein
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Electrolyte imbalances: Chyle has a similar composition of electrolytes as serum
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Vitamin deficiencies: Chyle contains a significant concentration of fat-soluble vitamins
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Immunosuppression: Chyle contains a large amount of immunoglobulins
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Chylothorax. This anteroposterior upright chest radiograph shows a massive left-sided pleural effusion with contralateral mediastinal shift. Image courtesy of Allen R Thomas, MD.
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Chylothorax. This computed tomography scan of the chest of a 3-year old child reveals a left-sided effusion and underlying parenchymal infiltrate and atelectasis. Image courtesy of Ibrahim Abdulhamid, MD.
