Chylothorax refers to the presence of lymphatic fluid in the pleural space secondary to leakage from the thoracic duct or one of its main tributaries. In 1875, H. Quinke described the first traumatic chylothorax. In 1948, R.S. Lampson performed the first thoracic duct ligation.
Chylothorax has no predilection for age or either sex. The prevalence of chylothorax after various cardiothoracic surgeries is 0.2-1%.
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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.
Malignant etiologies account for more than 50% of chylothorax diagnoses and are separated into lymphomatous and nonlymphomatous. Lymphoma is the most common cause, representing about 60% of all cases, with non-Hodgkin lymphoma more likely than Hodgkin lymphoma to cause a chylothorax. By comparison, nonlymphomatous causes are rare.
Nonmalignant etiologies are separated into idiopathic, congenital, and miscellaneous. Clinicians must rule out all possible malignant causes before designating the chylothorax as idiopathic. Congenital chylothorax is the leading cause of pleural effusion in neonates.  Miscellaneous causes include cirrhosis, tuberculosis, sarcoidosis, amyloidosis, and filariasis.
Trauma is the second leading cause of chylothorax (25%).
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. 
Milonakis et al examined their experience in managing chylothorax following congenital heart surgery. 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 diet of medium-chain triglycerides was given.
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).
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 has an increased association with postosurgical chylothorax.  Overall, 62 of 392 patients (15.8%) developed postsurgical chylothorax; affected patients more frequently had central venous line sites in the upper body (P = .03), had higher RACHS-1 scores (risk assessment for congenital heart surgery) (P = .03), had longer bypass times (P = .02); and had longer cross-clamp times (P = .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. 
Nonsurgical traumatic injury is a rare cause, usually secondary to penetrating trauma.
Pseudochylothorax: Chylothorax must be distinguished from pseudochylothorax, or cholesterol pleurisy, which results from accumulation of cholesterol crystals in a chronic existing effusion. The most common cause of pseudochylothorax is chronic rheumatoid pleurisy, followed by tuberculosis and poorly treated empyema.