Traumatic Thoracic Duct Injuries

Thoracic duct injuries may occur in both blunt and penetrating trauma. The thoracic duct transports up to four liters of chyle per day, and a tear in the thoracic duct causes chylous fluid to accumulate in the pleural cavity. Chyle is a milk-appearing fluid that is made up of lymph and emulsified fat extracted during digestions and passed through the bloodstream via the thoracic duct into the subclavian vein.

High suspicion for a thoracic duct injury arises when chest tube outputs do not decrease, have a milk color, or even appear purulent (sometimes these patients are mistaken for having empyemas).  Outputs of 400-600ml per 8-hour shift or more increases suspicion for a chyle leak when there is not active hemorrhage.  If there is no chest tube to evaluate outputs, a chylous effusion may be noted on chest xray, which may be ordered to evaluate symptoms such as dyspnea, decreased breath sounds, shifting dullness, and tachypnea.  It is the second-leading cause of chylothorax (25%).  Quite rarely a rapid accumulation of chyle can causes a tension chylothorax, similar to a tension pneumothorax.

Differential diagnoses include empyema, hemothorax, or pseudochylothorax (accumulation of cholesterol crystals in a chronic effusion -- often due to rhematoid pleurisy, TB, or unresolved empyema.

Diagnosis involves sending the pleural fluid for triglycerides.  If the TAG level is greater than 100, we are 99% certain the fluid is chyle, while a level less than 50 means there is only a 5% chance the fluid is chyle.  Between 50-110, send the fluid for lipoprotein analysis for chylomicrons or cholesterol crystals.  A pleural fluid cholesterol to triglyceride ratio of less than 1 can also diagnose chylous fluid.  A cream (60-90ml/hr for 3-6 hours) through NG tube or via PO challenge will change fluid substance from serous to milky white in a chyle leak.  Lymphangiography can localize the leak.  1% evans blue dye injected into the web spaces of toes can also end up in the chest tube output to diagnosis a leak . Pseudochylothorax will show a cholesterol fluid level of greater than 200 without chylomicrons, and with cholesterol crystals.

Thoracic duct leaks close spontaneously in 50% of cases simply with nil per os and total parental nutrition, along with tube thoracostomy decompression.  The goal remains to reduce chyle production, perhaps by a fat-restricted oral diet or medium-chain triglycerides.  Octreotide can also help resolve a thoracic duct injury.

Surgical intervention is indicated in traumatic thoracic duct injuries if the chyle leak is greater than 1L per day for 5 days or a persistent leak (noted by outputs or fluid triglycerides) greater than 2 weeks on nonoperative management, nutritional complications, loculated chylothorax or trapped lung.  Postesophagectomy patients must have their thoracic duct repaired as a high mortality rate is noted with nonoperative management.

Surgical procedures include thoracic duct ligation between the 8-12th thoracic vertebrae through the right chest by open thoracotomy or VATS.  Pleuroperitoneal shunt can be developed but the risks are infection and obstruction.  Pleurectomy can also be done.  Again, nonoperative management should be the first line of treatment.

Thanks to Dr. Amina Merchant for this post.