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Thoracic Duct and Chylothorax: General Considerations

last modified on: Wed, 02/19/2020 - 10:01

Iowa Thoracic Surgery

 

Please direct questions and comments to Evgeny V. Arshava, MD evgeny-arshava@uiowa.edu

 

Thoracic duct ligation for spontaneous chylothorax thoracoscopically VATS in patient with a metastatic carcinoma

 

See also

 

 

GENERAL CONSIDERATIONS

Thoracic duct (TD) ligation is performed exclusively for chylous pleural effusion or chylothorax. Chylothorax is a relatively uncommon condition and can be classified based on etiology into non-traumatic and traumatic (approximately equal in frequency). About 5 % of chylothorax cases are idiopathic, without an identifiable source after extensive work-up.

Non-traumatic chylothorax is usually a result of malignancy or infection (compressive obstruction, direct involvement of lymph nodes and lymphatics, excess amounts of lymphatic fluid production). Lymphoma is the most common culprit.

Traumatic chylothorax may occur with blunt or penetrating trauma or during surgery. Thoracic surgery is the major cause of surgical chylothorax and often requires surgical correction. Postsurgical chylothorax occurs in approximately 0.5% of all intrathoracic procedures, but is the most common indication for TD ligation.

The incidence of postoperative chylothorax may be as high as 10% after esophagectomy and up to 5% after lung resection with mediastinal lymph node dissection. Risk factors for chyle leak after esophagectomy include transthoracic approach, neoadjuvant chemoradiation, lower preoperative body mass index, and midesophageal location. Chylothorax may also develop after coronary artery bypass grafting (with left internal mammary artery dissection), large mediastinal tumor resection, aortic surgery, and other major chest surgeries. Iatrogenic chylothorax has been described after central venous catheter placement, pacemaker placement, and embolization of pulmonary arteriovenous malformations.

 

Physiology

  • Chyle is formed in the lacteal system of the small intestine.

    • The image below demonstrates lymphatics (marked with arrows) of the small bowel during trauma laparotomy in a patient soon after meal. 

Engorged lymphatic vessels of small intestines of nonfasting trauma patient_annotated

  • Intestinal enzymes break the small- and medium-chain triglycerides into free fatty acids that are readily absorbed into the portal circulation.

  • Long-chain triglycerides cannot be broken down and are fused with phospholipids, cholesterol, and cholesterol esters into chylomicrons.  Chylomicrons are absorbed into the lymphatic channels of the small intestine to form the chyle.

  • The normal lymphatic circulation is up to 2.5 L per day. This includes chyle formed in the small bowel and the residual interstitial fluid from tissues that is not drained by venous system. Ninety-five percent of the volume comes from the liver and intestinal lymphatic channels, while the amount from the extremities is negligible.

  • Lymph is the unique biofluid containing lipids, proteins, electrolytes, antibodies, and lymphocytes

  • Chyle leak, proportionally to its volume, thus leads to volume depletion, leukopenia, and malnutrition. All these factors have detrimental effects on the already compromised postoperative patients.

  • Large-volume effusion leads to compression of the lung and compromise of pulmonary function.

  • Infection with typical bactria is a rare complication of chylothorax because of the bacteriostatic properties of lecithin and fatty acids.

Spontaneous chylothorax in a patient with an atypical mycobacteria infection and positive AFB growth in the chyle culture

  • While the exact volume of chyle leak per day that requires TD ligation may be controversial, it is clear that very high output (>1 L/day) requires prompt interventions to stop physiologic derangements (hypovolemia, malnutrition, and immunosuppression) and to reexpand the lung (see Thoracic duct ligation). Uncontrolled chyle leak is associated with increased mortality and morbidity.

 

Anatomy

  • The superficial lymphatic vessels of the subcutaneous tissues follow the same routes as veins. The deep lymphatic vessels of the viscera generally follow the arteries.

  • The lymphatic drainage of the body is asymmetrical. The right lymphatic duct drains the lymph fluid from right sides of the head, thorax, and right upper limb into the right subclavian vein. The lymph from the rest of the body is carried into the bloodstream through the TD.

  • The cisterna chyli is an approximately 2 × 3 cm sac-like chamber that receives lymph flow from the lower abdomen, pelvis, and lower limbs. It may be absent, but is typically  is found along the vertebral column anywhere between L3 and T10, more commonly on the L1 vertebral body next to the right diaphragmatic crus.

  • The TD originates at cisterna chyli at the level of L1–T12 vertebrae to the right and behind the aorta. This location could be a backup approach to consider if the other interventions fail.  Most abdominal tributaries ascend through the aortic hiatus (T12) to the right of the aorta. Some branches ascend anteriorly or posteriorly to the aorta or through a separate opening in the diaphragm.

  • The TD is a thin-walled, 2–4 mm structure that can be difficult to visualize in human body. In most cases a TD is formed within 3 cm interval cranial to the esophageal hiatus (T10). Such high caudate confluence of abdominal tributaries is different from simplistic drawings of a single duct at the level of the diaphragm in common anatomic atlases. In most patients though, the duct is a single structure at T11–T8 levels, and this is the most predictable location of the TD in the chest. A right transthoracic approach is thus a preferred route for TD ligation regardless of the exact site of the leak and its laterality.

  • Duplications are present in almost half of individuals.

  • TD ascends posterior to the esophagus, between the aorta and azygos vein.

  • At the T5–T7 level the TD crosses to the left of the spine behind the aorta. This location is likely the most common area when the TD can be injured during esophagectomy (see also Transhiatal esophagectomy) or aortic arch surgery. Thus injury to the duct below this level usually results in a right chylothorax, and injury above it results in a left chylothorax.

  • On the left the TD ascends on the left side of the esophagus, beneath the pleural reflection and posterior to the left subclavian artery to the left neck approximately 4 cm above the clavicle. Then it turns laterally behind the carotic sheath. It drains variably into a venous system, more commonly into the junction of left subclavian vein with the internal jugular vein at the medial margin of the inferior scalene muscle.

  • Anatomy of the TD is only “constant only in its variability”.  Up to half of individuals have anomalous collaterals communicating with the azygos, intercostal, and lumbar veins. Large proportions of individuals have a duplicated left TD the level of the diaphragm.

  • Prophylactic ligation of the TD during esophagectomy is controversial. Routine TDL during esophagectomy has not been shown conclusively to be effective for preventing postoperative chylothorax. Additionally, prophylactic TDL may reduce overall survival after carcinoma resection, possibly associated with a decreased return of immune factors and proteins to circulation. It may be considered after extensive dissection or if a large amount of clear fluid or chyle (if preoperative fat was administered) is seen accumulating in the chest or abdomen during resection. 

 

Diagnosis

  • A chylothorax is suspected or diagnosed when a milky white chylous fluid is draining from the chest of a patient receiving oral or enteral nutrition. 

    • The image below demonstrates serosanguinous output in a right chest tube and milky output (chyle) from the left chest in patient after coronary bypass grafting.

Chylothorax after coronary bypass grafting with serosanguinous output in a right chest tube and milky chyle output from the left chest

 

  • The chyle is milky white only when fat is being transported from the gut. Thus the pitfall is that a patient with nil per os (NPO) status (early postoperative patient) may have only serosanguinous or clear output. With initiation of enteral nutrition, it immediately turns milky. Thus, a disproportionately high postoperative chest tube output (> 400mL/day) in a patient without enteral intake needs to be worked up for a chyle leak.

  • The definitive diagnosis is based on detection of triglycerides in the pleural fluid at a level >100 mg/dL. Levels <50 mg/dL exclude the diagnosis. When the triglyceride level is between 50 to 100 mg/dL, then the presence of chylomicrons on lipid electrophoresis can confirms the diagnosis.

  • Lymphocytes are the predominant cells in chyle, and a 90% lymphocyte count is virtually diagnostic in patients with NPO status.

 

Initial Management

  • Once the diagnosis is made, total parenteral nutrition and bowel rest with aggressive correction of fluid and electrolyte losses are initiated. Initial management is always conservative and includes drainage of the chyle with a chest tube to re-expand the lung.

  • Leaks <500 mL/day are classified as low-volume and leaks >1000 mL/day as high-volume.

  •  Total parenteral nutrition is started for patients with a high-volume chyle leak or in whom bowel rest is indicated.

  • A low-fat diet or a medium-chain triglyceride (MCT) diet can be attempted in cases of low-volume leaks. However, up to 80% of chylous triglycerides may be non-MCTs despite an MCT diet. Thus, the MCT diet more often does not abolish chyle production completely, and total parenteral nutrition may be indicated even in low-volume chyle leaks

  • Octreotide may slow the rate of leak, but it very rarely stops it completely. Pleurodesis through the chest tube has been described, but it should be discouraged because it is minimally effective and leads to pleural adhesions that complicate subsequent operations.

  • Further treatment depends on the level on injury and volume of chyle output.

  • Up to half of chyle leaks will close spontaneously within 2 weeks of conservative management.

  • There is no consensus as to the length of time that conservative therapy should be tried before performing TD ligation. If conservative therapy does not at least slow down a high-volume leak, TD ligation should be considered early (within several days) for high-volume leaks. Fourteen days has been suggested as a maximum limit of conservative management for low-volume leaks. The decision to perform TD ligation earlier than 2 weeks for low-volume leaks can be justified due to the high success rate of TD ligation.

  • A shorter course of conservative management is recommended in debilitated patients due to the potential for worsening their condition further with ongoing chyle losses.

  • A chylous output of >10 mL/kg on the 5th day or >13 mL/kg/day on the 3rd day of nonoperative management predicts failure of nonoperative treatment(, (Dugue 1998, Miao 2015)

  • High-volume chyle leaks after esophagectomy require prompt TD ligation within several days of diagnosis.

  • After pulmonary resection, a chylothorax most commonly occurs due to biopsy or dissection of mediastinal lymph nodes with engorged lymphatics involved with metastatic nodal disease, or in patients who have received neoadjuvant therapy for N2 disease. Most chyle leaks after pulmonary resections heal with non-operative management. Assuming the output is low, these patients can be initially managed with a MCT diet for 2 weeks. In carefully selected patients this can be done on an outpatient basis. Prior to the tube removal, patients are challenged with a fatty meal.

  • If the chyle leak decreases to <250 mL/day, or <10 cc/kg/day on the 5th day of non-operative management, then oral diet or tube feeds can be attempted.

 

Suggested reading:

 

Iosifov GM. Human lymphatic system with description of its structures and lymphatic flow. The Tomsk Imperial University. 1914;59: 1-96.

Иосифовъ ГМ. Лимфатическая система человѣка съ описанiемъ аденоидовъ и органовъ движенiя лимфы. Съ 80 рис. въ текстѣ и таблицахъ. Извѣстiя Императорскаго Томскаго Университета. 1914; 59:3:1-9 (in Russian)

Davis H. A statistical study of the thoracic duct in man. American Journal of Anatomy. Jan. 1915

Zhdanov DA. The functional anatomy of the lymphatic system. Gorky, The Soviet Union: Gorky State Medical Institute; 1940.

Bessone LN, Ferguson TB, Burford TH. Chylothorax. Ann Thorac Surg. 1971 Nov;12(5):527-50.

Stranahan A, Alley RD, Kausel HW, Reeve TS. Operative thoracic ductography. J Thorac Surg. 1956 Feb;31(2):183-95; discussion, 195-8.

Defize IL, Schurink B, Weijs TJ, Roeling TAP, Ruurda JP, van Hillegersberg R, Bleys RLAW. The anatomy of the thoracic duct at the level of the diaphragm: A cadaver study. Ann Anat. 2018 May; 217:47-53. doi: 10.1016/j.aanat.2018.02.003. Epub 2018 Mar 3.

Johnson OW, Chick JF, Chauhan NR, Fairchild AH, Fan CM, Stecker MS, Killoran TP, Suzuki-Han A. The thoracic duct: clinical importance, anatomic variation, imaging, and embolization. Eur Radiol. 2016 Aug;26(8):2482-93. doi: 10.1007/s00330-015-4112-6.

Hulscher JB, Tijssen JG, Obertop H, van Lanschot JJ. Transthoracic versus transhiatal resection for carcinoma of the esophagus: a meta-analysis. Ann Thorac Surg. 2001 Jul;72(1):306-13.

Hou X, Fu JH, Wang X, Zhang LJ, Liu QW, Luo KJ, Lin P, Yang HX. Prophylactic thoracic duct ligation has unfavorable impact on overall survival in patients with resectable oesophageal cancer.  Eur J Surg Oncol. 2014 Dec;40(12):1756-62. doi: 10.1016/j.ejso.2014.05.002. Epub 2014 May 22.

Dugue L et al. Output of chyle as an indicator of treatment for chylothorax complicating oesophagectomy. Br J Surg. 1998 Aug;85(8):1147-9.

Miao L, Zhang Y, Hu H, Ma L, Shun Y, Xiang J, Chen H. Incidence and management of chylothorax after esophagectomy. Thorac Cancer. 2015 May;6(3):354-8. doi: 10.1111/1759-7714.12240. Epub 2015 Feb 26.