Chylothorax is a topic covered in the Pediatric Surgery NaT.

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Pathophysiology

What is the normal and variant anatomy of lymphatic drainage in the abdomen and thorax?

By the ninth week of fetal life, the jugular and retroperitoneal lymphatic sacs connect and this sets the stage for lymphatic drainage from the abdomen to the left jugular vein that traverses the thoracic duct.

The thoracic duct originates at the cisterna chili, located at the level of the second lumbar vertebral body, posterior and to the right of the aorta and adjacent to the right crus of the diaphragm. The duct passes through the aortic hiatus into the chest, where it is found anterior to the vertebral bodies and right intercostal arteries and posterior to the esophagus. In general, in the region between the fourth and sixth thoracic vertebrae the duct passes toward the left side of the mediastinum and runs posterior to the aorta and the left subclavian artery adjacent to the ligamentum arteriosum, where it is susceptible to injury during duct ligation and other cardiac procedures.

thoracic duct anatomy

Schematic illustration (A) of the typical course of the thoracic duct arising from the cisterna chyli at T12 to L2 to the right of the midline coursing cranially to enter the thorax through the aortic hiatus. The intrathoracic portion of the duct courses to right of the descending aorta, along the vertebral column and crosses midline to the left at T5 to T6 ascending above the clavicle, behind the jugular vein and curving inferiorly to drain into the left jugulovenous angle. Corresponding fluorographic image (B) demonstrating the typical course of the thoracic duct (white arrows). (image courtesy of Johnson, Eur Radiol 26:2482-2493, 2016)

Above the thoracic inlet, the duct passes three to six cm above the left clavicle, anterior to the anterior scalene muscle and posterior to the left carotid artery and internal jugular vein then curves downward to drain into the internal jugular vein in 46%, the jugulosubclavian junction in 32% and the subclavian vein in 18% [1].

In about one-third of individuals, the anatomy of the thoracic duct differs from the standard description and awareness of these variants is important in order to avoid inadvertent operative injury and to diagnose the etiology of a chylothorax [2].

thoracic duct anatomic variants

Multiple schematic illustrations showing clinically relevant variants of the cisterna chyli and thoracic duct and their relation to the descending aorta, azygos vein, subclavian veins, and spine. Highlighted variants include: complete left sided course, complete right sided course, proximal and distal duplications, plexiform variation, and complete absence of the cisterna chyli. (image courtesy of Johnson, Eur Radiol 26:2482-2493, 2016)

The duct is partially duplicated in 15 to 20% of cases and in another 12 to 15% there are mirror image ducts on both sides of the aorta that empty into their corresponding jugulosublclavian venous system. In addition, eight percent of thoracic ducts are completely right or left sided. In cases of dextrocardia the thoracic duct is typically left sided which is potentially relevant to the treatment of chylothorax following a cardiac operation in these patients [3].

What congenital conditions lead to chylothorax?

The majority of cases of chylothorax in infants and children are secondary to thoracic duct obstruction or injury from thoracic and cardiac surgical procedures. However, when a chylothorax is the result of a congenital condition associated with a lymphatic malformation of the lungs or pleura, management may be more complicated and less successful.

chyle leak

Digital subtraction image of the thorax during lymphangiography shows oily contrast medium moving up the thoracic duct to the left supraclavicular region (arrow). After this, droplets of contrast medium could be seen within the left chest (arrowheads). (image courtesy of Fishman, J Pediatric Surg 36:1269-72, 2001)

Congenital pulmonary lymphangectasia is a condition in which the interlobar and subpleural pulmonary lymphatic vessels are dilated and prone to leakage [4]. This may occur due to the failure of pulmonary interstitial tissues to appropriately regress during fetal life [5]. Lymphangectasia may occur sporadically or in association with a variety of disorders including trisomy 21 [6][7], Noonan syndrome [8] and Turner syndrome [7]. Gorham-Stout disease is a condition in which there is extensive proliferation of lymphatic vessels within bone that leads to bone loss. When rib involvement extends beyond the bone a large volume chylous pleural effusion may develop [4][9] that is very difficult to treat [10].

In rare situations, infants are born with extensive central venous thrombosis and this can result in chylothorax that may be treated with thrombolysis [11].

Other rare congenital causes of chylothorax include a mutation in the integrin alpha 9 gene [12] and the syndrome of X-linked myotubular myopathy [13].

The occurrence of chylothorax after repair of congenital diaphragmatic hernia (CDH) was first reported in 1973 [14]. The Congenital Diaphragmatic Hernia Study Group recently found the incidence of chylothorax after CDH repair to be 4.7% [15] and, similar to a number of smaller series [16][17], noted that patch repair and extracorporeal life support (ECLS) were associated with a higher likelihood for chylothorax. A prevailing theory persists that chylothoraces develop in patients with CDH due to lymphatic disruption during repair based upon the finding that sac resection [18] and patch repair [17] are associated with a greater incidence of chylothorax. However, it is increasingly apparent that the embryological events that lead to CDH also predispose to lymphatic abnormalities [19] and chylothorax that is exacerbated by greater degrees of pulmonary hypertension.

Occasionally, a chylothorax can occur with transdiaphragmatic flow from a chylous ascites.

What is the mechanism of traumatic chylothorax?

For the purposes of this chapter, traumatic chylothorax is considered as distinct from iatrogenic injuries to the thoracic duct that result from operations or other medical interventions. It is extremely unusual for blunt trauma to the chest to result in a chylothroax [20] but when no other etiology for a chylothorax in a child is apparent, nonaccidental trauma should be considered [21]. A small series of thoracic duct injuries with chylothorax due to penetrating trauma to the lower neck and chest has been reported in adults [22] but because this mechanism is so rare in children only a single case has been published [23].

What are the iatrogenic causes of chylothorax?

The incidence of a chylothorax following operations for congenital heart disease is about three percent [24][25]. Younger and smaller patients are at a much greater risk and a chylothorax has been identified in as many as 9.2% of infants [26] and in as few as 1.3% of older children [27] undergoing cardiac procedures. Children with a postoperative chylothorax are more likely to have had longer cross clamp and cardiopulmonary bypass times [26].

Injury to the thoracic duct is probably not the causative event in most cases of postcardiac surgery chylothorax as the preceding operations often do not involve dissection near the duct’s course [27]. A more frequent etiology is likely to be disruption of small lymphatic vessels surrounding the aorta or pulmonary artery. In addition, operations that result in increased caval pressures, such as the Fontan procedure, are associated with a greater incidence of chylothorax [24]. Finally, central venous thrombosis is significantly more prevalent in children with chylothorax after cardiac surgery [28] suggesting that this may be a causative factor independent of lymphatic injury.

As with cardiac operations, chylothorax can result from venous thrombosis due to central venous catheterization for parenteral nutrition and medication [29][30] or ECLS [31].

Chylothorax has been reported after anterior and posterior spinal dissection and stabilization due to direct injury to the thoracic duct [32].

What are the consequences of chronic lymph loss?

Respiratory insufficiency is the typical presenting symptom of a chylothorax but after thoracic drainage morbidity is usually due to the loss of chylous fluid. The manifestations of chronic lymph depletion include fluid and electrolyte imbalance, malnutrition, intravascular thrombosis and immunodeficiency.

Ongoing, large volume chylous drainage leads to substantial protein loss [33] that must be managed with supplementation of enteral or parenteral protein intake beyond typical maintenance amounts in order to avoid growth failure, infection and poor wound healing. Optimally, this is done empirically, but monitoring of prealbumin, transferrin, retinol binding protein and the physical exam can aid in the detection of a recent deterioration in nutritional status [34].

Selenium is particularly prone to depletion with chylous drainage and deficiency may lead to cardiomyopathy [32]. Standard selenium concentrations in parenteral formulas are inadequate to compensate for losses that may occur with a chylothorax.

Children with chylothorax following cardiac operations have been found to have significantly lower antithrombin levels than similar children without chylous loss [35] suggesting that antithrombin is lost in chylous fluid. Antithrombin should be supplemented in children with a long standing chylothorax. In the context of a new thrombotic event, antithrombin deficiency should be strongly considered as the etiology.

Children with chylothorax are at a substantial risk for the development of immunodeficiency and infection is the typical cause of mortality when a chylous leak cannot be stopped or internalized. Chylothorax is associated with lymphopenia and immunoglobulin G deficiency [36] although levels of natural killer cell and memory T cells are maintained. Unfortunately, the administration of intravenous immunoglobulin has not been shown to reduce the incidence of infection in children with chylothorax [36].

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Last updated: May 24, 2018

Citation

TY - ELEC T1 - Chylothorax ID - 829672 A1 - Gollin,Gerald,MD AU - Cusick,Robert,MD AU - Tuggle,David,MD Y1 - 2018/05/24/ PB - Pediatric Surgery NaT UR - https://www.unboundmedicine.com/medline/view/Pediatric-Surgery-NaT/829672/all/Chylothorax ER -