Management of thoracic duct injury following radical neck dissection.

PAPER IV JUNE 2008
Q. Management of thoracic duct injury following radical neck dissection.

Chyle Leak

Chyle leaks have been reported to occur following neck dissections in 1–2.5% of cases, with 25% occurring on the right. Chyle is a mixture of lymph from interstitial fluid and emulsified fat from interstitial lacteals. It is mildly alkaline and on standing forms three layers, a cream top layer, milky middle layer, and a lower layer of cellular sediment. The fat content is 1–3%, largely triglycerides, which are responsible for the milky appearance and greasy feel. The daily drainage may reach two to four litres.

Anatomy

The thoracic duct begins at the cisterna chyli and continues upwards into the thorax posterior to the aorta through the aortic hiatus of the diaphram. It runs in the posterior mediastinum along the right anterior aspect of the vertebral bodies between the aorta and the azygous vein. The thoracic duct crosses the midline at the fifth or sixth thoracic vertebra and continues to extend superiorly along the left posterior border of the oesophagus. It exits the thorax posterior to the left common carotid artery between this vessel and the left subclavian artery. As it enters the neck, it arches superior, anterior and lateral to form a loop that terminates into the venous system. This loop is anterior to the vertebral artery and the thyrocervical trunk. It courses between the internal jugular vein and the anterior scalene muscle superficial to the deep cervical fascia overlying the phrenic nerve. The loop is always found within 2 cm of the internal jugular-subclavian vein junction, and its maximal height is usually 3–5 cm above the clavicle. The right jugular, subclavian, and the tracheobronchial trunks form the right lymphatic ducts. These usually terminate separately in the region of the right internal jugular — subclavian vein junction. A single duct on the right is thought to be rare.

Presentation

A chyle leak may present in the neck, chest or abdomen. If left untreated, it may result in a metabolic, nutritional and immunologic complication. Patients will eventually become weak, dehydrated, oedematous, and emaciated. Chylothorax can result from injury in the chest or neck. It may progress from the neck by tracking along fascial planes to the mediastinum, where it causes tissue maceration and inflammation, resulting in rupture of the pleura. The dangers of a chylothorax include cardiopulmonary compromise because of compression of the lungs, leading to a mediastinal shift with distortion of the great vessels. The diagnosis of a chyle leak can be intra or postoperative. During dissection of the lower left portion of the neck, chyle may macroscopically be recognised as a milky substance, or the thoracic duct itself may be seen with a tear in it. If a leak is suspected it can be confirmed by asking the anaesthetist to apply a continuous positive airway pressure and place the patient in the Trendelenburg position. Postoperatively, chyle may present in the drainage bottle, but if it is a low volume leak, it can be missed initially because it is mixed with blood. Even chemical analysis of the fluid may not be conclusive. However, >100 ng/dL triglycerides or >4% chylomicrons indicate possible chylous leakage.

Management

It is universally accepted that the optimum management of a chylous fistula is by prevention. If the leak is identified during surgery, every effort should be made to arrest it immediately. Ligation with 3-0 or 4-0 non-absorbable suture without going through the duct wall should be performed. It has been suggested that inclusion of the medial edge of the anterior scalene muscle will help prevent duct laceration during ligation. Leakage may continue to occur postoperatively, even when the procedure is apparently successful because of unidentified injuries to the duct or additional terminations. Medical management involves an elemental diet supplemented with medium chain triglycerides (MCT). These are absorbed directly into the portal circulation, bypassing the lymphatic system.Total parentral nutrition (TPN) is an alternative, but is not recommended by all. In theory, interruption of entral alimentation should reduce intestinal peristalsis and lymph flow.However, the disadvantages are the need for central venous access, associated morbidity, and cost. The application of pressure dressings to encourage closure and the formation of chyle collection are usually futile, as the anatomy is not contoured for such an efficient dressing to be applied continuously. Instead, the use of continuous suction drainage is recommended to prevent chyloma formation and avoid the associated intense inflammatory reaction. The indications and timing for surgical intervention, when a chyle leak is diagnosed in the postoperative phase, remain controversial. Surgery is appropriate if the leak is in excess of 500 ml per day for four or more consecutive days, or if a chyloma formation could not be controlled with pressure dressings or serial aspirations. Surgery is also recommended when chyle drainage is in excess of 500 ml per day after one week of medical management, in case of persistent low-output drainage for a prolonged period, or if complications develop. In these situations, a thorascopic approach to the thoracic duct, on the right side of the chest is considered the definitive management option, with minimal morbidity.

Ref: surgical complications 2007