Asian Cardiovasc Thorac Ann 2007;15:e58-e59
© 2007 Asia Publishing EXchange Ltd
Chylothorax Following Cardiac Surgery Caused by Unusual Lymphatic Anatomy
Pradeep Narayan, FRCS,
Natasha Rahaman, MRCS,
Thomas F Molnar, PhD1,
Massimo Caputo, MD
Bristol Heart Institute
1 Thoracic Surgery, Bristol Royal Infirmary, Bristol, United Kingdom
For reprint information contact: Massimo Caputo, MD, Tel: 44 117 928 3145, Fax: 44 117 929 9737, Email: massimocaputo{at}hotmail.com, Bristol Heart Institute, Bristol Royal Infirmary, Bristol BS2 8HW, United Kingdom.
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ABSTRACT
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Chylothorax due to injury to the thoracic duct and lymphatic channels during left internal thoracic artery harvest is well described. However, high volume leakage of chyle due to disruption of aberrant thymic collateral lymphatic channel in the anterior mediastinum has not been described previously. We describe such a case which was managed by early surgical exploration, ligation of the aberrant duct, and insertion of a pleuro-peritoneal shunt.
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INTRODUCTION
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Chylothorax following coronary artery bypass graft (CABG) is a rare complication1 but is associated with significant mortality. Management strategies of chylothorax are variable and recurrence is not uncommon. Moreover, relapse of chylothorax can result in life threatening cachexia.2 Management strategies include conservative treatment for low volume leaks (< 1000mL·day–1), percutaneous embolization of the thoracic duct, video assisted thoracic surgery (VATS) exploration with or without fibrin glue, talc pleurodesis, and surgical exploration.
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CASE REPORT
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A 65-year-old extremely frail lady weighing 45 kilos underwent a mechanical mitral valve replacement for deteriorating mitral regurgitation and a left internal thoracic artery (LITA) graft to the left anterior descending artery (LAD). Co-morbidities included persistent atrial fibrillation, poor left ventricular function secondary to cardiomyopathy, and hypercholesterolemia. The operative procedure was uneventful. However, drainage of a milky white fluid, confirmed to be chyle on biochemical analysis, was noted immediately after surgery and was almost a liter on the first postoperative day. Despite immediate standard conservative management with medium chain triglycerides and octreotide, chyle loss increased to almost 2 L·day–1 by the third postoperative day. Rapidly deteriorating nutritional and metabolic status prompted surgical exploration. High fat supplement was given preoperatively to localize the site of injury.
Re-exploration of the median sternotomy identified a severed duct in the thymic area measuring about 2 mm in diameter, and thought to be an aberrant lymphatic duct. This was secured with surgical clips. No other site of injury was detected. As the surgical finding was unusual and in the absence of a lymphangiogram was not entirely convincing; a prophylactic pleuro-peritoneal shunt was inserted in order to prevent a recurrence. However, the drainage of chyle ceased almost immediately and the pleuro-peritoneal shunt was removed after 24 hours. The patient remains well with no recurrence 4 months after the procedure.
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DISCUSSION
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The thoracic duct is prone to injury during thoracic surgery due to its extremely variable anatomical course. It occasionally divides at its upper part into two branches, right and left; the left ending in the usual manner, while the right opens into the right subclavian vein, in connection with the right lymphatic duct. It also may enter into a short plexus and terminate in the vein by two or more branches.3
Chylothorax following CABG commonly results from transection of the thoracic duct or the collateral lymphatic channels usually in the proximity of the origin of the left subclavian artery due to attempts to gain extra length on the conduit, and has been described previously.4 However, chylothorax in the magnitude of our case due to injury of the large aberrant thymic lymphatic duct in the anterior mediastinum has not been previously described. The thymus is routinely divided to gain adequate exposure to the aorta for cannulation and proximal anastomosis. Multiple small lymphatic channels are present in this area. A large lymphatic duct is unusual in this anatomical situation and owing to the rarity even when present may be mistaken for a venous tributary. Electrocautery which is adequate for securing blood vessels is inadequate to control leakage from the lymphatics. This is due to the fact that lymph contains less coagulable material than plasma, and hence clot formation is less reliable with the use of electrocautery in the case of lymphatics.4
Chylothorax following CABG can also occur due to duct injury following central line placements. Use of tape around the superior vena cava (SVC) and venous thrombosis during cardiopulmonary bypass causing an increased SVC pressure leading to obstruction to the drainage of chyle and subsequent extravasation; and thrombosis of the thoracic duct and subsequent backflow and extravasation through the disrupted lymphatic channels are other mechanisms.5
While the incidence of postoperative chylothorax is 0.5%, the resultant mortality is as high as 50% when adequate treatment is not promptly performed.7 Successful management of chylothorax following CABG is dependent on the volume and duration of drainage and also on the metabolic, nutritional, and immune status of the patient. The available options are conservative therapy, thoracic duct embolization, VATS duct ligation, and open surgical exploration. Conservative therapy is generally reserved for low volume drainage (< 1000 mL·day–1) and usually involves use of a low fat diet with medium chain triglycerides, which are absorbed directly from the portal venous system, or total parenteral nutrition. Octreotide, a somatostatin analog, has been used as an adjunct in conservative management with favourable outcome.5
Percutaneous catheterization and embolization of the thoracic duct have a technical success rate of less than 50%.6 Video assisted thoracic surgery has been advocated as a less invasive surgical option for identification and clipping of the disrupted duct with or without the use of fibrin glue or talc pleurodesis.7 However, experience is limited and identification of the site of disruption is not always possible. Pleuro-peritoneal shunt has been used successfully in children as well as adults and may offer a reasonable and effective management option for chylothorax in selected cases.8 Surgical exploration and ligation of the thoracic or lymphatic duct is generally recommended for high volume drainage (> 1000 mL·day–1) to expedite recovery and minimize hospital stay.
Despite successful ligation the possibility of leakage remains, either because of incomplete occlusion or due to the presence of other lymphatic channels.1 A relapse therefore may occur and can result in life threatening cachexia,2 and multiple re-operations to control chylothorax are not uncommon. Hence, the additional use of pleuro-peritoneal shunt as a prophylactic measure may be considered when the standard anatomy of the thoracic duct appears intact, the site of injury appears extremely unusual and unconvincing, and a lymphangiogram can not be performed.
Based on our experience during CABG the presence of a large thymic collateral lymphatic channel could not be excluded. Surgical clips or sutures are recommended to secure these ducts rather than electrocautery. Early surgical exploration is necessary for successful management of a high volume chylothorax.
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REFERENCES
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ABSTRACT
INTRODUCTION
