Q1: Describe the chest radiograph and thoracic computed tomography findings

On chest radiography and thoracic computed tomography left pleural effusion was detected. The left hemidiaphragm was raised because of phrenic nerve injury owing to the surgical intervention.

Q2: What is the most likely diagnosis?

The macroscopic appearance and the biochemical findings (triglycerides >1.2 mmol/l) of the pleural effusion were compatible with chylothorax.

Q3: What is the most likely mechanism of the disorder?

Chylothorax as a complication of CABG is probably a result of injury to the left internal mammary lymphatic during dissection of the vessel or from injury to the parasternal nodes.

Q4: What do you recommend for the treatment?

Conservative therapy is recommended. Oral nutrition by means of a low fat and high protein diet with medium chain triglycerides should be instituted. Total parenteral nutrition can also be tried in case the diet fails to reduce the chylous pleural effusion. The chyle may be drained through an intercostal chest tube and bleomycin pleurodesis may also be carried out.

Discussion

CABG surgery is known to cause pleural effusion due to various aetiologies (see box 1).

Chylothorax is the accumulation of chylous fluid containing high amounts of protein and fat within the pleural cavity due to damage to the thoracic duct. It may be traumatic, non-traumatic, or idiopathic. The traumas may be iatrogenic or non-iatrogenic. Iatrogenic chylothorax is a well recognised complication after thoracic surgery with an incidence of 0.5%.¹ Although unavoidable,² rare cases have been reported as a complication of CABG.^3–11 It usually results from injury to the left internal mammary lymphatic during dissection of the vessel or from injury to the parasternal nodes.³ This could be the most probable mechanism of chylothorax in the present case, as one of the grafts was the left internal mammary artery. Congenital malformations, reoperations, and the use of electrocautery instead of ligation are other mentioned risk factors for the occurrence of this complication.^4,5

The leakage of chyle with a high protein, fat and lymphocyte content, leads to malnutrition and lymphopenia.¹ The woman described here had hypoalbuminaemia and lymphopenia compatible with a substantial amount of chyle leakage.

The management protocol is controversial. Approximately half of the patients with traumatic chylothorax are successfully treated with conservative therapy.² Unless the patient is severely ill and debilitated, medical treatment is recommend before an operation for duct ligation.¹²

A low fat diet with medium chain triglycerides, mostly absorbed directly into the blood, would cause the chyle to decrease in amount. The next step can be total parenteral nutrition. In cases not responding to conservative therapy, chylous effusion can be tapped by repeated aspirations or via intercostal tube drainage. Pleurodesis may be carried out by classical chemicals to stop the leakage. In case the leakage is not relieved by conservative therapy in two or three weeks, thoracic duct ligation through thoracoscopy should be considered.

In the present case, oral nutrition by means of a low fat and high protein diet with medium chain triglycerides was started and a week later replaced by total parenteral nutrition. A control chest radiograph after three weeks revealed resolution of the pleural effusion and the patient was discharged after bleomycin pleurodesis. At follow up, she has been well for four years, without recurrence of the pleural effusion.

In conclusion, chylothorax, a rare complication of CABG, should be kept in mind in patients with pleural effusion. Conservative therapy should be considered and surgery reserved as a last option.

Final diagnosis

Chylothorax.