This came up in Question 10.2 from the second paper of 2013. The college presented the candidate with a picture of some creamy chest fluid, and invited them to reach the conclusion that this 75 year old man suffered some thoracic duct damage in the course of their elective oesophagectomy.
Causes of chylothorax
An excellent article from 2010 lists several causes of chylothorax beyond the immediately obvious "the surgeon did it". Sure, he just had an oesophagectomy, but the surgery was a total high-five success; couldn't this chyle leak be caused by sarcoidosis?
In brief, the causes of chylothorax are as follows:
- Thoracic surgery
- Specifically, oesophagectomy appears to carry a 3.4% risk of chylothorax
- Neck surgery
- Radiation to the mediastinum
- Thoracic knife or bullet wounds
- Blunt thoracic trauma
- Forceful emesis or cough
- Associated with infection
- Associated with disease states:
- Haemangiomatosis or lymphangiomyomatosis
- Retrosternal goitre
- SVC obstruction
- Transdiaphragmatic movement of chylous ascites
Diagnosis of chylothorax:
- Chylomicron content of pleural fluid is the gold standard. Chylomicrons are large (~1000 nm) lipid globules and they belong in chyle, and so to find them in pleural fluid is profoundly abnormal. Differential lipoprotein content of pleural drain fluid can be assessed by electrophoresis- the chylomicrons form a large discrete band on the gel. Studies of pleural fluid looking for other chacteristic features of chyle leak have used chylomicron presence as the unique identifying feature diagnostic of chyle.
- A Sudan III stain for fat is a more rapidly available test than the gold standard electrophoresis; the dye colours only oil, and will reveal the pleural fluid to be chyle if brightly coloured chylomicrons can be identified on microscopy.
- Other pleural fluid features have also been suggested as diagnostic of chylothorax. These are not as reliable. The linked study followed the pleural fluid results of 74 patients with chylothorax.
- Milky colour: only 44% of these patients had milky chest drain fluid
- Protein and LDH were usually high, but varied wildly. In 14% of patients, Light's criteria would have declared the fluid a transudate.
- Pleural fluid triglyceride level was high in most, but not all patients- again, 14% had a reasonably normal pleural triglyceride level.
- Overall, authors of the abovelinked study had concluded that "the use of traditional triglyceride cutoff values used in excluding the presence of chylothorax may miss the diagnosis in fasting patients".
- Fasting test and fat challenge is the answer to such concerns. Chylomicrons are only found in the circulation within 3 hours of eating; they disappear in the fasted state. Chyle transportation is maximal after a high fat meal. One is therefore able to test for a chyle leak by observing the chest drain output after some sort of "fat challenge", typically with ice cream.
- CT and lymphangiography may be helpful but practically speaking this could be difficult.
Why not just leave it?
Sure, to reopen a chest full of chyle seems to be a distatestful admission of defeat, especially if it was your own surgical skill which caused it. Indeed, what are the arguments for aggressive repair? What are the consequences of chyle leak and chylothorax?
- There is a serious mortality rate, reported up to 50%.
- The chyle collection is not a benign resident of the chest caivity.
- The overlying lung will collapse and become infected.
- The chyle itself can become infected, and turn into an empyema.
- Chyle is fat on its way to the systemic circulation. Loss of chyle into the chest drain will result in the loss of numerous useful substances:
- Caloric intake will be impaired
- Fluid loss will occur
- Chyle is full of lymphocytes; the loss of lymphocytes will occur (and it is diffuclt to replenish them)
- Fat-soluble vitamins will be depleted, and their replacement will be ineffective
Management of chylothorax
- Low fat diet - or at least a diet rich in medium-chain triglycerides (hoping with reduced chyle flow the defect will close on its own)
- TPN may be required - but is not an essential part of management. If one were to use TPN, one may wish to use medium-chain fatty acids - i.e. anything with a chain length shorter than laurate (12 carbon atoms)
- It seems octreotide is an effective treatment option
- Surgical ligation is always an option, and some say it should be the first option.