1

What is chylothorax?

Chylothorax is defined as the accumulation of lymphatic fluid in the pleural space.

2

How is chylothorax classified?

Chylothorax is usually classified as:

a)

traumatic;

b)

non-traumatic;

c)

idiopathic.

3

What are the non-traumatic causes of chylothorax?

Malignancy. Lymphoma is the most frequent but any malignancy may cause chylothorax either by direct infiltration or lymphatic involvement.

Thoracic irradiation.

Superior vena cava syndrome and subclavian vein thrombosis.

Infection (histoplasmosis, tuberculosis with lymphadenitis, filariasis).

Sarcoidosis.

Down’s syndrome.

Amyloidosis.

Constrictive pericarditis.

4

What are the traumatic causes of chylothorax?

Post-surgery (majority):

a)

cervical:

i)

neck dissection;

ii)

lymph node sampling;

b)

thoracic:

i)

oesophagectomy (occurs in 0.5-3.4% of cases);

ii)

lung resection;

iii)

mediastinal tumour surgery;

c)

cardiac:

i)

congenital cardiac surgery;

ii)

left internal thoracic artery harvesting;

d)

abdominal (trans-diaphragmatic passage of chylous ascites):

i)

lymph node dissection;

ii)

sympathectomy.

Invasive procedures:

a)

central venous line placement;

b)

pacemaker insertion;

c)

embolisation of pulmonary arteriovenous malformation.

Blunt trauma.

Penetrating trauma.

5

What is the composition of chyle?

The composition of chyle depends on the type of meal ingested and the time elapsed between ingestion and sampling of the effusion.

It is usually milky in colour but may be colourless during fasting or blood-stained following surgery.

The main constituents of chyle are:

a)

fat (triglycerides >110mg/dL or 1.24mM is diagnostic but may be reduced following fasting);

b)

chylomicrons;

c)

cholesterol: triglycerides ratio <1;

d)

protein (>3g/dL);

e)

glucose;

f)

urea;

g)

cells (lymphocytes, primarily T-cells, erythrocytes);

h)

enzymes, immunoglobulins and fat-soluble vitamins;

i)

electrolytes (similar to plasma concentrations).

6

What is the normal lymphatic drainage volume?

Chyle flow is usually 1.5-2.5L/day but is increased following ingestion of a diet high in fat, particularly long-chain triglycerides.

7

Describe the lymphatic drainage system

The thoracic duct carries lymphatic fluid originating below the diaphragm, from the left side of the chest, left upper limb and left side of the head and neck.

The lymphatic fluid from the right thorax, right limb and right head and neck is usually drained by the right lymphatic duct.

There is, however, wide anatomic variation.

The histological structure of a lymphatic vessel closely resembles that of a vein, although it contains less muscle and the individual layers of the wall are less sharply defined.

8

Describe the anatomical course of the thoracic duct (Figure 1)

The thoracic duct is the continuation of the cisterna chyli, which forms from the intestinal and two lumbar lymphatic trunks.

It usually ascends to lie anterior to the first or second lumbar vertebra.

It then passes cranially through the aortic hiatus of the diaphragm (at the level of T12) to enter the posterior mediastinum, continuing in the right hemithorax, lying between the descending thoracic aorta and the azygos vein (Figure 2).