In the case of mediastinal lymphadenopathy, the enlarged lymph node causes compression of the lymphatic channels and thoracic duct. This impedes the centripetal drainage of the flow of lymph from the edges of the lung parenchyma and pleural surfaces. This causes the chyle to ooze extensively into the pleural cavity, leading to a chylothorax. In the case of yellow nail syndrome, or lymphedema, chylothorax is caused by hypoplasia or dilation of the lymph vessels. In rare cases, like in hepatic chylothorax, chylous ascites crosses the diaphragm into the pleural cavity. In idiopathic cases like genetic disorders, the mechanism is not known. Up to three liters of chyle can easily drain into the pleural space daily. Diagnosis
Chest X-rays can detect a chylothorax. It appears as a dense, homogeneous area that obscures the costophrenic and cardiophrenic angles. Ultrasounds can also detect a chylothorax, which appears as an echoic region that is isodense with no septation or loculation. However, neither a normal chest x-ray nor an ultrasound can differentiate a chylothorax from any other type of pleural effusion. The cisterna chyli can be found in a thoracic MRI, making it possible to confirm chylothorax. However, MRI is not the ideal method to scan the thorax, and so it is rarely used. Another diagnostic technique is conventional lymphangiography. It is rarely used since there are equally sensitive yet less invasive techniques available to identify a chylothorax. Lymphangiography procedures use the contrast dye agent lipiodol, which is injected into the lymphatic vessels.
A large chylothorax may lead to breathlessness or a feeling of pressure in the chest, caused by fluid restricting the expansion of the lungs, although large chylothoraces may remain asymptomatic if the chylothorax has accumulated slowly, as the lungs may have had time to become used to the pressure. Fever or chest pain are not usually associated with chylothorax, as chyle does not generate inflammation by itself.On examination, chylothorax may lead to reduced breath sounds on the affected side, associated with a dull sound when the chest is tapped or percussed. In cases of postoperative chylothorax, the first sign may be persistent drainage from intercostal drains. Large chylothoraces may cause signs related to the loss of nutrients, including features of malnutrition or decreased ability to fight infections. Rapidly accumulating chylothoraces can cause a sudden drop in blood volume, leading to low blood pressure. Causes
There are three main types of chylothorax: traumatic, non-traumatic, and idiopathic. Historically the most common form of chylothorax was non-traumatic, but traumatic chylothoraces now represent the majority of cases, with most arising as postoperative complications of surgery. The most common cause of non-traumatic chylothoraces is cancer. Chylothoraces can also be classified as low- or high-output based on the rate of chyle accumulation: low-output chylothoraces accumulate <500 mL of chyle per 24 hours, while high-output chylothoraces accumulate >1000 mL per 24 hours. Non-traumatic
Malignancies are the most frequent cause of non-traumatic chylothorax. Cancers like chronic lymphocytic leukemia, lung cancer, lymphoma, Kaposi sarcoma, metastatic carcinoma or esophageal cancer are potential causes of chylothorax.