“Chylothorax”的意思、由来-开放百科全书

A chylothorax is a type of pleural effusion. It results from lymph formed in the digestive system called chyle accumulating in the pleural cavity due to either disruption or obstruction of the thoracic duct. In people on a normal diet, this effusion can be identified by its turbid, milky white appearance, since chyle contains high levels of triglycerides. It is important to distinguish chylothorax from pseudochylothorax (pleural effusions high in cholesterol), which has a similar appearance, but is caused by more chronic inflammatory processes, and has a different treatment.^[1] The condition is rare but serious. It results from leakage of lymph fluid from the thoracic duct or one of its tributaries. There are many treatments, both surgical and conservative.^[2] About 2 to 3 persent of pleural effusions are chylothoraces.^[2]

Causes

There are three main types of chylothorax: traumatic, nontraumatic, and idiopathic. In history, the most frequent cause of chylothorax was nontraumatic, but now traumatic is the most frequent cause, being more than 50% of cases reported. Traumatic has become the most common cause due to surgery, and chylothorax being a postoperative complication. It is more common on the right side of the thorax, with two thirds of the cases on the right. Most commonly, the cause of a nontraumatic chylothorax is a malignancy(cancer).^[3] It is also classified as low or high output based on the speed of chyle accumulation. If less that 500 mL of chyle accumulated in the first 24 hours, that is a low output chylothorax. If the leakage is more that 1000 mL every 24 hours, that is a high output chylothorax.^[4]

Non-traumatic

Malignancies are the most frequent cause of non-traumatic chylothorax. Cancers like chronic lymphoid leukemia, lung cancer, lymphoma, Kaposi sarcoma, metastatic carcinoma or esophageal cancer are possible causes of chylothorax. Recently, there are less cases of chylothorax caused by lymphoma. The most likely cause of this is that lymphoma is being diagnosed and treated earlier due to advancing techniques, and that chylothorax is a late complication. Chylothorax can also be infectious. This is most common in developing countries. The most common cause of an infectious chylothorax is a complication of tuberculous lymphadenitis. Other possible causative infections include aortitis, histoplasmosis, and filariasis. Chylothorax can also be congenital. Congenital chylothorax can be by itself, or occur with other lymphatic malformations like lymphangiectasis and lymphangiomatosis. Other conditions like tuberous sclerosis, congenital heart disease, trisomy 21 (Down syndrome), Noonan syndrome, or Turner syndrome (missing X chromosome) are other possible causes of congenital chylothorax. Other, rare causes of congenital chylothorax include castleman disease, yellow nail syndrome, Waldenstrom macroglobulinemia, sarcoidosis, venous thrombosis, thoracic radiation, macroglobulinemia, amyloidosis, and a goiter. These diseases cause chylothorax by obstructing or destroying the thoracic duct. Also parenteral nutrition has been a possible cause. A quick dose of total parenteral nutrition can overwhelm the thoracic duct, causing the chyle to leak into the surrounding pleural space.^[3]

Traumatic

Iatrogenic chylothorax after surgery is the most common cause of chylothorax.^[3] It is a common and serious complication of a pneumonectomy.^[5] It is especially common in surgeries requiring mediastinal dissection.^[9] The possibility of chylothorax depends on the surgery done. The surgery with the highest risk of chylothorax is an esophagostomy, with a 5 to 10 percent risk of chylothorax. Resecting a lung and mediastinal node dissection has the second highest risk, with 3 to 7 percent risk. Other operations like mediastinal tumor resection, thoracic aneurysm repair, sympathectomy, and any other surgeries that take place in the lower neck or the mediastinum. Chylotharax after trauma but not after surgery is also described after central line placement, pacemaker implantation, and embolization of a pulmonary arteriovenous malformation. Blunt trauma to the chest region is one cause of a chylothorax. Chylothorax has also occurred after blast injuries. It has also occurred after simple injuries like after coughing or sneezing.^[3]

Symptoms

The symptoms of chylothorax depends on what is causing the chylothorax. A small chylothrax can have no symptoms and only be detected on an X-ray. A large chylothorax usually causes symptoms by compressing the lungs when they expand. There is increasing shortness of breath. Another common symptom is the feeling of pressure in the chest. There is usually no fever or chest pain, as chyle does not create inflammation by itself.^[6] A large chylothorax can cause no symptoms if the chylothorax increases slowly, giving the lungs time to get used to the pressure. There can be reduced sound while breathing on the affected side, that side may also be dull to percussion. In the postoperative case, the first sign can be a pleural effusion or persistent draining from the tubes.^[3] Another way a chylothorax can cause symptoms is the leakage of nutrients, fats, and electrolytes, leading to low blood volume.^[7]

Mechanism

The main mechanism of chylothorax is the leaking of chyle from the thoracic duct. This is usually caused by a disturbance in the thoracic duct. Trauma affecting the thoracic duct is the most common disturbing mechanism of chylothorax. A central venous catheter can disrupt drainage of lymph into the subclavian veins, followed by the thoracic duct, resulting in chylothorax. In the case of mediastinal lymphadenopathy, the enlarged lymph node cause 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.^[7]

Diagnosis

Chest X-rays can detect a chylothorax. It appears as a dense, homogenous area that obligates the costophrenic and cardiophrenic angles. A normal chest x-ray cannot differentiate it from any other type of pleural effusion. Ultrasounds are being used increasingly more often. A chylothorax appears as an echoic region that is isodense with no septation or loculation. However, like in a chest X-ray, it cannot differentiate it from any other type of pleural effusion. Cisterna chyli can be fount in a thoracic MRI, making it possible to confirm chylothorax. However, it is not the ideal method to scan the thorax and so it is rarely used. Another treatment is a procedure called a conventional lymphangiography. It is rarely used due to the fact that there are less invasive techniques that are equally sensitive. It requires a lymph channel between the toes to be pried open, and injecting lipiodol in it. Then, every 5 to 10 minuted, floroscopic images are taken. It shows up on the images, and can identify any leak in the thoracic duct causing chylothorax. If the drug does not get to the location of interest, saline can be injected to push it through. Another, more commonly used type of lymphogram is a nuclear lymphoscintigraphy This procedure requires human diethylenetriaminepentaacetic acid labeled Tc99m is injected into the subcutaneous lesions of both sides of the dorsum of the foot.Then two images, anterior and posterior, are obtained using gamma-ray cameras. This test can be used with an integrated low-dose CT-scan with photon emission to get images that are more precise. Once pleural effusion is detected, thoracentesis should be performed.^[3]

Once the fluid is sent to a lab, it should be tested. The fluid of a chylothorax can be milky, serous or serosanguineous. If it is not milky, that does not mean it isn't a chylothorax. It should be tested for cell count, since the fluid has a large amount of lymphocytes, around 80%, mostly polyclonal T cells. One of the main measurements is the amount of large chain fatty acids. Chyle has a lot of large-chain fatty acids. If the test is negative, and there is still a suspicion, then there should be a lipid electrophoresis of the fluid. If that procedure detects chylomicrons in the fluid, that confirms a chylothorax. The fluid is usually alkali, with a ph of 7.4-7.8.^[3]

Treatment

The right treatment of chylothorax depends on the causative condition. It can include dietary modification, pleurodesis, and surgical ligation. Drugs like somatostatin/octreotide, midodrine and sirolimus have been used too. They work by preventing chyle from forming. More recently, surgeries like pleurovenous or pleuroperitoneal shunting and thoracic duct embolization have been performed with some success. The lymph vessels cannot be repaired directly since they are very friable.^[3]

Initially

Initially, drainage of the fluid out of the pleural space is essential to obviate damage to organs, especially the inhibition of lung function by the counter pressure of the chyle. It is usually used initially in most cases of chylothorax.^[3] In the case of a large chylothorax, people usually need nutritional support due to the massive amount of lost nutrition. There should be emergency aggressive nutritional support to correct protein and electrolyte deficiencies. Once the person is hemodynamically and nutritionally stable, then specific treatment can begin.^[7]

Surgical

Surgery in indicated if it is post-traumatic, iatrogenic, or refractory to other treatments. When chylothorax is by these causes, surgery reduces mortality by 40% if it is done. One surgical procedure is called a thoracic duct ligation. It is an invasive procedure that is done by closing off the thoracic ducts.^[3] Surgical pleurodesis is another procedure, and can be done if people fail to respond to conservative treatment and cannot handle surgery.^[21] This can treat up to 80% of cases of chylothorax. This done with ligation have resulted in high success rates.^[3]

Conservative

A conservative treatment is changing diet to include less long-chain fatty acids. In this treatment, omitting fat (in particular FFA) from the diet is essential. Since chyle is formed off these acids, chyle formation will reduce, allowing the defects to heal spontaneously. To do this, a diet of less than 5 kcal as fat per meal. However, it can lead to fat deficiency and malnutrition over time. A possible way to defeat this drawback is a venous fat hemorrhage. Small and medium chain fatty acids can be given in a diet, and long chain fatty acids can be given intravenously.Another treatment option is pleuroperitoneal shunting (creating a communication channel between pleural space and peritoneal cavity). Thoracentesis and an indwelling catheter for use at home is usually used to drain the chylothorax.^[3]

In the case of a malignant neoplastic chylothorax, the treatment should be radiotherapy and/or chemotherapy. Usually, 2000 rads of radiation can deal with a malignant chylothorax. Since surgery to close the leak is not reliable, talc pleurodesis should be used. In a case study of 19 people with refractory malignant chylothorax due to lymphoma, it resulted in success for all the patients.^[7] Chemical pleurodesis is an option, since the leaking of lymphatic fluids is stopped by irritating the lungs and chest wall, resulting in a sterile inflammation. This causes the lung and the chest wall to be fused together which prevents the leaking of lymphatic fluids into the pleural space.

Prognosis

In early times, the mortality rate of chylothorax was over 50%. The morbidity and mortality rates have reduced as treatments have improved. Malignant, bilateral, and chronic chylothoraces have an inferior prognosis to other types.^[7] Currently, the mortality and morbidity rates are about 10 percent if treated surgically.^[3] If it is post-operative and treated conservatively, mortality rates approach 50%.^[7]

Complications

A possible complication of thoracic duct ligation is lymphedema. It is usually self-limiting and resolves within months due to collateral lymph vessels.^[3] Other complications can include malnutrition, immunosuppression, and respiratory distress. The severity of the complications depend on how fast the chylothorax accumulated, how big it was, and how chronic it was.^[8]

Epidemiology

This disease is rare and usually is a complication of surgeries in the neck and mediastinium. It has no gender or age predisposition. It occurs in 0.2 to 1 percent of cardiothoracic surgeries, 5 to 10 percent of eseophagostomies, and 3 to 7 percent of lung resections.^[3]