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Benign pleural effusions
Benign pleural effusion is one of the asbestos-related diseases. How to understand this disease?
Your body produces pleural fluid in small amounts to lubricate the surfaces of the pleura, the thin membrane that lines the chest cavity and surrounds the lungs. A pleural effusion is an abnormal collection of this fluid.
Pleural effusion is a very common medical problem; like interstitial fibrosis, there are many potential causes (e.g., pneumonia, congestive heart failure, cancer, kidney disease, rheumatoid arthritis, tuberculosis). Asbestos can cause two very different types of pleural effusion - benign and malignant. Benign pleural effusion is a frequent condition, but is only rarely from asbestos. Malignant pleural effusion can be due to either lung cancer or mesothelioma, conditions which are discussed separately.
Benign pleural effusion, when attributable to asbestos, is presumably due to inflammation generated by reaction to asbestos fibers. When the pleural fluid becomes substantial (usually over a pint or 500 cc's) the patient may have symptoms (usually shortness of breath) and the chest x-ray will show the fluid collection. Asbestos is actually a rare cause of pleural effusion (pleural scarring and pleural plaques are a much more common result of asbestos inhalation). The only way to to reliably diagnose most causes of pleural effusion is to sample the fluid via a needle in the pleural space, and examine it in the lab. This is an invasive procedure (because it involves a needle) called 'thoracentesis', and is routinely performed in hospitals.
Benign pleural effusion - defined by four criteria: a history of asbestos exposure, radiologic or thoracentesis confirmation of pleural space fluid, absence of another cause for the pleural effusion, and no malignant tumor developing within three years. Benign asbestos pleural effusions are fairly uncommon (< 3% of workers with high occupational exposure), they are unilateral and usually develop within 10 years of first exposure. Most patients are aymptomatic, but some have pleuritic chest pain. The effusion is an exudate and it may be bloody in about half of the patients. Most benign asbestos pleural effusions resolve sponaneously over weeks to months, but they must be followed-up to rule out the development of a malignant mesothelioma.
Pleural effusions are usually asymptomatic unless they are large or infected. The progression of effusions is usually in parallel with the course of the articular symptoms. Reports of effusions before or at the time of diagnosis of RA are infrequent.
Three quarters of rheumatoid pleural effusions are unilateral and are of small to moderate volume. The left side seems to be more commonly involved. They tend to remain relatively unchanged for months to years.
There are two different types of effusions:
A transudate is a clear fluid, similar to blood serum, that forms not because the pleural surfaces themselves are diseased, but because the forces that normally produce and remove pleural fluid at the same rate are out of balance. When the heart fails, pressure in the small blood vessels that remove pleural fluid is increased and fluid "backs up" in the pleural space, forming an effusion. Or, if too little protein is present in the blood, the vessels are less able to hold the fluid part of blood within them and it leaks out into the pleural space. This can result from disease of the liver or kidneys, or from malnutrition.
An exudate--which often is a cloudy fluid, containing cells and much protein--results from disease of the pleura itself. The causes are many and varied. Among the most common are infections such as bacterial pneumonia and tuberculosis; blood clots in the lungs; and connective tissue diseases, such as rheumatoid arthritis. Cancer and disease in organs such as the pancreas also may give rise to an exudative pleural effusion.
Special types of pleural effusion
Some of the pleural disorders that produce an exudate also cause bleeding into the pleural space. If the effusion contains half or more of the number of red blood cells present in the blood itself, it is called hemothorax. When a pleural effusion has a milky appearance and contains a large amount of fat, it is called chylothorax. Lymph fluid that drains from tissues throughout the body into small lymph vessels finally collects in a large duct (the thoracic duct) running through the chest to empty into a major vein. When this fluid, or chyle, leaks out of the duct into the pleural space, chylothorax is the result. Cancer in the chest is a common cause.
When pleural effusion is suspected, the best way to confirm it is to take chest x rays, both straight-on and from the side. The fluid itself can be seen at the bottom of the lung or lungs, hiding the normal lung structure. If heart failure is present, the x-ray shadow of the heart will be enlarged. An ultrasound scan may disclose a small effusion that caused no abnormal findings during chest examination. A computed tomography scan is very helpful if the lungs themselves are diseased.
In order to learn what has caused the effusion, a needle or catheter is often used to obtain a fluid sample, which is examined for cells and its chemical make-up. This procedure, called a thoracentesis, is the way to determine whether an effusion is a transudate or exudate, giving a clue as to the underlying cause. In some cases--for instance when cancer or bacterial infection is present--the specific cause can be determined and the correct treatment planned. Culturing a fluid sample can identify the bacteria that cause tuberculosis or other forms of pleural infection. The next diagnostic step is to take a tissue sample, or pleural biopsy, and examine it under a microscope. If the effusion is caused by lung disease, placing a viewing tube (bronchoscope) through the large air passages will allow the examiner to see the abnormal appearance of the lungs.
The following tests may help to confirm a diagnosis:
The cause and type of pleural effusion is usually determined by thoracentesis (a sample of fluid is removed with a needle inserted between the ribs).
Benign asbestos-related effusions have the same radiographic appearance as effusions due to other etiologies; the diagnosis usually is one of exclusion. Effusions are usually small, they may be unilateral or bilateral, and they tend to resolve spontaneously over 3-4 months, although as many as 30% recur. Some effusions are associated with pleural plaques. Effusions tend to resolve over a period ranging from 1 month to 1 year, with residual blunting of the costophrenic angles due to pleural thickening in 50% of patients.
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