How do physicians and oncologists diagnose pleural mesotheliomas?

Mesothelioma is a rare malignant tumor that arises from mesothelium, which is a single layer of cells that lines body cavities. Four primary sites have been identified: pleura (87%), peritoneum (5%), pericardium and testis. Between 2000 and 3000 cases of mesothelioma are diagnosed each year in the United States.

The pleura is the lining of the pleural cavity, the thorax or the ribcage. It is usually smooth and normally contains 10 to 20 ml of pleural fluid, which permits the lungs to contract and expand against the pleural surfaces or chest wall without friction.

The first thing the health care provider should do is to ask the patient what his or her symptoms are.

According to Tanriluku et al, the three most common symptoms of a malignant pleural mesothelioma are:

1. difficulty breathing (dyspnea) (82%) occurs when malignant pleural effusions form, leading to changes in the diaphragm (a fibromuscular band between the thoracic and abdominal cavities) and chest wall during breathing. The large amount of fluid in the pleural cavity prevents the lung from expanding properly.
2. chest pain (68%): is caused by tumor invading the chest wall
3. weight loss (59%)

The health care provider will do a physical examination and order laboratory tests and imaging studies of the chest. In mesothelioma, the findings of dyspnea and chest pain are also accompanied by a pleural mass or effusion. Most physicians will start with a chest x-ray and then if needed, progress to a CT scan, often with a biopsy or an aspiration of the effusion.

It is important to realize that the symptoms of dyspnea, chest pain and pleural effusion do not automatically mean that a person has mesothelioma. Remember, mesotheliomas are rare tumors. According to Crawford, pleural effusions are much more common than mesotheliomas, with an incidence of 320 of 100,000 people per year, or as many as 1,000,000 in the United States each year. Pleural effusions can be caused by a number of different disease processes, the most common of which are:

• bacterial pneumonia
• congestive heart failure
• malignancy
• pulmonary embolus

Take a look at the CT scan below. On the patient's right (your left), you can see (1) which is the right lung, which occupies about 1/3 of the normal available lung space in the thoracic cavity. The large gray object indicated by the yellow arrows with the yellow star in the center is a malignant pleural effusion caused by mesothelioma. Below the pleural effusion should be the diaphragm, which has been invaded by tumor and the liver (9) and right kidney (8) which have been displaced downward. Normally the liver would be approximately as high as the spleen.

According to the National Cancer Institute, the most important risk factor for mesothelioma is exposure to asbestos, which is found in with 70 to 80 % of people diagnosed with mesothelioma. That means that 20 to 30 % of people with mesothelioma have no history of exposure to asbestos.

Also, mesothelioma usually does not develop until as long as 30 to 50 years after an individual has been exposed to asbestos. The health care provider should take a careful environmental and occupational history. Industries involved with asbestos include:

• automotive
• mining
• shipping

The next step is to obtain a sample of the mass or some pleural fluid for the pathologist to evaluate. The health care provider will work out the best method with the radiologist, which usually involves a guided aspiration of fluid or a guided biopsy of tissue.

When tissue is obtained (core biopsy, open biopsy), the pathologist will look at it under the microscope. There are three major histologic patterns of pleural mesothelioma:

• epithelial (50-70%)
• sarcomatous/sarcomatoid (7-20%)
• and mixed or biphasic (20-35%)

The pathologist will also look for ferruginous bodies, which are asbestos fibers covered with iron and calcium. It is important for the pathologist to be certain that this is a mesothelioma rather than metastatic tumor from an unknown primary, so the pathologist may order special stains called immunohistochemical stains to a) exclude the diagnosis of carcinoma and b) confirm the diagnosis of mesothelioma.

If the sample that is obtained is pleural fluid, the pathology lab will run studies on the fluid itself, for example, looking at glucose levels, and the pathologist will look at the type of cells found in the pleural fluid.

1. Tanrikulu AC et al. Respiration. 2010 Sep 28. [Epub ahead of print]. A Clinical, Radiographic and Laboratory Evaluation of Prognostic Factors in 363 Patients with Malignant Pleural Mesothelioma. Accessed 11/3/2010.
2. eMedicine Specialties > Emergency Medicine > Pulmonary.  Pleural Effusion

   Author: C Crawford Mechem, MD, MS, FACEP.  Updated: Nov 13, 2009.http://emedicine.medscape.com/article/807375-overview.