How is mesothelioma diagnosed?

If there is a reason to suspect you may have a mesothelioma, the doctor will use one or more methods to find out if the disease is really present.

Medical history and physical examination:

A complete medical history (interview) is taken to check for risk factors and symptoms. This will include questions to determine if you have been exposed to asbestos.

A physical exam will provide information about signs of mesothelioma and other health problems. Patients with pleural mesothelioma (mesothelioma of the chest) often have pleural effusion (fluid in their chest cavity) caused by the cancer. Ascites (fluid in the abdominal cavity) in cases of peritoneal mesothelioma, and pericardial effusion (fluid in the pericardium) in cases of pericardial mesothelioma can also be detected during a physical exam.

Imaging tests:

A chest x-ray may show irregular thickening of the pleura, pleural calcifications (mineral deposits), lowering of the lung fissures (spaces between the lobes of the lungs), and fluid in the pleural space. These findings suggest asbestos exposure leading to the development of a mesothelioma.

Imaging studies such as x-rays, computed tomography (CT) scans, and magnetic resonance imaging (MRI) scans will help determine the location, size, and extent of the cancer. The CT scan uses a rotating x-ray beam to create a series of pictures of the body from many angles. A computer combines these pictures to produce detailed cross-sectional images of a selected part of the body. To highlight details on the CT scan, you may be asked for permission to have a harmless dye injected into a vein. MRI uses magnetic fields instead of x-rays to create images of selected areas of the body. As with the CT scan, a computer generates a detailed cross-sectional image.

Tests of fluid and tissue samples:

In patients with a pleural effusion, a sample of this fluid can be removed by inserting a needle into the chest cavity. A similar technique can be used to obtain abdominal fluid and pericardial fluid. The fluid is then tested to show its chemical make up and viewed under a microscope to determine whether cancer cells are present.

A tissue sample of a pleural or pericardial tumor can be obtained using a relatively new technique called thoracoscopy. A thoracoscope (telescope-like instrument connected to a video camera) is inserted through a small incision into the chest. The doctor can see the tumor through the thoracoscope, and can use special forceps to take a tissue biopsy. Similarly, laparoscopy can be used to see and obtain a biopsy of a peritoneal tumor. In this procedure, a flexible tube attached to a video camera is inserted into the abdominal cavity through small incisions on the front of the abdomen. Fluid can also be collected during thoracoscopy or laparoscopy.

Surgery, either a thoracotomy (which opens the chest cavity) or a laparotomy (which opens the abdominal cavity), allows the surgeon to remove a larger sample of tumor or, sometimes, to remove the entire tumor.

For patients who might have pleural mesothelioma, the doctor may also do a bronchoscopy. In this procedure a flexible lighted tube is inserted through the mouth, down the trachea, and into the bronchi to see if there are other masses in the airway. Small samples of abnormal-appearing tissue can be removed for testing.

The patient may also have a mediastinoscopy. A lighted tube is inserted under the sternum (chest bone) at the level of the neck and moved down into the chest. Mediastinoscopy allows the surgeon to view the lymph nodes in this area and remove samples to check for cancer. Lymph nodes are bean-sized collections of immune system cells that help the body fight infections and cancers. Cancers arising in the lung often spread to lymph nodes, but mesothelioma rarely do this. Tests of lymph nodes can give the doctor information on whether a cancer is still localized or if it has started to spread, and can help distinguish lung cancer from mesothelioma.

It is often hard to diagnose mesothelioma by looking at the cells from the fluid around the lungs, abdomen or heart. It is even hard to diagnose mesothelioma with tissue from biopsies. Under the microscope, mesothelioma can look like several other types of cancer. For example, pleural mesothelioma may resemble some types of lung cancer and peritoneal mesothelioma may resemble some cancers of the ovaries. For this reason, special laboratory tests are often done to help distinguish mesothelioma from some other cancers. These tests often use special techniques to recognize certain markers (types of chemicals) known to be contained in mesothelioma. Different markers are present in cancer of the lung or ovary. The electron microscope can sometimes be helpful in diagnosing mesothelioma. This microscope can magnify samples more than 100 times greater than the light microscope which is generally used in cancer diagnosis. This stronger microscope makes it possible to see small parts of the cancer cells that distinguish mesothelioma from other types of cancer.

The diagnosis of mesothelioma presents problems primarily initially in the distinction between mesothelioma and other forms of cancer such as adenocarcinoma or benign, non-cancerous pleural inflammation. The best diagnostic tools at the moment remain the open pleural biopsy performed during thoracoscopy. This procedure also allows for direct visualization of the inside of the chest, and information of involvement of other organs and extension of disease. Other procedures with lower yields are CT guided pleural biopsy, or blind pleural biopsy. In addition to the gross appearance of the tumor, pathologists often rely on a panel of histochemical and immunohistochemical stains to diagnose or exclude mesothelioma. Currently markers linked to prognosis of mesothelioma are under study, but have not been validated for the general use.