If there is reason to suspect you may have a mesothelioma, one or more diagnostic methods will be used by your doctor.
Medical history and physical examination
A complete medical history is taken to establish risk factors and presence of symptoms. This interview includes questions to determine in which environment you may have been exposed to asbestos.
A thorough physical exam is conducted with an eye towards revealing signs of malignant mesothelioma and any other health problems. Patients with pleural mesotheliomas (malignant mesotheliomas 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.
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 malignant 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
If the patient has a pleural effusion, a sample of this fluid can be extracted by inserting a needle into the chest cavity.
A similar technique can be used to obtain abdominal fluid and pericardial fluid. The fluid sample is then tested to show its chemical make-up and analyzed under a microscope to determine the presence of cancer cells.
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. In much the same fashion, 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 via small frontal incisions. Fluid can also be collected during thoracoscopy or laparoscopy.
Surgery, either a thoracotomy (opening of the chest cavity) or a laparotomy (opening of the abdominal cavity), allows the surgeon to remove a larger sample of tumor or, at times, to remove it entirely.
For patients who might have pleural malignant 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.
Lymph Node Analysis
The patient may also have a mediastinoscopy. During this procedure a lighted tube is inserted under the sternum (chest bone) at the level of the neck and moved down into the chest. The surgeon is then able to view the lymph nodes in this region and take samples to check for malignant mesothelioma.
Lymph nodes are bean-sized collections of immune system cells that help the body fight infections and cancers. Lung cancers frequently spread to lymph nodes, but mesotheliomas rarely do this.
Examination of the lymph nodes allows the doctor to determine whether a cancer is still localized or if it has begun to spread. It can also aid the doctor in distinguishing lung cancer from malignant mesothelioma.
Magnification to Aid Detection/Recognition
Even with fluid samples from the area around the lungs, abdomen or heart, it is often difficult to diagnose malignant mesothelioma. It is even hard to diagnose malignant mesothelioma with tissue from biopsies.
This is because mesothelioma cells are difficult to distinguish from several other types of cancer when viewed under the microscope.
For example, pleural mesothelioma can resemble various types of lung cancer, and peritoneal mesothelioma can resemble various cancers of the ovaries. In recognition of this dilemna, special laboratory tests are often done to pinpoint mesothelioma amidst several possibilities.
These lab tests use special techniques to identify certain chemicals known to be present in mesotheliomas, and as importantly, known to be different than those present in cancer of the lung or ovary.
The electron microscope may also be helpful in diagnosing mesothelioma. The electron microscope has a magnification power 100 times greater than the light microscope which is generally used in cancer diagnosis. This allows detection of the small parts of the cancer cells that distinguish mesothelioma from other types of cancer.
The difficulty in distinguishing between malignant mesothelioma and other forms of cancer or benign, noncancerous pleural inflammation is the primary problem posed during the initial diagnosis.
The most favorable diagnostic tools presently remain the open pleural biopsy performed during thoracoscopy which allows for direct inspection of the inside of the chest, and provides information on the involvement of the other organs and any spread of disease. Less successful procedures 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 malignant meosothelioma. Currently chemicals linked to prognosis of malignant mesothelioma are under study, but have not been validated for the general use.
Because pleural mesothelioma has been better studied than peritoneal mesothelioma, we know more about factors associated with prognosis for pleural mesothelioma. Younger age at diagnosis, performance status (functional status) and absence of weight loss are associated with a more favorable prognosis.
Mesotheliomas are usually of three different cell types (histological analysis): 1) epithelial cell type – has the most favorable prognosis; 2) fibrosarcomatous cell type – carries the worst prognosis and 3) mixed cell type – has an intermediate prognosis.