Mesothelioma diagnosis
The diagnosis of any disease takes all the facts into consideration. These vital pieces of info are mainly gleaned from the patient’s history, the physical examination, and the investigations.
In mesothelioma patients, the occupational history is paramount. A patient with difficult breathing and chest pain could have a multitude of problems, but when the physician is informed of the patient’s long exposure to asbestos, the diagnostic choices are narrowed down. The last crucial step in diagnosis is the investigations, which will be discussed in detail below. A suggestive history and complaints alone cannot rule out a possible wildcard.
Firstly, radiological studies are done. An Xray of the chest may show a mass enveloping the pleura, changes in the appearance of the diaphragm, or various other features. This is done by sending electromagnetic waves that penetrate the chest and its structure, and that imprint on a radiographic film that is then looked at by the radiologist.
Another imaging modality that may be used is a CT scan, short for Computed Tomography. This can be thought of as a machine that virtually slices the chest into many sections so that the doctor can see all the structures inside at all planes. This scan is particularly useful in detecting the presence of any metastases. A third imaging technique is the MRI or Magnetic Resonance Imaging. This is the one where the patient lies on their back and is moved into a tunnel-like machine and hears clicking sounds for a while. What really happens is that a powerful magnet is used to collect high quality images from the patient’s body. While something like an Xray will primarily show high density structures such as bone, an MRI shows all structures in exquisite detail. The photos look exactly like what you would see in an anatomy textbook. However MRIs are expensive and take more time to perform than any other imaging modality. One other radiological study that may be employed is the PET (Positron Emission Tomography) scan, which can help rule out metastatic spread to distant body sites.
The single most useful investigation in the diagnosis of a malignant mesothelioma is a tissue biopsy taken with a small tube inserted into the chest. This is called a thoracoscopically guided biopsy. This is termed a “Keyhole surgery”, and is much less invasive than an “open biopsy”, where a surgeon uses a scalpel to cut open the patient’s chest in order to take the tissue sample. Alternatively, a needle may be inserted into the chest under CT guidance to take the specimen.
After the tissue biopsy is extracted, it is cut down to size, stained using one out of a plethora of medicinal stains, and put on a glass slide before being examined under the lens of a microscope by a pathologist. The type of mesothelioma will be determined by what the pathologist sees. Different types of the tumor have different distinguishing features under the microscope, and the type of the mesothelioma will have a very big impact on the treatment modalities used, the prognosis, and the survival rates.
The tissues may be stained by a normal histological stain or may be visualized using antibodies that bind to specific structures within the tumor. This advanced technique is known as immunohistochemistry.
One of the manifestations of mesothelioma is the accumulation of fluid inside the pleural cavity surrounding the lungs. This fluid build-up may compress the lungs and make it harder to breathe, but for diagnostic purposes we can aspirate some of this liquid and examine the cells floating within. This technique alone isn’t enough to diagnose the cancer but can contribute to the diagnostic process, in addition to relieving some pressure from the patient’s lungs. The same procedure is carried out if the fluid accumulates around the heart in the pericardial cavity or in the abdomen inside the peritoneal cavity.
