Mesothelioma diagnosis typically begins with a sufferer's visit to the doctor complaining of chronic chest pain. This pain is caused as a result of a buildup of fluid inside the pleural space; this is called pleural effusion and is the most common presenting symptom of malignant mesothelioma.
Preliminary mesothelioma detection can be achieved through a chest imagery scan (CT scan, x-ray); however, mesothelioma is often misdiagnosed as viral pneumonia at this stage because of certain symptomatic similarities between the two. The only way to definitively verify a suspected case of malignant mesothelioma is through a biopsy.
A biopsy is a relatively minor procedure (dependent on the location of the tumor) during which a small section of suspect tissue is removed. The removed section is examined by a histopathologist, an expert in the study of diseased tissue. Histopathological examination can confirm a case of malignant mesothelioma while also typing and staging it. Understanding the type and stage can help doctors suggest the best of treatment.
Histopathologists are focused on the microscopic study of diseased tissue. A field of pathology, histopathology is a particularly useful tool in forming an accurate diagnosis of cancer and other diseases. The first step in performing a histopathological examination is excising a section of suspect tissue from the patient in question (biopsy). In order to prevent the excised tissue from decaying, it is placed in a fixative (something that increases tissue durability), the most common of which is called formalin (formaldehyde mixed with water).
In order to be prepped for viewing under a high-powered microscope, tissue samples are bathed in a number of increasingly concentrated solutions of ethanol so as to dehydrate the tissue prior to it being dipped in a type of wax called paraffin. By undergoing this procedure, the tissue sample is transformed from a soft and moist section of tissue into a hard paraffin block. This process is called embedding and is performed for the purpose of making it possible to slice the tissue into incredibly thin sections (approximately five micrometers). The ultra-thin slices allow histopathologists to view the size and structure of individual tumor cells.
A tissue section with a thickness of five micrometers is virtually transparent, forcing histopathologists to "stain" the tissue with various types of pigments (hematoxylin and eosin are common) designed to make it viewable under the microscope. Once a section of tissue has been embedded and stained, it is ready for examination.
Mesothelioma Cellular Types
Histopathological examination provides a definitive mesothelioma diagnosis in addition to providing detailed information about the type of mesothelioma (pleural, peritoneal or pericardial) such as its cellular makeup. Mesothelioma cancer cells can be found in three distinct types: epithelioid, sarcomatoid and biphasic.
Epithelioid mesothelioma is the most common type of mesothelioma cancer cell, accounting for 50% to 70% of all mesothelioma cancer cells. Epithelioid cancer cells are distinguished by their unique cellular pattern. They are relatively uniform in shape with a tubular pattern and a clearly defined cell nucleus under magnification.
Sarcomatoid mesothelioma is the least common type of mesothelioma cancer cell, accounting for 10% to 15% of all mesothelioma cancer cells. Sarcomatoid cancer cells are typically oval shaped, but more irregular with a less visible cell nucleus under magnification.
Biphasic mesothelioma is the second most common type of mesothelioma cancer cell, accounting for 25% to 60% of all mesothelioma cancer cells. Biphasic cancer cells do not have a unique pattern because they are a combination of epithelioid cells and sarcomatoid cells. Biphasic mesothelioma cancer cells can be intertwined or isolated from one another across the tumor mass. The latter configuration can lead to a misdiagnosis of cellular type if an excised section of tissue contains only epithelioid or sarcomatoid cells.