If you have mesothelioma symptoms, your doctor may ask about your prior exposure to asbestos and perform a complete medical examination.    The following tests are a common part of the diagnostic process: Imaging tests allow doctors to see a picture of the area in question. These could include x-rays, CT scans (computed tomography), or MRI (magnetic resonance imaging). A bronchoscopy or a mediastinoscopy uses a lighted tube to let the doctor look at the affected area.  Cytology tests the pleural fluid for malignant cells after doctors remove it using a needle. Medical experts consider this test to have limited value in diagnosing this cancer, because negative or inconclusive readings account for nearly 85 percent of all fluid tested. Even with a positive fluid report, many doctors prefer to perform a confirming tissue biopsy as long as it does not compromise the patient's health. Fluid samples may be taken with a needle and sent to the lab to see if cancer cells are present. A doctor can perform a thoracoscopy or a laparoscopy to look directly at the tumor and to take a sample of tissue that a pathologist then examines. In these procedures, a doctor makes a small incision and uses a tiny video camera to look at the area in question.  During a needle biopsy, done under local anesthetic, a doctor inserts a large hollow needle through the skin and into the chest cavity. The doctor then rotates the needle and as the needle is taken out, the doctor can collect tissue samples. Because of the small sample size of the tissue, experts consider this type of biopsy to be only 25 to 60 percent accurate in diagnosing this cancer.  Experts consider the open biopsy the most accurate for diagnosis. It is the procedure of choice because it affords the pathologist a larger tissue sample. Surgeons perform open biopsies in hospitals under general anesthetic. Doctors often encounter difficulties in diagnosing mesothelioma. In some cases a pathologist may use an electron microscope to look at cells in greater detail.     Once the cancer has been diagnosed, the doctor will normally proceed with staging.