How is Mesothelioma Esothelioma Diagnosed? Mesothelioma is not easy to diagnose. There are multiple tests that doctors may use to diagnosis mesothelioma including: Chest X-Rays Computed Tomography (CT) Scans PET Scans Pathological Evaluation Cytology Thoracoscopy Biopsy A chest x-ray may show a buildup of fluid in the lining around the lung. The doctor may order a CT scan for further evaluation. A CT scan can also determine if fluid has built up inside the lungs. Some doctors may order a PET scan. The PET scan may reveal areas where there is abnormal, perhaps cancerous, tissue. After the CT and/or PET scan, a doctor may perform a biopsy or cytology to make a definitive diagnosis. If a biopsy is performed, a tissue sample taken from the body will be reviewed under a microscope to determine if the tumor is benign (non-cancerous) or malignant (cancerous). The tissue will often be "stained" to determine the type of cancer and examined to determine the typ...