Colonoscopy : The length of the colon can be directly viewed by colonoscopy. A gastroenterologist uses a thin, flexible tube equipped with a fiberoptic camera to view the inside lining of the colon. The appearance of the colonic lining often allows the doctor to make the diagnosis and also provides the opportunity to look for tumors and polyps. Biopsies (small bits of tissue) can be obtained from the mucosal lining during colonoscopy and evaluated under the microscope by a pathologist to determine the cause of colitis. Biopsy is the only way to diagnose microscopic colitis.