use of instruments for visual examination of interior structures of the body; there are rigid endoscopes and flexible fiberoptic endoscopes for various types of viewing for disease diagnosis and treatment; involves passing an optical instrument along either natural body pathways such as the digestive tract, or through keyhole incisions to examine the interior parts of the body; with advances in imaging, endoscopes, and miniaturization of endosurgical equipment, surgery can be performed during endoscopy.