Examination of a body cavity – for example, PLEURAL CAVITY, GASTROINTESTINAL TRACT, BILE DUCT and URINARY BLADDER – using an ENDOSCOPE in order to diagnose or treat a disorder in the cavity. The development of endoscopy has reduced the need for major surgery, as many diagnostic procedures can be performed with an endoscope (as can MINIMALLY INVASIVE SURGERY). The development of fibre optics (the transmission of light along bundles of glass or plastic fibres) has greatly advanced the practice of endoscopy and hospitals routinely run endoscopy clinics on an out-patient basis, often without the necessity for patients having a general anaesthetic.