The clinical yield of colonoscopy.

In the last 50 years Sir Francis Avery Jones has illuminated many fields within gastroenterology, not least the colon. The 1930s were a dark age in the investigation of the colon, little having changed since the introduction of the electric sigmoidoscope by Sir Percy Lockhart-Mummery in 1904. Fischer's doublecontrast barium enema of 1923 was little heeded in this country for decades. The unexplained predilection of most colonic disease for the relatively accessible distal bowel to some extent covered up the relative inadequacy of the investigative techniques then available. As an enthusiast for upper gastrointestinal endoscopy Avery, together with Sir Alan Parks, organised the introduction of colonoscopy to St Mark's and actively supported the British pioneers of this technique. The time-lag before the fibreoptic revolution in clinical gastroenterology reached the colon is a reflection both of anatomic and technical problems involved. In the mid1960s gastrocameras and fibregastroscopes were routinely used in pioneering departments but the relatively crude angulation mechanisms of these early instruments, adequate in the stomach, made them extremely difficult to guide through the tight and unpredictable bends of the colon. One uncomfortable compromise in the quest for total colonoscopy was to have the patient swallow a guide-string, recovered at the anus and pulled tight to shorten the colon and to allow a passive fibreoptic 'colon tube' to be passed over it (Provencale and Revignas, 1969). The first purpose-built colonoscopes-more flexible than gastroscopes and with 4way angling controls-had a working life of only 200-300 examinations, whereas 10 years later current instruments can last over 1,000 procedures and are much easier to use. The essential advance has been in the improved mechanical strength and agility facilitated by production of ever-smaller fibre-bundles which leave more room in the instrument shaft for stronger pull-wires and larger channels. Anatomic difficulties and technical limitations have also highlighted one of the major problems of colonoscopy-how to teach it. Persuading a fibrescope to pass through the redundant and elastic folds of some colons can face the clinician with problems similar to those of the Indian rope trick. Unlike the magician, the endoscopist cannot see the unwanted loops forming in his instrument unless he uses fluoroscopy, which is inconvenient and results in a 2dimensional image which sometimes only adds to his confusion. Textbook colonic anatomy suggests that the descending and ascending colon are fixed retroperitoneally, whereas in at least 10-20% of patients these regions prove to be mobile, resulting in weird and unpredictable loops for the endoscopist and pain for the patient. Although an understanding has gradually built up of the principles for successful colonoscopy (Hunt and Waye, 1981; Sakai, 1981; Cotton and Williams, 1983; Shinya, 1982) it remains a technique requiring a combination of manual dexterity, anatomic imagination and pertinacity which is not easy to pass on. Colon models are of some help but can only crudely represent the amazing variability of the bowel. At present most colonoscopists are essentially self-taught at the expense of their patients.