Theclinical yield ofcolonoscopy

Anatomicdifficulties andtechnical limitations havealsohighlighted oneofthemajorproblems of colonoscopy-how toteach it.Persuading a fibrescope topassthrough theredundant andelastic folds ofsomecolons canface theclinician withproblems similar tothose oftheIndian ropetrick. Unlike the magician, theendoscopist cannot seetheunwanted loopsforming inhisinstrument unless heuses fluoroscopy, whichisinconvenient andresults ina2dimensional image whichsometimes onlyaddstohis confusion. Textbook colonic anatomysuggests that thedescending andascending colon arefixed retroperitoneally, whereas inatleast 10-20%ofpatients these regions provetobemobile, resulting inweird andunpredictable loops fortheendoscopist andpain forthepatient. Although an understanding has gradually built upoftheprinciples forsuccessful colonoscopy (HuntandWaye,1981;Sakai, 1981; Cotton andWilliams, 1983; Shinya, 1982) itremains a technique requiring a combination ofmanual dexterity, anatomic imagination andpertinacity whichisnoteasytopasson.Colonmodels areof somehelpbutcanonlycrudely represent the amazing variability ofthebowel. Atpresent most colonoscopists areessentially self-taught attheexpenseoftheir patients.

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