Advances in technique
In addition to technological improvements in colonoscope design and adjunctive technologies, various techniques have been evaluated to improve the performance of colonoscopy for the detection of colorectal neoplasia and reduce the operator dependence of colonoscopy. These techniques are intended to assist in exposing hidden mucosa, and complement those technologies that can assist in highlighting and improving the recognition of mucosal lesions.
Overview of evidence (non-systematic literature review)
No systematic reviews were undertaken for this topic. Practice points were based on selected evidence and guidelines (see Guideline development process).
Water exchange is the technique of filling the colon with clean water during instrument insertion, while simultaneously removing dirty water. Several studies have shown that the improvement in quality of bowel preparation achieved through this technique is associated with improved adenoma detection rates. An infusion volume of at least 500mL appears necessary. Water exchange does, however, increase procedure time by prolonging the insertion time to caecum.
Mucosal inspection technique
Colonoscopy is a highly operator-dependent procedure. The magnitude of the difference in adenoma detection between high- and low-detector endoscopists in the same practice context far exceeds the improvements seen from technological adjuncts or advances in colonoscopy.
Colonoscopy fundamentally requires deliberate and systematic interrogation of the colorectal mucosa. The technique for mucosal inspection that has been shown to be associated with improved detection involves:
- systematic deflection of the instrument tip during withdrawal to scrutinise the proximal surfaces of colonic folds, flexures and valves
- intensive washing and suctioning of residual debris and pools and fluid
- adequate luminal distension.
Intraprocedural cleansing of the colon is essential to achieve high rates of adequate preparation, with reported mean washing times of over 4 minutes.
Both external review of technique (by videorecording) or audit of detection performance are known to motivate improvements in detection. Training in mucosal inspection behaviours and in lesion recognition improves adenoma detection.
The importance of withdrawal time for high quality colonoscopy has been over-emphasised after the initial landmark study demonstrating an association between longer withdrawal time and adenoma detection rates. While effective inspection of the colorectal mucosa takes time merely increasing the time taken is not the required behaviour. Rather, effective detection requires meticulous mucosal exposure technique together with recognition of neoplastic lesions. Institutional policies of forced withdrawal time targets have not been successful, unless combined with education and timed segmental inspection targets. Withdrawal time remains only a surrogate indicator of those mucosal inspection behaviours required for neoplasia detection.
Proximal colon examination
Observational studies from the USA and Germany have consistently shown lower levels of protection against cancer in the right colon/proximal colon (ie proximal to the splenic flexure). Studies have examined the benefit of instrument retroflexion in the proximal colon, performed after an initial inspection from the caecum to the hepatic flexure in the forward view. Retroflexion is possible in the right colon in over 90% of patients, although randomised controlled trials have shown that a second forward-view examination of the proximal colon is as effective for additional polyp detection as a second examination in retroflexion. The yield of a second right colon examination is higher when polyps have been found on the forward view, and in patients who are older, male or have bleeding indications.
Polyp size estimation
Once detected, polyps should be assessed prior to resection. Assessment should include documentation of the location, size and morphology of the lesion. Accurate measurement of polyp size is important for the determination of appropriate surveillance intervals.
Endoscopic measurement of polyp size is limited by human and technology bias. Endoscopists are known to be influenced by terminal digit preference for 'pleasing' numbers.[ref] The fish-eye lens of colonoscopes causes distortion in which objects in the centre of the display appear magnified, while objects at the periphery appear smaller and warped. Furthermore, the two-dimensional display creates a lack of depth awareness.
Accuracy of polyp measurement can be improved by the use of reference cues, such as comparison of the lesion with a device of known dimensions (e.g. the tip of a snare catheter or an open snare wire). To mitigate against technology bias and minimise visual size illusions, the lesion should be touching the measurement device and kept in the centre of the display.
The protective effect of colonoscopy on colorectal cancer incidence derives from the detection and removal of precancerous lesions. Polypectomy is therefore central to the practice of colonoscopy. However, like other aspects of colonoscopy practice, is highly operator dependent. Up to 27% of interval cancers may be due to incomplete endoscopic resection, and rates of incomplete hot snare resection of nonpedunculated neoplastic polyps vary significantly between endoscopists within a reported range of 6.5% to 22.7%.
Cold snare polypectomy has become the standard of care for diminutive (1–5mm) colorectal polyps and is the recommended technique in international guidelines for sessile polyps ≤9mm. Cold snaring is more effective and efficient than cold forceps resection and is virtually without risk. Cold biopsy forceps should be avoided because of high rates of incomplete resection.
The major benefit of cold snare techniques is safety, by avoiding the risk of thermal mural injury that is associated with post-polypectomy syndrome, perforation and delayed bleeding. Hot biopsy forceps are associated with unacceptably high rates of deep thermal injury but also incomplete resection, and should not be used. Because immediate bleeding can be visualised and treated, cold techniques can even be used safely in patients taking antiplatelet agents and anticoagulants.
Large (≥20mm) sessile and laterally-spreading polyps can increasingly be removed endoscopically, rather than with surgical resection. Patients with these lesions should be referred to centres with expertise in advanced colonoscopic resection techniques. Back to top
Fundamental colonoscopic inspection technique should ensure systematic exposure of the proximal sides of folds and flexures, intensive intraprocedural cleansing and adequate distension of the colon.
Water exchange should be considered to improve adenoma detection through an effect on mucosal cleansing and higher rates of adequate bowel preparation.
A second examination of the proximal colon in either the forward view or in retroflexion is recommended to improve lesion detection, particularly in patients with an expected higher prevalence of neoplasia.
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