Serrated Lesions in Colorectal Cancer Screening
Endoscopic resection is recommended for all polyps proximal to the sigmoid colon, all lesions in the recto-sigmoid colon >5 mm in size, and for conventional adenomas in the recto-sigmoid of any size. The overwhelming majority of serrated lesions ≤5 mm in the recto-sigmoid are hyperplastic and not SSPs, and recto-sigmoid SSPs ≤5 mm in size with cytological dysplasia are extremely rare. Therefore, serrated lesions ≤5 mm in size located in the recto-sigmoid colon remain the single group of colorectal polyps for which avoidance of resection is appropriate. Identifying this group of lesions and selecting them to be left in situ requires endoscopic estimation of pathology in real time during colonoscopy. Experts can exclude conventional adenomas by endoscopic criteria in the recto-sigmoid with >95% accuracy.
In a recent study of polyps 5 mm–20 mm in size, predictors of incomplete resection were the endoscopists, increasing polyp size and serrated histology. The overall rate of incomplete resection of serrated lesions was 32% compared with 7% for conventional adenomas. SSPs are characteristically flat or sessile, and have indistinct edges compared with HPs and conventional adenomas. The impact of indistinct edges on incomplete resection is readily understood, but can be overcome by endoscopic mucosal resection employing a contrast agent in the submucosal injection fluid and a high-definition colonoscope. This combination provides excellent delineation of the lesion edges, thereby enabling complete resection (figure 3). Inclusion of a margin of normal tissue and the use of snare resection for the entire lesion, with reservation of ablative techniques only for sections that cannot be snared, helps ensure lesion eradication. Adherence to these principles is associated with cure rates of endoscopic resection of serrated lesions equal to those for conventional adenomas.
(Enlarge Image)
Figure 3.
(A) A sessile serrated polyp with adherent mucus cap. Arrows mark the edges. (B) The same lesion seen in (A) after washing the mucus cap. The edges are less well defined. (C) The lesion after injection with hydroxyethyl starch containing indigo carmine. The edges are now well defined (arrows). (D) A stiff snare is used to facilitate capture of a margin of normal tissue (arrows) around the lesion. (E) The snare is closed very tightly before application of electrocautery. Note the large injection mound. The small red nodule (arrow) is an intramucosal haemorrhage in normal tissue and can be ignored. Larger lesions are resected piecemeal using the same principles. (F) The defect after transection. The blue colour in the submucosa indicates limited thermal injury. The contrast agent and high definition permit visualisation of a tiny nodule of residual serrated tissue (arrow) that requires further snaring or ablation.
Serrated lesions treated with endoscopic mucosal resection techniques are more often resectable en bloc (as opposed to piecemeal) when compared with conventional adenomas of equal size.
The frequent location of large serrated lesions in the caecum and ascending colon is not a deterrent to their endoscopic resection. There is currently no published evidence that the complication rate of endoscopic resection of serrated lesions is higher than for conventional adenomas; however, concerns have been raised due to the high complication rate seen in a large cohort from pre-2005 describing a subgroup of patients with large sessile lesions resected in the right colon.
Resection of serrated lesions by endoscopic mucosal resection is facilitated by use of a stiff snare, which allows the endoscopist to effectively grip the normal mucosa around the lesion and achieve a clear margin (figure 3). Once the snare is closed on tissue, the snare can be squeezed very tightly before application of electrocautery, with less risk of mechanical tissue tearing relative to conventional adenomas. This may be the result of more submucosal fat under serrated lesions compared to conventional adenomas. Some experts recommend tight snare closure before application of cautery to increases current density, speed transection during cautery application, and potentially limit thermal injury to the submucosa.
Endoscopic Resection of Serrated Polyps
Endoscopic resection is recommended for all polyps proximal to the sigmoid colon, all lesions in the recto-sigmoid colon >5 mm in size, and for conventional adenomas in the recto-sigmoid of any size. The overwhelming majority of serrated lesions ≤5 mm in the recto-sigmoid are hyperplastic and not SSPs, and recto-sigmoid SSPs ≤5 mm in size with cytological dysplasia are extremely rare. Therefore, serrated lesions ≤5 mm in size located in the recto-sigmoid colon remain the single group of colorectal polyps for which avoidance of resection is appropriate. Identifying this group of lesions and selecting them to be left in situ requires endoscopic estimation of pathology in real time during colonoscopy. Experts can exclude conventional adenomas by endoscopic criteria in the recto-sigmoid with >95% accuracy.
In a recent study of polyps 5 mm–20 mm in size, predictors of incomplete resection were the endoscopists, increasing polyp size and serrated histology. The overall rate of incomplete resection of serrated lesions was 32% compared with 7% for conventional adenomas. SSPs are characteristically flat or sessile, and have indistinct edges compared with HPs and conventional adenomas. The impact of indistinct edges on incomplete resection is readily understood, but can be overcome by endoscopic mucosal resection employing a contrast agent in the submucosal injection fluid and a high-definition colonoscope. This combination provides excellent delineation of the lesion edges, thereby enabling complete resection (figure 3). Inclusion of a margin of normal tissue and the use of snare resection for the entire lesion, with reservation of ablative techniques only for sections that cannot be snared, helps ensure lesion eradication. Adherence to these principles is associated with cure rates of endoscopic resection of serrated lesions equal to those for conventional adenomas.
(Enlarge Image)
Figure 3.
(A) A sessile serrated polyp with adherent mucus cap. Arrows mark the edges. (B) The same lesion seen in (A) after washing the mucus cap. The edges are less well defined. (C) The lesion after injection with hydroxyethyl starch containing indigo carmine. The edges are now well defined (arrows). (D) A stiff snare is used to facilitate capture of a margin of normal tissue (arrows) around the lesion. (E) The snare is closed very tightly before application of electrocautery. Note the large injection mound. The small red nodule (arrow) is an intramucosal haemorrhage in normal tissue and can be ignored. Larger lesions are resected piecemeal using the same principles. (F) The defect after transection. The blue colour in the submucosa indicates limited thermal injury. The contrast agent and high definition permit visualisation of a tiny nodule of residual serrated tissue (arrow) that requires further snaring or ablation.
Serrated lesions treated with endoscopic mucosal resection techniques are more often resectable en bloc (as opposed to piecemeal) when compared with conventional adenomas of equal size.
The frequent location of large serrated lesions in the caecum and ascending colon is not a deterrent to their endoscopic resection. There is currently no published evidence that the complication rate of endoscopic resection of serrated lesions is higher than for conventional adenomas; however, concerns have been raised due to the high complication rate seen in a large cohort from pre-2005 describing a subgroup of patients with large sessile lesions resected in the right colon.
Resection of serrated lesions by endoscopic mucosal resection is facilitated by use of a stiff snare, which allows the endoscopist to effectively grip the normal mucosa around the lesion and achieve a clear margin (figure 3). Once the snare is closed on tissue, the snare can be squeezed very tightly before application of electrocautery, with less risk of mechanical tissue tearing relative to conventional adenomas. This may be the result of more submucosal fat under serrated lesions compared to conventional adenomas. Some experts recommend tight snare closure before application of cautery to increases current density, speed transection during cautery application, and potentially limit thermal injury to the submucosa.
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