Classification of GI polyps. Level 1, dysplastic cells above muscularis mucosa of head of polyp; level 2, cell invasion into neck of polyp (junction of normal colonic epithelium in adenomatous epithelium); level 3, polyp stalk involved; level 4, bowel submucosa involved but no involvement of muscularis. All patients with level 4 polyps, and some with level 3 polyps, should undergo segmental colon resection.