colorectal adenoma colorectal adenoma the colorectal adenoma is a benign glandular tumor of the colon and the rectum. it is a precursor lesion of the colorectal adenocarcinoma (colon cancer). they often manifest as colorectal polyps. colorectal adenomatubulovillous adenoma (tubular component – left of image, villous component – right of image). h&e stain.specialtygastroenterologysymptomsasymptomatic, rectal bleedingcomplicationscolorectal cancerdiagnostic methodcolonoscopytreatmentpolypectomy comparison table incidences and malignancy risks of various types of colorectal polyps. adenomatous types are grouped at top. colorectal adenoma typerisk of containing malignant cellshistopathology definition tubular adenoma 2% at 1.5 cmover 75% of volume has tubular appearance. tubulovillous adenoma 20% to 25% 25–75% villous villous adenoma 15% to 40% over 75% villous sessile serrated adenoma (ssa) basal dilation of the crypts basal crypt serration crypts that run horizontal to the basement membrane (horizontal crypts) crypt branching. tubular adenoma normal (left) versus dysplastic (large at right) colonic crypts, the latter conferring a diagnosis of a tubular adenoma. in contrast to hyperplastic polyps, these display dysplasia. tubulovillous adenoma tubulovillous adenoma, tva are considered to have a higher risk of becoming malignant (cancerous) than tubular adenomas. villous adenoma these adenomas may become malignant (cancerous). villous adenomas have been demonstrated to contain malignant portions in about 15–25% of cases, approaching 40% in those over 4 cm in diameter. colonic resection may be required for large lesions. these can also lead to secretory diarrhea with large volume liquid stools with few formed elements. they are commonly described as secreting large amounts of mucus, resulting in hypokalaemia in patients. on endoscopy, a "cauliflower' like mass is described due to villi stretching. being an adenoma, the mass is covered in columnar epithelial cells. micrograph of a colorectal villous adenoma. h&e stain sessile serrated adenoma main article: sessile serrated adenoma micrograph of a sessile serrated adenoma. h&e stain sessile serrated adenomas are characterized by (1) basal dilation of the crypts, (2) basal crypt serration, (3) crypts that run horizontal to the basement membrane (horizontal crypts), and (4) crypt branching. the most common of these features is basal dilation of the crypts.