Adenoma of the Colon and Rectum
Definition
- Intramucosal glandular neoplasm of the colon or rectum
Covered Separately
- Adenoma with benign misplacement of glands / pseudoinvasion
- Invasive carcinoma involving an adenomatous polyp
- Familial polyposis coli
- Sessile serrated polyp/adenoma
- Traditional serrated adenoma
Diagnostic Criteria
- Low grade dysplastic changes (see following) should involve at least the upper half of the crypts and the luminal surface
- The deep proliferative zones of hyperplastic polyps and reactive processes closely mimic adenomatous changes
- Nuclear dysplasia is required for the diagnosis of adenoma
- Enlarged hyperchromatic nuclei
- Oval or frequently elongated
- High nucleus to cytoplasm ratio
- Frequent nuclear stratification and loss of polarity
- Changes in gland architecture invariably present including
- Enlarged crypts
- Budding, irregular glands
- Cribriform architecture (high grade lesions)
- Back to back gland lumens without intervening stroma
- Should clearly be a manifestation of total loss of polarity by atypical cells
- Frequently, well differentiated mucin producing cells will pile up, technically appearing cribriform
- Nuclei show regular basal orientation
- Nuclei typically not markedly enlarged
- This should not be considered high grade dysplasia
- Foci of squamous differentiation (morules) may be seen in rare cases
- Mucin depletion is frequent but not required
- Macroscopic / endoscopic classification
- Elevated
- Polypoid
- Sessile
- Flat
- Depressed
- Flat and depressed adenomas are more often associated with development of carcinoma
- Architecturally classified based on % of adenoma surface displaying tubular and villous formation
| Tubular Adenoma | Tubulovillous Adenoma | Villous Adenoma | |
| Tubules | >75% | 25-75% | <25% |
| Villi | <25% | 25-75% | >75% |
- Length of villi must be ≥2x normal mucosal thickness
- Tubules vs. villi may be difficult to distinguish on sections perpendicular to the luminal surface
- En face sections of tubules produce a central epithelial lined lumen surrounded by stroma
- En face sections of villi produce a central stromal core covered by epithelium with surrounding bowel lumen
- Villous adenomas have an increased incidence of associated carcinoma, especially mucinous
- Dissecting pools of mucin at the base of any adenoma should be examined closely for mucinous carcinoma
- Dysplasia of adenomas should be graded
- Adenomas by definition have at least low grade dysplasia
- Innumerable colorectal tubular adenomas are seen in familial adenomatous polyposis
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting/updates : 1/31/10, 11/12/11, 12/22/12
