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

• 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

Supplemental studies

Immunohistology

• Immunohistochemistry
• Some studies have shown increased p53 and Ki67 (proliferation) at the surface of adenomas
• This is not generally needed for the diagnosis

Genetic analysis

• Although genetic changes are present, they are not generally needed for the diagnosis

Differential Diagnosis

• Hyperplastic polyp
• Traditional serrated adenoma
• Filiform variant of traditional serrated adenoma
• Sessile serrated polyp
• Mucosal prolapse / cloacogenic polyp
• Sporadic juvenile polyp

High vs. Low Grade Dysplasia in an adenoma are distinguished based on architecture (usually) or cytology (see Grading for criteria)

Clinical

• Significance of high grade intra-mucosal invasive carcinoma is a subject of current debate (see Grading at left)
• The report of cases exhibiting aggressive behavior suggests that surgical re-excision be considered
• Effect of adenomas on guidelines for screening colonoscopy (Winawer 2006):
• Small rectal hyperplastic polyps
• No change from standard (10 years)
• 1 or 2 tubular adenomas (TA) <1 cm
• Every 5 to 10 years
• Any of the following
• 3-10 TA
• Any TA ≥1 cm
• Any tubulovillous or villous adenoma
• Presence of high grade dysplasia
• Repeat in 3 years
• More than 10 adenomas at one examination
  • Repeat in less than 3 years
  • Consider familial disorders
• Recommendations may vary based on factors such as:
• Family history
• Adequacy of excisions
• Comorbidities
• Sessile serrated adenomas are counted as TA for screening purposes

Grading / Staging

• Grading
• Dysplasia of adenomas should be graded
• Adenomas by definition have at least low grade dysplasia
• Low grade dysplasia thus need not be addressed in the report for the typical adenoma
• Moderate dysplasia is not an accepted term
• Anything less than high grade should be termed low grade
• The term moderate dysplasia has no accepted meaning and risks giving an unclear clinical message
• High grade dysplasia is characterized by any one of the following:
• Cribriform architecture
• 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, forming lumens, technically appearing cribriform
• Nuclei show regular basal orientation
• Nuclei typically not markedly enlarged
• This should not be considered high grade dysplasia
• Severe cytologic atypia
• This is unusual in the absence of cribriform architecture, but can occur
• Invasion with a desmoplastic response
• Invasion confined to the lamina propria including muscularis mucosae is designated high grade intramucosal neoplasia
• At other GI sites this is considered intramucosal carcinoma
• If that term is used for colorectal lesions, the report should make it clear that it represents an in situ lesion
• Significance of high grade intra-mucosal invasive carcinoma is a subject of current debate
• In a series of 15 such cases, all appeared to be adequately treated by polypectomy (Lewin 2007)
• Two cases exhibiting aggressive features have subsequently been reported (Shia 2008)

• Use TNM staging if high grade dysplasia or invasive carcinoma are present

Bibliography

• Bosman FT, Carneiro F, Hruban RH, Thiese ND (Eds). WHO Classifiication of Tumors of the Digestive System, IARC, Lyon 2010
• Winawer SJ, Zauber AG, Fletcher RH, Stillman JS, O'brien MJ, Levin B, Smith RA, Lieberman DA, Burt RW, Levin TR, Bond JH, Brooks D, Byers T, Hyman N, Kirk L, Thorson A, Simmang C, Johnson D, Rex DK. Guidelines for colonoscopy surveillance after polypectomy: a consensus update by the US Multi-Society Task Force on Colorectal Cancer and the American Cancer Society. CA Cancer J Clin. 2006 May-Jun;56(3):143-59.
• Lewin MR, Fenton H, Burkart AL, et al. Poorly differentiated colorectal carcinoma with invasion restricted to lamina propria (intramucosal carcinoma): a follow-up study of 15 cases. Am J Surg Pathol. 2007;31:1882-1886.
• Shia J; Klimstra DS. Intramucosal Poorly Differentiated Colorectal Carcinoma: Can it be Managed Conservatively? Am J Surg Pathol. 2008 Oct;32(10):1586-1588.