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Adenoma of the Colon and Rectum

Definition

  • Intramucosal glandular neoplasm of the colon or rectum

Covered Separately

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 with apical mucin
        • 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 (Bosman, Mahajan)
  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 that are not well oriented
      • 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
      • These have been termed "free floating villi" and are required by some for the diagnosis of villous pattern
        • They can be seen in adenomas with villi too short to qualify but will always be found in TVA or VA
    • 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 reported only if high grade
    • 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/last update : 1/31/10, 1/19/14

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

Tubular vs. Villous Adenomas are distinguished based on % of adenoma surface displaying tubular and villous formation
  Tubular Adenoma Tubulovillous Adenoma Villous Adenoma
Tubules >80% 20-80% <20%
Villi <20% 20-80% >80%
  • Length of villi must be ≥2x normal mucosal thickness
  • Tubules vs. villi may be easier to distinguish on en face sections (see Diagnostic Criteria at left for description)
  • High vs. Low Grade Dysplasia in an adenoma are distinguished based on architecture (usually) or cytology (see Grading for criteria)

    Hyperplastic Polyp Tubular Adenoma
    Lacks cytologic dysplasia Requires cytologic dysplasia
    Proliferative zone restricted to base Proliferative zone starts at the surface
    Gland lining cells mature at the surface No surface maturation
    Deep proliferative zone of HP can resemble TA; the surface must be examined to make the distinction in many cases

     

    Traditional Serrated Adenoma Colorectal Tubular Adenoma
    Serrated architecture Lacks prominent serration
    Complex buds (ectopic crypts) all communicate with lumen Complex glands may not always communicate with surface
    CK20 restricted to luminal surfaces CK20 staining random

     

    Filiform Variant of Traditional Serrated Adenoma Villous Adenoma
    Villi lined by complex serrations Villi lined by relatively uniform columnar cells
    Frequent edematous bulbous ends on villi Villi typically pointed

     

    Usual Colorectal Adenoma Sessile Serrated Polyp / Adenoma
    Cytologic dysplasia throughout Cytologic dysplasia, if present, is a focal lesion
    Typically complex architecture Basal dilation and flattening, boot or inverted T shaped, but overall, crypts are vertically arranged and not complex
    Lacks serrations Prominent serrations

     

    Mucosal Prolapse / Cloacogenic Polyp Colorectal Adenoma
    Nuclear atypia most prominent deep in the lesion with surface maturation Nuclear atypia involves surface of polyp
    Nuclei usually enlarged but round and not stratified and not densely packed Nuclei elongated, hyperchromatic, densely packed and frequently stratified
    Apoptosis not prominent Prominent apoptosis

     

    Sporadic Juvenile Polyp Tubular Adenoma
    Lacks cytologic dysplasia Requires cytologic dysplasia
    Prominent cystically dilated glands Cystic dilation usually not prominent
    Abundant inflamed stroma Inflamed stroma usually not prominent

    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.
    • Mahajan D, Downs-Kelly E, Liu X, Pai RK, Patil DT, Rybicki L, Bennett AE, Plesec T, Cummings O, Rex D, Goldblum JR. Reproducibility of the villous component and high-grade dysplasia in colorectal adenomas <1 cm: implications for endoscopic surveillance. Am J Surg Pathol. 2013 Mar;37(3):427-33.
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