Colonic Adenoma
Common sites:
- Villous – most commonly rectum and rectosigmoid
- Adenoma with epithelial misplacement (pseudocarcinoma):
- Left side more common (sigmoid in particular)
Gross features:
- Tubular – small and pedunculated
- Villous – large and sessile, up to 10cm in
diameter
- Velvety or cauliflower-like, projecting 1-3cm
above surrounding mucosa
- Adenoma with epithelial misplacement (pseudocarcinoma):
- Long stalk usually (thought to arise due to
torsion of stalk)
Histologic features:
- Dysplastic epithelium – tall, hyperchromatic,
somewhat disordered
- High-grade dysplasia:
- Loss of polarity
- Cribriform architecture
- Tubular:
- Stalk is fibromuscular tissue with prominent
blood vessels
- Villous:
- Frondlike villiform extensions of mucosa
- Adenoma with epithelial misplacement (pseudocarcinoma) (2-4 % of adenomatous polyps)
- Pedunculated (usually)
- Round, smooth, lobular arrangement of crypts
- Noncomplex crypts
- Mucin pools round, smooth, lined by dysplastic
epithelium at periphery or unlined
- No irregular floating carcinoma cells
- Hemorrhage usually
- Lamina propria around
crypts usually
- Communication to surface often
- Degree of dysplasia similar to surface of polyp
- Malignant adenoma:
- Invasive adenocarcinoma extending through muscularis mucosa into submucosa
Immunophenotype:
Marker:
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Sensitivity:
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Specificity:
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Molecular features:
Other features:
- “Advanced adenoma” (need a shorter follow-up
time):
- HG dysplasia
- Villous architecture
- Size > 1 cm
- Pseudoinvasion
(associated with torsion, esp. in sigmoid):
- misplaced / herniated adenomatous glands in the
submucosa
- lamina propria
surrounding the glands
- no cytoarchitectural
features of malignancy
- hemorrhage and hemosiderin in the surrounding
submucosa
- no desmoplastic stroma
- admixed normal glands maybe
- acellular mucin pools maybe
- ischemic changes (granulation tissue, erosions,
exudate) often at the surface of the polyp due to torsion
- HGD not seen within in the polyp (usually found
in association with invasive adenoCA)
- Adenomas with high-grade dysplasia or intramucosal carcinoma (invasion limited to lamina propria) have a negligible metastastatic
potential
- Malignant adenomas (see definition above): see Colorectal adenocarcinoma
- Appendix adenomas:
- Mucin outside of the appendix is not allowed
(call it LAMN if low-grade)
- Adenoma with high-grade dysplasia should only
be diagnosed if the lesion resembles an adenoma of the colon and the muscularis mucosae is clearly intact
References:
- WHO Classification of Tumours
of the Digestive System (2010)
- Odze
& Goldblum, eds. Surgical Pathology of the GI Tract,
Liver, Biliary Tract, and Pancreas, 3rd ed.
- National Colorectal Cancer Screening Network Classification of Benign Polyps: Pathology Working Group Report
(June 2011)
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