Chapter 8 - Colon Flashcards
What are the three indications for colon biopsy?
To evaluate a mass
To evaluate inflammatory bowel disease
To identify a cause of diarrhea
Describe the normal morphology of the colon.
Epithelium: Parallel crypts and a flat surface lined with goblet cells, endocrine cells, paneth cells and precursor cells.
Lamina propria: Dense lymphoplasmacytic infiltrate
Muscularis propria: Two layers
Serosa/Adventitia: Fat (note this on biopsy!)
Describe the morphology of tubular adenoma.
Nuclei that are tall and dark with pencillate shape.
Mitoses can be present, but not at the apex.
Dysplasia must reach the surface.
How can high-grade dysplasia be recognized on a colon biopsy?
Evaluate architecture; glands that are fused, back-to-back, or cribriform.
Ugly cytology.
Usually, a lesion that you think is cancerous but cannot prove invasion.
How is invasive carcinoma diagnosed on a colon biopsy?
Must see invasion into the lamina propria. Look for jagged border, desmoplasia, and “pinking” of invasive cells.
What is “intramucosal carcinoma”?
Invasive carcinoma that is limited to the lamina propria, for which resection is curative.
Note: Once the muscularis is reached, there is metastatic potential.
Describe the appearance of a hyperplastic polyp.
Glands with increased number of goblet cells outgrowing the lamina propria, resulting in a frilly appearance. Star-shaped lumen.
What are the diagnostic criteria for a sessile serrated polyp?
How are they treated clinically?
Large (< 1cm), hyperplastic-appearing polyp in the right colon with hyperplasia to the base of the crypt, resulting in a boot-like shape.
Handled like a tubular adenoma.
Describe the appearance of an inflammatory pseudopolyp.
What else does it resemble?
Granulation tissue or inflamed lamina propria with distorted crypts. Can have dysplasia but should have surface maturation. Essentially, like IBD. But if no background inflammation is present, diagnose juvenile polyp.
Describe the morphologic appearance of mucosal prolapse.
Extension of the muscularis mucosa into the lamina propria
Crypt distortion (diamond-shaped)
Hemosiderin, edema
Describe the two tumor pathways of colorectal adenocarcinoma.
APC pathway: 85% of cancers, also involves Ki67 and p53.
Mismatch pathway: 15% of cancers. Defective MLH1/MSH2 resulting in microsatellite instability.
What is medullary carcinoma of colon?
A rare variant of CRC with dense lymphoid population and a bland, neuroendocrine-like cytology.
Significantly, notes Lynch syndrome in the right colon of a young patient.
Where do carcinoid tumors usually occur?
How do they appear?
Appendix & small bowel
Neuroendocrine-cytology with bland, trabecular or spindled cells. Note, histology does not predict behavior.
What are the features of active IBD?
Intraepithelial neutrophils (cryptitis)
Neutrophils in crypt lumen (crypt abscesses)
Erosions/ulceration
What are the features of chronic IBD?
Crypt distortion
Crypt loss or atrophy
Basal plasmacytosis (should push up on crypts)
Paneth cell metaplasia (in left colon)
How can UC and CD be distinguished histologically?
CD: Patchy involvement with skip areas, granulomas, transmural inflammation, cobblestoning, creeping fat, fistulas.
UC: Continuous distal involvement, diffuse mucosal inflammation.
Note: Treated IBD can look patchy.
What is the significance of dysplasia in IBD?
It is more likely than sporadic dysplasia to progress, and must be reported.
The inflammatory background also makes it difficult to spot. Look for surface dysplasia.
What are the morphologic features of microscopic colitis?
Lack of chronic changes (IE, rule out IBD)
Top-heavy lymphocytic infiltrate
Intraepithelial lymphocytes
Damage to epithelium
Distinguish between the two types of microscopic colitis
Collagenous colitis: Affects women, has a collagen band along the basement membrane.
Lymphocytic colitis: Essentially doesn’t have the above features.
Describe the appearance of ischemic colitis.
Variable. Can be focally active or diffuse with pseudomembrane. Look for coagulative necrosis, fibrosis, and crypt atrophy.
What is diversion colitis?
Colitis of the Hartmann’s pouch which results from disconnection from the usual stream of fecal flora. Resembles IBD!
Normal colon
C: Crypts
LP: Lamina propria
MM: Muscularis mucosa
A: Artery
V: Vein
L: Lymphatics
Tubular adenoma
Arrow: Low-grade dysplasia in surface glands
Arrowhead: Uninvolved deeper gland
High-grade dysplasia in an adenoma
Arrow: Cribriforming
Invasive adenocarcinoma
Arrow: Poorly formed glands and single cells
Arrowhead: Desmoplastic stroma
Hyperplastic polyp
Arrow: Frilly goblet cell hyperplasia
Arrowhead: Star-shaped lumen
Sessile serrated polyp
Arrow: Branching crypts
Arrowhead: Surface resembling hyperplastic polyp
Mucosal prolapse
Arrow: Smooth muscle pulled into lamina propria
Arrowheads: Diamond-shaped crypts
Carcinoid tumor
Note delicate fibrovascular septa and speckled chromatin nuclei.
Active colitis
Arrow: Intraepithelial neutrophils
Arrowhead: Surface ulceration
Chronic inflammatory changes
- Crypt atrophy & distortion
- Elevation of crypts off muscularis
- Paneth cell metaplasia
Granuloma in Crohn’s disease (arrow)
Collagenous colitis
Top: H&E with lymphoplastmacytic infiltrate (arrow) and collagen (arrowhead)
Bottom: Trichrome stain highlighting collagen
Ischemic colitis
- Dark, regenerative crypts
- Hyalinization and fibrosis of the LP
- Ulceration
- Crypt dropout
