Colorectal Adenoma with Benign Misplacement of Glands / Pseudoinvasion

Definition

Nests of adenomatous epithelium in submucosa and/or stalk
- Usually circumscribed
Lacks infiltrative pattern
Frequently surrounded by chronic inflammation and granulation tissue
- Frequently accompanied by lamina propria
- Lacks desmoplastic stromal response
Frequently demonstrable continuity with overlying adenoma
- Traverses a gap in the muscularis mucosae
  - No infiltration of muscularis mucosae
  - Muscularis mucosae may be hyperplastic
  - May require multiple sections to demonstrate
Cytologically and architecturally bland, unless involved by high grade dysplasia
- High grade dysplasia usually accompanied by ordinary adenoma in misplacement
- Glands frequently show cystic dilation
Hemosiderin in stroma of stalk is frequent
- Hemosiderin is common in the stroma of the head of polyps but unusual in the stroma of the stalk
- Hemosiderin is uncommon around invasive carcinoma
- Fresh hemorrhage is also frequent in stalk
  - Less reliable because of procedural trauma
Virtually restricted to left colon
- Most in sigmoid
Stains for collagen type IV and E cadherin may be helpful, see Supplementary Studies at left
- Infrequently required
Similar features of mucosal entrapment have been reported in hyperplastic polyps and small bowel Peutz-Jeghers polyps

Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting/update : 1/31/10, 11/13/11