Features of pseudoinvasion:

1. cells same: epithelial cell changes deeply are same as in superficial head of polyp.

2. nondesmoplastic envelope of stroma around deep epithelium (it may be fibrotic, though).

3. round profiles: deep "glands" rounded, not angulated or squeezed.

4. hemosiderin in surrounding stroma.

5. mucin pools or cystic change with atrophy in deep component.

6. thick muscularis: lamina muscularis hypertrophy & reduplication.

Dealing With Malignant Cases:

1. stalk identity: much effort should be made to ID & orient...optimally done by endoscopist.

2. invasion: there are lymphatics in deepest lamina propria (deep to crypt bases³) and superficial submucosa; conventional thinking is that no (or it is just incredibly rare) metastasizing potential if does not invade through the lamina muscularis (muscularis mucosae)...and if not into lamina (is only CIS or intramucosal ca.), a specific note should be made as to lack of metastatic potential [but see L06-10720].
   Failure to invade through the lamina is TNM pTis.
3. Haggitt level: these 4 levels are for exophytic lesions and are divisions within T1 of the TNM system for intrapolypoidal cancer: [graphic of the 4 levels]
   • level 0: in head of polyp & muscularis mucosae not penetrated.
   • level 1: invades polyp submucosa within zone between extreme head of polyp & where transition of dysplastic adenomatous change to normal surface out on polyp head.  
   • level 2: short...maybe absent or nondiscernable...invades polyp submucosa within zone between where transition of dysplastic adenomatous change to normal surface out on head is not parallel with some dysplasia down on stalk.  
   • level 3: invasion in stalk zone beyond surface dysplasia & short of the plane of the bowel muscularis mucosae. Sessile adenoma with cancer is usually no better than level 3.
   • level 4: polyp carcinoma in polyp base & deep to the plane of the bowel lamina propria.
4. excision adequacy: is stalk margin clear and, as with a Breslow thickness, by how much (conservative thinking is that 2mm clear or more is best)? Many authorities agree that the endoscopist has the most reliable estimation of adequacy of excision when margin deemed close (so, it may be worth talking with him/her and then do final case signout).

Careful discernment can spare additional surgery [S10-10767] or mitigate concerns about adjuvant therapy (one might need to review & correlate the polypectomy with the segmental resection to show what an "early pT1" case it is with the pN0 [L11-8284].

1. Lewin D, Issues with Adenomatous Polyps, MUSC McKee-PT Seminar, 6 April 2005 (EBS...the basis of most of this page).
2. Rex DK, et. al., "Coming to terms with Pathologists Over Colon Polyps with Cancer or High-grade Dysplasia:, J. Clin. Gastroenterol., 39(1):1-3, January 2005.
3. West AB, et. al., "Cancer or High-grade Dysplasia? The Present Status of the Application of the Terms in Colonis Polyps", J. Clin. Gastroenterol., 39(1):4-6, January 2005.