Sessile Serrated Polyp / Adenoma
Differential Diagnosis
| Hyperplastic Polyp |
Sessile Serrated Polyp / Adenoma |
| ≥90% of bases of crypts straight, regular, narrow, frequently pointed |
At least 3 adjacent crypts with basal dilation and flattening, bases boot or inverted T shaped, <50% of bases are narrow |
| Proliferative zone reliably restricted to base |
Bases contain mature mucous cells |
| Serrations and CK20+ maturation limited to luminal 2/3 of crypt |
Serrations and CK20+ patches of maturation can be seen at all levels |
| Predominantly left sided and small |
Predominantly right sided and frequently ≥1 cm |
Polyps with mixed or intermediate features are designated indeterminate (e.g. between 50-90% narrow crypts and/or <3 flat crypt bases)
| Traditional Serrated Adenoma |
Sessile Serrated Polyp / Adenoma |
| Cytologic dysplasia throughout |
Cytologic dysplasia, if present, is a focal lesion |
| Multiple short crypts, right angled, not reaching the muscularis mucosae |
Basal dilation and flattening, boot or inverted T shaped, but overall, crypts are vertically arranged and span entire thickness of mucosa |
| Serration predominantly due to multiple adjacent ectopic crypts |
Serration predominantly due to exaggerated apical cytoplasm |
| Proliferation (Ki67) largely restricted to ectopic crypts |
Patches of proliferation can be seen at all levels |
| Predominantly polypoid and left sided |
Sessile and predominantly right sided |
| 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 |
