Adenoma of the Colon and Rectum

Differential Diagnosis

Tubular vs. Villous Adenomas are distinguished based on % of adenoma surface displaying tubular and villous formation

Length of villi must be ≥2x normal mucosal thickness

Tubules vs. villi may be easier to distinguish on en face sections (see Diagnostic Criteria at left for description)

High vs. Low Grade Dysplasia in an adenoma are distinguished based on architecture (usually) or cytology (see Grading for criteria)

Hyperplastic Polyp	Tubular Adenoma
Lacks cytologic dysplasia	Requires cytologic dysplasia
Proliferative zone restricted to base	Proliferative zone starts at the surface
Gland lining cells mature at the surface	No surface maturation

Deep proliferative zone of HP can resemble TA; the surface must be examined to make the distinction in many cases

Traditional Serrated Adenoma	Colorectal Tubular Adenoma
Serrated architecture	Lacks prominent serration
Complex buds (ectopic crypts) all communicate with lumen	Complex glands may not always communicate with surface
CK20 restricted to luminal surfaces	CK20 staining random

Filiform Variant of Traditional Serrated Adenoma	Villous Adenoma
Villi lined by complex serrations	Villi lined by relatively uniform columnar cells
Frequent edematous bulbous ends on villi	Villi typically pointed

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

Mucosal Prolapse / Cloacogenic Polyp	Colorectal Adenoma
Nuclear atypia most prominent deep in the lesion with surface maturation	Nuclear atypia involves surface of polyp
Nuclei usually enlarged but round and not stratified and not densely packed	Nuclei elongated, hyperchromatic, densely packed and frequently stratified
Apoptosis not prominent	Prominent apoptosis

Sporadic Juvenile Polyp	Tubular Adenoma
Lacks cytologic dysplasia	Requires cytologic dysplasia
Prominent cystically dilated glands	Cystic dilation usually not prominent
Abundant inflamed stroma	Inflamed stroma usually not prominent