Hyperplastic Polyp of the Colon and Rectum
Definition
- Cytologically bland lesion with regular, elongated serrated crypts
Alternate/Historical Names
- Microvesicular hyperplastic polyp
Covered Separately
Diagnostic Criteria
- Upper (luminal) portion of polyp has a “saw tooth” appearance
- Formed by tufts or folds of abundant apical cytoplasm
- Cross-sections of glands have a star-shaped lumen
- Nuclei are small, regular, round and basal
in luminal half of crypt
- Best evaluated on or near the luminal surface
- Crypts are elongated but straight, narrow and hyperchromatic at the base
- Base of crypts shows proliferative changes
- Proliferative zone on Ki67 stain expanded to basal 1/3 to ½ of crypt
- Nuclei enlarged
- Nucleus/cytoplasm ratio elevated
- The deep proliferative zones of hyperplastic polyps and reactive processes closely mimic adenomatous changes
- All crypts reach to the muscularis mucosae
- Base of crypts shows proliferative changes
- Basement membrane is frequently thickened
- Cytoplasm defines three types of hyperplastic polyp:
- Microvesicular mucin rich type (most common, described above)
- Goblet cell rich type (poorly defined)
- Elongated, fat crypts
- May not be obvious (compare to adjacent normal)
- Little to no serration
- Filled with goblet cells, extending to surface
- Surface tufting is common
- Elongated, fat crypts
- Mucin poor type, with eosinophilic cytoplasm (rare)
- Although there are genetic differences, no clear significance to these types
- CK20 positive zone expanded to luminal ½ or 2/3
- Irregular changes in architecture are not present including
- Dilation of crypts
- Branching
- Horizontal glands at base
- Mature mucinous cells at base of crypts
- Presence of any of these suggests sessile serrated adenoma
- Nuclear dysplasia is not permitted for the diagnosis of hyperplastic polyp
- Nuclear stratification and loss of polarity are not seen
- Presence of dysplasia in a lesion with hyperplastic features suggests either
- Traditional serrated adenoma or
- Sessile serrated adenoma with dysplasia
- See Differential Diagnosis at left
- Usually small sessile left sided lesions
- Either of the following features should raise the possibility of sessile serrated adenoma
- Size ≥0.5 cm
- Right sided lesion
- If both are present, it is almost always a SSA
- Infrequent epithelial misplacement into submucosa has been described
- Has also been termed inverted hyperplastic polyp
- Mucin depleted epithelium similar to basal 1/3 of polyp
- Accompanied by lamina propria
- Continuous with overlying polyp through a gap in the muscularis mucosae
- May require multiple levels to demonstrate
- Adjacent hemorrhage and hemosiderin common
- Collagen type IV stain demonstrates strong continuous staining around nests
- Apparently restricted to sigmoid and rectum
- Hyperplastic polyps may be associated with perineurioma
- No clinical significance
- Hyperplastic polyposis (serrated polyposis)
- Originally defined by the number and location of hyperplastic polyps
- It is now apparent that the polyps of this entity are hyperplastic polyps and sessile serrated adenomas
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting, last update: 1/31/10, 6/2/15
