Hyperplastic polyp

A hyperplastic polyp is a type of colorectal polyp.

Hyperplastic polyp
Micrograph of hyperplastic polyp.
Incidences and malignancy risks of various types of colorectal polyps, with hyperplastic polyps at bottom left.

Cancer risk

Most hyperplastic polyps are found in the distal colon and rectum.[1] They have no malignant potential,[1] which means that they are no more likely than normal tissue to eventually become a cancer.

Hyperplastic polyps on the right side of the colon do exhibit a malignant potential. This occurs through multiple mutations which affect the DNA-mismatch-repair pathways. As such DNA mutations during replication are not repaired. This leads to microsatellite instability which can eventually lead to malignant transformation in polyps on the right side of the colon.

Hyperplastic polyposis syndrome

Hyperplastic polyposis syndrome is a rare condition that has been defined by the World Health Organization as either:

  1. Five or more hyperplastic polyps proximal to the sigmoid colon, with two polyps greater than 10mm in diameter; or
  2. Any number of hyperplastic polyps proximal to the sigmoid colon in a person with a first degree relative who has hyperplastic polyposis syndrome; or
  3. More than 30 hyperplastic polyps of any size throughout the colon and rectum.[2]

Histopathology

Histopathologically, there are two main types of hyperplastic polyps, which have genetic differences, as well as different histologic structure, but no significant differences clinically:[3]

  • A microvesicular mucin-rich type
  • A goblet cell-rich type

There is also a mucin-poor type with eosinophilic cytoplasm, which is rare.[3]

Mucin-rich type

The luminal portion has a serrated (“saw tooth”) appearance formed by tufts or folds of abundant apical cytoplasm. It contains glands with star-shaped lumina.[3]

There are crypts that are elongated but straight, narrow and hyperchromatic at the base. All crypts reach to the muscularis mucosae.[3]

The basement membrane is frequently thickened.[3]

Goblet cell-rich type

Elongated, fat crypts and little to no serration. Therefore, they may not be obvious without comparing to adjacent normal intestinal wall.[3]

They are filled with goblet cells, extending to surface, which commonly has a tufted appearance.[3]

Epithelial misplacement

Infrequently, the epithelium is misplacement into the submucosa. Such polyps have been termed "inverted hyperplastic polyps". They appear to be restricted to the sigmoid colon and rectum. The misplaced epithelium is mucin-depleted , similar to the basal 1/3 of the polyp. The misplacement is accompanied by the lamina propria, and is continuous with overlying polyp through a gap in the muscularis mucosae. It may require slices at multiple levels to demonstrate microscopically.[3]

In such cases adjacent hemorrhage and hemosiderin deposition is common. Collagen type IV stain will have a strong continuous staining around nests.[3]

Cellular structure

Nuclei are small, regular, round and basal in the luminal half of the crypts, most reliably evaluated near the luminal surface.[3]

There are proliferative changes at the base of crypts, where nuclei are enlarged, the nucleus/cytoplasm ratio is elevated.[3]

Immunohistochemistry

Immunohistochemistry using Ki-67 stains the basal 1/3 to ½ of crypts, indicating a proliferative zone.[3]

CK20 is positive in the luminal ½ or 2/3 parts.[3]

Differential diagnoses

The deep proliferative zones and reactive processes closely mimic changes seen in colorectal adenomas.[3]

A sessile serrated adenoma or traditional serrated adenoma is suspected if there is either of the following:[3]

A sessile serrated adenoma is suspected in case of any of the following:[3]

  • Size ≥0.5 cm
  • Location in right colon

If both are present, it is almost always a SSA. Other features causing a suspicion for sessile serrated adenoma are:[3]

  • Dilation of crypts
  • Branching of crypts
  • Horizontal glands at the base
  • Mature mucinous cells at the base of crypts

References
  1. Kumar, Vinay (2010). "17 - Polyps". Robbins and Cotran pathologic basis of disease (8th ed.). Philadelphia, PA: Saunders/Elsevier. ISBN 978-1-4160-3121-5.
  2. Stoler, Mark A.; Mills, Stacey E.; Carter, Darryl; Joel K Greenson; Reuter, Victor E. (2009). Sternberg's Diagnostic Surgical Pathology. Hagerstwon, MD: Lippincott Williams & Wilkins. ISBN 0-7817-7942-1.
  3. Robert V Rouse (2010-01-31). "Hyperplastic Polyp of the Colon and Rectum". Stanford University School of Medicine. Last updated 6/2/2015
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