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inverted hyperplastic polyp

Tuesday 20 March 2012

A variant of the colorectal hyperplastic polyp, the so-called "inverted hyperplastic polyp", may simulate a carcinoma and may appear to invade the underlying submucosa.

The lesions affect both sexes and patients are generally older than 50 years.

The lesions tend to develop in the rectum or sigmoid and range in size from 0.2 to 1 cm with a mean size of 0.5. These lesions resemble hyperplastic polyps, but instead of being solely exophytic ,groups of glands lie beneath the level of the mucosa, forming one or more lobulated submucosal nodules.

There may also be a mixed pattern of lobules and distorted crypts.

The overlying mucosa contains glands typical of hyperplastic polyps arranged as a sessile nodule or in a flat patch.

Pedunculation is absent. The endophytic nodules show a peripheral hyper-basophilic proliferative zone and a central area of pale, more mature cells with characteristic serrated tubular profiles seen in hyperplastic polyps.

In contrast to the usual exophytic hyperplastic polyp, the endophytic elements exhibit a more complex growth pattern, sometimes demonstrating back-to-back glandular arrangements and intraluminal budding.

The epithelial lining lacks dysplasia. Occasionally, lymphoid nodules intermingle with the lesions.

Multiple endophytic lesions may be present.

The muscularis mucosae appears to stretch thinly around the deep aspect of smaller lesions andis incomplete around larger nodules.

When cut tangentially,one may see splaying and dissociation of the muscularis mucosae.

Downward extension of hyperplastic tubules projecting into the submucosal lymphatics when sectioned obliquely simulates invasion.

Fresh hemorrhage, vascular congestion, or hemosiderin may be present around the glands.

The lesions arise secondary to trauma-induced protrusion of the glands through breaks in the muscularis mucosae, often near lymphoid aggregates.

Synopsis

- prominent mucosal fold that contains an area of epithelium within the submucosa.
- The epithelium appears hyperplastic with a gradient of differentiation extending from the periphery of the lesion to its center.
- The crypt bases lie radially arranged at the periphery of this lesion.
- The absence of cytologic atypia distinguishes this from an invasive carcinoma.
- The presence of the glandular infoldings and prominent goblet cells distinguishes this lesion from colitis cystica profunda.
- Cytologically, the cells appear histologically identical to those seen in hyperplastic polyps