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colorectal adenoma with pseudocarcinomatous entrapment

Sunday 11 March 2012

Pseudocarcinomatous Entrapment (Pseudoinvasion)

A recognized histologic pitfall in diagnosing adenomas is the presence of pseudoinvasive foci surrounded by areas of hemosiderin deposition and fibrosis.

Its significance is its resemblance to invasive carcinoma and its potential to be misdiagnosed, thereby leading to needless colonic resections.

Pseudocarcinomatous entrapment, variously termed colitis cystica profunda, submucosal cysts, pseudocarcinomatous invasion, or epithelial misplacement, affects a small proportion ofpedunculated adenomas.

Affected adenomas usually measure > 1 cm in diameter, have at least a 1-cm stalk, and originate in the sigmoid colon (64% to 85%).

Repeated episodes of torsion lead to hemorrhage, inflammation, and ulceration of the adenoma.

As a result, the adenomatous epithelium herniates through the muscularis mucosae into the underlying submucosa.

The presence of thick-walled and occasionally thrombosed submucosal blood vessels supports the concept of torsion and subsequent ischemia as the initiating event.

Forceps biopsies may also cause epithelial displacement into the underlying submucosa.

The adenomatous tissue may be pulled further into the stalk by contraction of fibrous tissue as the biopsy site heals.

The changes reflect the time elapsed from the biopsy procedure and the polyp resection.

Displaced cells become embedded within capillary-rich granulation tissue during the first week following the biopsy.

Subsequent submucosal fibrosis results in persistent submucosal mucin pools.

Histologically, one recognizes areas of pseudo-invasion by the presence of adenomatous epithelium in a submucosa without cytologic evidence of malignancy.

The displaced glands sometimes lie in continuity with the neoplastic tissue overlying it, and the degree of dysplasia in the displaced glands often resembles that of the glands immediately overlying it.

The displaced glands may also coexist with non-neoplastic glands that were displaced along with the neoplastic ones, providing assurance that the submucosal glands are displaced rather than invasive.

Normal lamina propria surrounds displaced adenomatous glands (as opposed to a desmoplastic response surrounding an invasive carcinoma).

If the epithelial displacement occurs immediately prior to the polypectomy, the glands may be surrounded by a narrow rim of granulation tissue.

Fresh or old hemorrhage with hemosiderin deposits in the fibrotic stroma surrounding the displaced glands is known as
siderogenous desmoplasia.

Hemosiderin also deposits in the lamina propria and in the fibrotic stroma surrounding the glands and thick-walled blood vessels.

This contrasts with the lack of hemosiderin deposition in areas oftrue invasive carcinoma.

Rarely, areas of high-grade dysplastic mucosa become entrapped in the submucosa, a change that represents an even greater diagnostic challenge to the pathologist.

Occasionally, the displaced glands undergo cystic dilation with rupture and epithelial lining loss or atrophy.

Sometimes, the mucinous material within the submucosa calcifies.

The distinction between a mucus-secreting invasive adenocarcinoma and cystically dilated pseudoinvasive glandsmay also be difficult.

Pseudoinvasive glands usually appear regular, sometimes exhibiting a lobular distribution in the submucosa.

In contrast, mucinous carcinomas display an irregular distribution of angular glands or nests of atypical cells.

No lamina propria surrounds the cysts or glands; instead, a desmoplastic stroma usually lacking hemosiderin deposits is present.

Focal stromal desmoplasia may be present.

Differentiating pseudocarcinomatous entrapment in adenomas from localized colitis cystica profunda or the mucosal prolapse syndromes is also usually not difficult,since in the latter, the submucosal cysts are covered by an ulcerated, normal, or hyperplastic-appearing epithelium.

The overlying epithelium is not adenomatous in prolapse or colitis cystica profunda.

See also

- colorectal adenoma