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colorectal inflammatory polyps with bizarre stromal cells

Tuesday 20 March 2012

A small group ofinflammatory polyps contain bizarre stromal cells that may be mistaken for a malignancy.

Most lesions occur in middle-aged or elderly patients.

Large, bizarre, mesenchymal cells are present.

These appear as atypical, spindled, stellate, epithelioid, or large round cells within the lamina propria or in granulation tissue.

They haveabundant amphophilic cytoplasm, vesicular nuclei, and large eosinophilic inclusion-like nucleoli.

Because of the inclusion-like nature of the nuclei, the cells may be confused with CMV infections, but immunohistochemical stains for CMV are negative.

They are usually dispersed in a zone under the ulcerated or regenerated mucosa without infiltrating the deeper stroma.

Sometimes the atypical cells blend into the granulation tissue.

Multinucleated and giant cell forms are also present.

Rarely, atypical pale epithelioid cells form round, cohesive clusters resembling acini or vascular structures.

Lack of staining with cytokeratin rules out a carcinoma.

Mitotic figures are uncommon and atypical mitoses are absent.

The cells do not contain mucin or glycogen.

These cells lie within the inflammatory exudate and any associated epithelial elements usually appear benign or reactive in nature.

They stain strongly for vimentin and sometimes for muscle-specific actin, a phenotype that is consistent with reactive fibroblasts or myofibroblasts.

Misinterpretation of these reactive changes can result inunnecessary radical surgery.

These lesions can be particularly confusing when encountered in small biopsies in which the entire tissue context is lost.

However, immunostains should resolve their true nature, but in case of doubt the area can be rebiopsied.