Pseudosarcomatous changes in inflammatory pseudopolyps of the colon.

The occurrence of pseudomalignant changes in biopsy specimens from two patients with ulcerative colitis and pseudopolyposis is described. One lesion was characterized by the proliferation of large ganglion cell-like cells, similar to those observed in proliferative fasciitis. Ultrastructural and immunohistochemical findings supported a fibroblastic origin. Biopsy specimens of an inflammatory pseudopolyp from the second patient showed proliferation of oval to spindle cells that were initially interpreted as a possible neoplasm. The site of origin and reactive nature of this lesion became apparent on a subsequent polypectomy specimen. Attention is called to the occurrence of pseudosarcomatous changes in inflammatory pseudopolyps of the gastrointestinal tract that may lead to an erroneous diagnosis of malignancy.