¹Department of Surgical Pathology, Children's Memorial Hospital, Northwestern University, Chicago, Illinois

Correspondence: Pauline Chou, M.D., Department of Pathology, Box 17, Children's Memorial Hospital, 2300 Children's Plaza, Chicago, IL 60614; e-mail: pmchou@nwu.edu; fax: 773-880-8127.

Accepted 30 March 2001.

Abstract

Calcifying fibrous pseudotumor (CFP), a recently described lesion, is characterized by a predominantly lymphoplasmacytic infiltrate with abundant hyalinized collagen and psammomatous or dystrophic calcifications. The cause and pathogenesis are unclear, but it has been postulated that CFP may represent a sclerosing end stage of inflammatory myofibroblastic tumor (IMT). We compared the histological and immunohistochemical profiles of seven cases diagnosed as CFP and seven as IMT. Histologically, the CFP demonstrated varying degrees of calcifications in addition to fibroblastic proliferation admixed with inflammatory cells composed of lymphocytes, eosinophils, and mast cells. The IMTs rarely contain calcifications and had a myofibroblastic proliferation varying from hyalinized acellular collagen to florid fibroblastic proliferations simulating sarcoma. The inflammatory component was composed primarily of plasma cells and lym-phocytes, sometimes arranged as lymphoid aggregates with germinal centers. All CFP cases were diffusely positive for factor XIIIa and negative for smooth muscle actin, muscle-specific actin, and CD34. All IMTs demonstrated diffuse positivity for actin, variable positivity for CD34, and focal positivity for Factor XIIIa. This study demonstrates certain distinct histologic, immunohistochemical, and electron microscopic features between IMTs and CFPs.