Cardiac papillary fibroelastoma: an immunohistochemical investigation and unusual clinical manifestations.

Cardiac papillary fibroelastoma (CPF) is a morphologically distinctive, but rare, cardiac lesion that is usually found incidentally at autopsy or during open heart surgery. Because of improved diagnostic imaging techniques, the premortem or preoperative diagnosis of CPF is becoming more frequent. The histogenesis of CPF, however, remains controversial. Herein we report an immunohistochemical investigation of 11 cases of CPF; two cases showed unusual embolization phenomena, including one with histologically documented pulmonary arterial embolism. For comparison, nine cardiac myxomas (CMs) and eight examples of organizing thrombi were also studied. Immunohistochemical markers included keratin, vimentin, collagen type IV, muscle-specific actin, desmin, factor VIII-related antigen, CD34, and S-100 protein. The cells covering the surface of both CPFs and CMs were positive for vimentin, factor VIII-related antigen, and CD34, in keeping with their presumed vascular endothelial origin. Interestingly, the surface lining cells were also positive for S-100 protein in all CPF and in eight of nine CMs. In CPF, collagen type IV showed multilayered linear staining beneath the surface that was virtually identical to the staining pattern for elastic tissue. The major immunophenotypic difference between CPF and CM is the frequent presence of muscle-specific actin in the stellate cells of the stroma in CM but not in CPF. Although this study did not clarify whether CPF is a hamartomatous, neoplastic, or reparative process, it demonstrated active participation of the surface endothelial lining cells with excessive formation of basal membrane material in the formation of CPF.