CARDIAC MYXOMA IS RICH IN FACTOR-XIIIA POSITIVE DENDROPHAGES - IMMUNOHISTOCHEMICAL STUDY OF 4 CASES

Cardiac myxoma is an enigmatic tumour thought to arise from primitive cardiac mesenchymal cells. Factor XIIIa+ dendrophages are tissue histi ocytes that are active in tissue repair and thrombosis. To explore whe ther factor XIIIa+ dendrophages play a role in cardiac myxoma morphoge nesis, we stained four cases with an antiserum against coagulation fac tor XIIIa (FXIIIa), We also used antibodies recognizing CD34, CD31, an d S-100 protein. Samples of valvular endocardium from 12 and 16 week f etuses and two adult autopsies were compared with the four myxomas. Al l cardiac myxomas had rounded and dendritic FXIIIa+ cells admired with more numerous CD34+ spindle and stellate myxoma cells. The CD34+ cell s formed multicellular syncytia and capillary sprouts. Many of these s yncytial structures also expressed CD31 and, to a lesser extent, S-100 protein, strongly in two cases and more focally in two. Fetal subendo cardium was composed of CD34+ stellate fibroblast-like cells invested with scattered FXIIIa+ histiocytes; no S-100+ cells were detected. Our findings confirm that cardiac myxomas are composed of CD34+ primitive subendocardial cells. These cells show a capacity for CD31+ endotheli al differentiation. In cardiac myxoma, the CD34+ myxoma cells are acco mpanied by numerous FXIIIa+ dendrophages, the presence of which sugges ts abnormal organizing thrombus-like differentiation in cardiac myxoma morphogenesis.