Endocardial Spindle Cell Proliferation

Proliferation of spindle-shaped cells resembling fibro­blasts arise in the endocardium and subendocardial tissue (Fig. 2.57) as a frequent lesion in various stocks and strains of rats. These lesions may become expansive and invade the myocardium. They have been character­ized as fibroproliferative, giving rise to terms including endocardial fibromatosis, fibroelastosis, endocardiosis, and endocardial fibromatous proliferation. It has also been suggested that these changes are precursors to schwannomas.