LAUSR

Rheumatic carditis is a pancarditis, however, the parietal endocardium is affected to the least obvious degree. In 1924, MacCallum [1] described, in acute rheumatic fever, involvement of the endocardium of the posterior wall of the left atrium, above the base of the posterior mitral cusp, associated with numerous Aschoff nodules in the subendocardium. This was called MacCallum’s Patch or Triangle, because of its triangular distribution (Fig 1). The etiology was thought to be rheumatic. Today, this lesion is considered to be traumatic in origin, caused by the abnormally directed regurgitant stream of mitral regurgitation impinging upon the posterior wall of the left atrium, resulting in the formation of a systolic pocket. Our investigation of the parietal endocardium in acute rheumatic carditis, demonstrated the presence of acute parietal endocarditis, with a reaction similar to that present in the valves [2]. A separate examination of the left atrial endocardium above the base of the posterior mitral cusp, showed the presence of prominence and palisading of the endocardial cells (Fig. 1), with irregular outpouchingprotrusion of the endocardial surface. Our investigation of the parietal endocardium in acute rheumatic carditis, demonstrated the presence of acute parietal endocarditis, with a reaction similar to that present in the valves [2]. A separate examination of the left atrial endocardium above the base of the posterior mitral cusp, showed the presence of prominence and palisading of the endocardial cells (Fig. 1), with irregular outpouching-protrusion of the endocardial surface. There were raised, irregular edematous nodules of the endocardium (Fig. 2), with an infiltration of elongated histiocytes, fibroblasts and nongranular cells (Fig. 3) and macrophages. There was evidence of neovascularization and the formation of collagen fibrils. An increase, was noted, in the smooth muscle components of subendocardium. An endocardial nodule (Fig. 4) showed organization of fibrinoid necrosis. This finding supports the postulate that the endocardial fibrosis results from the organization of the acute rheumatic process.