In chronic rheumatic heart disease, an area of markedly thickened, opaque endocardium is found in the posterior wall of the left atrium above the mitral valve. This lesion, called the MacCallum patch, forms because of:

• A Direct extension of Aschoff inflammation into atrial myocardium
• B Deposition of immune complexes in atrial endocardium
• C Organization of a mural thrombus adherent to the atrial roof
• D Traumatic abrasion by a regurgitant jet of blood through the damaged mitral valve ✓

Explanation

The MacCallum patch is subendocardial thickening of the left atrium produced by the jet of regurgitant blood striking and abrading the posterior wall above the mitral orifice, followed by organization and fibrosis. It is a mechanical consequence of mitral insufficiency rather than a site of active Aschoff inflammation, immune complex deposition, or organized thrombus.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.