New fine structural features of cardiac rhabdomyoma: Report of a case

Abstract

Electron microscopy of a cardiac rhabdomyoma revealed two varieties of cells: (1) typical "spider cells' characterized by few myofibrils and large aggregates of glycogen particles free in the cytoplasm; and (2) cells with more myofibrils, less glycogen, and glycogen within membrane-limited vacuoles. These differences in myofibril development and glycogen content represent two succeeding stages in the early maturation of normal cardiocytes. The vacuoles containing glycogen were interpreted as autophagic and, consequently, active in the glycogen decrease typical of normal maturing cardiocytes. Rhabdomyoma cells did not show the structures, e.g., T system, characteristic of the late normal heart development. This study supports the theory that arrested cardiocyte maturation is a factor in the pathogenesis of cardiac rhabdomyoma.