[Pathological findings of cardiac rhabdomyomatosis in the guinea pig].

Cardiac rhabdomyomatosis of Hartley guinea pigs was examined by light and transmission electron microscopy, and its incidence and distribution were also described. Cardiac rhabdomyomatosis was found in 58 cases out of 345 animals, aged from 1.5 to 17 weeks. A few small lesions were noted in many cases, but large lesions were rare. Most lesions noted in the ventricle were found to measure from 1 mm2 to 5 mm2 in area. The larger lesions were seen near the cardiac apex. In terms of distribution of the lesions, they were observed most frequently in the left ventricular free wall. They were also distributed less frequently in the ventricular septum and in the right ventricular free wall. In bilateral free walls and the ventricular septum, this lesion was frequently noted on the endocardial side and in the tunica muscularis, respectively. Light microscopically, this lesion had a characteristic nodular-reticular structure with large vacuolated cells. Electron microscopy of cardiac rhabdomyomatosis revealed two cell types, A and B. Type A cells were characterized by large aggregates of glycogen particles distributed loosely in the cytoplasm and by myofibrils and mitochondria located at the periphery of the cytoplasm. Type B cells were characterized by large aggregates of mitochondria near the nucleus and at the periphery of the cytoplasm and by large aggregates of glycogen particles with a similar distribution to those in type in type A cells. Myocardial cells in the marginal regions of rhabdomyomatosis lesions showed mitochondrial swelling and rupture of myofibrils.(ABSTRACT TRUNCATED AT 250 WORDS)