Morphological features of adult rats of IS/Kyo and IS-Tlk/Kyo strains with lumbar and caudal vertebral anomalies

A case report of ventricular septal defect in an adult Sprague Dawley rat

A 20-week-old male Sprague Dawley rat noted with decreased body weight, dyspnea, and anorexia beginning 2 days before death was necropsied in the recovery period of a sub-chronic toxicity study. The heart was severely enlarged (30 × 20 × 20 mm), 3–4 times larger than normal, with an approximately 6 mm wide defect in the upper, membranous portion of the ventricular septum. Both ventricles measured 4 mm in thickness, and the right ventricle was 4 times thicker than normal. According to a microscopic examination, the myocardial fibers were severely hypertrophic in the right ventricle and mildly hypertrophic in the left ventricle and septum. Myocardial vacuolation, focal hemorrhages with hemosiderin-laden macrophages, myocardial necrosis, focal fibrosis, hyalinized myocardial fibers, and multifocal adhesive pericarditis were also present. This is the first report concerning severe ventricular septal defects in an adult Sprague Dawley rat with a detailed histopathological examination.