The diagnostic significance of left auricular thrombus in F344/N rats

In the process of assessing the main cause of death in F344/N rats from the aging farm of our institute, we have often found left auricular thrombus in autopsy cases of moribund animals. In 319 autopsy cases, 45 were of left auricular thrombus and 44 were accompanied by hematopoietic neoplasms, including overt leukemia and a pre-leukemic condition of leukemia. In cases without splenomegaly, this lesion was found in 13 of 21 animals (61.9%) whereas, in cases with splenomegaly, 31 of 239 were positive for this lesion (13.0%). Thus, left auricular thrombus may be an important macroscopic diagnostic criteria of hematopoietic neoplasms, especially when splenomegaly is absent. Furthermore, this lesion tended to arise in aged animals despite the presence of splenomegaly. These results would therefore greatly contribute to aging science by confirming the health condition of experimental rats and the accuracy of subsequent results.