ABSTRACT
A small cardiac tumor was detected in the posterior wall of the left atrium of a 110-week-old female Wistar Hannover rat (Slc: Wistar Hannover/Rcc) during a carcinogenicity historical control study. Tumor was consisted of 2 different cells. Most of the tumor cells were polygonal to oval in shape and had slightly basophilic and granular cytoplasm. These cells were arranged in distinctive cell nests, called 'Zellballen', and were separated by reticulin fibers. The nuclei were round to slightly oval. A few mitotic figures were found. Cytoplasmic granules of tumor cells were negative for Fontana-Masson and Periodic acid Schiff (PAS) staining. Immunohistochemical staining revealed that the chief cells in the tumor were positive for the neuroendocrine markers synaptophysin and chromogranin A but were negative for S-100 protein, vimentin, cytokeratin, α-smooth muscle actin, and calcitonin. In contrast, the surrounding sustentacular cells, other type of tumor cells, were positive for only S-100 protein. The immunohistochemical properties of the tumor cells were quite similar to those of the aortic body. The tumor cells had infiltrated the myocardium of the left atrium and were also noted within vessels. Based on these findings, the tumor was diagnosed as a paraganglioma originating from the aortic body.
