Endocardial schwannomas in rats. Their characterization by light and electron microscopy.

Thirty male Sprague-Dawley rats were given a single intravenous injection of methyl(acetoxymethyl)nitrosamine. Primary endocardial tumors developed in ten rats. By light and electron microscopy, the tumors had many of the typical features of schwannomas (neurinomas) in rats. Tumors were composed of masses of elongated cells surrounded by a fine reticulin network, occasionally forming Verocay bodies. Basement membrane was observed on the external surfaces of tumor cells, which had convoluted plasma membranes. To our knowledge, this is the first report of a spontaneous endocardial schwannoma in a rat. The literature addressing endocardial tumors in rodents and man is discussed, and criteria for distinguishing this neoplastic entity from other tumors and non-neoplastic endocardial proliferations are described.