Tumors in Amphibians. I. Histology of a Neuroepithelioma in Siredon mexicanum

Summary

A spontaneous tumor, transplantable only in some instances, developed in the roof of the mouth in two adult Mexican axolotls (Siredon mexicanum). Histological study showed that the tumor consisted of many lobes or tubes, and the central cavities or lumens often contained coagulated material. The surface of the tumor was covered with typical skin epithelium, containing Leydig cells, but there was no connection between the tumor and the skin. The interstitial connective tissue separating the lobes of the tumor was the usual loose connective tissue, typical of the adult axolotl. Mitosis was very rare in the skin epithelium covering the surface of the tumor and in the connective tissue separating the lobes. Mitotic activity was very great in some portions of the lobes of the tumor, but was limited in other portions of the tumor. Most of the cells of the tumor were bipolar. They were often fusiform, with a large, ovoid nucleus and prominent nucleoli. Intracellular fibrils were typically stained red with chromotrope aniline blue and black with the silver stain, and hence can be considered neurofibrils. The structure of the tumor, with a central lumen and a layer of bipolar cells, was highly reminiscent of the embryonic neuroepithelium. Accordingly, this tumor can be regarded as a neuroepithelioma.