Spontaneous and ethyl-nitrosourea-induced medullomyoblastomas in cerebellar vermis defect (CVD) mutant rats

A 26-week-old female cerebellar vermis defect (CVD) rat, a mutant with cere bellar vermis defect and cerebellar dysplasia, developed a brain tumor abou t 10 mm in diameter. Histopathologically, the tumor consisted of diffuse pr oliferation of small round to ovoid cells with hyperchromatic nuclei, occas ionally containing round to strap-shaped myoblastic cells. Immunohistochemi cally, the small round cells expressed neuron-specific enolase and synaptop hysin, indicating neuronal differentiation; myoblastic components reacted t o desmin, myoglobin, and vimentin. Based on these findings, the case was di agnosed as a medullomyoblastoma (MMB). Furthermore, two cerebella tumors in CVD rats, which were induced by transplacental application of ethyl-nitros ourea, showed histopathology similar to the aforementioned case. MMB is a v ery rare tumor in humans and animals; thus, it is noteworthy that MMBs deve loped in CVD rats, involving the dysplastic cerebellum with abnormal migrat ion of external granule cells.