A Spontaneous Ovarian Immature Teratoma in a Juvenile Rat

A spontaneous ovarian immature teratoma characterized by the presence of tissue derivatives of endoderm, mesoderm and ectoderm was investigated histopathologically in a 6-week-old juvenile Crj:CD(SD)IGS rat. The various kinds of tissue components observed in this teratoma were mainly mature elements derived from three embryonic germ layers, such as nervous tissue, skin, pancreas, salivary gland, gastrointestinal tract, respiratory tracts, striated and smooth muscle, bone with bone marrow, cartilaginous tissue and adipose tissue. Remarkable features were that this teratoma contained immature tissues intermingled with mature tissues, which typically took the form of primitive neuroepithelial rosettes and tubules and islands of immature cartilage, showing evidence of malignancy. A small yolk sac carcinoma-like focus was also observed. Neither invasion nor distant metastases were found in the other organs and tissues. This is the first report of an ovarian immature teratoma in a rat.