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Craniopharyngioma is a rare neoplasm in the rat, and few cases have been described. These lesions are thought to originate from squamous cell remnants of Rathke's pouch, an evagination of primitive stomatodeum. This neoplasm is usually locally invasive, and neither cranial nor extracranial metastases have been described. A spontaneously occurring malignant, metastasizing craniopharyngioma arising from the neurohypophysis was detected in a 2-year-old male albino rat. The infiltrative growth was observed in the wall of the vessels of the circle of Willis, in the perivascular space of Virchow and Robin, in the submeningeal space near the hypothalamus, through the fissura chorioidea, in the medulla oblongata, and along the optic nerve into the periocular region. Metastases were detected in the thalamus and hippocampus. The diagnosis was made on the basis of microscopic, immunocytochemical and ultrastructural findings.

A search of the rat tumor literature revealed no papers on naturally occurring primary osteosarcoma of meninges. In humans, this tumor, arising primarily from the meninges, is unusual; only two cases have been reported. We report on a spontaneously occurring osteosarcoma arising from meninges in a 2-year-old female albino rat. The diagnosis was made on the basis of gross, microscopic, and ultrastructural findings. The diagnosis of this neoplasm is supported by the fact that a primitive mesenchymal cell in the meninges is capable of giving rise to a wide variety of neoplasms.