The incidence of naturally-occurring primary brain tumours in the laboratory rat.

Histological analysis of 90 spontaneous primary tumours of the brain observed among 8960 ageing rats (Sprague-Dawley-derived) revealed 55 granular-cell meningiomas, 19 neoplastic reticuloses, 11 neuroglial tumours, 4 pineal tumours, and one pleomorphic, meningeal sarcoma. Although all these tumour types can occur in man and other animal species, the high incidence of granular-cell tumours, and the low degree of differentiation of some neuroglial and pineal tumours, appear to be characteristic attributes of the rat.