Ultrastructure of Meningeal Tumors Induced in Dogs With Rous Sarcoma Virus

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Abstract
Leptomeningeal tumors induced in 11 dogs by intracerebral inoculation of Rous sarcoma virus (RSV) were studied with the electron microscope. The strains of RSV used were: Schmidt-Ruppin, Bryan high-titer, and CT559. Two main types of tumors were recognized from their ultrastructure: 1) meningothelial meningiomas consisting of cells closely similar to the normal arachnocyte and having the ultrastructural characteristics observed in human meningiomas; 2) meningeal sarcomas consisting predominantly of a fibroblastic type of cell showing various degrees of anaplasia. The histogenesis of the leptomeningeal sarcoma from the arachnocytes, rather than from the endothelial or the adventitial cells of blood vessels, is suggested. Viral particles morphologically indistinguishable from those associated with the avian-leukosis-virus complex were noted in the tumors of 5 of the 11 dogs. Cytoplasmic crystalline aggregates were observed in the neoplastic cells of 10 dogs. The nature of these formations remains unknown. No viral particles or crystals were observed in the meninges of 3 normal dogs.