The leptomeningeal vein. A site of re-entry of leukemic cells into the systemic circulation

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Abstract
The possible routes of transvascular migration of leukemic cells were studied in guinea pigs with an L2C lymphoblastic cell-line inoculation leukemia. The leukemic infiltrates were found mostly in and around the superficial leptomeningeal veins, paralleling findings in human leukemia. Reconstructions, based on thin serial sections (Epon blocks), allowed us to conclude: (1) leukemic cells do proliferate under the vascular endothelium; (2) the endothelium when pushed away from its basement membrane degenerates and ultimately disintegrates; (3) junctions between adjacent endothelial cells tend to be preserved, even when the rest of the endothelial cytoplasm has disintegrated; (4) leukemic cells will eventually re-enter the circulation; (5) leukemic cells, either singly or in groups, cross through endothelial pores in otherwise intact endothelial cells, rather than through opened-up junctions. It is concluded that leukemic cells cross the endothelium either through endothelial pores, which they in some way engender, or through large gaps left by disintegrating endothelium, the latter possibly intravasation.