The fine structure of blood vessels in ethylnitrosourea-induced tumours of the rat nervous system: with special reference to the breakdown of the blood-brain barrier.

The fine structure of capillaries in and around ethylnitrosourea-induced tumours, gliomas and schwannomas, was examined in rats. A great variation was observed in the severity of changes: the degree of abnormality depended on the histological type and size of the tumour and on the site of the capillaries within the neoplasm. Endothelial cells, basement membranes and pericytes all demonstrated changes in their fine structure. The most striking alterations occurred in the endothelial cells: luminal cell membranes, tight junctions and pinocytotic activity were all modified. The widened extracellular spaces, particularly around capillaries, were frequently seen to contain proteinaceous material and haematogenous cells. Invasion of these spaces by neoplastic cells, however, rarely occurred. Formation of new capillaries was indicated by the mitotic activity of endothelial cells. These changes in the blood vessels of cerebral tumours have an important role in the breakdown of the blood-brain barrier.