[Ultrastructure of capillary permeability in human brain tumors. 2: Mechanisms of contrast enhancement in gliomas].

In order to elucidate the mechanism of contrast enhancement on computerized tomography (CT), the alteration of capillary permeability was studied in 3 cases of medulloblastoma, 2 cases of ependymoma, 5 cases of glioblastoma and 5 cases of astrocytoma. The surgical specimens were studied with conventional ultrathin section and freeze-fracture replica techniques. Contrast enhancement on CT scan defined in order of medulloblastoma, ependymoma, glioblastoma and astrocytoma. In the medulloblastomas and glioblastomas, the cell junctions of the capillaries were short, elongated, and, in fact open. Other capillary abnormalities included endothelial hyperplasia with extensive vesicular formation, surface infolding of endothelial cells, irregularity of the basal lamina, and a large extravascular space. Tight junctions were seen as one or twe strands. These tight junctions presented irregular lining of intramembranous particles. In the astrocytomas, the blood vessels appeared relatively normal, and the tight junction were seen as networks of seven strands. The particles lines were not disrupted. In the ependymomas, the tight junctions in one area were seen as a network of six strands, but in the other areas as three strands, and the fenestrae were observed in the replicas but not confirmed in the ultrathin sections. The conclusion drawn from this study is that osmotic opening of the tight junctions that have fewer strands play an important role in the marked contrast enhancement of the gliomas, in addition to transcellular transport of increased pinocytotic vesicles and fenestrations. The irregular basal lamina and large perivascular space also increase extravasation of contrast medium.