[Ultrastructural systematization of vascular changes in gliomas].

The fine structural features of microcirculation in benign gliomas, as compared to those in glioblastomas have insufficiently been studied. 36 astrocytomas and oligoastrocytomas (grades I and II) were examined with the electron microscope in order to classify the arterioles, capillaries and venules of these tumours. In all the gliomas, the number of arterioles was smaller than in the normal brain parenchyma. A thickening of the subendothelial basement membrane could be assessed regularly. In the architecture of the small vessels numerous transitional forms could be found in many cases. On this basis the designation "capillary-like" and "venule-like" vessels seems to be justified. As a rule, the venule-like vessels are more numerous than the capillaries. The pericapillary and particularly the perivenular spaces are frequently dilated. In a few areas no continuous perivascular sheath of astrocytic foot processes are formed. At places glial processes can be found in the perivascular spaces which are not covered by a basement membrane. Lack of arterioles can lead to disturbances in autoregulation, and the frequently pathological structure of the capillaries and venules can result in disordered transport of water and ions with consecutive oedema.