Perivascular edema fluid pathway in astrocytic tumors

Perivascular spaces are anatomical routes for the bulk flow drainage of fluid from the gray matter to the subarachnoid space in normal rat brain. Perivascular cells are the resident scavengers in perivascular spaces. Following focal brain damage, perivascular cells upregulate MHC Class II antigens associated with uptake of edema fluid. Similar cells can be defined in damaged human brain. In the present investigation, the distribution of MHC Class II upregulated perivascular cells was measured in 30 astrocytic tumors and adjacent edematous tissues by immunocytochemistry using the following antibodies: HLA-DR (MHC Class II), PGM1 and MAC387 (macrophages). Perivascular cells were PGM1+/MAC387- and were located in perivascular spaces along blood vessels of all sizes. MHC Class II+ perivascular cells were distributed mainly in the tumors but in some cases (4 of 10 in astrocytomas, 4 of 10 in anaplastic astrocytomas, and 7 of 10 in glioblastomas) they were also found in adjacent edematous brain. The extensive MHC Class II expression on perivascular cells suggests that perivascular cells play a scavenging role in the perivascular spaces in human brain. The results of the present study indicate the similarity between perivascular spaces in human and rat brains and emphasize the significance of perivascular spaces as anatomical routes for edema fluid drainage from human brain tissue.