Immunohistological evaluation of macrophage infiltrates in brain tumors

Peritumoral edema is one of the most serious complications of intracranial neoplasms; however, the exact pathogenesis of this condition is still unknown. To explore the effect of macrophages in brain tumors on the pathogenesis of peritumoral edema, 42 specimens of primary or metastatic brain tumors were studied. Frozen sections were examined by an immunoperoxidase staining technique with anti-Leu-M3 monoclonal antibody. Eight of 14 gliomas demonstrated Leu-M3-positive cell (macrophage) infiltration. The two glioblastomas showed a moderate or marked degree of macrophage infiltration. Twelve of 16 meningiomas demonstrated varying degrees of macrophage infiltration. All six metastatic brain tumors exhibited prominent macrophages in intra- and peritumoral tissues. Four acoustic neurinomas and two hemangioblastomas showed a slight to moderate degree of macrophage infiltration. Excellent correlation was found between the degree of macrophage infiltration seen on immunoperoxidase staining and the peritumoral edema detected on computerized tomography brain scans of patients with supratentorial tumors, especially meningiomas. Macrophages are known to secrete various substances (including arachidonate metabolites) that may interfere with vascular permeability. These data suggest that macrophages infiltrating brain tumors may play an important role in the pathogenesis of peritumoral edema.