[Delayed cerebral radionecrosis associated with brain edema].

In a patient with a delayed cerebral radionecrosis, we examined the ultrastructural changes of capillaries and discussed the cause of the development of severe brain edema which is one of specific features of the radionecrosis. A 42-year-old male was found to have cerebral radionecrosis two and one-half years following split-course radiotherapy which was done after subtotal excision of a left parasagittal meningioma. The surgical specimens were studied with conventional ultrathin section and freeze-fracture replica techniques. The common characteristics of capillary endothelia were attenuation of its electron density, less degree of surface infolding, irregular thin and thick width, increased pinocytotic vesicles which were calculated as 37 per square micron with replica preparations. The discontinuity of endothelia was also revealed. The basal laminae were irregular in thickness. The pericapillary space was markedly enlarged. A fibrin-like substance accumulated in the extravascular space. Inflammatory cells also infiltrated the pericapillary zone. The tight junctions were preserved. The intercellular junctions were composed of 5 strands which appeared to be a continuous array of particles. We concluded that activated pinocytotic vesicles (vesicular transport) played an important role in increasing the permeability in the vessels of delayed cerebral radionecrosis, in addition to a possible leakage through discontinuity of endothelia.