Vascular invasion by glioma cells in man: an electron microscopic study.

Abstract

O NE of the unique characteristics of primary brain tumors is that they rarely metastasize outside the central nervous system, irrespective of their grade of malignancy. Although at present cases of extracranial metastasis are being reported with increasing frequency, they still remain relatively uncommon. 1,8,a9--01,2' Such metastases are supposedly based on hematogenous dissemination of the tumor cells since there is no lymphatic system in the central nervous system although the role of propagation along the sheaths of cranial or spinal nerves must also be taken into consideration. It has been assumed that the vascular invasion by neoplastic cells takes place through a physically damaged wall of a blood vessel within the tumor or in its vicinity, but meningeal vasculature and venous sinuses are rarely involvedY ~ The hematogenous metastases develop according to a certain sequence: 3,~ 1) direct intravasation of the tumor cells into the blood stream across the wall of a blood vessel in the brain or spinal cord; 2) embolization of a group of tumor cells in the small vessels of a distal organ; and 3) implantation of tumor cells in a new location where they survive to produce a secondary neoplasm. The stages of embolization and implantation have been studied in detail, both experimentally and clinically, ~ but the first step, that of the invasion of cerebral vasculature, has not been adequately investigated. Our observations are centered on the ultrastructural sequence of vascular invasion by gliomatous cells with particular reference to glioblastoma multiforme.