Ventricular and subarachnoid seeding of intracranial tumors of neuroectodermal origin--a study of 26 consecutive autopsy cases with reference to focal ependymal defect.

: In a series of 26 consecutive autopsy cases of intracranial tumors of neuroectodermal origin, tumor seeding on the ventricular surface and in the subarachnoid space was studied. Five cases of glioblastoma multiforme, six of malignant astrocytoma, six of medulloblastoma, one mixed glioblastoma-fibrosarcoma, one unclassified glioma, and one ependymoma showed ventricular and/or subarachnoid seeding of tumor. The incidence of tumor seeding in our series (76.9%) is much higher than in other series. This discrepancy is probably due to the inclusion of a large number of very small tumor metastases that may have been overlooked in other series. In all cases where metastases were observed the primary tumor extended into the cerebrospinal fluid (CSF). Tumor seeding via the cerebrospinal pathway was more frequently associated with malignant tumors. The distribution of tumor metastases correlated with CSF flow and with the site of focal ependymal defects, which were present in normal brains but occurred more frequently and widely in hydrocephalus.