A murine model of intracranial invasion: morphological observations on central nervous system invasion by murine melanoma cells.

We describe a model of tumour invasion in which murine melanoma/lymphocyte hybrid cells are injected into the lateral ventricle of neonatal mice. CSF circulation carries cells to the third ventricle where attachment to the ependyma and invasion of the underlying brain may be observed. At this distance from the injection site, invasion can be studied free from trauma or inflammation induced by the injection procedure. Accordingly we restricted our attention to the third ventricle. Our results reveal an unusual form of tumour invasion of the ependyma characterized by progressive attenuation of the ependymal cell layer immediately beneath tumour cell aggregates. Continuity of the ependymal cell layer is ultimately lost at a focal point immediately beneath the tumour, permitting direct contact between tumour cells and the neuropil. Subsequent deep invasion of the brain parenchyma is accomplished by pericapillary infiltration.