The invasive potential of 15 brain tumors (seven meningiomas, and eight astrocytomas) as studied in cultures with Gelfoam used as a substrate. A three-stage system is introduced to classify in vitro invasiveness according to the depth of Gelfoam infiltration after 2 weeks' culture. This system proved to be simple and accurate. Meningiomas revealed greater activity in culture as compared to astrocytomas and infiltrated deeper into the Gelfoam. Dura mater explants were placed next to the culture of the tumors to study their interaction. Dura mater acted as a relatively strong barrier against tumor cell invasion in culture. In the majority of the explants, tumor cells revealed either contact arrest or spread underneath the dura and rarely spread over it. Tumor cells were seen infiltrating the dural explants in three cases, all of which were meningiomas.

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