On the primary meningeal tumors with special concern to the hemangiopericytoma pathology and biology.

5 hemangiopericytomas have been studied together with 678 tumors of the CNS including 579 meningiomas, 13 fibrosarcomas, 4 malignant meningiomas, 3 unclassified malignant tumors and 79 angioblastic meningiomas. The main clinical and histological features of this series are discussed in order to identify the more useful criteria for biological and microscopical characterization of the hemangiopericytoma. Beside a pure type of growth, the presence of histological intermediate variants and mixed cell proliferations have been observed. The possibility of transitional features and mixed tumors is then outlined.