Histological subtypes and prognostic problems in meningiomas.

The incidence of the various histological subtypes of meningiomas was examined in 1238 patients with surgically treated meningiomas, about 80% arising within the cranial cavity. The histological classification used was that of Courville (1950) and Rubinstein (1972), but "angioblastic" meningiomas were segregated into 3 groups: highly vascularized meningiomas, hemangioblastomas, and hemangiopericytomas. Endotheliomatous and transitional forms constituted 85% of the total (71.5% of intracranial tumors), fibroblastic forms 6.6 and 7.5%, respectively, and highly vascularized (endotheliomatous or transitional) meningiomas 5.2% of the intracranial tumors, while true "angioblastic" meningiomas (hemangioblastomas and hemangiopericytomas) amounted to 2.8% of the total (3.1% of the intracranial tumors). 1.2% were "atypical" (so-called malignant) meningiomas; true meningeal sarcomas were excluded. The incidence of recurrence in patients surviving at least 5 years after apparently complete removal of the tumor was 13% for all sites, and 14.2% for intracranial tumors, but almost twice as high after partial removal. There were no significant differences in the recurrence rate and intervals between first and second operation according to the various histological subtypes of meningiomas, except for hemangiopericytomas which recurred with significantly higher frequency and, together with atypical meningiomas, at much shorter intervals than the others. The prognostic significance of some histological criteria in "non-angiomatous" meningiomas was examined in 211 patients surviving at least 5 years after apparently complete removal of the tumor. Among the recurrences, there was a significantly higher degree of cellularity and increased mitotic rate and, probably, of cortical invasion, while nuclear pleomorphism, increased vascularity, and focal necroses showed no definite differences. The presence of mitotic figures alone appeared to be of no prognostic value. While most recurrent meningiomas did not change their basic morphological type significantly, about 12.5% of the recurrences appeared to have a different rate of growth as suggested by increased cellularity and mitotic rates. In 2 cases an isomorphic (benign) meningioma became a true spindle cell sarcoma.