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fossa and foramen magnum), convexity (parasagittaJ region and free convexity), falx cerebri,
intraventricular and spinal cord meningiomas (Casalone et al., 1990). Total surgical resection
is dependent on the anatomic localization of the tumor and influences the recurrence rate
(Black, 1991).
4.4 Histopathology
Microscopic examination of meningiomas by many neuropathologists resulted in 1979 in the
following WHO classification scheme (Ziilch, 1979):
1. meningotheliomatous (endotheliomatous, syncytial, arachnotheliomatous)
2. fibrous (fibroblastic)
3. transitional (mixture of type 1 and 2)
4. psammomatous
5. angiomatous
6. haemangioblastic
7. haemangiopericytic
8. papillary
9. anaplastic (malignant)
Other subtypes are also known but less common such as Iipoblastic and xanthomatous
meningiomas (Kepes, 1982). Most tumors show features corresponding with a mixture of
different histological subtypes, from which the first four occur most predominantly (de la
Monte et aI., 1986). From a histopathological point of view, most of these tumors are
considered to be benign and only very rarely truly malignant invasive meningiomas occur.
However, different degrees of anaplasia, which may to some extent influence biological
behaviour, can be identilied in all classes of benign tumors (Jiiiiskeliiinen et aI., 1985; de la
Monte et aI., 1986; Vagner-Capodano et aI., 1993). A significant association was observed
in this respect between the in vivo growth rate of meningiomas and the histopathological
grade of the tumors (JiiiiskeHiinen et aI., 1985). The grading system according to increasing
anaplasia used in this thesis involves the following six histological parameters: loss of
architecture, increased cellularity, nuclear pleomorphism, mitotic figures, focal necrosis and
brain infiltration (Hiaskeliiinen et aI., 1985; Vagner-Capodano et .1., 1993). Three different
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