View PDF Version - RePub - Erasmus Universiteit Rotterdam

grades can be distinguished using these criteria: grade I: benign; grade II: atypical and grade
III: anaplastic. It remains to be established whether this grading system is of clinical
relevance.
4.5 Etiology
From the literature different studies suggest that the following factors may be involved in the
etiology of meningioma. These include: I) genetic predisposition (section 4.2) 2) steroid
hormones and their receptors 3) radiation 4) head injury 5) SV-40-related papova viruses.
The postulated role of the steroid hormones and their receptors came from differenl
lines of evidence. First, a higher incidence of these tumors is observed in women and an
accelerated growth has been observed during pregnancy (Zang, 1982; Roelvink et aI., 1987).
In other studies this association was not found (Schlehofer et aI., 1992; and cited references),
Second, the majority of meningiomas and normal leptomeningeal tissue contain progesterone
receptors. The presence of oestrogen receptors is still a matter of discussion. The significance
of the progesterone receptors in these tumors was further investigated with in vitro
experiments using progesterone and progesterone inhibitors. The results of these experiments
are not very conclusive, although they might point to a slight growth promoting role for
progesterone (Koper et aI., 1990).
Radiation is nowadays a well established causative factor in meningioma development.
Meningiomas have occlirred with increased frequency and at an earlier age in people
receiving high-dose irradiation for the treatment of an intracranial growth or after low-dosage
scalp irradiation for fungal infections (Russell and Rubinstein, 1989).
A large number of reports going back as far as 1813 suggest the involvement of
previous head injury and the development of meningioma years later (AI-RodIJan and Laws,
1990), Some investigators found a statistically significant association between meningioma
occurrence and a history of head trauma, others observed site-specific head injuries with
subsequent tumor development at the same site years later (Russell and Rubinstein, 1989).
Different reports reviewed by Zang (1982) might support the role of SV40-related
papova viruses and the formation of meningiomas. In about 35 % of histological sections or
34