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Statistical analyses concerning age and sex were performed only on the sporadic
meningioma cases, omitting the multiple meningioma and NF2 patients, to avoid any kind
of bias. All the other analyses were carried out on the complete group minus the tumors
described above in the case of loss of chromosome 22 or number of chromosomal
abnormalities. When we looked at the age distribution, after correcting for population
distribution (Damhuis et a!., 1993), we observed a biphasic curve in both male and female
patients with a decline in incidence between the age of 50 to 54 years. Two other studies
revealed a similar decline in number of female patients (Dumanski et a!., 1990; Vagner­
Capodano et a!., 1993), but one other study by Casalone et a!. (1990) did not. A subdivision
of our patients in two groups J over and under 50 years of age at surgery I did not result in
any significant association with one of the in the methods section mentioned variables.
Therefore, Jarger studies are necessary to further investigate the significance of this incidence
profile, if any. Other patient and tumor characteristics however revealed some interesting
associations (table 4). Three of them were marginally significant: 1) We found that only
18.5% of the male meningiomas were located at the base, whereas 43.8% of the female
tumors were observed at that site (P=0.058). 2) Female patients predominated in the group
of meningiomas with :5 2 chromosomal abnormalities (74.3% versus 33.3%, P=0.06). 3)
Loss of (parts of) chromosome 22 was found in 88.5 % of the grade WIll tumors but in only
64.2% of the grade I tumors (P=0.079). Statistically significant associations were observed
in all the following instances: I) Grades WIll meningiomas were more often found in male
than in female patients (46.4% versus 22%). 2) Base meningiomas were mostly grade I
(88.9%) and grade WIll meningiomas were more frequently derived from the convexity
(70.6%). 3) In 87.8% of the convexity meningiomas partial or complete loss of chromosome
22 was found, but in only 40.6% of the base tumors this was the case. All intraventricular
and falx meningiomas showed (partial) loss of chromosome 22. 4) Almost all (92 %) base
meningiomas had::; 2 chromosomal abnormalities, whereas 52.4% of the convexity tumors
and only 14.3% of the intraventricular and falx meningiomas had $ 2 chromosomal
abnormalities. 5) All fibroblastic meningiomas were grade I, while 60% of the meningothelial
meningiomas were graded IIIIII and grade IIIIlI comprised only 27.4 % of all tumors
analyzed. 6) Most (94.7%) of the fibroblastic meningiomas showed (partial) loss of
chromosome 22. Tumors without loss of chromosome 22 were predominantly of the
transitional type (74.1 %).7) In 78.6% of the grade II/III meningiomas> 2 chromosomal
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