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defined by evaluating 6 histological parameters (loss of architecture, increased cellularity,
nuclear pleomorphism, mitotic figures, focal necrosis and brain infiltration). This resulted
in three different grades: grade I (benign), grade II (atypical), and grade III (anaplastic). The
grading o[ the meningiomas was carried out by one of us (SZS).
The anatomic sites of tumor origin were subdivided in convexity (C), base (B), falx
(F), and intraventricular (IV).
Cytogenetic analysis and in sitll hybridization:
Cytogenetic analysis was carried out on cultured samples, from passage a (pO) corresponding
to the first outgrowth of cells to passage 3 (p3). Cytogenetic results were only taken into
account when the cells were cultured for less than 50 days. Cells were harvested and fixed
according to standard methods. Chromosomes were identified using RFA, QFQ and GTG
banding techniques and described according to ISCN (1991).
Fluorescent in situ hybridization (FISH) was performed on interphase nuclei directly
obtained from the fresh tumor sample or after short term culture. Competitive in situ
hybridization was applied using at least two chromosome 22 specific cos mid or centromere
probes following the technique as reported by Arnoldus et al. (1991). For all probes used,
the number of signals per nucleus after hybridization was counted in at least 100 nuclei. As
a control, 34 lymphocyte cultures of the patients (when available) and 23 lymphocyte cultures
of normal donors were used. In both control groups we observed similar hybridization
results: one spot (apparent monosomy) in about 5 % of nuclei and two spots (disomy) in more
than 90% of the nuclei. This allowed us to conclude the absence of constitutional loss of
chromosome 22 in patients lymphocytes. Control data were lIsed to determine the sensitivity
of the technique used and to define the cut off rate (mean % of nuclei with one spot + two
times the standard deviation) of 13.5% and 12%, respectively above which a cell popUlation
with (partial) monosomy could be safely identified.
The following probes cited from centromere to telomere of chromosome 22 were
used: p22!l:2.1 (centromere, McDermid et al. 1986); 2 cosmids in the lambda
immunoglobulin light chain gene region: lambda 2.2, lambda 3.1 (Goyns et al., 1984); 4
cos mid probes 40D2, 58B12, 50BII, 76A4 ordered from centromere to telomere within 100
kb from D22S193 (Chapter VI); 29B5 (D22S72); 103DI2 (D22S56); 4 cosmid probes in the
NF2 region: 115D7 (NEFH), 121G 10, 96CIO, 74BI. The cosmid probes in the vicinity of
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