Cytogenetical findings of recurrent meningiomas. A study of 10 tumors

Deletions in the 17q chromosomal region and their influence on the clonal cytogenetic evolution of recurrent meningiomas

Objective

Meningiomas are among the most frequent intracranial tumors. Although the majority of meningiomas can be cured by surgical resection, up to 20% of the patients develop an aggressive clinical course with tumor recurrence or progressive disease.

Cytogenetically, meningiomas frequently harbour a normal karyotype or monosomy of chromosome 22 as the sole anomaly. However, progression of meningiomas is associated with a non-random pattern of secondary losses of the chromosomes and chromosomal regions 1p, 6, 10, 14, 18, and 19. There is evidence, that loss of chromosome 17 might be involved in the clonal cytogenetic evolution of recurrent meningiomas. The aim of this study was to determine the role of deletions in the 17q chromosomal region in patients with recurrent meningiomas.

Results

The authors retrospectively reviewed all patients that underwent repeated surgery for recurrent meningiomas between 1999 and 2015 at the Department of Neurosurgery of the Saarland University Hospital. Patients were included in this study if tumor samples from two or more different meningiomas were available.

A total of 7 patients underwent repeated surgery for recurrent meningiomas (4 males, 3 females, mean age: 45.4 years at the date of surgery) between 1999 and 2015. Collectively, 22 biopsies were analyzed with FISH (fluorescence-in-situ-hybridization) for the chromosomal region 17q23.3. In 20/22 (90.1%) specimens, the tumor samples harboured a significant deletion in the chromosomal region 17q (range: 10 to 63% of the cells). In 3/3 (100%) cases, deletion in the 17q chromosomal region was detectable in the primary tumor. In the tumor evolution, there was no steady in- or decrease in the percentage of this deletion.

Conclusion

Deletion in the 17q chromosomal region was present in the patients’ primary tumors as well as in late recurrences. Overall, a significant deletion in the 17q chromosomal region was detected in 90.1% of the tumors. Thus, the authors assume that deletion in the 17q chromosomal region displays rather an early event in meningioma progression. Accordingly, deletion in the 17q chromosomal region might clinically serve as a potential early marker for malignancy and a higher risk for recurrence in meningiomas.

De novo versus transformed atypical and anaplastic meningiomas: comparisons of clinical course, cytogenetics, cytokinetics, and outcome

OBJECTIVE

The clinical course of atypical and anaplastic meningiomas is heterogeneous. As malignant gliomas, aggressive meningiomas may arise de novo or transform from a benign tumor. This study aims to compare differences in clinical behavior, cytogenetics, cytokinetics, receptor status, and outcome between de novo malignant meningiomas and meningiomas that progressed to malignancy.

METHODS

Data from 36 patients with atypical or anaplastic meningiomas were selected for retrospective analysis and divided into two subgroups: 1) de novo atypical or anaplastic tumors and 2) tumors that progressed from a lower grade. We analyzed data concerning patients' sex, age, tumor location, number of operations, status of hormone receptors, proliferative indices, cytogenetic findings, additional therapy, and survival. For meningiomas with progression, we calculated the interval between initial diagnosis and tumor progression.

RESULTS

For atypical meningiomas, the subgroups had significant differences in status of progesterone receptors, proliferative indices, cytogenetics, and patients' outcome. The anaplastic group had similar differences, but they did not reach statistical significance because of the small numbers. There was a loss of part or monosomy of chromosome 10 and an increased monosomy or derivative chromosome 1 combined with monosomy of chromosome 14. These phenomena occurred mainly in patients with malignant transformation who had a worse outcome.

CONCLUSION

De novo malignant meningiomas and meningiomas with malignant transformation may represent distinct subgroups of atypical and anaplastic meningiomas.

The cytogenetic relationship between primary and recurrent meningiomas points to the need for new treatment strategies in cases at high risk of relapse

PURPOSE

Recurrence is the major factor influencing the clinical outcome of meningioma patients although the exact relationship between primary and recurrent tumors still needs to be clarified. The aim of the present study is to analyze the cytogenetic relationship between primary and subsequent recurrent meningiomas developed within the same individual.

EXPERIMENTAL DESIGN

Multicolor interphase fluorescence in situ hybridization was done for the identification of numerical abnormalities of 12 chromosomes in single-cell suspensions from 59 tumor samples corresponding to 25 recurrent meningioma patients. In 47 of these tumors, the distribution of different tumor cell clones was also analyzed in paraffin-embedded tissue sections. In parallel, 132 nonrecurrent cases were also studied.

RESULTS

Most recurrent meningiomas showed complex cytogenetic aberrations associated with two or more tumor cell clones in the first tumor analyzed. Interestingly, in most individuals (74%), exactly the same tumor cell clones identified in the initial lesion were also detected in the subsequent recurrent tumor samples. In the recurrent tumor samples of the remaining cases (26%), we observed tumor cell clones related to those detected in the initial lesion but which had acquired one or more additional chromosome aberrations associated with either the emergence of new clones with more complex karyotypes or the disappearance of the most representative clones from the primary lesions. Multivariate analysis of prognostic factors showed that the Maillo et al. prognostic score, based on age of patient, tumor grade, and monosomy 14, together with tumor size was the best combination of independent variables for predicting tumor recurrence at diagnosis.

CONCLUSION

Overall, our results indicate that the development of recurrent meningiomas after complete tumor resection is usually due to regrowth of the primary tumor and rarely to the emergence of an unrelated meningioma, underlining the need for alternative treatment strategies in cases at high risk of relapse, particularly those with a high Maillo et al. prognostic score and larger tumors.

Molecular genetics of meningiomas

In this article the authors provide a brief description of the current understanding of meningioma genetics. Chromosome 22 abnormalities, especially in the Neurofibromatosis Type 2 (NF2) gene, have been associated with meningioma development. Loss of heterozygosity of chromosome 22 occurs in approximately 60% of meningiomas; however, loss of NF2 gene function occurs in only one third of these lesions. This discrepancy supports the theory that a second tumor suppressor gene exists on chromosome 22, and the authors introduce several possible gene candidates, including BAM22, LARGE, INI1, and MN1 genes. Deletions of 1p have also been shown to correlate with meningioma progression. The genetic similarities and differences among sporadic, NF2-associated, pediatric, and radiation-induced meningiomas are discussed, with the observation that the nonsporadic meningiomas have a higher incidence of multiple chromosomal abnormalities at presentation. Ultimately, a better understanding of the molecular pathways of meningioma tumorigenesis will lead to new, successful treatments.

Cellular DNA content parameters as prognostic indicators in human astrocytomas

OBJECTIVE

Clinical parameters such as grade, size and/or location of the tumor are good predictors of outcome in patients with astrocytoma. The objective of this study was to determine whether DNA content parameters have a prognostic significance for this group of tumors.

METHODS

Following optimization and validation of methodology for evaluating cellular DNA content parameters (CDCP), tumor DNA ploidy and percent S phase fraction (SPF) were determined from 64 patients using formalin fixed, paraffin embedded specimens (mean coefficient of variation=4.94) obtained over a 10-year period. Median survival times correlated with grade (I/II=1154 vs. III/IV=483days, P=0.0317). Fifty-five percent of the specimens contained DNA aneuploid (DNA-A) components (average SPF=18.3%) and 45% were DNA diploid (DNA-D) (average SPF=9.6%). Survival did not correlate with overall differences in DNA ploidy (DNA-D=181 vs. DNA-A=206days, P=0.6314) when treated and untreated tumors were analyzed. However, a trend for prolonged median survival was observed in patients whose tumors were untreated with respect to cytotoxic therapy based on DNA ploidy status (DNA-D=275 vs. DNA-A=15days, P=0.3408). Survival for all patients did not correlate with median SPF (<13.5% av.=121 vs. >13.5% av.=154days, P=0.6534).

CONCLUSION

DNA content parameters may correlate with the natural history and treatment outcome of newly diagnosed untreated patients with astrocytomas.

Malignant progression in meningioma: documentation of a series and analysis of cytogenetic findings

Object. The malignant progression of benign tumors is well documented in gliomas and other systemic lesions. It is also well known that some meningiomas become progressively aggressive despite their original benign status. The theory of clonal evolution is widely believed to explain malignant progression in meningioma; however, the data used to explain stepwise progression have typically been derived from the cytogenetic analysis of different types of tumors of different grades and in different patients. In this study, the authors examined the data obtained in a group of patients with meningiomas that showed clear histopathological progression toward a higher grade of malignancy and then analyzed the underlying cytogenetic findings.

Methods. Among 175 patients with recurrent meningiomas, 11 tumors showed a histopathological progression toward a higher grade that was associated with an aggressive clinical course. Six tumors progressed to malignancy and five to the atypical category over a period averaging 112 months. Tests for MIB-1 and p53 and cytogenetic studies with the fluorescence in situ hybridization (FISH) method were performed in successive specimens obtained in four patients.

The MIB-1 value increased in subsequent samples of tumors. Cytogenetic analysis with FISH showed deletions of 22, 1p, and 14q. In all but one case, these aberrations were also present in the previous specimen despite its lower hispathological grade.

Conclusions. The authors documented the progression of meningiomas from benign to a higher histological grade. These tumors were associated with a complex karyotype that was present ab initio in a histologically lower-grade tumor, contradicting the stepwise clonal evolution model. Although it was limited to the tested probes, the FISH method appears to be more accurate than the standard cytogenetic one in detecting these alterations. Tumors that present with complex genetic alterations, even those with a benign histological grade, are potentially aggressive and require closer follow up.

Association of loss of 1p and alterations of chromosome 14 in meningioma progression

Meningiomas are usually benign tumors; however, they can recur after surgical resection and occasionally show histologic progression to a higher grade II and III malignancy. The second most frequently reported genetic abnormality after 22q loss is deletion of 1p, although alterations in 9q, 10q, and 14q are also implicated in meningioma progression. Fourteen tumors comprising six benign, four atypical, and four malignant meningiomas were examined by means of cytogenetic and fluorescence in situ hybridization analysis. All tumors showed losses in different regions of 1p, with 1p11, 1p13, 1p21, 1p22, 1p32, and 1q21 breakpoints; eight tumors also presented alterations of chromosome 14. Five of the six cases with deletions on 1p and normal chromosome 14 were grade I, and two were recurrent. All but one of the eight cases with simultaneous 1p deletion and alterations of chromosome 14 were grade II (3 cases) and grade III (4 cases); all the grade III cases were recurrent. These results support the possible association between changes in 1p and chromosome 14 with the evolution of aggressive meningiomas through tumor progression.

New classification scheme for the prognostic stratification of meningioma on the basis of chromosome 14 abnormalities, patient age, and tumor histopathology

PURPOSE

Meningiomas are usually considered benign tumors. However, relapses occur in 10% to 20% of all patients, including both histopathologically aggressive and benign tumors. This study explored the value of numerical abnormalities for 10 different chromosomes in meningiomas for predicting relapse-free survival (RFS).

PATIENTS AND METHODS

This study prospectively analyzed the frequency of numerical abnormalities of chromosomes 1, 9, 10, 11, 14, 15, 17, 22, X, and Y in 70 meningioma patients by fluorescence in situ hybridization and their relationship with disease characteristics at diagnosis and patients' outcome.

RESULTS

Results showed the presence of numerical abnormalities for one or more chromosomes in most patients (77%). Chromosome 22 in the whole series and chromosome Y in males were those more frequently altered, followed by chromosomes 1, 14, and X in females. Patients with abnormalities of chromosomes 1, 9, 10, 11, 14, 15, 17, the sex chromosomes, and gains of chromosome 22 were associated with adverse prognostic features, more frequent relapses, and shorter RFS. Multivariate analysis showed that tumor grade together with chromosome 14 status and age were the best combination of independent variables for predicting RFS. According to these variables, all patients with a score of two or more than two adverse prognostic factors had experienced relapse at 5 years, whereas none of those with a score of zero had experienced relapse 10 years after surgery.

CONCLUSION

In addition to age and histologic grade, abnormalities of chromosome 14 contribute to a better prognostic stratification of meningioma patients at diagnosis. Additional prospective studies in larger series of patients, also including larger numbers of patients who experienced relapse, are necessary to confirm the utility of the proposed predictive model.

Histologically benign metastatic meningioma: morphological and cytogenetic study. Case report

The authors report on a 75-year-old man with histologically benign fibroblastic meningioma metastasizing to the lung, liver, spleen, and kidney. The original tumor exhibited a complex karyotype involving different structural and numerical anomalies associated with monosomy of chromosome 22. The implication of chromosome 1p36 was confirmed by fluorescence in situ hybridization in most interphase nuclei. Metastases occurred 4 months after incomplete resection with prior therapeutic embolization. The recurrent tumor in turn displayed anaplastic features and an increased Ki-67 labeling index. Genetic alterations in such morphologically benign meningiomas have been implicated in the malignant development and progression of these tumors.

Meningioma: Un modelo de evolución citogenética en la iniciación y progresión tumoral

Meningiomas are tumors of the central nervous system with a great morphological heterogeneity. They are generally benign, and have the capacity to progress to a higher histological grade (atypical and anaplastic), which is associated with an increase in biological aggressivity and/or capacity to recur. Citogenetically this evolution is characterized by total or partial monosomy 22 in the early phase, continued by numerical and structural changes during tumor progression. In this study, we present a review of 85 cases of meningiomas: 43 benign, 28 atypical and 14 anaplastic. We study the clinical and histopathological features, and their correlation with cytogenetie abnormalities present in these tumors. Numerical aberrations such as monosomy of chromosome 10, 14 and 18, and structural abnormalities such as deletions on 1p are directly associated with a higher agressivity of tumors. An association of aberatons on 1p and chromosome 14 are more commonly found in atypical and anaplastic meningiomas. These facts imply that the presence of complex karyotypes progressively increases from grade I to grade III meningiomas. Furthermore, these karyotypes are common in recurrent tumors.

Predictive value of progression-associated chromosomal aberrations for the prognosis of meningiomas: a retrospective study of 198 cases

OBJECT

The goal of this study was to determine whether in meningiomas cytogenetic findings are suitable as a predictive parameter relevant to prognosis.

METHODS

Between 1992 and 1998 at the Department of Neurosurgery, Saarland University, 198 patients underwent surgery to resect meningiomas. The meningiomas were investigated cytogenetically and the patients were followed up for a mean period of 33 months. On the basis of the cytogenetic findings, the meningiomas were subdivided into four groups: Group 0 meningiomas displayed a normal diploid chromosome set; Group 1 tumors were found to have monosomy 22 as the sole cytogenetic aberration; Group 2 tumors were markedly hypodiploid meningiomas with loss of additional autosomes in addition to monosomy 22; and Group 3 meningiomas had deletions of the short arm of a chromosome 1, as well as additional chromosomal aberrations including loss of one chromosome 22. One hundred ninety-eight patients in whom tumor resections were determined to be Simpson Grade I or II could be followed up after complete tumor extirpation. In 20 patients, one or several recurrences were documented during the period of observation. The tumors were classified according to their different, but mostly uniform chromosomal aberrations. Recurrences were found in six (4.3%) of 139 tumors in Groups 0 and 1 and in two (10.5%) of 19 tumors in Group 2; the highest rate of recurrence was found in 12 (30%) of 40 tumors in Group 3. This supports the notion that the deletion of the short arm of one chromosome 1 is an important prognostic factor in meningiomas. The results of this study document a significant correlation between histological grade (p < 0.0001), location (p < 0.0001), and recurrences of meningiomas (p < 0.0001) (significance determined using chi-square tests).

CONCLUSIONS

The cytogenetic classification of meningiomas provides a significant contribution to the predictability of tumor recurrence and is, therefore, a valuable criterion for the neurosurgeon's postoperative management protocol.

Analysis of p73 gene in meningiomas with deletion at 1p

The p73 gene has been mapped to 1p36.33, a chromosome region that is frequently deleted in a wide variety of neoplasms including meningiomas. The protein encoded by p73 shows structural and functional similarities to p53 and may thus represent a candidate tumor suppressor gene. To determine whether p73 is involved in the development of meningiomas, we examined 30 meningioma samples with proven 1p deletion for mutations of p73. Sequence analysis of the entire coding region of the p73 gene revealed previously reported polymorphisms in eight cases. A tumor-specific missense mutation as a result of an A-to-G transition with an Asn204Ser change was found in one meningioma that nevertheless retained the normal allele. These results suggest that if p73 plays a role in meningioma carcinogenesis, it must be in a manner different from the Knudson two-hit model.

Cytogenetic analysis and clinical significance in adult T-cell leukemia/lymphoma: a study of 50 cases from the human T-cell leukemia virus type-1 endemic area, Nagasaki

Identification of cytogenetic abnormalities is an important clue for the elucidation of carcinogenesis. However, the cytogenetic and clinical significance of adult T-cell leukemia/lymphoma (ATLL) is still unclear. To address this point, cytogenetic findings in 50 cases of ATLL were correlated with clinical characteristics. Karyotypes showed a high degree of diversity and complexity. Aneuploidy and multiple breaks (at least 6) were observed frequently in acute and lymphoma subtypes of ATLL. Breakpoints tended to cluster at specific chromosomal regions, although characteristic cytogenetic subgroups of abnormalities were not found. Of these, aberrations of chromosomes 1p, 1q, 1q10-21, 10p, 10p13, 12q, 14q, and 14q32 correlated with one or more of the following clinical features: hepatosplenomegaly, elevated lactate dehydrogenase, hypercalcemia, and unusual immunophenotype, all indicators of clinical severity of ATLL. Multiple breaks (at least 6); abnormalities of chromosomes 1p, 1p22, 1q, 1q10-21, 2q, 3q, 3q10-12, 3q21, 14q, 14q32, and 17q; and partial loss of chromosomes 2q, 9p, 14p, 14q, and 17q regions correlated with shorter survival. These cytogenetic findings are relevant in predicting clinical outcome and provide useful information to identify chromosomal regions responsible for leukemogenesis. This study also indicates that one model of an oncogenic mechanism, activation of a proto-oncogene by translocation of a T-cell–receptor gene, may not be applicable to the main pathway of development of ATLL and that a multistep process of leukemogenesis is required for the development of ATLL.

Loss of 1p in recurrent meningiomas

Deletion of 1p is associated with histological progression to meningiomas. Detection of this alteration may be a predicting factor for recurrences in this tumor. We present 8 meningiomas from four patients: the original tumor and the first recurrence in one patient, and the first and second recurrences in the other three were studied. We compared results of monosomy 22 and deletion of chromosome 1p with cytogenetic methods and fluorescence in situ hybridization (FISH) analysis obtained from slides of direct preparations, of cultured cells and slides of touch preparations. The cytogenetic study showed normal chromosome 22 and deletion on 1p32 in both samples of one patient; only monosomy 22 in both recurrences in another patient, and normal karyotypes with different non-clonal anomalies in the other tumors. However, with FISH analysis, monosomy 22 in both recurrences of three patients was demonstrated, as well as the loss of 1p in all tumors. These results were more evident in the analysis of direct and touch preparations than in those of cultured cells.

High-resolution analysis of chromosome arm 1p alterations in meningioma

Loss of heterozygosity (LOH) for loci on chromosome arm 1p is a relatively common event in human meningioma, and this anomaly has been proposed to be associated with the development of grade II or grade III forms (atypical and anaplastic meningiomas). Nevertheless, the limited data available do not allow the establishment of the frequency and the extent of the affected 1p regions. To determine the status of chromosome 1p in meningiomas, we have performed a comprehensive analysis of LOH on 1p in 100 meningiomas using a high density of 1p-marker loci. Allelic loss was found in 35% of tumors, most corresponding to nontypical meningiomas that also displayed losses for loci on chromosome 22. Although some tumors displayed complex rearrangements leading to distinct 1p deletions, the patterns of loss indicated two main target regions: 1p36 and 1p34-p32, which represent the most frequently involved regions, whereas 1p22 and 1p21.1-1p13 regions appeared deleted in some tumors. These results suggest that there may be several putative tumor suppressor genes on 1p, the inactivation of which may be important in the pathogenesis of meningiomas, as well as in other tumor types.

Histopathological and cytogenetic findings in benign, atypical and anaplastic human meningiomas: a study of 60 tumors

Meningiomas may display benign (Grade I), atypical (Grade II) and anaplastic (Grade III) histopathological findings. The cytogenetic studies strongly suggest that secondary changes (moreover loss of chromosome 22) appear to be associated with more atypical features and with greater clinical aggressivity. We studied 60 tumors from 52 patients. Histopathological features such as nuclear pleomorphism, nucleolar prominence, mitosis, necrosis, cellular density, PCNA labeling index, and karyotype have been evaluated. Nuclear pleomorphism and nucleolar prominence showed a progressive increase in Grades I-III. Multifocal micronecrosis was considered a criterion of malignancy. A significant correlation was observed between PCNA-LI, mitotic index and grades. Complex karyotypes increased progressively: benign (34% of cases), atypical (45% of cases) and anaplastic (70% of cases). The most common numerical alterations were losses of chromosomes 10, 14, 18 and 22. The chromosomes most often involved in structural anomalies were: 1, 4, 7, 14 and 22. Telomeric associations was present in four cases and double minutes in two cases. Prognostic criteria for these tumors have been analyzed on the basis of these data.

NF2 gene mutations and allelic status of 1p, 14q and 22q in sporadic meningiomas

Formation of meningiomas and their progression to malignancy may be a multi-step process, implying accumulation of genetic mutations at specific loci. To determine the relationship between early NF2 gene inactivation and the molecular mechanisms that may contribute to meningioma tumor progression, we have performed deletion mapping analysis at chromosomes 1, 14 and 22 in a series of 81 sporadic meningiomas (54 grade I (typical), 25 grade II (atypical) and two grade III (anaplastic)), which were also studied for NF2 gene mutations. Single-strand conformational polymorphism analysis was used to identify 11 mutations in five of the eight exons of the NF2 gene studied. All 11 tumors displayed loss of heterozygosity (LOH) for chromosome 22 markers; this anomaly was also detected in 33 additional tumors. Twenty-nine and 23 cases were characterized by LOH at 1p and 14q, respectively, mostly corresponding to aggressive tumors that also generally displayed LOH 22. All three alterations were detected in association in seven grade II and two grade III meningiomas, corroborating the hypothesis that the formation of aggressive meningiomas follows a multi-step tumor progression model.

Meningioma grading: an analysis of histologic parameters

Histologic grading of meningiomas has prognostic and sometimes therapeutic implications, but diagnostic criteria for atypical meningioma are vague, and the significance of brain invasion in the determination of malignancy remains controversial. We reviewed our experience with 581 patients whose meningiomas were resected at Mayo Clinic during the years 1978 through 1988. All patients were followed until death or a median of 9.0 years. Ten histologic parameters were assessed and compared with recurrence-free survival. On univariate analysis, six variables were associated with recurrence, although most were statistically significant only in the subset of patients having undergone gross total tumor resection. On multivariate analyses, the most significant parameters were histologic brain invasion (when assessable) and maximal mitotic rate of at least four per 10 high-power fields (HPF). Also significant were combinations of at least three of the following four parameters: hypercellularity, architectural sheeting, macronucleoli, and small cell formation. Proposed grading criteria based on these findings yielded 81% classic, 15% atypical, and 4% brain invasive meningiomas with respective 5-year recurrence rates of 12%, 41%, and 56%. There was no association between histologic grade and either extent of surgical resection or patient age. However, male sex was associated with high-grade (atypical/brain invasive) tumors. Too few frankly anaplastic meningiomas were encountered for statistical analysis. Brain invasion and an increased mitotic index (at least four per 10 HPF) are the most powerful histologic factors prognostic for recurrence in meningiomas. We propose an objective definition for atypical meningioma based on our data. Because the difference in recurrence rates for brain invasive and atypical meningiomas was not statistically significant, it could not be determined whether brain invasion alone warrants a designation of malignancy. Likewise, we were unable to determine what constitutes histologic anaplasia due to the rarity of such cases.

Prognostic variables in surgery for skull base meningiomas

The authors have retrospectively analyzed selected surgical and pathological observations made among a group of 20 patients harboring recurrent cranial base meningiomas in an attempt to reveal which factors may be important in predicting tumor recurrence. This cohort was compared with a group of 34 patients with cranial base meningiomas that underwent primary resection and in whom tumor recurrence has not been demonstrated over a median follow-up period of 33 months. Features analyzed included brain, cranial nerve, carotid artery, or muscle invasion as well as tumor cellularity, nucleolar prominence, cellular pleomorphism, and percentage of cells staining positive for the Ki-67 antigen. As expected, increased cellularity and tumor necrosis were relatively more prevalent in recurrent tumors. With regard to tumor type, atypical and anaplastic tumors were more common in the group of patients with recurrent tumor compared with the primary group (p < 0.02). As expected, increased cellularity was relatively more prominent in recurrent tumors. Invasion of muscle and bone (72%) was more frequently associated with recurrent tumors, suggesting that these characteristics may be important features of recurrent skull base meningiomas.