Meningiomas represent between 13 and

RESEARCH EXPERIMENTAL (LABORATORY) Mitotic Count, Brain Invasion, and Location Are Independent Predictors of Recurrence-Free Survival in Primary Atypical and Malignant Meningiomas: A Study of 86 Patients Andrej Vranic, MD Department of Neurosurgery, University Medical Centre, Ljubljana, Slovenia Mara Popovic, MD, PhD Institute of Pathology, Medical Faculty, University of Ljubljana, Ljubljana, Slovenia Andrej Cör, MD, PhD College of Health Care Izola, University of Primorska, Izola, Slovenia Borut Prestor, MD, PhD Department of Neurosurgery, University Medical Centre, Ljubljana, Slovenia Joze Pizem, MD, PhD Institute of Pathology, Medical Faculty, University of Ljubljana, Ljubljana, Slovenia Reprint requests: Joze Pizem, MD, PhD Institute of Pathology, Medical Faculty, Ljubljana, 1000 Ljubljana, Slovenia. E-mail: joze.pizem@mf.uni-lj.si Received, May 26, 2009. Accepted, April 12, 2010. BACKGROUND: Since precise diagnostic criteria for atypical and malignant meningiomas (AMMs) were provided for the first time in the 2000 World Health Organization (WHO) criteria, there is only sparse information about possible prognostic factors in the group of AMMs. OBJECTIVE: To evaluate the prognostic significance of various histological and clinical parameters in AMMs, with an emphasis on location, mitotic count, brain invasion, and Ki67 labeling index. METHODS: We analyzed 86 primary AMMs, 76 of which were atypical and 10 of which were malignant, diagnosed according to the 2000 WHO classification. Multivariate Cox survival analyses were performed. RESULTS: High mitotic count, brain invasion, and the parasagittal-falcine location of the tumor were significantly associated with decreased recurrence-free survival in multivariate analysis. Brain invasion was present in 25 of 37 cases in which brain tissue was identified in the tumor specimens. When brain invasion was not included in the analysis because of the limited number of cases in which it could be assessed, high mitotic count, Ki67 index.4%, the presence of macronucleoli, and parasagittal-falcine location were significant predictors of shorter recurrence-free survival. CONCLUSION: AMMs, as defined by 2000 WHO, are biologically heterogeneous. Recurrence-free survival can be further stratified by location and histological parameters, especially mitotic count, brain invasion, and Ki67 labeling index. Not only brain invasion, but also the presence or absence of brain tissue in surgical specimens should be reported, because the absence of brain invasion, when brain tissue is identified, provides very important positive prognostic information. KEY WORDS: Atypical meningioma, Brain invasion, Cleavability, Malignant meningioma, Mitotic count, Recurrence Neurosurgery 67:1124 1132, 2010 DOI: 10.1227/NEU.0b013e3181eb95b7 www.neurosurgery-online.com Copyright ª 2010 by the Congress of Neurological Surgeons Meningiomas represent between 13 and 26% of all intracranial tumors, with an annual incidence rate of approximately 6/100 000. 1 Although generally considered benign, meningiomas can cause significant morbidity and mortality. 2,3 Much effort has been ABBREVIATIONS: AMM, atypical and malignant meningioma; HPF, high-power field; OS, overall survival; RFS, recurrence-free survival; WHO, World Health Organization invested in identifying those meningiomas that are likely to pursue an aggressive clinical course. The 1993 World Health Organization (WHO) classification introduced meningioma grading into classic (WHO grade I), atypical (WHO grade II), and malignant (WHO grade III). 4 For the first time, histological features important for the diagnosis of atypical meningiomas were listed, but the extent of such features required for the diagnosis was not defined. Similarly, malignant meningiomas were vaguely defined as exhibiting histological features of frank 1124 VOLUME 67 NUMBER 4 OCTOBER 2010 www.neurosurgery-online.com

ATYPICAL AND MALIGNANT MENINGIOMAS malignancy, based on malignant cytology, a high mitotic index, and conspicuous necrosis. More precise criteria for meningioma grading were provided in the 2000 WHO classification. 5 Depending on the diagnostic criteria used in different studies, atypical meningiomas constitute between 5% and 17%, whereas malignant meningiomas constitute between 1% and 3% of all meningiomas. 1,2,6,7 The significance of brain invasion as a criterion of malignancy has been controversial. It has been traditionally considered to be indicative of malignancy, 2,3,8 but it was shown recently that brain-invasive meningiomas without anaplasia (ie, otherwise benign or atypical meningiomas) pursue a less aggressive course than histologically malignant meningiomas. 3 The 2000 WHO classification acknowledges that brain invasion increases the risk of recurrence but does not specifically recommend that otherwise benign meningiomas that invade the brain should be classified as atypical (or malignant). 1,5 According to the latest 2007 WHO classification, otherwise benign meningiomas with brain invasion should be considered WHO grade II. 6 The usefulness of brain invasion as a marker of meningioma aggressiveness is limited by the fact that brain tissue is identified only in a minority of surgical specimens and it is often not reported by pathologists. 2,3,7,9 We identified only 8 studies published since 1990 with a survival analysis that included more than 50 cases of either atypical or malignant meningiomas. 2,3,7,9-13 It is difficult to compare and interpret the results of these studies, because different diagnostic (grading) criteria were applied (2000 WHO, 1993 WHO, or even older criteria), different proportions of atypical and malignant, primary, and recurrent cases were included, and sometimes brain invasion was used as a criterion for malignancy. 2,3,7,9-13 To the best of our knowledge, only 3 studies have included more than 50 cases of either atypical or malignant meningiomas diagnosed according to the 2000 WHO grading criteria. 2,3,12 In only one of them was the prognostic significance of brain invasion and mitotic count in primary meningiomas studied. 2 In the present study, we analyzed 86 consecutive primary atypical (WHO grade II) and malignant (WHO grade III) meningiomas, diagnosed according to 2000 WHO and treated at a single institution. Our aim was to determine prognostic factors in atypical and malignant meningiomas, with an emphasis on location, brain invasion, mitotic count, and Ki67 labeling index. METHODS Patients Eighty-six consecutive patients with WHO grade II (atypical) and WHO grade III (malignant) meningiomas diagnosed between 1990 and 2005 were included in the study. In the same period, 790 primary benign meningiomas were diagnosed. All patients were surgically treated at the Department of Neurosurgery, University Medical Centre, Ljubljana, Slovenia, and histologically diagnosed at the Institute of Pathology, Medical Faculty, Ljubljana, Slovenia. The selection of patients was based on the original pathological reports. All original histological slides were reviewed when the original diagnosis was either atypical or malignant meningioma, or any atypical feature was mentioned in the report in a meningioma considered benign. Because reporting of atypical and malignant meningiomas was inconsistent before 1997, we reevaluated all meningiomas (including benign), diagnosed between 1990 and 1996. Only primary meningiomas that met the 2000 WHO diagnostic criteria 5 for atypical or malignant meningioma at reevaluation (see below) were included in the study. Meningiomas diagnosed as either atypical or malignant at recurrence were excluded. The selection of patients was not based on or influenced by the presence of brain invasion. Clinical data, including location, size, signs, and symptoms and their duration, extent of surgical resection according to the Simpson grade, 14 presence of brain edema, cleavability, and information on radiation therapy after surgical resection of a primary tumor were retrieved from the patients medical records. Brain edema was graded as absent, mild, or severe. Data on cleavability were obtained from original operative reports with special emphasis on the tumor/brain interface. According to Sindou et al, 15 meningiomas were classified as noncleavable when pial invasion was observed by the surgeon and cleavable when dissection in the extrapial plane could be performed. Follow-up data were collected for all patients, including recurrencefree survival (RFS, time from surgical resection to local recurrence) and overall survival (OS, time from surgical resection to death). The dates of patients death were collected from the Cancer Registry of Slovenia. No attempts were made to determine the cause of death. Pathological Review All original histological slides of each case were reviewed without knowledge of clinical outcome and other clinical data. The number of tissue blocks per meningioma included in the study ranged from 2 to 17 (mean, 6). The following histological parameters were assessed: mitotic count, presence of atypical mitoses, necrosis, significant pleomorphism, macronucleoli, sheeting (patternless growth), foci of small cells, hypercellularity, presence of brain tissue, presence of brain invasion, and at least focal, clearly malignant appearance (carcinoma-, sarcoma-, or melanoma-like). 5 The mitotic count was defined as the number of mitoses per 10 high-power fields (HPFs). The mitoses were counted in 10 consecutive HPFs in the area with the most prominent mitotic activity. Necrosis was assessed as present or absent regardless of the extent or type (spontaneous or infarct-like). Brain invasion was defined as irregular projections of tumor into adjacent brain tissue without an intervening layer of leptomeninges. Meningiomas having $4 mitoses per 10 HPFs or displaying at least 3 of 5 features, including sheeting, macronucleoli, small-cell formation, hypercellularity, and necrosis, were classified as atypical. Meningiomas having $20 mitoses per 10 HPFs or displaying at least focal carcinoma-, sarcoma-, or melanoma-like appearance were classified as malignant. In addition, clear cell and chordoid meningiomas were considered WHO grade II (atypical) and rhabdoid meningiomas were considered WHO grade III (malignant), regardless of the criteria listed above. 5 In this study, we used the designations atypical synonymous with WHO grade II and malignant synonymous with WHO grade III. In most cases, Ki67 proliferative indices were determined at the time of original diagnoses. In all other cases, we performed Ki67 immunostaining at the time of slide review. We also performed progesterone receptors immunostaining in all cases. Immunohistochemistry was performed according to the routine protocols used in everyday practice at the Institute of Pathology, Ljubljana. We used monoclonal mouse anti-human Ki67 antibody, clone MIB-1 (DAKO, Glostrup, Denmark), at a dilution of 1:20, and monoclonal mouse anti-human progesterone receptor antibody, NEUROSURGERY VOLUME 67 NUMBER 4 OCTOBER 2010 1125

VRANIC ET AL clone 1A6 (Novocastra, Newcastle upon Tyne, UK), at a dilution of 1:20. The Ki67 labeling index was determined as a percentage of positive tumor cell nuclei in the area of most prominent positivity by systematically counting at least 1000 tumor cell nuclei. Statistical Analysis The statistical analysis was performed with SPSS for Windows (SPSS Inc., Chicago, Illinois). The differences between groups in relation to other clinicopathological parameters were analyzed by Kruskal-Wallis and x 2 tests. Survival analysis was performed by the Cox model and survival curves were estimated using the Kaplan-Meier method. The final multivariate models were achieved using a stepwise backward elimination of non-significant variables. RESULTS We analyzed 86 consecutive primary atypical and malignant (WHO grades II and III) meningiomas (AMMs) diagnosed between 1990 and 2005. Among 86 AMM cases, 76 (88%) were atypical and 10 (12%) were malignant. A diagnosis of WHO grade II meningiomas was made solely on the basis of mitotic count ($4 mitoses/10 HPF) in 13 (17%) cases and solely on the basis of at least 3 criteria, including hypercellularity, sheeting, macronucleoli, necrosis, and small-cell formation in 22 (29%) cases (including 2 clear-cell meningiomas). Both criteria were met in 38 (50%) cases (including one clear-cell meningioma). Three cases (4%) were considered WHO grade II attributed to the histological type (2 clear-cell meningiomas, one chordoid) without other criteria for atypical meningiomas. A diagnosis of WHO grade III meningiomas was based solely on mitotic count in one case ($20 mitoses/10 HPFs), obvious malignant histological features in 7 cases (including one rhabdoid), and on both in two cases. Clinical and pathological characteristics of 86 AMMs are shown in Tables 1 and 2, respectively. There was no difference in the various clinical parameters presented in Table 1, including sex, age, size, location, signs, and symptoms and their duration, cleavability, and the extent of resection between atypical and malignant groups. Brain edema was strongly associated with malignant meningiomas (P =.002); severe edema was present in all 5 malignant meningiomas with available data. There was no correlation between cleavability and brain edema. Male patients were younger (mean, 52.8 years) than female (mean, 57.2 years), but the difference was not statistically significant (P =.189). There were no associations between sex and WHO grade, location, mitotic count, or Ki67 index. Simpson grade I resection was achieved in 6 of 24 (25%) parasagittal-falcine meningiomas and in 30 of 53 (57%) meningiomas of other locations (P =.014). The information on radiation therapy was available for 67 patients with atypical and 9 patients with malignant meningiomas. Only 3 patients with atypical (one with a residual tumor in the bone, one with a residual tumor in the sagittal sinus, and one with an original diagnosis of malignancy) and 3 with malignant meningiomas (3 patients refused radiation therapy; 3 malignant meningiomas were originally diagnosed as atypical) received radiation therapy after surgical resection of the primary tumor. TABLE 1. Clinical Characteristics of 86 Cases of Atypical and Malignant Meningiomas Parameter n (%) a Sex 86 Male 42 (48.8) Female 44 (51.2) Age, y 86 Range, 13.5-85.4 Mean, 55.0 Median, 57.2 Size, cm 78 Range, 2.0-8.5 Mean, 4.9 Median, 5.0 Location 86 Parasagittal-falcine 26 (30.2) Convexity 35 (40.7) Base 24 (27.9) Intraspinal 1 (1.1) Duration of signs/symptoms, mo 80 Range, 0-36 Mean, 7.5 Median, 4.0 Signs/symptoms 81 Paresis 28 (36.6) Headache 21 (25.9) Seizures 20 (24.7) Others 9 (11.1) Simpson grade 77 I 36 (46.8) II 33 (42.9) III 5 (6.5) IV 3 (3.9) Edema 58 Absent 10 (17.2) Mild 31 (53.4) Severe 17 (29.3) Cleavability 42 Cleavable 18 (42.9) Noncleavable 24 (57.1) Radiation therapy 76 Yes 6 (7.9) No 70 (92.1) a The information on size, signs/symptoms, Simpson grade, edema, cleavability, and radiation therapy was not available for all patients. Brain tissue was identified in 37 (43%) tumor specimens. Of these 37 cases, brain invasion was present in 25 (67.6%) cases and absent in 12 (32.4%) cases. Brain tissue in surgical specimens was found more frequently in larger tumors (P =.012) and was strongly associated with the presence of brain edema (P =.003). Brain tissue was not identified in any of 10 cases without brain edema, whereas it was found in 16 of 31 (51.6%) cases with mild brain edema and in 11 of 17 (64.7%) cases with severe brain edema. The finding of brain tissue tended to be related to the higher number of tissue blocks examined (P =.103), tended to be more frequent in malignant meningiomas (P =.092), and was not 1126 VOLUME 67 NUMBER 4 OCTOBER 2010 www.neurosurgery-online.com

ATYPICAL AND MALIGNANT MENINGIOMAS TABLE 2. Pathological Characteristics of 86 Cases of Atypical and Malignant Meningiomas Parameter All (n = 86), n (%) Atypical (n = 76), n (%) Malignant (n = 10) P Value Histological type Meningothelial 52 (60.5) 49 (64.5) 3 Transitional 17 (19.8) 17 (22.4) 0 Fibroblastic 4 (4.6) 4 (5.3) 0 Clear cell 5 (5.8) 5 (6.6) 0 Chordoid 2 (2.3) 1 (1.3) 1 Secretory 1 (1.2) 0 1 Rhabdoid 1 (1.2) 0 1 Not apparent 4 (4.6) 0 4 Brain tissue (present) 37 (43.0) 30 (39.5) 7.092 Brain invasion (present) 25 (67.6) 19 (63.3) 6 (86).389 Mitotic count Range, 0-40 Range, 0-15 Range, 6-40,.001 Mean, 6.3 Mean, 4.9 Mean, 16.6 Median, 5.0 Median, 5.0 Median, 11.5 Atypical mitoses (present) 15 (17.4) 8 (10.5) 7,.001 Necrosis (present) 49 (57.0) 41 (53.9) 8.177 Macronucleoli (present) 57 (66.3) 49 (64.5) 8.484 Sheeting (present) 62 (72.1) 52 (68.4) 10.056 Increased cellularity (present) 69 (80.2) 61 (60.2) 8.984 Small cells (present) 54 (62.8) 52 (68.4) 2.005 Pleomorphism (present) 46 (53.5) 39 (51.3) 7.327 Ki67 (%) Range, 0-39.2 Range, 0-39.2 Range, 4.5-30.8,.001 Mean, 9.4 Mean, 8.1 Mean, 19.5 Median, 6.8 Median, 6.0 Median, 21.3 Ki67 (.4 %) 58 (67.4) 48 (63.2) 10.019 Progesterone receptors (positive) 10 (11.6) 8 (10.5) 2.328 related to the location of the tumor or cleavability. Brain invasion was associated with a higher mitotic count (mean, 9.0 for invasive and mean, 4.8 for noninvasive; P =.019) and tended to be more frequent in males (14 of 17 males and 11 of 20 females, P =.077). It was not associated with age, size of the tumor, location, Simpson grade, brain edema, cleavability, WHO grade, the presence of atypical mitoses, or Ki67 index. Progesterone receptors were positive in 10 cases (11.6%). Of the positive cases, up to 5% of tumor cell nuclei were positive in 3 cases, 6% to 50% of nuclei in 6 cases, and more than 50% in one case. Patients were followed up until death or for a median of 96 months (range, 28-204 mo). At the time of follow-up, the tumor had recurred in 31 patients (36%), from 4 to 76 months (median, 31) after the diagnosis, whereas 37 patients (43%) died, from 0 to 216 months (median, 45) after the diagnosis. The 5- and 10-year RFS for the entire group of 86 AMMs was 60% (95% CI, 48-71) and 55% (95% CI, 43-68), respectively. The 5- and 10-year OS was 76% (95% CI, 67-86) and 56% (95% CI, 44-68), respectively. The univariate Cox analyses of the RFS and OS are shown in Table 3. There were significant differences in RFS among noninvasive, invasive atypical, and invasive malignant meningiomas (Figure 1). None of the 7 cases of atypical meningiomas, including 2 brain-invasive, with a mitotic count of 0, recurred. A Ki67 index.4% was associated with decreased RFS, not only in the entire group of 86 AMMs, but also in the subgroup of 76 atypical meningiomas (HR, 2.7; P =.036). Kaplan-Meier survival curves of RFS according to the Ki67 index and location are shown in Figures 2 and 3, respectively, and of OS for brain-invasive and non brain-invasive meningiomas in Figure 4. Because brain invasion was assessable in only 37 cases, separate multivariate analyses of RFS and OS were performed with and without brain invasion (Table 4). High mitotic count, the presence of macronucleoli, high Ki67 index, and parasagittalfalcine location were independent negative predictors of RFS when brain invasion was not included, whereas high mitotic count, brain invasion, and parasagittal-falcine location were independent negative predictors of RFS when brain invasion was included. Male sex and parasagittal-falcine location were the only parameters associated with decreased OS in both analyses, with and without brain invasion. DISCUSSION In our series of 86 consecutive primary AMMs treated at a single institution and diagnosed according to 2000 WHO criteria, we showed that mitotic count (as a continuous variable), brain invasion (when assessable), and location were the most powerful predictors of RFS. In addition to mitotic count and parasagittal-falcine location, Ki67 index.4% and the presence of macronucleoli were significantly associated with decreased RFS in multivariate analysis, when brain invasion was not included because of the limited number of cases in which it could be assessed. NEUROSURGERY VOLUME 67 NUMBER 4 OCTOBER 2010 1127

VRANIC ET AL TABLE 3. Univairate Cox Survival Analysis a Recurrence-Free Survival Overall Survival Variable n HR 95% CI P Value HR 95% CI P Value Sex (male vs female) 86 1.9 0.9-4.0 0.077 1.9 1.0-3.8.064 Age ($55 vs,55) 86 0.9 0.5-1.8 0.776 3.19 1.5-6.7.002 Size, cm 78 1.2 0.9-1.5 0.225 1.1 0.9-1.3.493 Location (parasagittal-falcine vs others) 86 2.3 1.1-4.7 0.021 1.5 0.8-3.0.238 Simpson grade 77 II vs I 1.8 0.8-4.0 0.149 1.1 0.5-2.3.794 III and IV vs I 1.9 0.5-7.0 0.310 1.9 0.6-5.7.281 Edema 58 Mild vs absent 0.8 0.3-2.7 0.768 2.4 0.7-8.3.169 Severe vs absent 0.8 0.2-3.4 0.810 3.4 0.9-12.5.063 Cleavability (noncleavable vs cleavable) 42 3.0 1.0-9.4 0.056 2.7 1.0-7.5.051 Radiation therapy (yes vs no) 76 1.1 0.2-4.4 0.946 0.9 0.2-3.6.846 WHO grade (III vs II) 86 2.0 0.8-5.3 0.145 1.7 0.6-4.3.293 Necrosis (present vs absent) 86 1.5 0.7-3.2 0.256 0.8 0.4-1.6.595 Pleomorphism (present vs absent) 86 2.4 1.1-5.1 0.024 2.2 1.1-4.7.031 Sheeting (present vs absent) 86 1.1 0.5-2.4 0.793 2.0 0.8-4.8.120 Macronucleoli (present vs absent) 86 2.1 0.9-5.0 0.076 2.6 1.1-6.1.037 Small cells (present vs absent) 86 1.0 0.4-2.0 0.932 1.9 0.8-4.4.133 Hypercellularity (present vs absent) 86 2.2 0.8-6.3 0.114 4.0 1.0-16.7.058 Mitotic count (continuous) 86 1.08 1.03-1.13 0.001 1.03 0.99-1.08.158 Atypical mitoses (present vs absent) 86 2.3 1.0-5.2 0.038 1.18 0.5-2.6.690 Brain tissue (absent vs present) 86 1.2 0.6-2.3 0.571 0.6 0.3-1.2.151 Brain invasion when assessable (present vs absent) 37 7.2 0.9-55.7 0.059 4.4 1.0-19.2.049 Ki67 (%) 86 1.00 0.97-1.05 0.701 1.00 0.95-1.03.606 Ki67 (.4% vs #4%) 86 2.7 1.1-6.7 0.027 1.9 0.9-4.0.104 Progesterone receptors (positive vs negative) 86 1.4 0.5-3.8 0.599 1.2 0.5-3.0.746 a HR, hazard ratio; CI, confidential interval; WHO, World Health Organization. Bold P values are considered statistically significant.. Male sex and parasagittal-falcine location were 2 independent predictors of shorter OS. We consider the results of OS less relevant, because it is difficult to determine disease-related death in meningioma patients. 2,3,6 Our results show that the group of AMMs as defined by 2000 WHO is biologically heterogeneous and RFS can be further stratified by histological parameters, especially mitotic count, brain invasion, and Ki67 labeling index. AMMs as a group represent from 6% to 23% of meningiomas. 2,5,12,16-19 The differences in reported frequencies reflect different grading criteria used, the highest frequencies being reported with more current definitions, 2,6,17 and possibly poor adherence to the WHO criteria in everyday practice, because the grading of meningiomas is relatively tedious work, requiring examination of many slides and consideration of several histological features. 5 It is clear that many cases of AMMs, diagnosed before the 2000 WHO classification, were either underdiagnosed or overdiagnosed compared with 2000 WHO criteria. 12,17 The reported ratio of atypical relative to malignant meningiomas has been from approximately 1.5:1 to 6:1. 7,10-12,18,19 The large proportion of malignant meningiomas in some studies of AMMs may well be attributed to overdiagnosing meningiomas as malignant. 12,20 In our study, AMMs represented approximately 10% of all primary meningiomas; the ratio of atypical vs malignant was 7.6:1. Although benign meningiomas are more common in women (female to male ratio of approximately 2:1), AMMs are relatively more frequent in men (female to male ratio, 0.8-1.4:1). 3,9-12,18,21 In our series, the female to male ratio was 1.1:1. Male sex tended to be associated with decreased RFS and OS in univariate analysis and was an independent predictor of OS in multivariate analysis, together with location of the tumor. A similar trend of a worse prognosis of AMMs in male patients has been reported in other studies, 9,21 but no association between sex and prognosis was found in most studies. 3,10-12 In our series, the RFS of malignant cases was shorter than that of atypical, but the difference was only of marginal significance. In multivariate analysis, WHO grade had no prognostic significance, which is probably attributable to a strong correlation between the WHO grade and both mitotic count and Ki67 index. Although limited by the small number of malignant cases, our results suggest that malignant cases represent only the end of a continuous atypical spectrum in terms of mitotic activity and the extent of other histological parameters. Whereas most studies showed 1128 VOLUME 67 NUMBER 4 OCTOBER 2010 www.neurosurgery-online.com

ATYPICAL AND MALIGNANT MENINGIOMAS FIGURE 1. Kaplan-Meier curves of recurrence-free survival for noninvasive, brain-invasive atypical, brain-invasive malignant meningiomas, and meningiomas in which brain invasion could not be assessed (HR = 4.4, P =.019, for invasive malignant vs invasive atypical; HR = 23.1, P =.005, for invasive malignant vs noninvasive; HR = 5.2, P =.123, for invasive atypical vs noninvasive). The survival curve for meningiomas in which brain invasion could not be assessed is similar to that of invasive atypical meningiomas and is only slightly above the combined curve (not shown) for all invasive meningiomas (atypical and malignant). significantly shorter survival of malignant meningiomas, 3,11-13 this finding could be attributed, to some extent, to a selection bias and grading criteria. 3,11,12 Nevertheless, we believe that malignant meningiomas, although rare, can be reproducibly diagnosed and their recognition is clinically relevant. 1 FIGURE 3. Kaplan-Meier curves of recurrence-free survival according to location (HR = 2.7, P =.023, for parasagittal-falcine vs convexity location, the differences between base meningiomas and the other 2 groups were not statistically significant). The prognostic significance of mitotic count as a continuous variable in AMMs has not been analyzed in previous studies. 3,7,9-13 Perry et al 3 reported mitotic counts of either $4 or$20 (the cutoffs for atypical and malignant) to be associated with decreased OS, but in a heterogeneous group of meningiomas, which consisted of malignant and otherwise atypical or benign meningiomas with brain invasion. Pasquier et al 10 reported high mitotic count to be a negative prognostic marker in multivariate analyses of RFS and OS in a series of 119 AMMs, but the cutoff value was not stated. On the other hand, in a recent study of AMMs by Aghi FIGURE 2. Kaplan-Meier curves of recurrence-free survival according to the Ki67 labeling index (HR = 2.7, P =.027, for.4% vs 0%-4%). FIGURE 4. Kaplan-Meier curves of overall survival for brain invasive and nonbrain invasive meningiomas (HR = 4.4, P =.049). NEUROSURGERY VOLUME 67 NUMBER 4 OCTOBER 2010 1129

VRANIC ET AL TABLE 4. Multivariate Cox Survival Analyses a Variables HR 95% CI P Value Recurrence free survival, without brain invasion (n = 86) Mitotic count (continuous) 1.07 1.01 1.12.013 Ki67 (.4% vs #4%) 3.2 1.2 8.5.021 Macronucleoli (present vs absent) 3.5 1.4 8.5.006 Location (parasagittal-falcine vs others) 3.4 1.6 7.3.001 Recurrence-free survival, with brain invasion (n = 37) Mitotic count (continuous) 1.12 1.04 1.21.003 Brain invasion 8.4 1.0 69.0.046 (present vs absent) Location (parasagittal-falcine vs others) 3.8 1.1 13.4.038 Overall survival (n = 86) Sex (male vs female) 2.1 1.1 4.3.029 Location (parasagittal-falcine vs others) 3.5 1.7 7.3.001 a HR, hazard ratio; CI, confidential interval. et al, 9 mitotic count was not a statistically significant predictor of RFS (although there was a trend toward worse survival) but, again, the cutoff value was not stated. Nevertheless, these studies and the cornerstone study of meningioma grading by Perry et al 2 indicate the importance of mitotic count for risk stratification of AMMs. Perry et al 2 showed that AMMs are not a homogeneous group and the RFS of those AMMs diagnosed solely on the basis of 3 of 5 criteria, with mitotic count,4, was better compared with AMMs with a mitotic count $4. As can be anticipated from the diagnostic criteria, there was a very wide distribution of mitotic count in our series of AMMs and there was a considerable overlap between atypical and malignant cases. We showed that mitotic count as a continuous variable can be a valuable tool to further stratify the risk of recurrence of AMMs. Indeed, the mitotic count has been incorporated in treatment algorithms of AMM. 1 The importance of brain invasion as a determinant of poor survival and for meningioma grading has been controversial. 1,3,5,6 The most important shortcoming is the fact that brain invasion is assessable only in a proportion of cases, when brain tissue is present in the surgical tumor specimen. 3 We identified brain tissue in 37 of 86 (43%) AMMs. Perry et al 2 identified brain tissue in 89 of 581 (15%) consecutive primary meningiomas (benign, atypical, and malignant). On the other hand, Yang et al reported brain tissue in 56 of 64 (88%) AMM tumor specimens, but they stated that adjacent brain parenchyma was intentionally removed to assess the brain invasion, when a clear arachnoid plain disappeared. 12 The presence of brain tissue seems therefore to be highly related to a surgeon s approach. Other factors potentially associated with the likelihood of brain tissue being identified could be: the size and location of the tumor, grade of the tumor, invasive growth, cleavability, and the number of tissue blocks examined from a given tumor. In our series, brain tissue was more often present in larger tumors and in cases with brain edema. It was not related to the location or cleavability 15 but tended to be more often present in malignant meningiomas and in cases with a higher number of tissue blocks examined. Since there was no difference in the RFS in relation to the presence of brain tissue in surgical specimens, it seems that the removal of brain tissue during surgery is not directly related to invasion itself (ie, the likelihood of a meningioma being invasive when no brain tissue is identified seems not to be different than for a meningioma with brain tissue identified). In the literature, little attention has been paid to the assessability of brain invasion and its relation to factors associated with it. 7,9-11 Since the importance of brain invasion in predicting meningioma aggressiveness has been emphasized only recently, 2,3,5,6 it is very likely that brain invasion and brain invasion assessability have been underreported. To increase the assessability of brain invasion, an important prognostic determinant, we recommend thorough sampling and examination of the surgical meningioma specimens, especially the surface of the tumor. 2 In our series, 25 AMMs were brain invasive of 37 (68%) AMMs in which brain invasion could be assessed. Similarly to our results, Yang et al 12 reported brain invasion in 41 of 56 (73%) AMM cases in which brain invasion could be assessed. The frequencies of brain invasion in different meningioma grades are difficult to estimate because the assessability of brain invasion among grades is usually not specified, but it is probably approximately 10% in otherwise benign, 50% to 70% in otherwise atypical, and 80% to 90% in malignant meningiomas. 2,12 Because brain invasion can usually be assessed in a minority of meningiomas, most brain-invasive meningiomas remain unrecognized. According to our results, brain invasion in AMM cannot be predicted by brain edema or cleavability. 15,22,23 In accordance with the study by Perry et al, 3 the RFS of brain-invasive atypical meningiomas was significantly better than for invasive malignant meningiomas. On the other hand, the RFS of atypical meningiomas without brain invasion (but brain tissue identified in surgical specimens) tended to be better than that of brain-invasive atypical meningiomas. Similar results were reported by Perry et al 2 in a subset of 76 meningiomas of all grades in which brain invasion could be assessed. Although often studied and even used in everyday diagnostics of meningiomas, the prognostic significance of the Ki67 index still remains poorly defined. 1,6,19 Ki67 indices significantly increase from benign through atypical and malignant meningiomas, but there is a considerable overlap between different grades. 6,12,19,24 The principal limitation of the Ki67 index seems to be the lack of standardization of the technique and difficulties in defining cutoff values. 1,6,12,24 In most larger series of AMMs, the Ki67 index has not been reported. 2,7,10,11 In line with our results, Aghi et al 9 failed to show any prognostic significance of the Ki67 index as a continuous variable in a series of atypical meningiomas but, in their study, no attempt was made to categorize Ki67 indices. Yang et al 12 showed a Ki67 index of.5% to be of borderline significance for RFS in malignant but not atypical meningiomas. In a series of primary meningiomas (benign, atypical, and 1130 VOLUME 67 NUMBER 4 OCTOBER 2010 www.neurosurgery-online.com

ATYPICAL AND MALIGNANT MENINGIOMAS malignant), Perry et al 25 reported a Ki67 index $4.2% associated with decreased RFS in univariate but not in multivariate analysis with mitotic count, in which the latter was the only prognostic factor. The authors concluded that the Ki67 index appears to be of greatest value in evaluating meningiomas with borderline atypia. Because there is only limited information on the prognostic significance of the Ki67 index in AMM and possible cutoff values, we decided on a cutoff value of.4%, similar to that used by Perry et al. 1,3,25 All malignant and 63% atypical meningiomas had a Ki67 index.4%. In the entire group of AMMs, a Ki67 index.4% was an independent predictor of poor RFS in multivariate analysis, but lost its prognostic significance when brain invasion was included in the analysis. Our study indicates an important role of the Ki67 labeling index in risk stratification of AMM. 1 The prognostic significance of other histological parameters, such as necrosis, pleomorphism, macronucleoli, sheeting, increased cellularity, and small cells, is difficult to interpret because most of them are also among inclusion criteria for AMM. Nevertheless, our results show that some of them (macronucleoli, pleomorphism) could be prognostically more important than others. In accordance with a recent study, 9 the presence of macronucleoli was associated with decreased RFS in multivariate analysis. Similarly to benign meningiomas, the extent of surgical resection of AMM is prognostically important. 2,3,11,12,26 It is difficult to compare the results of different studies because the extent of resection is reported according to Simpson grade in some 11,12 and as gross total vs subtotal in others. 2,3,10 Moreover, the extent of resection considerably varies among studies. 2,3,10-12 In our series, Simpson grade I resection was achieved in 47% of patients and gross total resection (Simpson grades I and II) in 90% of patients, being more radical compared with other studies. 3,10-12 The RFS of patients with Simpson grade I resection tended to be better compared with Simpson grades II to IV, but it was not statistically significant. The survival of patients with convexity meningiomas, including AMMs, seems to be better compared with meningiomas of other locations, partially but not entirely attributed to the resectability of the tumor. 1,11,12 As noted in previous reports, 26 we found that parasagittal-falcine AMMs present with the highest recurrence rates, probably because residual tumor remains along the superior sagittal sinus. 1 Prognostic significance of cleavability has not been studied in AMMs. 15,23 In the univariate analyses, the RFS and OS of patients with cleavable meningiomas tended to be better compared with noncleavable meningiomas. Although cleavability is not correlated with brain invasion, it may have some prognostic value. AMMs, as defined by the 2000 WHO, are biologically heterogeneous and recurrence-free survival can be further stratified by histological parameters, especially mitotic count, brain invasion, and Ki67 labeling index. Brain invasion and mitotic count as a continuous variable are the two 2 most important parameters associated with the recurrence-free survival of AMM. The Ki67 labeling index may provide useful prognostic information, especially when brain tissue is not identified in the surgical specimen and brain invasion cannot be assessed. The mitotic count and brain invasion should be included in pathological reports of all meningiomas. Not only brain invasion, but also the presence or absence of brain tissue in surgical specimens should be reported, because the absence of brain invasion when brain tissue is identified provides very important positive prognostic information. Because of the importance of brain invasion, the surgical specimens of meningiomas should be thoroughly sampled and histologically examined. Disclosure The authors have no personal financial or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Modha A, Gutin PH. 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