Molecular neuropathology of brain‐invasive meningiomas

Invasion of brain tissue by meningiomas has been identified as one key factor for meningioma recurrence. The identification of meningioma tumor tissue surrounded by brain tissue in neurosurgical samples has been touted as a criterion for atypical meningioma (CNS WHO grade 2), but is only rarely seen in the absence of other high‐grade features, with brain‐invasive otherwise benign (BIOB) meningiomas remaining controversial. While post‐surgery irradiation therapy might be initiated in brain‐invasive meningiomas to prevent recurrences, specific treatment approaches targeting key molecules involved in the invasive process are not established. Here we have compiled the current knowledge about mechanisms supporting brain tissue invasion by meningiomas and summarize preclinical models studying targeted therapies with potential inhibitory effects.     

A conceptual shift in the grading of meningiomas

Grading schemes for meningiomas have traditionally designated tumors as "meningioma," "atypical meningioma," or "anaplastic (malignant) meningioma," depending upon the presence of histopathologic features thought to indicate aggressive behavior. In the past, most systems have considered brain invasion by tumor as the best evidence of malignancy. Perry et al. have recently investigated the significance brain invasion as a prognostic feature in meningiomas. The authors studied a series of 116 patients who had been diagnosed previously with "malignant meningioma" due to the presence of brain invasion, histologic anaplasia, or metastasis. On the basis of a multivariate analysis of histopathologic features and their relationship to tumor recurrence and patient survival, the authors concluded that brain invasion should be considered one of the diagnostic features of atypical meningioma. Accordingly, the diagnosis of malignant meningioma should be reserved for those tumors that are frankly anaplastic and/or contain (> = 20 mitoses per 10 high-power fields (HPF). Due in large part to the strength of evidence in this study, the World Health Organization (WHO) has adopted a grading scheme for meningiomas that incorporates many of the authors' proposals. New diagnostic criteria will result in improved reproducibility with fewer diagnoses of malignant meningioma (WHO grade III).     

Osteopontin predicts the behaviour of atypical meningioma

Lin C‐K, Tsai W‐C, Lin Y‐C & Hueng D‐Y
(2012) Histopathology  60, 320–325
Osteopontin predicts the behaviour of atypical meningioma Aim: Although the World Health Organization (WHO) histological criteria distinguishing benign from atypical and malignant meningioma are clear, discerning benign from atypical meningioma is still somewhat difficult, leading to interobserver diagnostic variability. Osteopontin (OPN) and cortactin play important roles in tumorigenesis, invasion and metastasis of several human cancers. The aim of this study was to evaluate the usefulness of OPN and cortactin immunohistochemistry for distinguishing between benign, atypical and malignant meningioma and predicting their recurrence. Methods and results: Seventy‐five specimens (48 benign, 17 atypical and 10 malignant meningiomas) were investigated immunohistochemically. The mean immunohistochemical scoreimmunohistochemical score ± SE of the mean of both OPN and cortactin were significantly higher in grade II or grade III meningiomas than in grade I meningioma. Discriminant analysis of immunohistochemical OPN expression showed correct classification of 97.7% of WHO grade I meningiomas and 88.2% of WHO grade II meningiomas (95.4% accuracy). However, the same analysis of cortactin expression showed correct classification of 95.8% of WHO grade I meningiomas and only 23.5% of WHO grade II meningiomas (76.9% accuracy). A cut‐off for predicting grades I and II meningioma recurrence was determined for OPN (3.0) but not for cortactin. Finally, logistic regression identified both this cut‐off (P < 0.05) and WHO grade (P < 0.05) as independent risk factors for recurrence. Conclusions: OPN expression is a valuable marker for diagnosis of atypical meningioma and prediction of grades I and II meningioma recurrence.     

Cystic papillary meningioma with subarachnoid dissemination: A case report and review of the literature

Meningiomas usually present as benign tumors corresponding to WHO grade I. The development of the papillary variant of meningiomas with cyst formation in the central nervous system is extremely rare. We report a case of cystic papillary meningioma in a young female occurring in the lateral ventricle with invasion of brain parenchyma and dissemination of subarachnoid space. The tumor exhibits a marked peritumoral cyst, with contrast enhancement on magnetic resonance imaging (MRI) in accordance with type 2 of Zee's classification of cystic meningioma. Histologically, the tumor displays a classical perivascular pseudopapillary pattern with focal necrosis and subarachnoid space dissemination. Tumor cells are diffusely positive for epithelial membrane antigen (EMA) and vimentin, but lack immunoreactivity for cytokeratin (CK) and glial fibrillary acidic protein (GFAP). MIB-1 labeling is high, accounting for 5% of tumor focally. A diagnosis of primary intraventricular cystic papillary meningioma with subarachnoid space dissemination (WHO grade III) was made. To our knowledge, there is no report describing the radiological and histological characteristics of cystic papillary meningioma presenting in the lateral ventricle. In addition, the biological behavior and the clinical outcome of this tumor are also discussed.     

Mitotic Index is an Independent Predictor of Recurrence‐Free Survival in Meningioma

While World Health Organization (WHO) grading of meningioma stratifies patients according to recurrence risk overall, there is substantial within‐grade heterogeneity with respect to recurrence‐free survival (RFS). Most meningiomas are graded according to mitotic counts per unit area on hematoxylin and eosin sections, a method potentially confounded by tumor cellularity, as well as potential limitations of accurate mitotic figure detection on routine histology. To refine mitotic figure assessment, we evaluated 363 meningiomas with phospho‐histone H3 (Ser10) and determined the mitotic index (number of mitoses per 1000 tumor cells). The median mitotic indices among WHO grade I (n = 268), grade II (n = 84) and grade III (n = 11) tumors were 1, 4 and 12. Classification and regression tree analysis to categorize cut‐offs identified three subgroups defined by mitotic indices of 0–2, 3–4 and ≥5, which on univariate analysis were associated with RFS (P < 0.01). In multivariate analysis, mitotic index subgrouped in this manner was significantly associated with RFS (P < 0.01) after adjustment for Simpson grade, WHO grade and MIB‐1 index. Mitotic index was then examined within individual WHO grade, showing that for grade I and grade II meningiomas, mitotic index can add additional information to RFS risk. The results suggest that the use of a robust mitotic marker in meningioma could refine risk stratification.     

Multiple meningioma with different grades of malignancy: case report with genetic analysis applying single-nucleotide polymorphism array and classical cytogenetics

Multiple meningiomas with synchronous tumor lesions represent only 1-9% of all meningiomas and usually show a uniform histology. The simultaneous occurrence of different grades of malignancy in these nodules is observed in only one third of multiple meningiomas. We report a case of a sporadic multiple meningioma presenting with different histopathological grades (WHO I and II). The tumor genome of both nodules was analyzed by GTG-banding, spectral karyotyping (SKY), locus-specific FISH, and single nucleotide polymorphism array (SNP-A) karyotyping. GTG-banding and SKY revealed 25 structural and 33 numerical aberrations with a slightly increased aberration frequency in the WHO grade II nodule. We could confirm terminal deletions on chromosomes 1p [ish del(1)(p36)(p58-,pter-) 16.5% WHO grade I and 20.9% WHO grade II], partial deletions on 22q, and/or monosomy 22 (monosomy 22 14% WHO grade I and 34% WHO grade II) as the most frequent aberrations in both meningioma nodules. In the meningioma WHO grade II, in addition, a de novo paracentric inversion within chromosomal band 1p36 was detectable. Furthermore, for meningiomas de novo, dicentric chromosomes 4 could be identified in both tumor nodules. We also detected previously published segmental uniparental disomy regions 1p31.1, 6q14.1, 10q21.1, and 14q23.3 in normal control DNA of the patient and in both tumor nodules. Taken together, we describe a very rare case of multiple meningioma with overlapping but also distinct genetic aberration patterns in two nodules of different WHO grades of malignancy.     

Atypical meningioma: morphometric analysis of nuclear pleomorphism

The revised edition of the WHO classification of brain tumours now includes the "atypical" meningioma (grade II) which should be placed between the common type (grade I) and anaplastic type (grade III) according to histomorphological features and prognosis. However, diagnostic criteria for atypical meningioma are vague and the significance of brain invasion in the determination of malignancy is controversial. Nuclear pleomorphism and mitoses are usually considered the most important parameters to distinguish atypical and malignant meningiomas. According to WHO classification we selected eight cases of meningioma diagnosed as atypical (3 cases) and malignant (5 cases). All the tumours were supratentorially located. Nine cases of benign meningiomas were also studied as a control group. Morphometrical analysis was carried out by S.A.M. (Shape Analytical Morphometry) system. S.A.M. logical architecture assumes that each irregular shape contains elements of two distinct logical domains: gross distortions that interest the contour and its local perturbations. These features were investigated separately by analytical procedures to acquire independent parameters both on the logical and the numerical level. The results, statistically evaluated, show that nuclear pleomorphism is not a satisfactory criterion, if used alone, to distinguish atypical from malignant meningioma (Discriminant Analysis: 19% of minimum error).     

Increased Co-Expression of Macrophage Migration Inhibitory Factor and Matrix Metalloproteinase 9 Is Associated with Tumor Recurrence of Meningioma

Background and Objective: We detected the expression of MIF and matrix metalloproteinase 9 (MMP9) in meningiomas to determine whether they are valuable recurrence predictor for meningioma.Methods: 67 cases of meningiomas, including 57 benign tumors (WHO grade I) and 10 non-benign tumors (WHO grade II and III), were collected, and expression of MIF and MMP9 in tissue microarray was evaluated immunohistochemically. The correlations between immunostainings and clinicopathological parameters, as well as the follow-up data of patients, were analyzed statistically.Results: Increased expressions of both MIF (58.2%, 39/67) and MMP9 (55.2%, 37/67) were significantly associated with microvessel density (MVD) of tumor, but only dual high-expression of MIF and MMP9 was in relation to tumor invasion (P=0.016) and tumor recurrence (P=0.001). Based on univariate analysis, histological grade, tumor invasion and co-expression of MIF and MMP9 were significant predictors for recurrence. However, only histological grade and co-expression of MIF and MMP9 in tumor were independent recurrence factors with a hazard ratio of 49.033 (P=0.002) and 37.766 (P=0.002) in multivariate analysis.Conclusions: Together with histological grade, increased co-expression of MIF and MMP9 in tumor might be a valuable predictor for recurrence, especially for benign meningiomas.     

June 2004: a male in his late 60s with recurrent extracerebral tumor

June 2004: Over the past year, this man in late-60s had complained about progressive weakness of concentration and memory disturbances, associated with word finding difficulties. MRI examination revealed an extra-axial, parasagittal tumor 3 cm in diameter located in the left frontoparietal region. Five years ago, a meningioma in the same region, with radiographic appearance comparable to the present tumor had been totally removed. The histological picture of the current tumor was dominated by sheets of large rounded pleomorphic tumor cells with abundant eosinophilic cytoplasm and eccentric nuclei (rhabdoid cells). Cytoplasmic inclusions were frequent; occasionally,multinucleatedtumorcellswereseen. Mitoticfigures were absent and the MIB was 3%. Meningothelial lobules were scarce, and regions with fibroblastic appearance were absent. There were no psammoma bodies, necrosis or brain invasion. Moderate immunoreactivity for EMA was found. Additionally, strong cytoplasmic immunoreaction for vimentin within the rhabdoid cells was observed. Review of the previous material showed small islets of rhabdoid cells. Rhabdoid meningioma is an uncommon meningioma variant. It has been suggested that rhabdoid meningiomas are highly aggressive tumors (WHO grade III)and that the rhabdoid phenotype represents a marker of malignant transformation in meningiomas. Histologically, rhabdoid meningiomas usually exhibit signs of anaplasia, a high mitotic activity, and a markedly increased MIB-1 labeling index. Extracranial metastases may occur in the course of the disease. However, not all rhabdoid tumors appear to have anaplastic features (as this case illustrates). Another interesting feature of rhabdoid meningiomas is that in a significant number of cases, the rhabdoid cells appear only at the time of recurrence. Alternatively, as seen in this case, the rhabdoid cells may be already present in the primary meningioma, but not as the predominating histological feature.     

Immunohistochemical expression of SPARC is correlated with recurrence,survival and malignant potential in meningiomas

Meningioma is a common neoplasm that constitutes almost 30% of all primary central nervous system tumors and is associated with inconsistent clinical outcomes. The extracellular matrix proteins play a crucial role in meningioma cell biology and are important in tumor cell invasion and in progression to malignancy. SPARC (secreted protein, acidic and rich in cysteine) (osteonectin) is a matricellular glycoprotein that regulates cell function by interacting with different extracellular matrix proteins. The aim of this study was to evaluate the expression of SPARC with proliferation index, p53 reactivity in WHO grade 1 (benign), grade 2 (atypical) and grade 3 (anaplastic) meningiomas and correlate with clinical features of the patients, including location of the tumor, recurrence of the tumor and survival of patients. We studied 111 meningiomas, 69 being benign, 34 being atypical and eight being anaplastic meningiomas of various histological types. Using immunohistochemical analysis, we evaluated the expression of SPARC, Ki‐67 (MIB‐1) and p53 in meningiomas. Immunohistochemical scores of SPARC were determined as the sum of frequency (0–3) and intensity (0–3) of immunolabeling of the tumor cells. A high immunohistochemical score (4–6) for SPARC was more frequent in atypical and in anaplastic meningiomas than in benign meningiomas (p < 0.01). MIB‐1 proliferation index showed significant association between tumor grades in meningiomas (p < 0.01). At the end of a follow‐up period of 47.53 ± 25.04 months, 30 tumors recurred. A high SPARC expression was significantly associated with tumor recurrence (p = 0.02). The immunoreactivity of p53 protein and MIB‐1 score were significantly higher in recurrent meningiomas than in non‐recurrent meningiomas. The cumulative survival of patients with high SPARC expression was significantly lower than patients with low SPARC expression. The high SPARC expression scores were predominantly identified in meningothelial, fibrous and chordoid meningiomas; low SPARC expression scores were mostly spotted in secretory and psammomatous meningiomas. Evaluating SPARC expression might help assessing recurrence risk and survival estimation in meningiomas.     

The expression of fatty acid metabolism‐associated proteins is correlated with the prognosis of meningiomas

The expression of fatty acid metabolism‐associated proteins is correlated with the prognosis of meningiomas. Meningioma is a common tumor of the nervous system; however, reliable prognostic markers for meningioma are currently insufficient. High fatty acid synthase (FAS) expression occurs in many tumors, and is associated with tumor progression and grade. Few studies have previously investigated fatty acid metabolism in meningioma; thus, in this study, we investigated the expression of FAS and brain fatty acid‐binding protein (BFABP) proteins in all grades of meningioma and determined the association to meningioma grade, invasiveness, recurrence, and progression. We determined expression levels of FAS and BFABP in all grade meningiomas by immunohistochemical analysis in 314 patients diagnosed with meningioma. The expression levels of FAS and BFABP increased significantly in correlation with meningioma grade (p < 0.01). Compared with benign meningioma, the expression levels of FAS and BFABP were significantly higher in brain invasive meningioma (p < 0.01). Compared with nonrecurrent meningioma (benign meningioma), the expression of FAS was also increased in recurrent meningioma (p < 0.01). The expression of fatty acid metabolism‐associated proteins potentially correlates with meningioma grade, invasiveness, aggressiveness, and recurrent status and provides evidence for a novel therapeutic target for meningioma.     

TERT promoter mutations in primary and secondary WHO grade III meningioma

Purpose: TERT promoter mutation (TERTp^Mut) has a strong association to recurrence and has been suggested to act as a driver mutation for malignant transformation of WHO grade I and II meningiomas. TERTp^Mut has been investigated in selected high‐grade meningioma samples. The existence of TERTp^Mut across recurrent tumors in a population‐based cohort needs to be investigated in order to identify when TERTp^Mut emerges across recurrent samples and to validate prognostic impact among WHO grade III tumors. Methods: We gathered material from a consecutive single‐center cohort of 40 patients with malignant meningioma (WHO grade III) treated between 2000 and 2018, including specimens from primary and secondary malignant meningiomas with the corresponding earlier benign specimens and later malignant recurrences. In total 107 tumor samples were studied by Sanger sequencing for TERT promoter mutational status. Results: Seven of 40 patients (17.5%) harbored TERTp^Mut thus validating the incidence of TERTp^Mut in previous non‐population‐based cohorts. In 6/7 patients, the TERTp^Mut was present at initial surgery (WHO grade I–III) while in one patient the TERTp^Mut was found de novo when the meningioma became malignant. The incidences were 2/1.000.000/year for TERTp^Mut WHO grade III meningioma and 8/1.000.000/year for TERTp^wt WHO grade III meningioma in our catchment area. We found a 1.7 times higher recurrence rate (CI 95% 0.65–4.44) and a 2.5 higher mortality rate per 10 person‐years (CI 95% 1.01–6.19) for TERTp^Mut compared to TERTp^wt. Conclusion: TERTp^Mut can occur independently of malignant progression in meningioma and was most often present from the first tumor sample across recurring tumors. TERTp^Mut in WHO grade III may represent a marker of an aggressive subset of tumors.     

Expression of extracellular matrix-degrading proteins in classic, atypical, and anaplastic meningiomas

Although the majority of meningiomas, commonly benign tumors (WHO I), are amenable to surgical resection, a percentage of up to 3% will recur as higher-grade meningiomas with potential brain invasion. Our study aims at the in situ identification of proteolytic, extracellular matrix-degrading enzymes in a broad spectrum of meningiomas. We examined 80 meningiomas (50 classic meningiomas WHO I, 19 meningiomas WHO II, including atypical, chordoid, and clear cell types, as well as 11 anaplastic meningiomas WHO III) for the immunohistochemical expression patterns of cathepsin D and metalloproteinases MMP-2 and MMP-9. Meningiomas of all types and grades revealed a distinct expression of MMP-9 and cathepsin D, while MMP-2 was found predominantly in WHO II and III meningiomas. There was a significant increase in positive tumor cells from WHO grade I to II and III for MMP-2 (p<0.001), but not for cathepsin D (p=0.099). MMP-9 displayed an increased number of positive tumor cells from WHO grade I to II, but a decrease in WHO III meningiomas (p<0.002). Routine screening for the expression of metalloproteinases and cathepsin D will not reveal any new diagnostically or prognostically relevant information. However, these factors may represent a potential target for pharmacological blocking as an anti-invasive therapy.     

Significance of COX‐2 and VEGF expression in histopathologic grading and invasiveness of meningiomas

Meningiomas are slow‐growing neoplasms that recur locally. Their morphologic grading does not always correlate with patient outcome. We evaluated the status of several immunohistochemical markers with histopathologic parameters in various grades of meningioma.Eighty‐eight meningioma specimens were examined immunohistochemically to determine the status of Ki‐67, cyclin D1, epidermal growth factor receptor (EGFR), cyclooxygenase‐2 (COX‐2), vascular endothelial growth factor (VEGF), and bcl‐2. Several clinical and pathological parameters were investigated.Forty‐nine Grade I, 33 Grade II, and 6 Grade III meningiomas were observed. VEGF and Ki‐67 expression was correlated with higher tumor grade. The association between grade and other immunohistochemical markers expression was not significant. A correlation was observed between COX‐2 expression and invasiveness to the brain or adjacent soft tissue. Tumor recurrence was correlated with brain or adjacent soft tissue invasion. We also observed a relationship between VEGF level and COX‐2 expression, and they were both correlated with necrosis.Immunohistochemical evaluation of VEGF, COX‐2, and Ki‐67 expression can provide information regarding the behavior of meningiomas, particularly for cases in which histological grading is not straightforward.     

The histopathological spectrum of human meningiomas

Histopathological examination and grading of meningiomas gives valuable prognostic information, although the method is subject for interobserver variability. The aim of this study was to review a large series of human meningiomas in order to examine the frequency of benign (grade I), atypical (grade II), and anaplastic (grade III) forms depending on various WHO classification schemes. In addition, we wanted to describe the frequency of various histopathological features and their mutual correlations. Sections from 196 consecutively treated primary human meningioma patients were revised retrospectively. The established criteria to grade meningiomas, which are also known to be associated with tumorigenesis, were shown to correlate significantly. The number of grade II meningiomas increased when using the WHO 2007 classification (30%) compared with previous editions, mainly due to the definition of brain infiltrating meningiomas as atypical (grade II). bimodal frequency distribution among age groups of females was observed. Continuous revision of histopathological classification systems is required to improve the diagnostic accuracy.     

Rhabdoides Meningeom

Of the numerous morphological variants of meningiomas only few, and among these the rhabdoid meningioma, have prognostic importance. Rhabdoid meningiomas were described for the first time in 1998 as an unusual variant with increased proliferative activity. In 2000 they have been included in the revised WHO classification of tumours of the CNS as a subtype of meningiomas with increased risk of recurrence and more aggressive growth, corresponding to WHO grade III. We report the case of a rhabdoid meningioma in a 21-year-old woman presenting as a intracerebral tumour mimicking an oligodendroglioma. The tumour showed features of a meningioma and a rhabdoid morphology with angiomatous components and was considered to be a rhabdoid meningioma. After surgery a small residual tumour remained. The patient received postoperative radiotherapy resulting in regression of the residual tumour in control examinations after 4 and 8 months. Using the presented case we discuss the differential diagnosis and prognostic significance of recognition of a rhabdoid meningioma.     

New developments in the pathology of skull base tumors

As an anatomical interface between various tissues, the skull base harbors an exceptionally broad variety of neoplasms, some of which pose a major challenge for surgical pathology. The characterization of distinct immunohistochemical expression profiles and the identification of molecular genetic alterations associated with different tumor entities have significantly advanced this field. The new World Health Organization (WHO) classification of tumors of the nervous system lists 15 histopathological variants of meningioma. Of clinical importance are those entities that carry an increased risk of recurrence and a poor prognosis, i.e., the atypical meningioma (WHO grade II), clear-cell meningioma (WHO grade II), chordoid meningioma (WHO grade II), rhabdoid meningioma (WHO grade III), papillary meningioma (WHO grade III), and anaplastic meningioma (WHO grade III). Diagnostic criteria for atypical and anaplastic meningioma variants have now been stringently defined. The differential diagnosis of meningiomas includes hemangiopericytoma, hemangioblastoma, solitary fibrous tumor, sarcomas, and chordoid neoplasms. Recent data highlight the importance of distinguishing chordoma and chondrosarcoma of the skull base since chondrosarcomas show a significantly better clinical outcome. Among the less common, aggressive tumor entities in this anatomical region, infiltrating pituitary adenoma/pituitary carcinoma, superficial malignant gliomas, rhabdomyosarcoma, olfactory neuroblastoma, various sarcomas, and malignant lymphoma must be considered. Profiles of molecular genetic alterations have been established for several of these neoplasms and may facilitate the differential diagnosis. This review summarizes recent developments in the histopathological characterization, classification, and molecular pathology of neoplasms arising at the skull base.     

An orthotopic skull base model of malignant meningioma

Meningioma tumor growth involves the subarachnoid space that contains the cerebrospinal fluid. Modeling tumor growth in this microenvironment has been associated with widespread leptomeningeal dissemination, which is uncharacteristic of human meningiomas. Consequently, survival times and tumor properties are varied, limiting their utility in testing experimental therapies. We report the development and characterization of a reproducible orthotopic skull-base meningioma model in athymic mice using the IOMM-Lee cell line. Localized tumor growth was obtained by using optimal cell densities and matrigel as the implantation medium. Survival times were within a narrow range of 17-21 days. The xenografts grew locally compressing surrounding brain tissue. These tumors had histopathologic characteristics of anaplastic meningiomas including high cellularity, nuclear pleomorphism, cellular pattern loss, necrosis and conspicuous mitosis. Similar to human meningiomas, considerable invasion of the dura and skull and some invasion of adjacent brain along perivascular tracts were observed. The pattern of hypoxia was also similar to human malignant meningiomas. We use bioluminescent imaging to non-invasively monitor the growth of the xenografts and determine the survival benefit from temozolomide treatment. Thus, we describe a malignant meningioma model system that will be useful for investigating the biology of meningiomas and for preclinical assessment of therapeutic agents.