Effect of embolisation of meningioma on Ki-67 proliferation index

Volumetric tumor growth rates of meningiomas involving the intracranial venous sinuses

OBJECT

There is currently no consensus as to whether meningiomas located inside the venous sinuses should be aggressively or conservatively treated. The goals of this study were to identify how sinus-invading meningiomas grow, report and compare growth rates of tumor components inside and outside the different venous sinuses, identify risk factors associated with increased tumor growth, and determine the effects of the extent of tumor resection on recurrence for meningiomas that invade the dural venous sinuses.

METHODS

Adult patients who underwent primary, non-biopsy resection of a WHO grade 1 meningioma invading the dural venous sinuses at a tertiary care institution between 2007 and 2015 were retrospectively reviewed. Rates of tumor growth were fit to several growth models to evaluate the most accurate model. Cohen's d analysis was used to identify associations with increased growth of tumor in the venous sinuses. Logistic regression was used to compare extent of resection with recurrence.

RESULTS

Of the 68 patients included in the study, 34 patients had postoperative residual tumors in the venous sinuses that were measured over time. The growth model that best fit the growth of intrasinus meningiomas was the Gompertzian growth model (r² = 0.93). The annual growth rate of meningiomas inside the sinuses was 7.3%, compared to extrasinus tumors with 13.6% growth per year. The only factor significantly associated with increased tumor growth in sinuses was preoperative embolization (effect sizes (ES) [95% CI], 1.874 [7.633-46.735], p = 0.008).

CONCLUSIONS

This study shows that meningiomas involving the venous sinuses have a Gompertzian-type growth with early exponential growth followed by a slower growth rate that plateaus when they reach a certain size. Overall, the growth rate of the intrasinus portion is low (7.3%), which is half of the reported growth rates for other studies involving primarily extrasinus tumors.

Pathology and molecular genetics of meningioma: recent advances

Meningiomas are the most common intracranial primary neoplasm in adults. Although the spectrum of clinical and molecular genetic issues regarding meningiomas remains undefined, novel genetic alterations that are associated with tumor morphology, malignancy, or location have recently been discovered. This review focuses on recent advances in understanding of the heterogenous pathology of meningiomas, particularly on associations between the clinical, histological, etiological, epidemiological, and molecular genetical aspects of the neoplasm.

Preoperative embolization of intracranial meningiomas: efficacy, technical considerations, and complications

BACKGROUND AND PURPOSE

Preoperative embolization for intracranial meningiomas offers potential advantages for safer and more effective surgery. However, this treatment strategy has not been examined in a large comparative series. The purpose of this study was to review our experience using preoperative embolization to understand the efficacy, technical considerations and complications of this technique.

MATERIALS AND METHODS

We performed a retrospective review of patients undergoing intracranial meningioma resection at our institution (March 2001 to December 2012). Comparisons were made between embolized and nonembolized patients, including patient and tumor characteristics, embolization method, operative blood loss, complications, and extent of resection. Logistic regression analyses were used to identify factors predictive of operative blood loss and extent of resection.

RESULTS

Preoperatively, 224 patients were referred for embolization, of which 177 received embolization. No complications were seen in 97.1%. There were no significant differences in operative duration, extent of resection, or complications. Estimated blood loss was higher in the embolized group (410 versus 315 mL, P=.0074), but history of embolization was not a predictor of blood loss in multivariate analysis. Independent predictors of blood loss included decreasing degree of tumor embolization (P=.037), skull base location (P=.005), and male sex (P=.034). Embolization was not an independent predictor of gross total resection.

CONCLUSIONS

Preoperative embolization is a safe option for selected meningiomas. In our series, embolization did not alter the operative duration, complications, or degree of resection, but the degree of embolization was an independent predictor of decreased operative blood loss.

Cytological changes induced by embolization in meningiomas

OBJECTIVE

To describe cytological changes in meningiomas induced by embolization, which may be carried out a few days before surgery in order to soften the tumour and minimize intraoperative bleeding. Although histological changes have been described, we have found no description of such changes in the cytological literature.

METHODS

We reviewed 22 cases of meningiomas with prior embolization in which cytological material was obtained during intraoperative consultation. In 13 of them recognizable cytological changes induced by embolization were present. On histology, these 13 tumours were grade I and showed intravascular embolic material.

RESULTS

Cellular dissociation was prominent, with frequent single cells and small groups. Ischaemic cellular changes were a common finding and consisted of cell shrinkage, nuclear pyknosis and karyorrhexis. Confluent areas of necrosis were seen in one case. Additionally, numerous macrophages were present, many containing cellular debris, and neutrophils, giving a characteristic appearance of acute cellular ischaemia. Embolic material was seen cytologically in four cases as well-defined spherules surrounded by empty halos. Features of viable meningioma were recognized in all cases.

CONCLUSION

Embolization of meningiomas induces cytological changes that mirror those seen on histology, but cellular dissociation with changes of ischaemia may result in a worrisome image. When faced with such changes the pathologist should consider the possibility of embolization, avoiding misdiagnosis of higher grade meningioma or metastatic carcinoma.

Histological classification and molecular genetics of meningiomas

Meningiomas account for up to 30% of all primary intracranial tumours. They are histologically classified according to the World Health Organization (WHO) classification of tumours of the nervous system. Most meningiomas are benign lesions of WHO grade I, whereas some meningioma variants correspond with WHO grades II and III and are associated with a higher risk of recurrence and shorter survival times. Mutations in the NF2 gene and loss of chromosome 22q are the most common genetic alterations associated with the initiation of meningiomas. With increase in tumour grade, additional progression-associated molecular aberrations can be found; however, most of the relevant genes are yet to be identified. High-throughput techniques of global genome and transcriptome analyses and new meningioma models provide increasing insight into meningioma biology and will help to identify common pathogenic pathways that may be targeted by new therapeutic approaches.

Expression of hypoxia inducible factor-1 alpha and correlation with preoperative embolization of meningiomas

OBJECT

Vascular endothelial growth factor (VEGF) has been implicated in meningioma tumorigenesis and growth. The production of VEGF is regulated by hypoxia inducible factor-1alpha (HIF-1alpha), especially under conditions of hypoxia. In this study, the authors examine the expression of HIF-1alpha and VEGF in meningiomas, with a special emphasis on conditions of hypoxia, such as preoperative embolization, and on in vitro studies in cultured cells.

METHODS

Meningiomas obtained in 142 patients were studied using immunohistochemical methods to detect HIF-1alpha and the results were correlated with the extent or lack of preoperative embolization and expression of VEGF. Primary meningioma cell cultures were established and cell culture experiments were performed using a hypoxia chamber to stimulate HIF-1alpha and VEGF production. Expression of HIF-1alpha in primary meningioma cell cultures was measured using immunoblot assays. The VEGF secretion was measured using enzyme-linked immunosorbent assay. Half of the meningiomas studied were positive for HIF-1alpha, with a strong correlation between complete embolization and HIF-1alpha expression. Most of the meningiomas studied expressed VEGF protein, and VEGF expression did not correlate with the degree of embolization. A strong correlation was found between VEGF and HIF-1alpha expression in immunohistochemical studies. Secretion of VEGF is increased by hypoxia and growth factor stimulation. In meningiomas, growth factors stimulate HIF-1alpha expression. The role of hypoxia is less clear.

CONCLUSIONS

The expression of HIF-1alpha is increased by complete preoperative embolization of meningiomas. The expression of HIF-1alpha also correlates with VEGF secretion in meningiomas. Growth factor and hypoxic stimulation both contribute to VEGF control, but which is most important (or whether both are equally important) will require further studies.

Clinicopathologic assessment and grading of embolized meningiomas: a correlative study of 64 patients

BACKGROUND

Preoperative embolization of meningiomas is commonly performed to minimize intraoperative bleeding, thereby facilitating surgery and reducing the necessity for transfusion. However, the resulting necrosis and compensatory proliferation reportedly have hampered subsequent histologic grading.

METHODS

The clinicopathologic features of 64 meningiomas embolized between 1989 and 1997 were assessed. Tumors were graded according to recently published criteria.

RESULTS

A good embolization result (> 75% reduction in angiographic blush) was achieved in 52%. Histologically, embolized meningiomas showed higher frequencies of necrosis (89%), nuclear atypia (72%), macronucleoli (58%), sheeting (31%), high mitotic index (30%), and brain invasion (14%) when compared with nonembolized counterparts. Median mitotic and MIB-1 indices were slightly elevated (1.5 of 10 high-power fields and 1.6%, respectively). A significant degree of necrosis (> 10%) was found in 43% and was only roughly correlated with extent of angiographic blush reduction or embolization particle size. Histologic grade was benign in 57.8%, atypical in 40.6%, and anaplastic in 1.6%. At last follow-up, there were 13 recurrences, 11 in the atypical/anaplastic (41%) versus 2 in the benign (5%) subsets (P = 0.001).

CONCLUSIONS

The authors conclude that 1) their grading scheme accurately stratifies embolized meningiomas, 2) extent of necrosis is difficult to predict using standard clinical parameters, and 3) their high incidence of atypical meningioma more likely reflects patient selection biases rather than artifacts induced by the embolization procedure.

[Preoperative embolization in meningioma of the ponto-cerebellar angle. Indications and advantages]

Preoperative embolization of meningiomas has been performed in order to reduce surgical hemorrhage during the removal of these vascularized tumors. In this paper we emphasize the fact that occlusion of the tumoral vessels by artificial emboli produces an ischemic necrosis that greatly helps tumor exeresis. This is especially useful in meningiomas of certain localizations requiring complex surgical approaches. In our case, a giant ponto-cerebellar meningioma was dried up totally and then removed with relative ease through a conventional suboccipítal lateral craniectomy. The technique, indications and control of preoperative embolization are reviewed.

Alteration of bcl-2 and bax expression in embolized meningiomas

We examined the expression of the p53 and bcl-2 family in embolized meningiomas and investigated the interaction between them. p53 and its downstream effector p21 accumulated mainly in perinecrotic areas, where apoptosis was also observed. bcl-2 was often expressed in the areas distant from necrosis, whereas Bax was immunostained more intensely in the perinecrotic areas. Double staining for both p53 and Bcl-2 showed a reciprocal pattern. This appeared to be due to the down-regulation of Bcl-2 by p53. However, regulation of Bax by p53 was not distinct. The expression of p21 was not apparent 13 days after embolization, and apoptosis was observed until 6 days after embolization. The effect of embolization was most likely temporary, although growth arrest has been reported to persist for a long time in a limited number of embolized cases.

Increased proliferative activity due to necroses induced by pre-operative embolization in benign meningiomas

The proliferative behaviour of 35 benign intracranial meningiomas was investigated which were embolized for devascularization 3 to 268 hours prior to surgical exstirpation. The nuclear proliferation antigen Ki-67 was visualized by means of the monoclonal antibody MIB1 on formalin fixed and paraffin embedded tissue. Tumor cells and inflammatory reactions were recognized by means of conventional staining procedures and by immunohistochemical detection of HAM56, LCA, HLA-DR, CD15-epitope and vimentin. Extravasation and proliferation of granulocytes, macrophages, lymphocytes and the degree of expression of MHCII antigens was estimated according to a 7-point ordinal scale. Confirming preliminary observations of others the proliferation index within the perinecrotic tumor rim (PIperinec) exceeded that of intact tissue highly significantly. PIperinec peaked at the third to fourth day after embolization and kept this level until the seventh day. The time course of PIperinec was paralleled by that of macrophages, whereas--expectedly--granulocytes occured earlier and lymphocytes and HLA-DR-positivity somewhat later. The timely relationships suggested that the perinecrotic increase in tumor cell proliferation was mainly due to macrophage-born mitogens. Perinecrotic proliferative activity in embolized meningiomas does not reflect genuine tumor proliferation and should not be used for assessment of the presence or degree of malignancy in a given tumor.

Expression of p53, MDM2 protein and Ki-67 antigen in recurrent meningiomas

Association of p53 gene abnormalities with tumor progression and prognosis of many neoplasms has been demonstrated, but little is known about the clinical significance of p53 abnormalities in meningiomas. The significance of p53 protein expression in recurrent meningiomas and its relationships with MDM2 protein and proliferation activity were investigated by analyzing 39 meningiomas immunohistochemically. p53 protein was expressed in 11 (35%) of 31 non-recurrent and 7 (88%) of 8 recurrent meningiomas. A high frequency of p53 expression was observed in recurrent meningiomas, which tended to have a high p53 positive index (p53 PI), indicating that p53 immunoreactivity may be a marker for predicting tumor recurrence. Four recurrent meningiomas with high p53 PIs were analyzed by the polymerase chain reaction-single strand conformation polymorphism method to detect p53 gene mutations, but none were found in exons 4-8 of this gene. Fifteen (71%) of 21 MDM2-positive and 3 (17%) of 18 MDM2-negative tumors expressed p53 protein, showing that MDM2 expression was more common in meningiomas with p53 expression. p53 immunoreactivity in the absence of mutation may indicate stabilization of the wild type through interaction with the MDM2 protein. The Ki-67/MIB-1 proliferation index (MIB-1 PI) correlated well with recurrence. The p53-positive tumors had a significantly higher mean MIB-1 PI than p53-negative tumors, suggesting that wild-type p53 inactivation by the MDM2 protein may be involved in controlling the proliferative activity in meningiomas. In conclusion, immunohistochemical examination for p53 protein as well as proliferative activity may help predict the malignant potential of tumor recurrence.

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.

Histopathology of post-embolized meningiomas

Although embolization of meningiomas has been performed for many years as a preoperative adjunct to reduce tumor vascularity and facilitate surgical excision, little has been written about the features of the histological artefacts introduced by the process. In particular, the fact that it may produce tumor necrosis may potentially cause confusion with atypical or malignant meningiomas. In this study, 25 meningeal tumors of different histological subtypes, all of which had been previously embolized, were reviewed histologically as well as with immunostaining for the MIBI antigen and proliferating cell nuclear antigen (PCNA). Necrosis, in the form of confluent necrosis as well as micronecrosis, was the most common feature (48%). Other characteristic features included florid ischemic changes (16%), intravascular Ivalon particles (24%), and fibrinoid necrosis of vascular walls (12%). Histological changes showed no obvious relationship with the interval between embolization and surgery. There was an increase in MIB1 and PCNA labelling indices in those tumor exhibiting necrotic foci, but it did not seem to have any prognostic significance. We believe pathologists should be familiar with the histological changes induced by embolization in meningiomas so that an erroneous diagnosis of a high-grade lesion will not be made.