Evolution of a Treatment Paradigm for Atypical Meningiomas
Evolution of a Treatment Paradigm for Atypical Meningiomas
Object: The World Health Organization (WHO) reclassified atypical meningiomas in 2000, creating a more clear and broadly accepted definition. In this paper, the authors evaluated the pathological and clinical transition period for atypical meningiomas according to the implementation of the new WHO grading system at their institution.
Methods: A total of 471 meningiomas occurring in 440 patients between 1994 and 2006 were retrospectively reviewed to determine changes in diagnostic rates, postoperative treatment trends, and early outcomes.
Results: Between 1994 and 2000, the incidence of the atypical meningiomas ranged from 0 to 3/year, or 4.4% of the meningiomas detected during the entire period. After 2002, the annual percentage of atypical meningiomas rose over a 2-year period, leveling off at between 32.7 and 35.5% between 2004 and 2006. The authors also found a recent trend toward increased use of adjuvant radiation therapy for incompletely resected atypical meningiomas. Prior to 2003, 18.7% were treated with this therapy; after 2003, 34.4% of lesions received this treatment. Incompletely resected tumors were treated with some form of radiation 76% of the time. In cases of complete resection, most patients were not given adjuvant therapy but were expectantly managed by close monitoring using serial imaging and by receiving immediate treatment for tumor recurrence. The overall recurrence rate for expectantly managed tumors was 9% over 28.2 months, and 75% of recurrences responded to delayed radiation therapy.
Conclusions: The authors documented a significant change in the proportion of meningiomas designated as atypical during a transition period from 2002 to 2004, and propose a conservative strategy for the use of radiation therapy in atypical meningiomas.
Approximately 20% of all primary intracranial tumors are meningiomas, and historically the majority of these are considered benign. Pathological grading of meningiomas prior to 2000 varied widely, with many highly subjective classification systems in place and little uniformity for the definition of an atypical meningioma. Most of these systems relied heavily on mitotic rates but remained subjective even with regard to the mitotic rate needed to classify a tumor as atypical. The not widely used 1993 WHO criteria describe atypical meningiomas as "meningiomas in which several of the following features are evident: frequent mitoses, increased cellularity, small cells with high nuclear to cytoplasmic ratios and/or prominent nucleoli, uninterrupted patternless or sheet like growth, and foci of "spontaneous" or geographic necrosis." In 2000, the WHO reclassified meningiomas and created diagnostic criteria that became the standard for grading meningiomas in the years following their publication. Clarified subclasses of WHO Grade II meningiomas include clear cell, chordoid, and atypical meningiomas. Atypical meningiomas according to the WHO 2000 classification have at least 4 mitoses in 10 hpf or 3 of the following criteria: increased cellularity, high nuclear-to-cytoplasm ratios, prominent nucleoli, uninterrupted patternless or sheet-like growth, or necrosis. Notably, neither elevated MIB-1 labeling nor brain invasion are part of these WHO criteria despite recognized predisposition for tumor recurrence when these factors are noted. Although the criteria clarification has benefited the evaluation of meningiomas by making interobserver and intrainstitutional comparisons more valid, the change has required most institutions to adopt new and substantially different criteria for the grading of meningiomas.
In the years following the WHO reclassification, many institutions began to record different rates of atypical meningiomas than they had in the past. Some investigators perceived a decline in the diagnosis, while other institutions, including ours, placed more meningiomas in the atypical WHO Grade II category than were diagnosed as atypical before 2000.
Whereas the overall effect of a better-defined classification scheme is clearly positive, pathologists must become acquainted with the new grading system and develop a consensus on the components of diagnosis that remain subjective. Clinicians must also recognize and adapt to changes in the subtleties of this pathological diagnosis. In addition, new research and experience must be compiled to better guide future treatment of these neoplasms. The focus of this study is to evaluate the pathological and clinical transition period for atypical meningiomas following the WHO 2000 grading system implementation, and to reevaluate our postoperative treatment for atypical meningiomas.
Object: The World Health Organization (WHO) reclassified atypical meningiomas in 2000, creating a more clear and broadly accepted definition. In this paper, the authors evaluated the pathological and clinical transition period for atypical meningiomas according to the implementation of the new WHO grading system at their institution.
Methods: A total of 471 meningiomas occurring in 440 patients between 1994 and 2006 were retrospectively reviewed to determine changes in diagnostic rates, postoperative treatment trends, and early outcomes.
Results: Between 1994 and 2000, the incidence of the atypical meningiomas ranged from 0 to 3/year, or 4.4% of the meningiomas detected during the entire period. After 2002, the annual percentage of atypical meningiomas rose over a 2-year period, leveling off at between 32.7 and 35.5% between 2004 and 2006. The authors also found a recent trend toward increased use of adjuvant radiation therapy for incompletely resected atypical meningiomas. Prior to 2003, 18.7% were treated with this therapy; after 2003, 34.4% of lesions received this treatment. Incompletely resected tumors were treated with some form of radiation 76% of the time. In cases of complete resection, most patients were not given adjuvant therapy but were expectantly managed by close monitoring using serial imaging and by receiving immediate treatment for tumor recurrence. The overall recurrence rate for expectantly managed tumors was 9% over 28.2 months, and 75% of recurrences responded to delayed radiation therapy.
Conclusions: The authors documented a significant change in the proportion of meningiomas designated as atypical during a transition period from 2002 to 2004, and propose a conservative strategy for the use of radiation therapy in atypical meningiomas.
Approximately 20% of all primary intracranial tumors are meningiomas, and historically the majority of these are considered benign. Pathological grading of meningiomas prior to 2000 varied widely, with many highly subjective classification systems in place and little uniformity for the definition of an atypical meningioma. Most of these systems relied heavily on mitotic rates but remained subjective even with regard to the mitotic rate needed to classify a tumor as atypical. The not widely used 1993 WHO criteria describe atypical meningiomas as "meningiomas in which several of the following features are evident: frequent mitoses, increased cellularity, small cells with high nuclear to cytoplasmic ratios and/or prominent nucleoli, uninterrupted patternless or sheet like growth, and foci of "spontaneous" or geographic necrosis." In 2000, the WHO reclassified meningiomas and created diagnostic criteria that became the standard for grading meningiomas in the years following their publication. Clarified subclasses of WHO Grade II meningiomas include clear cell, chordoid, and atypical meningiomas. Atypical meningiomas according to the WHO 2000 classification have at least 4 mitoses in 10 hpf or 3 of the following criteria: increased cellularity, high nuclear-to-cytoplasm ratios, prominent nucleoli, uninterrupted patternless or sheet-like growth, or necrosis. Notably, neither elevated MIB-1 labeling nor brain invasion are part of these WHO criteria despite recognized predisposition for tumor recurrence when these factors are noted. Although the criteria clarification has benefited the evaluation of meningiomas by making interobserver and intrainstitutional comparisons more valid, the change has required most institutions to adopt new and substantially different criteria for the grading of meningiomas.
In the years following the WHO reclassification, many institutions began to record different rates of atypical meningiomas than they had in the past. Some investigators perceived a decline in the diagnosis, while other institutions, including ours, placed more meningiomas in the atypical WHO Grade II category than were diagnosed as atypical before 2000.
Whereas the overall effect of a better-defined classification scheme is clearly positive, pathologists must become acquainted with the new grading system and develop a consensus on the components of diagnosis that remain subjective. Clinicians must also recognize and adapt to changes in the subtleties of this pathological diagnosis. In addition, new research and experience must be compiled to better guide future treatment of these neoplasms. The focus of this study is to evaluate the pathological and clinical transition period for atypical meningiomas following the WHO 2000 grading system implementation, and to reevaluate our postoperative treatment for atypical meningiomas.
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