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Histological‑subtypes and anatomical location correlated in meningeal brain tumors (meningiomas)

Context: Not enough literature is available to suggest a link between the histological subtypes of intracranial meningeal brain tumors, called ‘meningiomas’ and their location of origin. Aim: The evidence of correlation between the anatomical location of the intracranial meningiomas and the histopathological grades will facilitate specific diagnosis and accurate treatment. Materials and Methods: The retrospective study was conducted in a single high‑patient‑inflow Neurosurgical Center, under a standard and uniform medical protocol, over a period of 30 years from December 1982 to December 2012. The records of all the operated 729 meningiomas were analyzed from the patient files in the Medical Records Department. The biodata, x‑rays, angiography, computed tomography (CT) scans, imaging, histopathological reports, and mortality were evaluated and results drawn. Results: The uncommon histopathological types of meningiomas (16.88%) had common locations of origin in the sphenoid ridge, posterior parafalcine, jugular foramen, peritorcular and intraventricular regions, cerebellopontine angle, and tentorial and petroclival areas. The histopathological World Health Organization (WHO) Grade I (Benign Type) meningiomas were noted in 89.30%, WHO Grade II (Atypical Type) in 5.90%, and WHO Grade III (Malignant Type) in 4.80% of all meningiomas. Meningiomas of 64.60% were found in females, 47.32% were in the age group of 41‑50 years, and 3.43% meningiomas were found in children. An overall mortality of 6.04% was noted. WHO Grade III (malignant meningiomas) carried a high mortality (25.71%) and the most common sites of meningiomas with high mortality were: The cerebellopontine angles, intraventricular region, sphenoid ridge, tuberculum sellae, and the posterior parafalcine areas. Conclusion: The correlation between the histological subtypes and the anatomical location of intracranial meningeal brain tumors, called meningiomas, is evident, but further research is required to establish the link.


Original Article
Introduction Meningeal brain tumors, called meningiomas, are now known to arise from arachnoidal cap cells of the leptomeninges. In 1915, Harvey Cushing considered that meningeal tumors arose from arachnoidal cap cells. Seven years later, Cushing proposed the term ‛meningioma' for these tumors and the term achieved global acceptance. Working together with his student, Percival Bailey, at the Peter Bent Brigham Hospital, he adopted a histopathological classification system that listed four variants: Meningothelial, fibroblastic, angioblastic, and osteoblastic. Later, Bailey and Bucy expanded the initial histopathological classification of meningiomas, which was similar to the new WHO histopathological classification 2007, despite new discoveries made by molecular biology, biochemistry, and a recent technology in the last few years. [1] Intracranial meningiomas are always dural-based, but entities like intraventricular meningiomas arise independent of such a base. Similarly, histopathological atypicality occurs among meningiomas of the posterior fossa, base of the skull, intraventricular, and parasagittal/falcine regions. As the WHO grading has categorized meningiomas in benign, atypical, and malignant types, the curiosity to know the probable histological type preoperatively, by the site of origin, may change the future management of meningiomas, in the form of extension of resection and adjuvant treatment.

Materials and Methods
The authors sought to analyze all the admitted 729 surgically treated meningiomas (meningeal tumors of the brain) and those treated under a standard medical protocol in a high-patient-inflow and the only Neurosurgical Unit in the State, from December 1982 to December 2012. Ethnically, all the patients belonged to the same area. Retrospectively, the biodata, surgical procedure, histopathological findings, mortality, and imaging reports (in the form of initial X-rays, two-fourth vessel angiography, CT Scans, and recent MRI) of all the patients were recorded from the patient files in the Medical Records Department. The histopathological findings and types were categorized according to the WHO 2000 Classification of Meningiomas. [2] The histological patterns recognized by the WHO are: After compiling the whole data, observations were made, inferences drawn, and statistically, the Law of Variance used wherever applicable.
An overall operative mortality of 6    for meningiomas originating from the cerebellopontine angle, sphenoid ridge, and the tentorial, intraventricular, tubercular sellae, and posterior parafalcine regions.

Discussion
The lesion, most comparable with a meningioma, was first reported by Felix Plater in 1614. [3] A French surgeon, Antoine Louis in 1774, described a tumor-like meningioma and called it 'fungus durae matris'. [4] However, Harvey Cushing was the first to use the term 'meningioma' in 1922. [3] The present study on 729 patients noted a female to male ratio of 1.82:1.0, the most involved being in the 41-50 year age group, and 3.43% childhood meningiomas. Benign (Grade I) meningiomas occurred in 89.30%, and 57.75% of all meningiomas were of the meningothelial (syncytial) type and the most common site of origin for these was the parasagittal area. The malignant (Grade II) variety occurred in 4.80% of the patients with common sites of origin in the cerebellopontine angles, intraventricular region, sphenoid ridge, and posterior parafalcine areas. A report of female preponderance was documented by Marin et al., with a female to male ratio of 2.5:1. [5] Gabriela et al. reported 100% cerebellar convexity meningiomas histologically as being fibrous alone, although most of the angiomatous subtypes originated from the cerebellopontine angles. The petroclival meningiomas accounted for a higher incidence of 11.42% for all posterior fossa meningiomas. [6] Park et al. reported that the vast majority of intracranial meningiomas (92%) had a benign histology, whereas, 8% showed atypical or malignant features. For all meningiomas, the most common histopathological subtype was the meningotheliomatous type (63%), followed by transitional (19%), fibrous (13%), and psammomatous (2%) meningiomas. Also, fewer than 10% of the meningiomas were malignant. [7] Gabriela et al. mentioned that grade I meningiomas were encountered in a majority of cases (82.85%), whereas, grade II meningiomas were diagnosed in 11.42% of the operated cases. The anaplastic meningiomas (grade III) accounted only for 5.71%. About 82% (29 patients) of the patients had an anatomically distinct attachment to the dura. The most common benign histological subtypes among the posterior fossa meningiomas were the fibrous (37.79%) and psammomatous (24.13%). [6] Marin et al. reviewed 492 intracranial and spinal meningiomas, among which, seven patients were identified to have foramen magnum meningiomas. These were five women and two men aged 39-66 years (mean 53.3 years). They found a female preponderance with a female to male ratio of 2.5:1. [5] Various studies show that foramen magnum meningiomas are rare and account for only 0.3 to 3.2% of all meningiomas, and between 4.2 and 20% of all posterior fossa meningiomas. [8][9][10] The authors from the two studies reported that cerebellar convexity meningiomas represent about 1.5% of all meningiomas. [10,11] Avninder et al. presented a case of a lymphoplasmacyte-rich meningioma arising at the foramen magnum. [12] Mahx Bracho et al. reported a three-year-six-month-old boy with chordoid meningioma of the foramen magnum. [13] On account of the rarity of the published cases, there is only limited information about the histology of these meningiomas. Tsao et al. presented the histopathology of a foramen magnum meningioma as a meningothelial type. [14] The present study, analyzing 729 meningiomas, in a age group of 8-72 years, revealed [ Table 3  arachnoid membrane was formed by the arachnoid cap cells, whereas, the trabecular (fibroblast) cells formed the inner layers, which were separated by the basal lamina. Histologically, the fibrous and transitional meningioma subtypes had features similar to the fibroblast found in the deeper layers of the arachnoid, close to the subarachnoid space, whereas, the meningothelial subtype resembled the arachnoid cap cells of the outer layers. Therefore, Lee considered that differential leptomeningeal embryogenesis could result in the predominance of one cell type (i.e. the arachnoid cap cells and/or trabecular cells) in certain locations. [17] Finally, Chung et al. gave another explanation for histopathological variations of meningiomas, as he considered that meningiomas arose from polyblastic and functionally multipotent arachnoid cells. [18] The present study found that the high occurrence of meningiomas (such as Meningothelial, Fibroblastic, Transitional, and Psammomatous) at common anatomical sites (such as parasagittal, anterior parafalcine, cerebral convexity, and sphenoid ridge) led to a proportional decrease in the frequency of atypical and malignant meningiomas at such sites in comparison to the posterior fossa, base of skull, and intraventricular regions. The survival of Benign (WHO Grade I) was more than 95% as compared to the less than 25% survival of Malignant (WHO Grade III) meningiomas.

Conclusion
The present study finds a correlation between the histological type of meningeal brain tumors (meningiomas) and the location of origin. The uncommon types of meningiomas, Atypical (WHO Grade II) and Malignant (WHO Grade III), were found in high proportions at the jugular foramen, tentorium, sphenoid ridge, cerebellopontine angle, peritorcular, petroclival, orbital groove, posterior parafalcine, tuberculum sellae, and intraventricular regions. A mortality of 16.28% for the atypical histological type and 25.71% for the malignant type was mostly found in the above-mentioned areas. The survival of the benign or WHO Grade I types in the convexity, parasagittal, anterior parafalcine, and intraorbital areas was more than 95%. However, this study needs a further research-oriented study, hence, a specific histological examination has been established for meningiomas in specific locations, for specific treatment. If the preoperative milieu and cell of origin of a meningioma is known, the management might change to a better end in future because of this established correlation.