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Meningioma |
| Meningioma Classification and external resources |
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| A contrast enhanced CT scan of the brain, demonstrating the appearance of a Meningioma. | |
| ICD-10 | C70, D32 |
| ICD-9 | 225.2 |
| ICD-O: | 9530 |
| OMIM | 607174 |
| DiseasesDB | 8008 |
| eMedicine | neuro/209 radio/439 |
| MeSH | D008579 |
Meningiomas are the most common primary tumor of the central nervous system, arising from the arachnoid "cap" cells of the arachnoid villi in the meninges.1 These tumours are usually benign in nature; however, they can be malignant.2
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Most cases are sporadic while some are familial. Persons who have undergone radiation to the scalp are more at risk for developing meningiomas.3
The most frequent genetic mutations involved in meningiomas are inactivation mutations in the neurofibromatosis 2 gene (merlin) on chromosome 22q.
Other possible genes/loci include:
Small tumors (e.g., < 2.0 cm) are usually incidental findings at autopsy without having caused symptoms. Larger tumors can cause symptoms depending on the size and location.
Meningiomas arise from arachnoidal cells,7 most of which are near the vicinity of the venous sinuses, and this is the site of greatest prevalence for meningioma formation. They are most frequently attached to the dura over the superior parasagittal surface of frontal and parietal lobes, along the sphenoid ridge, in the olfactory grooves, the sylvian region, superior cerebellum along the falx cerebri, cerebellopontine angle, and the spinal cord. The tumor is usually gray, well-circumscribed, and takes on the form of space it occupies. They are usually dome-shaped, with the base lying on the dura.
Histologically, the cells are relatively uniform, with a tendency to encircle one another, forming whorls and psammoma bodies (laminated calcific concretions).8 They have a tendency to calcify and are highly vascularized.
Meningiomas are readily visualized with contrast CT, MRI with gadolinium, and arteriography, all attributed to the fact that meningiomas are extra-axial and vascularized. CSF protein is usually elevated if lumbar puncture is attempted.
Though the majority of meningiomas are benign, they can have malignant presentations. Classification of meningiomas are based upon the WHO classification system. 9
In a recent retrospective review of atypical and anaplastic meningioma cases, it was found that the mean overall survival for atypical meningiomas was 11.9 years vs. 3.3 years for anaplastic meningiomas. Mean relapse free survival for atypical meningiomas was 11.5 years vs. 2.7 years for anaplastic meningiomas.10
Observation with close imaging follow-up can be used in select cases if a meningioma is small and asymptomatic. In a retrospective study on 43 patients, it was found that 63% of patients had no growth on follow-up, and the 37% found to have growth grew at an average of 4 mm / year.11 In this study, younger patients were found to have tumors that were more likely to grow on repeat imaging, thus are poorer candidates for Observation.
Observation is not recommended in tumors that are already causing symptoms. Furthermore, close follow-up with imaging is required with an Observation strategy to rule out an enlarging tumor.12
Meningiomas can usually be surgically resected with permanent cure if the tumor is superficial on the dural surface and easily accessible. Transarterial embolization has become a standard preoperative procedure in the preoperative management.13 If invasion of the adjacent bone occurs, total removal is nearly impossible. Malignant transformation is rare.
The probability of tumor recurrence or growth after surgical resection can be estimated by the tumor's WHO Grade and by the extent of surgery by the Simpson Criteria.14
| Simpson Grade | Completeness of Resection | 10-year Recurrence |
|---|---|---|
| Grade I | complete removal including resection of underlying bone and associated dura | 9% |
| Grade II | complete removal + coagulation of dural attachment | 19% |
| Grade III | complete removal w/o resection of dura or coagulation | 29% |
| Grade IV | subtotal resection | 40% |
Radiation therapy may include Gamma Knife, proton beam treatment, or fractionated external beam radiation. Gamma Knife radiosurgery can be used in lieu of surgery in small tumors located away from critical structures.15 Fractionated external beam radiation can also be used as primary treatment for tumors that are surgically unresectable, or for patients who are inoperable for medical reasons.
Radiation therapy is often considered for WHO Grade I meningiomas after subtotal (incomplete) tumor resections. The clinical decision to irradiate after a subtotal resection is somewhat controversial as no class I randomized controlled trials exists on the subject.16 Numerous retrospective studies, however, have strongly suggested that the addition of post-operative radiation to incomplete resections improves both progression free survival (i.e. prevents tumor recurrence) and improves overall survival.17
In the case of a Grade II or Grade III meningioma, the current standard of care involves post-operative radiation treatment regardless of the degree of surgical resection.18 This is due to the proportionally higher rate of local recurrence for these higher grade tumors.
Current chemotherapies are likely not effective. Antiprogestin agents have been used, but with variable results.19 Recent evidence that hydroxyurea has the capacity to shrink unresectable or recurrent meningiomas is being further evaluated.20
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