Meningiomas are the most commonly diagnosed primary brain tumors, accounting for approximately 33%1. In most cases, these are benign tumors that arise from the dura mater. The main known risk factors for the development of meningiomas are ionizing radiation and mutations in the NF2 gene2. Meningiomas can occur supratentorially, infratentorially, and spinally. Meningiomas are classified according to the WHO classification3.
WHO Classification of Meningiomas
| WHO Grade | Meningioma type |
|---|---|
| WHO Grade I | meningothelial <br /> fibrous (fibroblastic) <br /> transitional (mixed) <br /> psammomatous <br /> angiomatous <br /> microcystic <br /> secretory <br /> lymphocyte-rich <br /> metaplastic <br /> |
| WHO Grade II | chordoid <br /> clear cell <br /> atypical |
| WHO Grade III | papillary <br /> rhabdoid <br /> anaplastic |
The proliferation rate and recurrence rate of meningiomas also differ depending on the WHO grade4:
| WHO Grade | Average proliferation index (Ki-67 index) | Recurrence rate |
|---|---|---|
| Conventional meningioma (WHO Grade I) | 0.7% | 9% |
| Atypical meningioma (WHO Grade II) | 2.1% | 29% |
| Anaplastic meningioma (WHO Grade III) | 11% | 50% |
Diagnosis
Meningiomas are generally very slow-growing tumors and, at the time of diagnosis, have usually already been present for several years or months. The symptoms of meningiomas can vary widely; however, meningiomas most commonly become symptomatic through headaches (approximately 70%), personality changes (approximately 42%), paresis (37%), or an epileptic seizure (approximately 36%)5. MRI is the gold standard in the imaging diagnosis of meningiomas. In meningiomas with osseous involvement, supplementary CT imaging before surgery is useful. Meningiomas are also frequently found as incidental findings during cranial imaging in patients. Preexisting calcification within the meningioma is often associated with absent meningioma growth6.
Location
Meningiomas can theoretically arise anywhere along the dura mater and may occur both cranially and spinally. The surgical difficulty of removal varies depending on the location and size of a meningioma.
Conservative Treatment
Observation
Meningiomas are frequently identified as small incidental findings during cranial imaging; these meningiomas are often very small and do not cause symptoms in patients. Depending on the location and size of the suspected meningioma, a completely observational approach may also be considered, with follow-up MRI to monitor growth.
Radiotherapy
For small meningiomas that are surgically difficult to access, such as those infiltrating a sinus, a conservative treatment approach using radiotherapy may also be considered. Radiotherapy also plays an important role in the postoperative treatment of incompletely resected meningiomas if complete removal is not possible. In some cases, a combination of surgery and radiation is the best solution for the patient.
Indication for Surgery
Surgical removal should be considered for meningiomas that are symptomatic or demonstrate progressive growth. The decision to operate depends on many different factors, such as the patient's age, the size of the meningioma, its growth rate, and its location.
Surgery
In meningiomas with pronounced vasogenic edema, preoperative reduction of the edema can be induced through medical treatment with dexamethasone or mannitol.
The surgical approach depends on the location of the meningioma. If there is osseous infiltration by the meningioma, the affected portion of bone can be removed and replaced with Palacos. In highly vascularized meningiomas, preoperative embolization of the tumor-feeding vessels may be considered to minimize the risk of intraoperative bleeding and reduce operative time. The postoperative extent of resection is reported according to the Simpson classification.
Surgical Risks
The risk of intraoperative and postoperative complications increases with the patient's age, the complexity of the surgical procedure, and the duration of the operation7 8 The following complications may occur relatively frequently during meningioma surgery:
- Edema: There is a risk that edema may develop intraoperatively or postoperatively in the brain parenchyma adjacent to the surgical site.
- Epileptic seizures: Meningioma surgery carries a risk of both intraoperative and postoperative epileptic seizures, which may necessitate continued antiepileptic medication.
- Bleeding: There is a risk of intraoperative or postoperative hemorrhage at the surgical site; depending on the severity of the bleeding, this may lead to revision surgery.
- Thrombosis: The risk of a postoperative thromboembolic event is significantly higher with meningiomas than with other cranial procedures and is approximately 3% during the first 4 weeks after surgery9.
References
Wiemels J, Wrensch M, Claus EB. Epidemiology and etiology of meningioma. J Neurooncol. September 2010:307-314. ↩ ↩
Book: Neurosurgical Knowledge Update - A comprehensive review. Robert E. Harbaugh et al. Thieme Verlag. ↩ ↩ ↩ ↩
Kolles H, Niedermayer I, Schmitt C, et al. Triple approach for diagnosis and grading of meningiomas: histology, morphometry of Ki-67/Feulgen stainings, and cytogenetics. Acta Neurochir (Wien). 1995;137:174-181. ↩ ↩
Rockhill J, Mrugala M, Chamberlain MC. Intracranial meningiomas: an overview of diagnosis and treatment. FOC. October 2007:E1. ↩ ↩
Sughrue ME, Rutkowski MJ, Shangari G, et al. Risk factors for the development of serious medical complications after resection of meningiomas. JNS. March 2011:697-704. ↩ ↩
Boviatsis EJ, Bouras TI, Kouyialis AT, Themistocleous MS, Sakas DE. Impact of age on complications and outcome in meningioma surgery. Surgical Neurology. October 2007:407-411. ↩ ↩
Levi ADO, Wallace CM, Bernstein M, Walters BC. Venous Thromboembolism after Brain Tumor Surgery: A Retrospective Review. Neurosurgery. June 1991:859-863 ↩ ↩