Meningiomas are benign, slow-growing intracranial extracerebral tumours, which account for 15–20 per cent of all intracranial tumours. Only 25 per cent of meningiomas are symptomatic at presentation and the frequency of meningiomas increases with age (Radhakishnan et al. 1995).
From large autopsy series, meningiomas are estimated to comprise between 13 and 26% of primary brain tumors and have an annual incidence of approximately 6 per 100,000 persons. Meningiomas usually occur in adults, with a peak occurrence during the sixth and seventh decades of life. Women are affected more frequently than men, with a female-tomale ratio as high as 2:1.
Risk factors include:
- gender (women are more commonly affected, female : male ratio 2.2 : 1),
- previous ionizing radiation,
- type 2 neurofibromatosis.
One can also differentiate low-grade or typical from atypical meningiomas (WHO grade II), which constitute 4.7–7.2% of meningiomas, while the anaplastic or malignant meningiomas (WHO grade III) account for 1.0–2.8% of meningioma cases. These higher-grade meningiomas may show a conspicuous predominance in males. Malignant behavior, including brain or bony invasion, may occur with any grade of meningioma. Multiple meningiomas are often associated with neurofibromatosis type 2 (NF2) and in subjects from other, non-NF2 families with a hereditary predisposition to meningioma.
Imaging and Location
Meningioma is a mass that has clear and even contours, a broad base adjacent to the dura mater. The structure of education is more often homogeneous, it has a mass effect. On MRI, the meningioma of T2 can →, ↓ and ↑ (depending on the content of calcium salts and the presence of cysts), according to T1 most often →. CT can be →, but more often ↑. The dimensions of the meningiomas range from small, hardly noticeable, to giant, with their mass effect causing significant dislocation of brain structures.
18% of meningiomas are supratentorial. Most meningiomas arise within the intracranial, orbital, and intravertebral cavities. Spinal meningiomas are most common in the thoracic region; atypical and anaplastic meningiomas are more common in the falx cerebri and the lateral convexities.
The most common sites:
- convexities of the skull,
- falx or tentorium,
- followed by the sphenoid ridge,
- suprasellar areas, and
- olfactory groove.
The orbits and the optic nerve are also common locations (Mafee et al. 1999). The tumors may arise from the optic nerve sheath directly or may extend into the orbits from the sellar region
On imaging studies, meningiomas are usually broad based and attached to the adjacent dura. In some cases, if the tumor originates from pial meningeal cells, no dural attachment may be visible. This is also the case with intraventricular meningiomas that arise from the choroid plexus cells (Majos et al. 1999). The main differential diagnosis for the intraventricular localizaas a nodular, heterogeneous mass in contrast to the smooth margin and oval configuration of meningioma.
Calcification is common, and tumoral bleeding is rare. A typical finding is also the hyperostosis of the adjacent calvarium, which is commonly seen in lesions adjacent to the bone. A penetration of the bone into the subcutaneous region was also reported. The degree of bone thickening is not related to the histological subtype or malignancy of the tumor; however, the bone is usually invaded by tumor cells. In some cases, e.g., en plaque meningiomas, the bony reaction far exceeds the volume of the tumor itself. En plaque meningiomas consist of a thin layer of neoplasm that closely follows the contour of the inner table (Chabel et al. 1999). They present themselves as flat lesions with no or only minor mass effect.
On MRI most meningiomas, in some series more than 85%, present with heterogeneous signal characteristics, both on T1- and T2-weighted sequences (Zimmerman et al. 1985; Spagnoli et al. 1986; Elster et al. 1989). This heterogeneity is related to the variety of histological subtypes of meningiomas, their vascularity, percentage of calcification, and cystic and fatty components. In general, the T1 signal is more hypointense and the T2 signal more hyperintense. Edema is a common finding in high-grade gliomas; however, it may also be present in large lesions with benign histology.
The contrast enhancement pattern is pronounced and homogeneous in most cases, even those that present with a large amount of calcifications. The enhancement can be central or ring-shaped and is more intense shortly after contrast media application, which reflects the high rate of vascularity and the fact that the meningioma capillaries have no BBB. The contrast enhanced scans allow a more precise definition of the tumoral boundaries and better detection of small meningiomas.
The most typical finding is the so-called dural tail, a dural enhancement adjacent to the lesion (Fig. 3.3.34). This enhancement may or may not be associated with a dural thickening. Dural enhancement may also be present in other diseases, e.g., metastases or invasive brain tumors, but the dural tail sign is a very important diagnostic feature for the diagnosis of a meningeal tumor.
In large series, most meningiomas present such an enhancement, but it does not automatically represent dural invasion by the tumor. Investigations have found: - neoplastic invasion and - reactive vascular changes.
Treatment and prognosis
In symptomatic meningiomas with brain oedema, dexamethasone (2–4 mg three times a day) will usually produce speedy relief of symptoms. Although meningiomas are benign tumours, operation is not always straightforward.
Asymptomatic meningiomas, especially in the elderly, are best left alone. Large, symptomatic meningiomas will usually require surgery. Surgical mortality can be as high as 14 per cent and the 10-year survival can range from 43 to 77 per cent. Convexity, parasagittal, lateral sphenoid, and olfactory groove meningiomas can usually be resected completely with low morbidity. Suprasellar, cavernous sinus, clivus, tentorial, and posterior fossa meningiomas are more difficult, although improved surgical techniques have resulted in more radical resection. Morbidity is much higher in these areas and there can be a high recurrence rate.
In symptomatic meningiomas in the elderly, or at sites that increase operative risk, stereotactic radiation therapy or radiosurgery, as sole treatment, may reduce the size of the tumour or slow the growth rate. Radiosurgery is usually only considered for relatively small tumours (<3 cm in diameter) that do not impinge on structures such as the pituitary/optic nerves or abut the ventricles or where operation would be hazardous.
Antiprogesterones have been used with some apparent success in some patients with meningioma (Black 1993). Anti-oestrogens such as tamoxifen (40 mg/m2 twice daily for 4 days followed by 10 mg twice daily) may produce a reduction in size of the tumour in 15 per cent of patients (Goodwin et al. 1995).
The author of the article: radiologist, Ph.D. Vlasov Evgeniy Alexandrovich
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