Background
In 1614, Felix Plater first described meningiomas at an autopsy. In 1938, Harvey Cushing introduced them as a separate category of extraparenchymal tumors. [1] Meningiomas are believed to arise from arachnoid cap cells, and they usually are attached to the dura. These tumors may arise from any location where meninges exist (eg, nasal cavity, paranasal sinuses, middle ear, mediastinum).
In children, the more common locations of meningiomas include the orbit, the temporal region, the foramen magnum, the tentorial region, the subfrontal base, the sellar region, and the ethmoidal air sinus. Such locations for meningiomas are rare in adults. Histologically, the meningothelial type is seen most frequently. As compared to adults, the tumors in children tend to be more aggressive in terms of growth rate, tumor size, propensity to undergo malignant changes, and recurrence rate.
Pathophysiology
The term optic nerve sheath meningioma (ONSM) does not indicate a definite site of origin. ONSM may be either primary or secondary. Primary ONSMs arise from the cap cells of the arachnoid surrounding the intraorbital or, less frequently, the intracanalicular optic nerve. Secondary ONSM are extensions of intracranial meningioma into the orbit. Secondary ONSMs are much more common than primary ONSMs, but the unqualified term "optic nerve sheath meningioma" ordinarily refers to primary ONSM.
Another rare group of meningiomas consists of tumors that arise from ectopic arachnoid cells within the orbital cavity, either in the muscle cone or in the walls of the orbit. These ectopic, extradural meningiomas do not appear to have a connection to the optic nerve sheath or the optic canal and do not appear to originate intracranially. They probably arise from congenitally displaced nests of meningothelial cells along the orbital wall or within the muscle cone.
Epidemiology
Frequency
United States
The frequency of meningiomas has been the topic of relatively few reports. Hospital-based brain tumor series indicate that the incidence is approximately 20% of all intracranial tumors; population-based studies indicate an overall incidence of 2.3 cases per 100,000.
International
Meningiomas account for approximately 13-19% of all intracranial tumors.
Mortality/Morbidity
In one series by Coke et al, the overall survival rate for all patients at 5 years and 10 years were 87% and 58%, respectively. [2]
Race
Variability has been shown in the prevalence of meningiomas among Caucasians, Africans, African Americans, and Asians. A greater incidence among Africans than among Caucasians exists.
Sex
Although intracranial tumors as a whole show a higher prevalence in males than in females, meningiomas have a 2:1 female-to-male ratio in Caucasians.
In one series of 517 patients with meningiomas at Brigham and Women's Hospital, the female-to-male ratio was 24:1.
In children, the male-to-female ratio is 2:1, with an average age at presentation of 10.1 years (range, 1-16 y).
In Africans, an equal gender ratio is evident.
Age
The incidence of meningiomas increases with age, 2-7 cases per 100,000 in women and 1-5 cases per 100,000 in men. Peak incidence is in the seventh decade in women and in the eighth decade in men. [3, 4]
Meningiomas rarely occur in infants.
Meningiomas rarely occur in children [4] and differ from those in adults and other childhood tumors. Incidence in children is estimated to be approximately 2%. In one retrospective series at the King Faisal Hospital from 1980-1993 that included a total of 318 patients with meningiomas, only 2.8% of patients were children aged 16 years or younger. Meningiomas made up only 2.2% of all CNS tumors seen in children.
In one series by Sheikh et al, the mean age of juvenile cases was 8 years and the mean age for adults was 50 years. [5] Mean ages reported in other series range from 31.7-43 years. The male-to-female ratio is 27:29, adding together all series. Neurofibromatosis occurs in 4.2-16% of cases.
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Meningioma of the orbit. Axial sequence on T1-weighted MRI with gadolinium that shows enhancing lesion of the orbit causing proptosis and en plaque invagination laterally around the temporal pole and medially above the ethmoid sinus.
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Meningioma of the optic nerve sheath. Coronal section of T1-weighted MRI of the orbits that shows a left orbital mass lesion occupying most of the orbital lumen, diffusely enhancing with gadolinium.
