Epidemiology and Location
Meningiomas comprise approximately 20% of adult intracranial tumors, have a female predominance, and occur most often during middle and older ages. They may be found in intracranial and intraspinal compartments. In the head, meningiomas are most commonly located in frontal, parasagittal, and parietal convexities (50% of cases). Less than 10% of tumors are infratentorial; multiple meningiomas occur less than 10% of the time. Clinical presentation is varied, depending on particular structures compressed by the mass. Headache and visual changes are frequently reported. A large number of patients with meningiomas are asymptomatic.
Origins, Growth, and Histology
The majority of meningiomas are histologically benign tumors, arising from the cap cells of the arachnoid layer. In many cases, serial imaging studies have revealed a cessation of growth after the time of initial tumor detection. These tumors project inward from the dura, and can cause clinically significant effects due to compression of surrounding neurological structures. A variety of classification systems based on cytology and histopathology are used with meningiomas. While the overwhelming majority of meningiomas are histologically benign, the malignant type may result in rapid, widespread infiltration with small (microscopic) "finger" projections into adjacent cortex. In patients with malignant meningiomas, marked deficits in physical and mental status may culminate in death.
Plain films may reveal hyperostosis, erosion, or calcification adjacent to tumor site. Noncontrast CT's of meningiomas often reveal sharply demarcated, rounded, homogenous masses with slightly increased density when compared to surrounding cortex. Up to 10% of meningiomas may appear isodense with respect to surrounding brain. CT may reveal focal cerebral atrophy, edema, or widening of subarachnoid spaces, direct effects of tumor compression of surrounding structures. Contrast enhanced CT most often reveals homogenous enhancement in approximately 85% of cases.
On MRI, T1 images are often hypo- or isointense; T2 images often reveal isointense or slightly hyperintense masses. Gadolinium increases signal intensity of meningiomas. A "dural tail" consisting of tissue tapering into the dura may be appreciated. Imaging studies may reveal extension of mass into cortical structures, or invasion of the calvarium. Angiography often reveals a homogenous, hypervascular pattern.
A variety of clinical and experimental treatment options exist, including surgery, radiotherapy, stereotactic radiosurgery, brachytherapy, chemotherapy, and hormonal therapy. Resection is the most widely utilized treatment option, although advanced age, concern about loss of neurological function due to surgery, advanced age, and being a poor surgical candidate preclude some from surgical options. Tumor embolization may be employed 3-5 days prior to surgery in an attempt to decrease blood supply to the meningioma. Recurrence of tumor is a possibility after resection. Complete removal of initial tumor and all affected bone results in recurrence rates of less than 10%.
Radiotherapy is often employed during the presurgical period. Likewise radiotherapy after incomplete resection of a meningioma may be of considerable benefit to patients. Stereotactic radiosurgery with a "gamma knife" has shown decrease in tumor size in approximately 50% of cases. Since this technology is relatively new, long term outcome of gamma knife therapy is not known. Brachytherapy with iodine-125 has been described in the literature; long term outcomes have yet to be determined. Medical treatment options include recommendations of anticonvulsant prophylaxis in patients with supratentorial masses; corticosteroids to reduce brain swelling may also be warranted. The use of traditional antineoplastic agents in treating meningiomas has not been met with great success. Hormonal manipulation may have a beneficial effect on stopping tumor growth; research this area continues.