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Pathophysiology and Pathogenesis. Many classification schemes are used for meningiomas, usually based on the histological appearance (see Ta.ble,,46-6. ). Meningiomas have a firm off-white appearance, and because they are extra-axial, they are usually well demarcated from the surrounding brain. Microscopically, they display a characteristic


Histological Label



Narrow, long cells in sheets; less commonly,

whorls, psammoma bodies


Meningothelial cells, whorls, psammoma



Features of both syneytial and fibroblastic


Intertwined, complex, thickened blood

vessels, reticulin background, seldom

contain whorls, psammoma bodies

whorled pattern with calcifications (psammoma bodies). Discussion abounds about the classifications and subtypes and the histological characteristics of these tumors and their clinical course. For example, proposed papillary and clear cell forms appear to be found more commonly in younger people and children and seem to behave more aggressively. Various cell labeling tests and analysis of estrogen and progesterone receptor concentrations have been proposed to predict biological growth. However, the pathological features of brain invasion and mitotic activity are the most important pathological determinants of aggressive behavior. Hemangiopericytomas are highly vascular tumors that are seen equally often in usually younger men and women. Histologically similar tumors can be found in non-CNS regions. They are more prone to malignant behavior.

Epidemiology and Risk Factors. Meningiomas are extra-axial tumors that arise from dural elements within the cranial and spinal spaces. Although considered benign, they can enlarge and cause compression of neural elements and can behave aggressively, invading the bone or brain and threatening life. They comprise about 15 percent of all intracranial tumors and increase in incidence with age. Meningiomas have estrogen and progesterone receptors, possibly explaining why they occur in women almost a third more often than in men. Because of these receptors, meningiomas show increased growth during pregnancy. Further, meningiomas in the spine are almost always found in women. However, in blacks, men are more often affected. Several risk factors have been proposed for their occurrence, including trauma, infections, electrical exposure, and exposure to radiotherapy. Meningiomas are common in patients with neurofibromatosis II, in whom multiple tumors are commonly found.

Clinical Features and Associated Findings. Meningiomas can arise in virtually any location in the central nervous system, although certain locations predominate ( Ia.bIe.46-7 ). Patients can present with epilepsy or subtle symptoms such as progressive headache, memory loss, or cognitive changes, which occur over an extended period of time. Slow progressive dementia or chronic depression in an older patient are also common presentations. Location of the tumor along the motor strip may present, possibly suddenly, with hemiparesis. Sagittal tumors along the falx may cause the development of bilateral leg weakness. Sphenoid area tumors may cause ophthalmological or cavernous sinus symptoms, and olfactory groove meningiomas



Presenting Manifestation


Urinary incontinence, dementia, gradual paraparesis, seizures

Lateral convexity

Variable depending on structures compressed, including slow hemiparesis, speech abnormalities

Olfactory groove

Anosmia, visual disturbance, dementia, Foster-Kennedy syndrome


Hormonal failure, bitemporal hemianopia, optic atrophy

Sphenoid ridge

Extraocular nerve paresis, exostoses, proptosis, seizures

Figure 46-9 MRI picture of a posterior fossa meningioma, demonstrating an extra-axial, homogeneously contrast-enhancing mass arising from the tentorium and compressing the cerebellar hemisphere.

may lead to anosmia. Because these tumors grow slowly, they may be identified incidentally in asymptomatic patients. Although hydrocephalus is extremely rare, children are more likely to present with symptoms of this entity.

Differential Diagnosis. Meningiomas are often "diagnosed" from neuroradiological scans. The typical features and location do offer a reasonable amount of certainty in this diagnosis, yet clinicians must always be vigilant for unexpected possibilities. The ability to characterize these tumors radiographically still does not allow differentiation of a benign from a malignant meningioma. Malignant forms are more commonly seen in men, and unexpected metastatic deposits may be discovered. Suprasellar lesions may be confused with pituitary adenoma or craniopharyngioma. Extremely vascular lesions may be hemangiopericytomas.

Evaluation. MRI with gadolinium remains the diagnostic method of choice. Contrast agents demonstrate significant homogeneous enhancement ( . Fig.;. 46:9 ) and may highlight a dural "tail." CT may complement MRI findings and should include bone windows to show evidence of hyperostosis, calcifications within the tumor, and bone invasion. MRI angiography or routine angiography may reveal a tumor blush and can help with presurgical planning. In elderly patients preoperative and postoperative neuropsychological testing can be performed to evaluate patient response to and recovery from surgical resection.

Management. Meningiomas can be cured surgically. The location and size of the tumor and its involvement with close vital structures partially determine the extent of resection that is feasible. For example, sphenoid ridge meningiomas are rarely fully removed. The main decision is whether surgery is required. In patients in whom the

tumor is an incidental finding or who are poor surgical risks, observation with serial scanning may be appropriate. y In those with large meningiomas, angiography and embolization are frequently used to aid in surgical removal. Extremely vascular lesions may be hemangiopericytomas. Following surgery, whether complete or near-complete, patients should be observed with serial MRI or CT scans for evidence of regrowth. Recurrence is related to extent of resection and location because the site of resection may preclude complete removal. Radiotherapy can be given for relapse following a second surgery or for anaplastic meningiomas. y Stereotactic radiotherapy and brachytherapy are under evaluation, but the early results appear promising, although observation times have been short. Patients must be watched closely for evidence of cognitive decline from these intensive radiation doses. Chemotherapy with cytotoxic agents has met with limited success. Because meningiomas do possess estrogen and progesterone receptors, endocrine manipulation of the tumor residua with hormonal or biological agents such as tamoxifen, beta-interferon, or RU-486 is under study and at this point remains investigational.

Prognosis and Future Perspectives. As the population continues to age, the frequency of meningiomas can only increase. Histological variations and groups must be standardized to allow more timely and thorough evaluation of therapeutic treatments designed for a homogeneous population of tumors. Because meningiomas are amenable to resection but can remain to invade and disrupt vital neurological structures, future work must include detailed studies of their nonsurgical management, in relation to both timing and type of therapy. Attempts to predict biological behavior through histological and cell kinetic studies can help in management by identifying which patients are at increased risk of tumor regrowth and which have the potential to respond to medical management.


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