Meningiomas (Continued)

Because the majority of meningiomas are very slowly growing, the brain has time to adapt to the enlarging mass. Thus tumors in the frontal or occipital lobe can become quite large before the tenuous pressure relationships decompensate, resulting in symptomatic presentation. Those tumors arising in the frontal lobe may present with cognitive or personality changes or other mental status changes.

Diagnostic Studies. Both magnetic resonance imaging (MRI) and computed tomography (CT) can be used to diagnose meningiomas, although MRI is the preferred imaging modality. Typically, meningiomas are isointense to hypointense on T1 and isointense to hyperintense on T2, with strong homogeneous enhancement. Often, there is a characteristic “dural tail,” the marginal dural thickening that tapers at the periphery. On CT, the meningioma appears as a wellcircumscribed extra-axial mass that is sometimes calcified. Similar to the MRI, homogenous enhancement is seen when intravenous contrast is administered. Occasionally, areas of necrosis, cyst formation, or hemorrhage are seen. CT is also helpful to evaluate for bony involvement. Although bony involvement from cerebral convexity tumors is rare, almost 50% of skull base tumors will have secondary involvement of the bone.

Treatment. With the availability of imaging modalities, such as MRI and CT, meningiomas are often asymptomatic incidental findings. Frequently, these tumors are unchanging or slow growing. It is reasonable to follow these patients conservatively with active surveillance, withholding treatment until the tumor becomes symptomatic or increases in size significantly. This is especially true for elderly patients (older than 70 years) or those with multiple surgical comorbidities.

The threshold for surgical intervention in younger patients is lower because morbidity is less than in older patients and because it is assumed that these lesions will eventually progress. Thus surgical intervention may be recommended for lesions in surgically accessible locations even if they are asymptomatic. In patients with symptomatic lesions or asymptomatic tumors that appear to be infiltrative or associated with vasogenic edema, surgical resection is recommended. Complete surgical resection is potentially curative, and the extent of resection correlates with prognosis. Advances in neurosurgery, such as microsurgery, intraoperative imaging, and the widespread use of MRIs have improved a surgeon’s ability to successfully resect these lesions while minimizing injury to surrounding normal tissue.

In some cases, only a subtotal resection can be achieved. In these cases, adjuvant radiotherapy should be considered because retrospective studies have reported improved progression free survival, although not overall survival. Radiotherapy alone can be effective for those lesions that are surgically inaccessible with local control rates of greater than 90% in 5 years. For WHO grade II tumors, the frequency of recurrence is increased. Despite the lack of large prospective trials, adjuvant radiotherapy is recommended for incompletely resected tumors. The role of radiotherapy for after complete resection is controversial. Grade III tumors invariably require irradiation.

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