mercoledì 19 luglio 2006

Atypical meningioma


CT without contrast demonstrates an extra-axial heterogeneous mass with solid and cystic components in the left frontal lobe adjacent to the falx. There is calcification along its medial attachment with the falx.
Figure 2: CT with contrast demonstrates homogeneous enhancement of the solid component of the left frontal lobe mass.
Figure 3: Axial T1-weighted MRI with gadolinium contrast demonstrates homogeneous enhancement of the solid peripheral component.
Figure 4: Sagittal T1-weighted MRI demonstrates a hypointense mass in the left frontal lobe. There is curvilinear increased signal intensity along the periphery of the mass, which represents calcifications as demonstrated on CT.

Diagnosis: Atypical meningioma

World Health Organization (WHO) Classification of Meningiomas
- Meningioma (typical benign)
- Atypical meningioma
- Anaplastic (malignant) meningioma

The peak incidence of atypical meningioma occurs in the fourth decade, whereas benign meningiomas show a peak incidence in the fifth decade. Men are affected equally as women with atypical meningioma. In contradistinction, women are affected more frequently with benign meningioma. The most common anatomical location of atypical meningioma is in the parasagittal region (43.7%), followed by the cerebral convexities (15.6%). The recurrence rate of atypical meningioma is 28% within two years, compared to 9.3% for benign meningioma. Atypical meningiomas represent an intermediate category of tumor that has a higher relative risk for recurrence.

Neuroradiologic features of meningiomas

The typical meningioma is a homogeneous, hemispheric, markedly enhancing extraaxial mass located over the cerebral convexity, in the parasagittal region, or arising from the sphenoid wing. However, typical meningiomas and several histologic variants of meningioma can have unusual or misleading radiologic features that may not be suggestive of meningioma. Unusual imaging features, such as large meningeal cysts, ring enhancement, and various metaplastic changes (including fatty transformation), can be particularly misleading. Because meningiomas are so common, the radiologist must be aware of their less frequent and uncharacteristic imaging features in order to suggest the correct diagnosis in atypical cases.

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