NEURORADIOLOGY


Case 24 :
A 40-year-old female presents with recurrent headaches. No other positive history is elicited. Clinical examination is normal, with no positive neck signs or any focal neurological deficit. An MRI of the brain is requested.

Click here for bigger picture
Click here for bigger picture
Click here for bigger picture
Click here for bigger picture
Click here for bigger picture
Axial T2w.
Axial Flair
Coronal T2w
contrast.
Coronal contrast

__________SCROLL FOR ANSWER__________



Findings
MRI shows an extraaxial mass in the right middle cranial fossa, as evidenced by the CSF sleeve around the mixed intensity mass in the right middle cranial fossa, with vasogenic odema in the temporal lobe. Contrast shows homogenous enhancement with a dural tail that is suggestive of meningioma.

Discussion

Several criteria help to establish the extracerebral localization of the meningioma, and these criteria represent the key to the diagnosis. A broad, dural-based margin is strongly suggestive, but not definitive for this localization. Bony hyperostosis and/or invasion is highly specific for an extra-axial origin. However, it is infrequently present. Another highly specific characteristic for extra-axial localization is the identification of various anatomic interfaces interposed between the tumor surface and the brain surface. Three different anatomic interfaces may be identified with MRI. These consist of pial vascular structures, CSF clefts, and dural margins. With high-resolution and multiplanar MRI, one or more of these interfaces can usually be identified in essentially all cases. The interfaces are frequently not found along the full tumor-brain margin but in most instances are sufficient to make a highly reliable determination of extra-axial localization.

For those tumors located at the base of the brain or in the proximal portions of the sylvian and interhemispheric cisterns, displaced larger brain arteries are likely to be identified at the interface. Meningiomas tend to develop large marginal draining veins located at their brain surface interface. These veins are most likely the large marginal vascular structures seen with the more peripherally located meningiomas and at tumor-brain interface locations, where large arteries are not expected to be seen. CSF interfaces are also identifiable in about 80% of meningiomas on MRI. Vascular rims may be seen to lie within regions of the CSF clefts. In approximately two-thirds of the meningiomas, vascular rims and CSF clefts are both present at the brain-tumor interface. The dural margin interface is seen primarily in meningiomas of the cavernous sinus. It appears as a low-intensity rim on all imaging sequences covering the lateral margin of the tumor and separating it from the adjacent temporal lobe.

In comparison with CT, MRI is superior for extra-axial localization of the tumor. CT without and with contrast can define these interfaces in less than 50% of the cases in which they are identified on MRI. Contrast enhancement on MRI is almost always identifiable, even when meningiomas are densely calcified. Enhancement may either be central or ring-like. This enhancement relates to the fact that meningioma capillaries have no blood-brain barrier. Intravenous contrast is useful in demonstrating and defining the borders of symptomatic small lesions that compress or infiltrate around cortical neural structures such as the optic nerves and other cranial nerves, which may be occult on nonenhanced MRI. The anatomic boundaries of larger lesions that may be isointense to brain are clearly definable on T1-weighted enhanced scans. The most striking finding of contrast-enhanced MRI in meningiomas is the finding of dural enhancement adjacent to the lesion. En plaque meningiomas as well as globular convexity and basal meningiomas may infiltrate adjacent dural surfaces for several centimeters. Recognition of this infiltration can be of significant importance in surgical planning for complete tumor removal.


 

References

Bydder GM, Kingsley DPE, Brown J, Niendof HP, Young IR. MR imaging of meningioma including studies with and without Gadolinium DTPA. J. Compt Assist Tomog 1985; 9: 690-697.

Felix R, Svhorner W, Laniado M et al. Brain tumors: MR imaging with gadolinium DTPA. Radiology 1985:156:681-688

Berry I, Bront-zavadzki Osaki L, Brasch R Musovoic, Newton TH: Gd DTPA in clinical MR of the brain AJNR:1986:7: 789-798.

O'Moore PV, Goldberg HI, Gonatas N. Factors relating to meningioma brain odema AJNR 1983;4;1138

Spagnoli MV, Goldberg HI, Grossman RI, et al. Intracranial meningiomas: High field MR imaging Radiology 1986:161:369-375.

Dr. Ashok Raghavan, Manipal Hospital, Bangalore