OPTIC NERVE SHEATH MENINGIOMA
IntroductionAn optic nerve sheath meningioma arises either from the meningothelial cells of the arachnoid that are situated along the optic nerve sheath or from an extension of an intracranial meningioma into the orbit. As the tumor grows, it compresses the optic nerve. Painless loss of vision and proptosis are the cardinal clinical features of optic nerve sheath meningiomas.
The imaging diagnosis is primarily based on the CT and MR imaging findings. Optic nerve sheath meningioma is confined to the dura mater, and so it often appears as a well-defined, tubular thickening of the optic nerve. Optic nerve sheath meningiomas are commonly seen as a diffuse, tubular enlargement or as a localized, eccentric expansion of the optic nerve, often at the orbital apex. CT and MRI scans are best obtained both before and after infusion of contrast agent. Meningiomas often show homogeneous and well-defined contrast enhancement.
Observation, radiation, tumor excision, tumor and optic nerve excision can be the choice of treatment, but results of treatments are not so good. According to many researches, primary radiation treatment or radiation following surgical removal was associated with a better chance of visual improvement.
Case Report40 years old woman admitted to hospital with loss of vision on her right eye. After the examination clinicians decided to evaluate the patient with orbit MRI. MRI showed the lesion that surrounds the right optic nerve and extends through the intracranial compartment. Fat suppression T1 weighted axial images with contrast agent revealed the enhancing optic nerve sheath meningioma (Figure 1) and its extension to the apex of the orbit (Figure 2) and intracranial duramater (Figure 3).
Differential diagnosis includes optic glioma, optic neuritis and sarcoidosis. Meningiomas surround the optic nerve, and thus the caliber of the nerve itself is attenuated within the surrounding tumor. This is in contrast to optic nerve gliomas and optic neuritis, where the nerve itself appears expanded. This feature is best appreciated on MR imaging.
On MR images, meningiomas can be seen as a localized or fusiform enlargement of the optic nerve. Tumor may be eccentric. The tumor has an isointense signal to the optic nerve and brain tissue on most MR imaging pulse sequences. The T1- and T2-weighted MR images usually show no significant change in the intensity of meningiomas compared with that of the normal optic nerve or brain tissue (Figure 4-5-6). Compared with the brain, however, meningiomas may also be hypointense on T1-weighted and proton weighted images and hyperintense (Figure 7)or even hypointense on T2-weighted MR images.
Gadolinium-enhanced fat-suppression T1-weighted pulse sequences have made a significant contribution to the imaging evaluation of optic nerve sheath meningiomas as well as disorders of the optic nerve. Images obtained following intravenous injection of the gadolinium-DTPA disclose marked or moderate contrast enhancement of meningiomas (Figure 8-9).
In conclusion, enhanced fat suppression T1-weighted MR images are most valuable for defining an enhancing optic nerve sheath meningioma or other optic nerve pathology. En plaque meningiomas of the optic nerve where the tumor, spread along the optic nerve sheath as a thin of tumor, can often only be diagnosed on enhanced fat suppression T1-weighted MR images.
References1) Mafee MF: Case 25: Optic nerve sheath meningioma. In Siegel BA, Proto AV (eds): Head and Neck Disorders (Fourth Series) Test and Syllabus. Reston, VA, American College of Radiology, 1992, p 553
2) Ortiz O, Schochet SS, Kotzan JM, Kostick D: Radiologic-pathologic correlation: Meningioma of the optic nerve sheath. AJNR Am J Neuroradiol 17:901, 1996.
3) Mafee MF, Goodwin J, Dorodi S. Optic nerve sheath meningioma. Role of MR imaging. Radiol Clin North Am. 1999 Jan; 37(1): 37-58, ix. Review.
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