Meningioma

Meningiomas are invasive tumors that arise from the arachnoid villi. Orbital meningiomas usually originate intracranially along the sphenoid wing, with secondary extension through the bone into the orbit (Fig 5-11), the superior orbital fissure, or the optic canal; or they may arise primarily in the orbital portion of the optic nerve sheath. Ophthalmic manifestations are related to the location of the primary tumor. Meningiomas arising near the sella and optic nerve cause early visual field defects and optic nerve edema or optic atrophy. Tumors arising near the pterion (the posterior end of the parietosphenoid fissure, at the lateral portion of the sphenoid bone) often produce a mass in the temporal fossa and may be associated with proptosis or nonaxial displacement of the globe (see Fig 5-11A, B). Eyelid edema (especially of the lower eyelid) and chemosis are common. Interestingly, although primary optic nerve sheath meningiomas can, in rare cases, produce axial proptosis with preserved vision, depending on their anatomic location, some meningiomas can cause early profound vision loss without any proptosis.

Figure 5-11 Sphenoid wing meningioma. A, External photograph shows right temporal fullness (arrow). B, Worm’s eye view shows right proptosis. CT (C) and MRI (D) show hyperostosis of the sphenoid bone (arrow) from the associated meningioma (arrow).

(Courtesy of Bobby S. Korn, MD, PhD.)

Sphenoid wing meningiomas produce hyperostosis of the involved bone (see Fig 5-11C) and hyperplasia of associated soft tissues. Contrast-enhanced MRI helps define the extent of meningiomas along the dura (see Fig 5-11D). The presence of a dural tail (reactive thickening of the dura adjacent to the meningioma) helps distinguish a meningioma from fibrous dysplasia.

Primary orbital meningiomas usually originate in the arachnoid of the optic nerve sheath. They occur most commonly in women in their third or fourth decade of life. Symptoms usually include a gradual, painless, unilateral loss of vision. Examination typically shows decreased vision and a relative afferent pupillary defect. Proptosis and ophthalmoplegia may also be present. The optic nerve head may appear normal, atrophic, or swollen; and tortuous vessels may be visible (Fig 5-12A, B). Occasionally, optic nerve sheath meningiomas are present bilaterally, or meningiomas occur ectopically in the orbit; these are associated with neurofibromatosis.

Figure 5-12 Optic nerve sheath meningioma. A, Swollen right optic nerve with tortuous arteries and dilated veins. B, Normal left optic nerve. Coronal (C) and axial (D) T1-weighted, gadoliniumenhanced MRI scans show optic nerve sheath meningioma. Note enlargement of the optic nerve sheath.

(Courtesy of Wayne Cornblath, MD.)

Optic nerve sheath meningiomas can usually be diagnosed by means of imaging characteristics. Both CT and MRI show diffuse tubular enlargement of the optic nerve with contrast enhancement (Fig 5-12C, D). In some cases, CT can show calcification within the meningioma, referred to as tram-tracking. MRI reveals a fine pattern of enhancing striations emanating from the lesion in a longitudinal fashion. These striations represent the infiltrative nature of what otherwise appears to be an encapsulated lesion. As with sphenoid wing meningiomas, dural extension through the optic canal into the intracranial space can be seen on MRI.

Malignant meningioma is rare and results in rapid tumor growth that is not responsive to surgical resection, radiotherapy, or chemotherapy. On histologic examination, malignant meningiomas are indistinguishable from the more common benign group.