5.6.2  Natural History and Prognosis,

i.e., Signs, Symptoms, Timing, etc.

Patients with ONSM generally experience slowly progressive vision loss, which can result in complete blindness of the eye. Other visual complaints include diplopia, transient visual obscurations and gaze-evoked amaurosis [128]. Occasionally, patients may have headaches and proptosis. Visual field defects include central scotomas, enlarged blind spots, and generalized constriction. Fundus examination reveals an essentially abnormal optic nerve either atrophic or swelling, and 15–33% of patients may have optociliary collateral vessels (shunting blood from retina to choroidal circulation) (Fig. 5.15) [126, 129, 130]. The triad of optociliary veins, disc pallor, and visual loss should arouse suspicion of a perioptic meningioma. Rarely, neovascular glaucoma may ensure [131]. Patients with more posterior tumors may have a normal looking optic nerve without proptosis. Primary orbital meningiomas are more aggressive in children than in adults [132].

5.6.3  Pathophysiology

The tumor arises from meningothelial cells (cap cells) in the arachnoid villi. ONSMs grow circumferentially

a

around the optic nerve, impair axonal transport, and interfere with the pial blood supply to the nerve.

5.6.4  Incidence

Meningiomas arising from the intraorbital optic nerve sheath occur predominantly in middle-aged women (male:female ratio 1:2) and are almost always unilateral [133]. In NF-2 patients, the tumors occur bilaterally and are multifocal. It can occur at a younger age. Karp and associates [134] found that 40% of patients were under the age of 20 years.

5.6.5  Diagnosis and Diagnostic Aids

Neuroimaging is usually diagnostic. On CT, a “tram track sign” refers to two parallel lines along the length of the nerve (Fig. 5.16). Calcification may be identified in 20–50% of the cases [106, 130]. MRI is more reliable in determining the presence and extent of an ONSM (Fig. 5.17) [135, 136]. The tumor is isointense with the brain on T1and T2-weighted images and enhances homogeneously with gadolinium. It also demonstrates the details of the intracranial optic nerve, helps to identify intracranial extension of

b