FIG. 17.8. Optic sheath meningioma. This 45-year-old woman had decreasing vision in her left eye. Vvhen intracranial extension became apparent, operation was recommended. (A and B) MRI axial TI images (A and B) after gadolinium show the tumor involving the left optic nerve in the orbit, with intracranial extension (arrows). (C and D) MRI coronal TI images after gadolinium show encasement of the left optic nerve by the tumor (C) (arrow) and the intracranial extension (D) (arrow).

Contents

• Introduction to the therapy of Meningiomas (File 1)
• General Considerations in Management of Meningiomas (File 1)
  • Surgery of Meningiomas (File 1)
  • Radiation Therapy of Meningiomas (File 1)
  • Observation of Meningiomas (File 1)
• Summary of Dr. Ojemann's Meningioma Series (File 1)
  • OPTIC SHEATH MENINGIOMAS (This File)
    • Management (This File)
    • Results (This File)
• References (File 22)

OPTIC SHEATH MENINGIOMAS

(Meningioma Management, File 7)

Management

MRI clearly outlines the extent of the tumor (Fig. 17.8). Angiography is not needed. Decisions regarding treatment are difficult when the patient still has useful vision. Generally we have observed the patients with useful vision and also those with poor vision with the tumor confined to the orbit. The indications for surgery have been poor vision and intracranial extension or increasing orbital symptoms. Wiight et al. (78) have emphasized the more aggressive nature of these tumor in younger patients and have recommended an earlier surgical approach in that age group.

Since the prognosis for vision is so poor, radiation therapy has been used in a few patients in whom there is worsening but still useful vision (31, 45). The radiographic appearance is so characteristic that a tissue diagnosis is not needed.

The surgical approach is through a frontal-temporal craniotomy. The key considerations in the operation include:

1. Removal of bone in the roof of the orbit and over the optic canal.
2. Exposure of the tumor by retracting the levator and superior rectus muscles laterally.
3. Division of the optic nerve at the back of the globe.
4. Opening of the dura over the inferior frontal and anterior temporal region and division of the optic nerve as far forward as possible to avoid injury to fibers from the opposite side that may loop into the proximal nerve (Wilband's knee).
5. Removal of the tumor and optic nerve from the optic canal.
6. Division of the annulus of Zinn and after removal of the tumor, which may be densely adherent in this area, resutuiing of the annulus.
7. Closure without replacement of the orbital roof.

Results

Fifteen patients had operations for removal of an optic sheath meningioma usually because of intracranial extension (Table 17.6). There were 13 females and two males ranging in age from 16 to 65 years. All had poor or absent vision preoperatively. All made a good recovery. The intracranial tumor was completely removed in 14. Four patients had a small a,mount of tumor left growing into the back of the globe. One patient had a radical subtotal removal with a small piece of tumor left adherent to the internal carotid artery. There has been no recurrence.

Postoperatively every patient had ptosis and extraocular muscle paresis but this usually recovered within a few months. There was one complication of a cerebrospinal fluid leak from an ethmoid air cell. This was repaired by a transethmoid approach.

One patient, a 30-year-old man, had complete removal of an optic sheath meningioma. In less than a year a tumor in the other optic sheath developed with beginning visual loss. This has been treated with radiation therapy.

Good results following operation have been reported by others (8, 45, 61). In one report of 32 patients in whom it was thought total removal had been done, three tumors recurred and all were described as showing an infiltrative pattern of growth (17). Kennerdell et al. (31) reported that, of six patients treated with radiation therapy (5400-5500 cGy), five had improvement in visual acuity with follow-up ranging from 3 to 7 years.

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