Risk of injury to cranial nerves after gamma knife radiosurgery for skull base meningiomas: experience in 88 patients

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Object. In this study the authors sought to determine the neurological risks and potential clinical benefits of gamma knife radiosurgery for skull base meningiomas.

Methods. A consecutive series of 88 patients harboring skull base meningiomas were treated between 1990 and 1996 by using the Leksell gamma knife in a prospective clinical study that included a strict dose—volume protocol. Forty-nine patients had previously undergone surgery, and six had received external-beam radiotherapy. The median treatment volume was 10 cm3, and the median dose to the tumor margin was 16 Gy. The radiosurgical dosage to the optic nerve, the cavernous sinus, and Meckel's cave was calculated and correlated with clinical outcome. The median patient follow-up time was 35 months (range 12–83 months).

Two tumors (2.3%) progressed after radiosurgery; the progression-free 5-year survival rate was 95%. At last follow-up review, 60 (68%) tumors were smaller and 26 (29.5%) remained unchanged. Clinical improvement (in vision, trigeminal pain, or other cranial nerve symptoms) occurred in 15 patients. Functioning optic nerves received a median dose of 10 Gy (range 1–16 Gy), and no treatment-induced visual loss occurred. Among nine patients with new trigeminal neuropathy, six received doses of more than 19 Gy to Meckel's cave.

Conclusions. Gamma knife radiosurgery appeared to be an effective method to control the growth of most skull base meningiomas in this intermediate-term study. The risk of trigeminal neuropathy seemed to be associated with doses of more than 19 Gy, and the optic apparatus appeared to tolerate doses greater than 10 Gy. Considering the risks to cranial nerves associated with open surgery for comparable tumors, the authors believe that gamma knife radiosurgery is a useful method for the management of properly selected recurrent, residual, or newly diagnosed skull base meningiomas.

Article Information

Address reprint requests to: Robert J. Coffey, M.D., 1333A North Avenue, New Rochelle, New York 10804. email: robert@elekta.com.

© AANS, except where prohibited by US copyright law.



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    Coronal and axial MR images illustrating the dosimetry-evaluation method for the optic apparatus (optic nerve, chiasm, optic tract), cavernous sinus, and Meckel's cave using the KULA program in one of our early cases. This cavernous sinus meningioma received a maximum dose of 30 Gy. Left: The left optic chiasm received at least 10.5 Gy (35% of maximum dose) for half of its cross sectional area. Right: The cavernous sinus received 18 Gy (60% of the maximum dose), and Meckel's cave received 21 Gy (70% of the maximum dose).

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    Kaplan—Meier plot showing the estimated actuarial progression-free survival of patients with skull base meningiomas after gamma knife radiosurgery.

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    Axial and coronal MR images illustrating a cavernous sinus—petroclival tumor that was treated with a maximum radiation dose of 32 Gy. Left: The treatment-planning MR image showing that the tumor margin was covered by the 50% isodose line (16 Gy). Center: Coronal MR image showing that the 30% isodose line (9.6 Gy) covered the right optic nerve. Right: Follow-up MR image obtained 46 months after radiosurgery, showing a significant decrease (by > 25%) of the tumor mass. No optic neuropathy developed.

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    Coronal MR images depicting a cavernous sinus—petroclival meningioma that had progressed at 67 months after radiosurgery. Left: The treatment planning coronal MR image depicts a shaded area that was found in retrospect not to have received the intended 16-Gy margin dose. Center: The MR image obtained 2 years after radiosurgery showing significant early shrinkage of the tumor. Right: The MR image obtained 67 months after treatment showed that the shaded area shown on the left had grown significantly.



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