Gamma surgery for vestibular schwannoma

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Object. The goal of this study was to assess the results of gamma surgery (GS) for vestibular schwannoma (VS) in 200 cases treated over the last 10 years and to review the role of this neurosurgical procedure in the management of VS.

Methods. Follow-up reviews ranging from 1 to 10 years were available in 153 of these patients. Follow-up images in these cases were analyzed using computer software that we developed to obtain volume measurements for the tumors, and the clinical condition of the patients was assessed using questionnaires.

Gamma surgery was the primary treatment modality in 96 cases and followed microsurgery in 57 cases. Tumors ranged in volume from 0.02 to 18.3 cm3. In the group in which GS was the primary treatment, a decrease in volume was observed in 78 cases (81%), no change in 12 (12%), and an increase in volume in six cases (6%). The decrease was more than 75% in seven cases. In the group treated following microsurgery, a decrease in volume was observed in 37 cases (65%), no change in 14 (25%), and an increase in volume in six (11%). The decrease was more than 75% in eight cases. Five patients experienced trigeminal dysfunction; in three cases this was transient and in the other two it was persistent, although there has been improvement. Three patients had facial paresis (in one case this was transient, lasting 6 weeks; in one case there was 80% recovery at 18 months posttreatment; and in one case surgery was performed after the onset of facial paresis for presumed increase in tumor size). Over a 6-year period, hearing deteriorated in 60% of the patients. Three patients showed an improvement in hearing. No hearing deterioration was observed during the first 2 years of follow-up review.

Conclusions. Gamma surgery should be used to treat postoperative residual tumors as well as tumors in patients with medical conditions that preclude surgery. Microsurgery should be performed whenever a surgeon is confident of extirpating the tumor with a risk—benefit ratio superior to that presented in this study.

Article Information

Address reprint requests to: Dheerendra Prasad, M.D., Lars Leksell Center for Gamma Surgery, Primary Care Building, Room G512 (Box 800742, HSC), Lee Street, Charlottesville, Virginia 22908. email: dprasad@virginia.edu.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Histogram depicting age distribution of patients included in this study.

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    Bar graph demonstrating the response to GS over time. All 153 patients were separated into three outcome classes (decreased, unchanged, and increased tumor size) at progressive posttreatment intervals. Note that increase in tumor size may appear as late as 6 years post-GS, emphasizing the need for long follow-up review.

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    Magnetic resonance images demonstrating the response of VS to GS. This 84-year-old woman presented with a 6-year history of hearing loss. She was treated for a 3.4-cm3 tumor located in the left cerebellopontine angle (A) with a dose to the periphery of 10 Gy. The tumor started to decrease in size 12 months after treatment and is shown 5 years post-GS (B), although it had already reached this volume (0.2 cm3) at 24 months. The patient is in good health with no new neurological deficits.

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    Magnetic resonance images demonstrating the results of GS in a patient with a moderately sized VS. This 71-year-old physician underwent GS electively despite receiving intensive counseling that he undergo microsurgery. The tumor (A), measuring 6.2 cm3, was treated with 14.5 Gy to the periphery. Two years post-GS (B) the tumor is 48% smaller (3.2 cm3). The patient has no new symptoms.

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    Magnetic resonance images obtained during long-term follow up in the case of a large VS. This 63-year-old patient underwent GS for a large (9.3 cm3) tumor located on the right side. Images were obtained at treatment (A) and at 6 (B), 12 (C), and 72 months (D) posttreatment, at which time the tumor measured 2.5 cm3. The tumor has remained stable at this size for the past 2 years. The patient is doing well with no side effects.

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    Graph depicting the time of onset of volume decrease in tumors treated by GS. Depiction of the time course of response of VSs treated either primarily (PGS group) or following microsurgery (MSGS group). The trends in the two groups are very similar.

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    Graph demonstrating the onset of central nonenhancement on contrast-enhanced CT or MR images obtained in patients who underwent GS for VS.

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    Graph showing the onset of hearing deterioration among those cases in which hearing worsened after GS. Hearing begins to deteriorate at least 2 years after GS. After a long follow-up review (> 5 years), 60% of the patients had experienced deterioration in ipsilateral auditory function. Fraction unchanged = fraction of cases in which hearing was unchanged.

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