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William A. Friedman and Kelly D. Foote

Despite major advances in skull base surgery and microsurgical techniques, surgery for vestibular schwannoma (VS) carries a risk of complications. Some are inherent to general anesthesia and surgery of any type and include myocardial infarction, pneumonia, pulmonary embolism, and infection. Some are specific to neurosurgery in this area of the brain, and include hydrocephalus, cerebrospinal fluid leak, facial nerve paralysis, facial numbness, hearing loss, ataxia, dysphagia, and major stroke. Even in the hands of very experienced acoustic surgeons, these risks cannot be eliminated.

Radiosurgery provides an outpatient, noninvasive alternative for the treatment of small acoustic schwannomas. Initially radiosurgery was undertaken in “high-risk” patients, including the elderly, those with severe medical comorbidities, and those in whom tumors recurred after surgery. Additionally, a high rate of cranial nerve morbidity was reported. With improvements in dosimetry planning and dose selection, however, authors practicing at radiosurgical centers now report very low complication rates, as well as high tumor control rates.

In this report the authors specifically review the results of linear accelerator–based radiosurgery for VS and compare these outcomes with the best surgical alternatives.

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Justin D. Hilliard and Kelly D. Foote

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Francisco A. Ponce, Kelly D. Foote and Andres M. Lozano

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Genko Oyama, Michael S. Okun, Theresa A. Zesiewicz, Tiffany Tamse, Janet Romrell, Pamela Zeilman and Kelly D. Foote

Object

The purpose of this paper is to present 4 cases that illustrate the management and outcome of subdural hematoma (SDH) following deep brain stimulation (DBS) lead implantation.

Methods

The authors identified 4 cases of SDH following DBS lead implantation from a pool of 500 consecutive lead implantations (incidence 0.08%) performed at the University of Florida. Cases were characterized by chart review, serial Unified Parkinson's Disease Rating Scale evaluations, and changes on serial postoperative imaging studies.

Results

Two of the 4 patients with DBS-related SDH were clinically symptomatic. In the other 2 cases the SDH was incidentally discovered on routine postoperative lead localization imaging studies. None of the patients required craniotomy for evacuation of the SDH in the acute phase. Three of the 4 cases were managed with bur hole drainage in the chronic phase, and one was successfully managed nonoperatively. In all 4 cases, thresholds for stimulationinduced side effects were lower during initial postoperative programming than during intraoperative macrostimulation. Expected clinical improvement from DBS was achieved without lead revision in all 4 cases, but only after a significant delay.

Conclusions

Subdural hematoma is a rare and potentially avoidable complication of DBS that does not typically mandate acute hematoma evacuation or hardware revision and does not preclude an excellent outcome from DBS therapy. The clinical picture and apparent lead position tend to improve with time, and it may be wise to delay repositioning of an ineffective DBS lead following a hemorrhage until the DBS lead and surrounding brain tissue have settled into their final position and the insulted brain has had sufficient time to recover.

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Kelly D. Foote, William A. Friedman, John M. Buatti, Sanford L. Meeks, Frank J. Bova and Paul S. Kubilis

Object. The aim of this study was to identify factors associated with delayed cranial neuropathy following radiosurgery for vestibular schwannoma (VS or acoustic neuroma) and to determine how such factors may be manipulated to minimize the incidence of radiosurgical complications while maintaining high rates of tumor control.

Methods. From July 1988 to June 1998, 149 cases of VS were treated using linear accelerator radiosurgery at the University of Florida. In each of these cases, the patient's tumor and brainstem were contoured in 1-mm slices on the original radiosurgical targeting images. Resulting tumor and brainstem volumes were coupled with the original radiosurgery plans to generate dose—volume histograms. Various tumor dimensions were also measured to estimate the length of cranial nerve that would be irradiated. Patient follow-up data, including evidence of cranial neuropathy and radiographic tumor control, were obtained from a prospectively maintained, computerized database. The authors performed statistical analyses to compare the incidence of posttreatment cranial neuropathies or tumor growth between patient strata defined by risk factors of interest. One hundred thirty-nine of the 149 patients were included in the analysis of complications. The median duration of clinical follow up for this group was 36 months (range 18–94 months). The tumor control analysis included 133 patients. The median duration of radiological follow up in this group was 34 months (range 6–94 months).

The overall 2-year actuarial incidences of facial and trigeminal neuropathies were 11.8% and 9.5%, respectively. In 41 patients treated before 1994, the incidences of facial and trigeminal neuropathies were both 29%, but in the 108 patients treated since January 1994, these rates declined to 5% and 2%, respectively.

An evaluation of multiple risk factor models showed that maximum radiation dose to the brainstem, treatment era (pre-1994 compared with 1994 or later), and prior surgical resection were all simultaneously informative predictors of cranial neuropathy risk. The radiation dose prescribed to the tumor margin could be substituted for the maximum dose to the brainstem with a small loss in predictive strength. The pons—petrous tumor diameter was an additional statistically significant simultaneous predictor of trigeminal neuropathy risk, whereas the distance from the brainstem to the end of the tumor in the petrous bone was an additional marginally significant simultaneous predictor of facial neuropathy risk.

The overall radiological tumor control rate was 93% (59% tumors regressed, 34% remained stable, and 7.5% enlarged), and the 5-year actuarial tumor control rate was 87% (95% confidence interval [CI] 76–98%). Analysis revealed that a radiation dose cutpoint of 10 Gy compared with more than 10 Gy prescribed to the tumor margin yielded the greatest relative difference in tumor growth risk (relative risk 2.4, 95% CI 0.6–9.3), although this difference was not statistically significant (p = 0.207).

Conclusions. Five points must be noted. 1) Radiosurgery is a safe, effective treatment for small VSs. 2) Reduction in the radiation dose has played the most important role in reducing the complications associated with VS radiosurgery. 3) The dose to the brainstem is a more informative predictor of postradiosurgical cranial neuropathy than the length of the nerve that is irradiated. 4) Prior resection increases the risk of late cranial neuropathies after radiosurgery. 5) A prescription dose of 12.5 Gy to the tumor margin resulted in the best combination of maximum tumor control and minimum complications in this series.

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Kelly D. Foote, William A. Friedman, Thomas L. Ellis, Frank J. Bova, John M. Buatti and Sanford L. Meeks

Object. The goal of this study was to evaluate the outcomes of patients who underwent repeated radiosurgery to treat a residual intracranial arteriovenous malformation (AVM) after an initial radiosurgical treatment failure.

Methods. The authors reviewed the cases of 52 patients who underwent repeated radiosurgery for residual AVM at the University of Florida between December 1991 and June 1998. In each case, residual arteriovenous shunting persisted longer than 36 months after the initial treatment; the mean interval between the first and second treatment was 41 months. Each AVM nidus was measured at the time of the original treatment and again at the time of retreatment, and the dosimetric parameters of the two treatments were compared. After retreatment, patients were followed up and their outcomes were evaluated according to a standard posttreatment protocol for radiosurgery for AVMs.

The mean original lesion volume was 13.8 cm3 and the mean volume at retreatment was 4.7 cm3, for an average volume reduction of 66% after the initial treatment failure. Only two AVMs (3.8%) failed to demonstrate size reduction after the primary treatment. The median doses on initial and repeated treatment were 12.5 and 15 Gy, respectively. Five patients were lost to follow up and five refused neuroimaging follow up. One patient died of a hemorrhage shortly after retreatment. Of the remaining 41 patients, 24 had evidence of cure, 15 on angiographic studies and nine on magnetic resonance (MR) images. Seventeen had evidence of treatment failure, 10 on angiographic studies and seven on MR images. By angiographic criteria alone, the cure rate after retreatment was 60%, whereas according to angiographic and MR imaging results, the cure rate was 59%.

Conclusions. Although initial radiosurgical treatment failed to obliterate the AVM in these 52 patients, it did produce a substantial therapeutic effect (volume reduction). This size reduction commonly allowed higher doses to be delivered during radiosurgical retreatment. The results show rates of angiographically confirmed cure comparable to primary treatment and a low incidence of complications, indicating that salvage radiosurgical retreatment is a safe and effective therapy in cases of failed AVM radiosurgery.

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William A. Friedman, Gregory J. Murad, Patrick Bradshaw, Robert J. Amdur, William M. Mendenhall, Kelly D. Foote and Frank J. Bova

Object. In this paper the authors review the results of a single-center experience in the use of linear accelerator (LINAC) surgery for radiosurgical treatment of meningiomas.

Methods. A retrospective analysis of all patients treated with LINAC surgery for meningiomas between May 1989 and December 2001 was performed. All patients participated in follow-up review for a minimum of 2 years, and no patients were excluded. Two hundred ten patients were treated during the study interval.

The actuarial local control rate for benign tumors was 100% at both 1 and 2 years, and 96% at 5 years. The actuarial local control rate for atypical tumors was 100% at 1 year, 92% at 2 years, and 77% at 5 years; and that for malignant tumors was 100% at both 1 and 2 years, and only 19% at 5 years. Of the 210 patients 13 (6.2%) experienced temporary radiation-induced complications, and only five (2.3%) experienced permanent complications. In all patients with a permanent complication the histological characteristics of the meningioma were malignant.

Conclusions. Linear accelerator surgery produced high local control rates and very low rates of permanent morbidity in patients harboring benign meningiomas.

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Editorial

Unilateral or bilateral deep brain stimulation

Kim J. Burchiel

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Abuzer Güngör, Şevki Serhat Baydın, Vanessa M. Holanda, Erik H. Middlebrooks, Cihan Isler, Bekir Tugcu, Kelly Foote and Necmettin Tanriover

In Brief

Familiarity with the complex 3D anatomy of the STN and peri-subthalamic area is important for more effective targeting of the STN and better understanding of DBS side effects. The combination of meticulous anatomic dissections of the STN region and detailed discussions of pertinent anatomo-functional relationships in this paper will provide DBS practitioners with a more sophisticated understanding of this important brain region and empower them to improve the outcomes of STN DBS for their patients.

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Takashi Morishita, Kelly D. Foote, Samuel S. Wu, Charles E. Jacobson IV, Ramon L. Rodriguez, Ihtsham U. Haq, Mustafa S. Siddiqui, Irene A. Malaty, Christopher J. Hass and Michael S. Okun

Object

Microelectrode recording (MER) and macrostimulation (test stimulation) are used to refine the optimal deep brain stimulation (DBS) lead placement within the operative setting. It is well known that there can be a microlesion effect with microelectrode trajectories and DBS insertion. The aim of this study was to determine the impact of intraoperative MER and lead placement on tremor severity in a cohort of patients with essential tremor.

Methods

Consecutive patients with essential tremor undergoing unilateral DBS (ventral intermediate nucleus stimulation) for medication-refractory tremor were evaluated. Tremor severity was measured at 5 time points utilizing a modified Tremor Rating Scale: 1) immediately before MER; 2) immediately after MER; 3) immediately after lead implantation; 4) 6 months after DBS implantation in the off-DBS condition; and 5) 6 months after implantation in the on-DBS condition. To investigate the impact of the MER and DBS lead placement, Wilcoxon signed-rank tests were applied to test changes in tremor severity scores over the surgical course. In addition, a generalized linear mixed model including factors that potentially influenced the impact of the microlesion was also used for analysis.

Results

Nineteen patients were evaluated. Improvement was noted in the total modified Tremor Rating Scale, postural, and action tremor scores (p < 0.05) as a result of MER and DBS lead placement. The improvements observed following lead placement were similar in magnitude to what was observed in the chronically programmed clinic setting parameters at 6 months after lead implantation. Improvement in tremor severity was maintained over time even in the off-DBS condition at 6 months, which was supportive of a prolonged microlesion effect. The number of macrostimulation passes, the number of MER passes, and disease duration were not related to the change in tremor severity score over time.

Conclusions

Immediate improvement in postural and intention tremors may result from MER and DBS lead placement in patients undergoing DBS for essential tremor. This improvement could be a predictor of successful DBS lead placement at 6 months. Clinicians rating patients in the operating room should be aware of these effects and should consider using rating scales before and after lead placement to take these effects into account when evaluating outcome in and out of the operating room.