Impact of target location on the response of trigeminal neuralgia to stereotactic radiosurgery

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Object

The authors evaluate the impact of target location on the rate of pain relief (PR) in patients with intractable trigeminal neuralgia (TN) undergoing stereotactic radiosurgery (SRS).

Methods

The authors conducted a retrospective review of 99 patients with idiopathic TN who were identified from a prospectively maintained database and were treated with SRS targeting the dorsal root entry zone with a maximum dose of 80 Gy. Targeting of the more proximal portion of a trigeminal nerve with the 50% isodose line overlapping the brainstem was performed in 36 patients (proximal group). In a matched group, 63 patients received SRS targeting the 20% isodose line tangential to the emergence of the brainstem (distal group). The median follow-up time was 33 months (range 6–124 months).

Results

The actuarial rate of maintenance of Barrow Neurological Institute (BNI) Pain Score I–IIIa was attained in 89% of patients at 1 year, 81% at 2 years, and 69% at 4 years, respectively, after SRS. Kaplan-Meier analysis revealed that durability of PR was only associated with the proximal location of the radiosurgical target (log-rank test, p = 0.018). Radiosurgery-induced facial numbness (BNI Score II or III) developed in 35 patients, which was significantly more frequent in the proximal group (19 patients [53%] compared with 16 [25%] in the distal group [p = 0.015]).

Conclusions

The radiosurgical target appears to affect the duration of pain relief in patients with idiopathic trigeminal neuralgia with the target closer to the brainstem affording extended pain relief. However, the proximal SRS target was also associated with an increased risk of mild to moderate facial numbness.

Abbreviations used in this paper:BNI = Barrow Neurological Institute; DREZ = dorsal root entry zone; GKRS = Gamma Knife radiosurgery; MVD = microvascular decompression; PR = pain relief; RGZ = retrogasserian zone; SRS = stereotactic radiosurgery; TN = trigeminal neuralgia.

Object

The authors evaluate the impact of target location on the rate of pain relief (PR) in patients with intractable trigeminal neuralgia (TN) undergoing stereotactic radiosurgery (SRS).

Methods

The authors conducted a retrospective review of 99 patients with idiopathic TN who were identified from a prospectively maintained database and were treated with SRS targeting the dorsal root entry zone with a maximum dose of 80 Gy. Targeting of the more proximal portion of a trigeminal nerve with the 50% isodose line overlapping the brainstem was performed in 36 patients (proximal group). In a matched group, 63 patients received SRS targeting the 20% isodose line tangential to the emergence of the brainstem (distal group). The median follow-up time was 33 months (range 6–124 months).

Results

The actuarial rate of maintenance of Barrow Neurological Institute (BNI) Pain Score I–IIIa was attained in 89% of patients at 1 year, 81% at 2 years, and 69% at 4 years, respectively, after SRS. Kaplan-Meier analysis revealed that durability of PR was only associated with the proximal location of the radiosurgical target (log-rank test, p = 0.018). Radiosurgery-induced facial numbness (BNI Score II or III) developed in 35 patients, which was significantly more frequent in the proximal group (19 patients [53%] compared with 16 [25%] in the distal group [p = 0.015]).

Conclusions

The radiosurgical target appears to affect the duration of pain relief in patients with idiopathic trigeminal neuralgia with the target closer to the brainstem affording extended pain relief. However, the proximal SRS target was also associated with an increased risk of mild to moderate facial numbness.

Stereotactic radiosurgery (SRS) has shown promise in treating patients with medically refractory trigeminal neuralgia (TN).8,10,12,17–19,21 However, the duration of pain relief (PR) tends to lessen over time. Therefore, various modifications of the radiosurgical technique for TN have been devised to improve outcomes including duration of PR.4,6

The lack of a precise pathophysiology for TN poses a significant hindrance to curative treatment. It remains uncertain whether different targeting locations8,12,13,17 impact the rate of postoperative pain control and the morbidity of radiosurgery. The dorsal root entry zone (DREZ), a transition area on the trigeminal nerve from peripheral myelin to central myelin, is theoretically more susceptible to radiation damage or vascular compression.8,11 However, to date, no consensus has been reached regarding the efficacy of SRS and the induced morbidities relative to the exact targeting location within the DREZ. While a number of groups have published reports with a variety of targeting definitions, to our knowledge no comparative study or randomized clinical trial has been undertaken to investigate the impact of different targeting locations within the DREZ on the clinical outcomes of patients with idiopathic TN undergoing SRS using a single dose and varying only the SRS target location.

In this series we evaluate the effect of targeting location in 99 patients with idiopathic TN undergoing Gamma Knife radiosurgery (GKRS) with a maximum dose of 80 Gy, specifically examining duration of PR and adverse effects of the treatment.

Methods

Patient Population

This study was a retrospective review of a prospectively created, institutional review board–approved database at the University of Virginia Gamma Knife Center. At our institution, microvascular decompression (MVD) is highly recommended to patients with classic TN who are young and healthy. Gamma Knife radiosurgery is generally reserved for those who are older, those with significant comorbidity that may increase the surgical and anesthesia risks, or those in whom previous surgical procedures have failed.

We examined the records of patients treated with GKRS for idiopathic TN between July 2001 and July 2011 with a minimum follow-up of 6 months. Patients with multiple sclerosis were excluded. Two targeting groups were defined: The proximal target was defined as a location on the trigeminal nerve with the 50% isodose line extending into the pons with a distance of approximately 3 mm between the deepest penetration of the 50% isodose line and the boundary of the pons (Fig. 1 upper). The distal target was defined as a location anterior to the emergence of the nerve from the pons, in which there was no overlap between the 20% isodose line and the pons (Fig. 1 lower).17 A total of 36 patients constituted the proximal group. After controlling for demographics and clinical attributes including pain level, distribution, prior treatment modalities, and preoperative hypesthesia, we identified a matched cohort of 63 patients as a distal group. Hence, no statistical discrepancies between the 2 groups were found with regard to patient demographic and clinical characteristics other than the radiosurgical target location (Table 1). In the patient who presented with bilateral facial pain, only the side that was more symptomatically severe was treated with GKRS; therefore, the analysis of outcomes was based on the treated side only.

Fig. 1.
Fig. 1.

Proximal targeting. Axial 1-mm T1-weighted MR image obtained during the procedure, illustrating the location of 50% isodose lines (yellow circle) relative to the trigeminal nerve root entry zone into the pons (upper). Distal targeting. Axial 1-mm T1-weighted MR image obtained during the procedure, illustrating the location of a 20% isodose line (green circle) touching the emergence of the pons (lower).

TABLE 1:

Patient demographic and clinical features*

ParametersValuep Value
TotalProximalDistal
no. of patients993663
age at SRS in yrs0.217§
 mean64.86466
 median65.56367
 range32–9634–8632–96
sex0.268
 male33 (33)15 (42)18 (29)
 female66 (67)21 (58)45 (71)
duration of TN in yrs0.904§
 mean7.57.57.5
 median555
 range1–301–301–30
pain type0.768**
 typical69 (70)27 (75)42 (67)
 atypical27 (27)8 (22)19 (30)
 indeterminate3 (3)1 (3)2 (3)
branch(es) affected0.764**
 V13 (3)03 (5)
 V223 (23)8 (22)15 (24)
 V317 (17)7 (19)10 (16)
 V1 & V218 (18)5 (14)13 (21)
 V2 & V330 (30)13 (36)17 (27)
 V1, V2, & V38 (8)3 (8)5 (8)
affected side0.621**
 rt51 (52)21 (58)30 (48)
 lt47 (47)15 (42)32 (51)
 bilat1 (1)01 (2)
facial numbness prior to SRS0.306
 yes31 (31)9 (25)22 (35)
 no68 (69)27 (75)41 (65)
prior surgical procedures0.853
 yes30 (30)10 (28)20 (32)
 no69 (70)26 (72)43 (68)
type of prior surgical procedures0.701**
 glycerol injection14 (14)3 (8)11 (17)
 MVD6 (6)3 (8)3 (5)
 RF rhizotomy1 (1)01 (2)
 GKRS3 (3)1 (3)2 (3)
 peripheral nerve block2 (2)1 (3)1 (2)
 multiple procedures4 (4)2 (6)2 (3)

RF = radiofrequency.

Values are number of patients (%) unless noted otherwise.

Statistical analysis between groups of proximal and distal.

t-test.

Chi-square test.

Fisher's exact test.

Radiosurgical Technique

Radiosurgery was delivered using the Model C (July 2001–2007) and Perfexion (since 2007) Gamma Knife (Elekta AB). The technique of GKRS for patients with TN has been previously described.21,25 In brief, the Leksell G frame was applied in the operating room under local anesthesia with propofol sedation. Imaging for localization of the trigeminal nerve was performed using a 1.5-T MRI scanner (Avanto model, Siemens Medical Solutions). Acquired images included volumetric T1-weighted gradientecho sequences (1.2-mm slice thickness, no gap) through the entire head as well as constructive interference in steady-state sequences26 (0.8-mm slice thickness, no gap) through the level of the pons, trigeminal nerves, and skull base. A single 4-mm isocenter was positioned along the symptomatic trigeminal nerve, and the maximum dose was 80 Gy. The selection of either proximal or distal targeting was based on the treating neurosurgeons' radiosurgical technique, and to some degree the target evolved to a more distal one as time elapsed.

Patient Follow-Up

Our patients routinely undergo a telephone questionnaire during an immediate follow-up period of up to 1 month after GKRS. Clinical follow-up visits were conducted at a time point 3–6 months after GKRS and every 6–12 months thereafter. The first 3- to 6-month clinical evaluation included follow-up MRI (thin-slice, T1-weighted with and without contrast through the entire brain, and T2-weighted through the region of the trigeminal nerve and brainstem). Clinical follow-ups after the first visit were performed using a combination of direct clinical evaluation, telephone interview, and written questionnaires. Clinical assessment focused on neurological conditions with special attention paid to facial sensory status, facial weakness, hearing impairment, mastication muscle power and volume change, and corneal reflexes. Patients' medical records were carefully reviewed to determine the length of follow-up; the postoperative Barrow Neurological Institute (BNI) score (I–V) immediately postoperatively (within 6 weeks) and at 6 months, 1, 2, 3, and 4 years postoperatively and/or at last follow-up; and any postoperative complications, including new-onset or worsened preoperative numbness. Patient records were also reviewed to document any further surgical intervention for TN.

Statistical Analysis

Pain outcomes were evaluated using the well-established BNI pain scale (Table 2) while facial numbness was defined as BNI Scores I–IV in Table 3.18,19 Treatment failure was defined as a reported pain scale that was stratified as BNI Pain Score IV or V after the initial GKRS treatment. Significant PR was defined as a BNI Score I–IIIa. Twenty-one patients (21%) underwent additional GKRS due to pain recurrence after an initial period of post-GKRS PR. For those patients only data from the first GKRS were included in this study; PR after additional GKRS was not included in the statistical analyses. The comparison of length of PR maintenance was performed using the Kaplan-Meier product-limit method. An independent Student t-test, chi-square test, or Fisher's exact test was computed as appropriate. Correlations of clinical outcomes were investigated using the Cox proportional hazards regression models in terms of parameters detailed in Tables 1 and 4. All actuarial statistical tests were calculated over an 11-year period. Statistical analyses were conducted using a commercially available statistics package, SPSS version 20, IBM SPSS), except chi-square or Fisher's exact tests were performed using R-project (R 2.15.1, http://www.r-project.org). All statistical analyses were 2-tailed and a p value < 0.05 was deemed statistically significant.

TABLE 2:

Barrow Neurological Institute pain intensity scale

Definition & ScoreCriteria
adequate pain relief
 Ino trigeminal pain, no medications
 IIoccasional facial pain, not requiring medication
 IIIano pain, continued medication
 IIIbpersistent pain, controlled w/ medications
treatment failure
 IVsome pain, not adequately controlled w/ medication
 Vsevere pain/no pain relief
TABLE 3:

Barrow Neurological Institute facial hypesthesia scale

ScoreCriteria
Ino facial numbness
IImild facial numbness that is not bothersome
IIIsomewhat bothersome facial numbness
IVvery bothersome facial numbness
TABLE 4:

Outcomes after SRS*

Clinical ParametersValuep Value
TotalProximalDistal
no. of patients993663
BNI pain score
 prior to SRS0.805
  IV81 (82)29 (81)52 (83)
  V18 (18)7 (19)11 (18)
 immediately after SRS0.071§
  I29 (29)12 (33)17 (27)0.504
  II7 (7)3 (8)4 (6)
  IIIa16 (16)4 (11)12 (19)
  IIIb24 (24)6 (17)18 (29)
  IV18 (18)11 (31)7 (11)
  V5 (5)05 (8)
 at last follow-up0.463§
  I23 (23)10 (28)13 (21)0.574
  II9 (9)5 (14)4 (6)
  IIIa7 (7)2 (6)5 (8)
  IIIb30 (30)12 (33)18 (29)
  IV28 (28)7 (19)21 (33)
  V2 (2)02 (3)
newly developed or worsening facial numbness (BNI score)0.015§
 I64 (64)17 (47)47 (75)
 II26 (26)15 (42)11 (17)
 III9 (9)4 (11)5 (8)
 IV000
satisfaction after SRS0.018§
 satisfied38 (38)20 (56)18 (29)
 not satisfied11 (11)1 (3)10 (16)
 unsure3 (3)03 (5)
 indeterminate47 (47)15 (42)32 (51)
BNI pain Score I–IIIa (actuarial rate after SRS)0.018
 1 yr89%96%83%
 2 yrs81%92%69%
 3 yrs75%92%60%
 4 yrs69%82%60%
BNI pain Score I (actuarial rate after SRS)0.034
 1 yr85%100%73%
 2 yrs77%89%55%
 3 yrs63%78%0%
 4 yrs59%72%0%
additional procedures0.797§
 yes35 (35)12 (33)23 (37)
 no60 (61)22 (61)38 (60)
 indeterminate4 (4)2 (6)2 (3)
type of additional procedures0.140§
 glycerol injection4 (4)2 (6)2 (3)
 MVD3 (3)03 (5)
 GKRS21 (21)10 (28)11 (17)
 multiple procedures6 (6)06 (10)
 V1 stimulator implant trial1 (1)01 (2)
 indeterminate4 (4)2 (6)2 (3)

Values are number of patients (%) unless noted otherwise.

Statistical analyses between proximal and distal groups. Values in boldface are statistically significant.

Chi-square test.

Fisher's exact test

Log-rank test, Kaplan-Meier method.

Results

Initial PR Response

The median follow-up after SRS was 33 months (range 6–124 months). Follow-up for the purposes of the study analysis terminated once the pain recurred after a response to SRS. All clinical outcomes are displayed in Table 4 including BNI scores prior to SRS. By 1 month after SRS, 52 patients achieved relief to BNI Grade I–IIIa with 19 patients in the proximal group and 33 patients in the distal group (chi-square test, p = 1). Over the entire period of the study BNI Grade I–IIIa was achieved in 65 patients (66%) with a median latency of 1 month. There were 28 patients (94%) with BNI Grade I–IIIa in the proximal group and 37 patients (88%) in the distal group (Fisher's exact test, p = 0.353). The median interval between the date of SRS and significant PR was 1 month (range 1 day to 6 months). No statistical significance was observed between the 2 groups (p = 0.682, Kaplan-Meier method, log-rank test).

Maintenance of Pain Relief

Barrow Neurological Institute Grade I–IIIa pain relief at the last follow-up in relation to the target location is displayed in Table 4. The actuarial rate of PR duration was 96%, 92%, and 82% in the proximal group as compared with 83%, 69%, and 60% in the distal group at 1 year, 2 years, and 4 years, respectively, after the response to SRS (log-rank test, p = 0.018; Fig. 2 left).

Fig. 2.
Fig. 2.

Kaplan-Meier estimate of significant facial pain relief maintenance (BNI Grade I–IIIa) in relation to target location following GKRS (left), and maintenance of pain relief in those who achieved BNI Score I in relation to target location after GKRS (right).

Durability of BNI Grade I is illustrated in Table 4 and Fig. 2 right. Stereotactic radiosurgery with proximal targeting conferred an extended duration of BNI Grade I pain relief. Kaplan-Meier analysis indicated that the only factor associated with prolonged maintenance of adequate PR was the proximal targeting location (log-rank test, p = 0.034). Absence of facial numbness prior to SRS, sex, age at the time of SRS, pain type, prior surgical treatment, length of symptomatic history, or new-onset facial numbness showed no statistical association.

Clinical Complications

No acute post-SRS neurological complications were found in this series. Facial numbness classified as BNI Grade II or III is displayed in Table 4. Prior to SRS 27 patients in the proximal group had no facial numbness compared with 41 patients in the distal group. New-onset hypesthesia on the treated side after SRS was experienced by 15 patients (56%) in the proximal group while 11 patients (27%) developed facial numbness in the distal group (chi-square test, p = 0.017). Nine of 31 patients (29%) who had developed partial facial numbness prior to SRS experienced some changes in symptoms including location alterations or deteriorated symptoms. This included 4 patients (11%) in the proximal group and 5 patients (8%) in the distal group (Fisher's exact test, p = 0.385). No patients reported numbness that they considered to be overly bothersome.

None of the patients developed other complications such as mastication muscle weakness, hearing impairment, decreased corneal sensation, facial weakness, or more severe complications including anesthesia dolorosa.

Imaging Outcome

Imaging changes presenting with a focal contrast enhancement at the targeted portion of the trigeminal nerve or focal T2-weighted signal change secondary to SRS were detected in 22 patients (22%), with 5 patients (14%) in the proximal group and 17 patients (27%) in the distal group (chi-square test, p = 0.132). Of these 22 patients, newly developed or worsening facial numbness presented in 3 patients (60%) in the proximal group compared with 10 patients (59%) in the distal group (Fisher's exact test, p = 1). There was no relationship between the presence of radiosurgery-induced contrast enhancement and the length of PR (log-rank test, p = 0.228). No brainstem necrosis was detected in this cohort of patients.

Additional Procedures

Eventually 12 (33%) of 36 patients in the proximal group and 23 (37%) of 63 patients in the distal group underwent additional surgical procedures due to the recurrence of TN (Fisher's exact test, p = 0.797). Overall, the median time to recurrence was 14 months (range 2–111 months). No statistical difference of the time to recurrence was found between these two groups. The types of further management are detailed in Table 4.

Discussion

Very few existing studies have examined the effect of target location and SRS outcome for facial pain. Of the available studies, none rigidly controlled for the effects of dose, prior interventions, and types of trigeminal neuralgia (that is, idiopathic TN compared with pain associated with multiple sclerosis), all of which have been shown to affect outcome. The lack of a consistent dose given within the prior studies (doses often ranged from 70 to 90 Gy) renders clinical extrapolation of the effect of target location difficult, as dose has been clearly associated with both PR and complication rate.7,12,20 The variable doses used and mixed facial pain patient population in prior studies may confound any conclusion regarding target location on SRS outcomes. Park and colleagues presented a study directly comparing 2 targeting locations in a total of 39 patients who underwent SRS with a mean follow-up of 32.8 months in the DREZ group and 16.5 months in the retrogasserian zone (RGZ) group.15 A maximum dose with a range of 80–90 Gy was used for DREZ targeting and a range of 83 Gy to 90 Gy for RGZ targeting. The study identified no difference in the risk of postradiosurgical complications, but the authors did find a shorter response time in the RGZ group (4.1 weeks vs 6.4 weeks, p = 0.044). In contrast, using a maximum dose of 90 Gy, a far-anterior RGZ target was used by Massager et al., who found that favorable facial PR was correlated with a higher dose of radiation to the brainstem and a shorter distance between the target and brainstem,13 which seems in part consistent with the prolonged pain relief observed in the proximal targeted group in our study. However, the study was conducted in 47 patients with a mean follow-up of 16 months (range 6–42 months). A similar study performed by Matsuda et al. in which the authors used doses ranging from 80 to 90 Gy reported comparable follow-up times of 30 months in 100 patients and found that the DREZ targeting was superior to RGZ targeting in terms of favorable pain control and a lower complication rate.14 While individually difficult to interpret, taken together these findings support the hypothesis that the DREZ is more susceptible to radiation damage than the RGZ.

To the best of our knowledge, the current series represents the first case-matched study investigating different targeting locations using a consistent maximum dose (in this case 80 Gy) to the trigeminal nerve. The distal targeting location as defined in this study corresponds to the definition of the DREZ targeting location in prior studies, with the center of the targeting location approximately 3–5 mm anterior to the entrance of the nerve into the brainstem. The proximal target as defined in the current study is closer to the brainstem and was defined as a location on the trigeminal nerve where the isodose line representing approximately 50% of the maximum dose extended into the pons with a distance of approximately 1–3 mm. In this study, we demonstrated that the proximal targeting conferred significantly prolonged pain relief, with the limitation that the percentage of patients with facial numbness secondary to SRS was much higher in the proximal group.

It has been generally accepted that the DREZ is situated 3 mm away from the emergence of the nerve from the pons. Central myelin in the DREZ is susceptible to radiation or vascular compression leading to demyelination, which is supported by pathological findings in patients undergoing MVD.5,23 Furthermore, TN attributed to microvascular compression at the site of the DREZ is by far the most accepted theory in terms of the mechanism of TN based on the findings of Barker et al.1 The disparity in PR duration in this study may indicate that the location of the DREZ is highly variable, and this variability in DREZ location has been described by De Ridder et al.3 Our group previously published a study regarding the impact of vascular compression on the efficacy of radiosurgery for TN.22 In that study of 106 patients with TN, GKRS proved more effective when the radiosurgery was delivered closer to the point of vascular impingement on the trigeminal nerve. That finding may recapitulate the more favorable pain relief after radiosurgery when targeting the proximal DREZ.

In general, clinical complications after SRS for TN are associated with the dose to the brainstem.16,24 This was likely the rationale considered by Régis et al., who advocated moving the targeted isocenter location more anteriorly in an attempt to minimize the complication rate.17 By using a lower dose of 75 Gy to target the DREZ, Brisman observed that while the pain control was less favorable, the complication rate was as low as 3.3%.2 In contrast, Pollock et al. compared a maximum dose of 90 Gy versus 70 Gy and found that the higher dose conferred a significantly increased risk of complications (54% vs 15%). However, the number of patients was small and follow-up was relatively short with a mean follow-up period of only 14.4 months.16 Notably, the isodose line tangent to the pons was 20% for 90 Gy and 40% for 75 Gy in that study, and, therefore, the targeted region of nerve was anterior to our proximal target and in proximity to the distal target in our series.

The rate of facial numbness attributed to SRS was higher in our study than in other studies. The study conducted by Kondziolka and colleagues revealed that only 53 patients (10.5%) developed new or increased subjective facial hypesthesia postoperatively in their 503-patient analysis utilizing a median maximum dose of 80 Gy (range 60–90 Gy).9 We believe the rate of facial numbness is higher in our study because the target, even for the distal targeting location, is more proximal to brainstem. Although the complication rate of facial numbness in our proximal group was significantly higher than that in the distal group, no patient experienced intolerable numbness. Thus, the complication of partial facial numbness in the current series seems acceptable given the extended duration of PR.

The radiosurgical dose for treatment of medically refractory TN (typically 80 Gy) represents the highest maximum dose of ionizing radiation in widespread use for clinical indications. The available evidence shows the substantial dose used for TN has a profound effect on the targeted nerve. It seems quite plausible that the neuroanatomical location of the target will lead to differences in the benefits and risks of this approach. In this study, we demonstrated that the proximal targeting conferred significantly prolonged PR; however, the percentage of patients with facial numbness due to SRS was higher in the proximal group. Given a choice of pain or numbness, satisfactory PR is of paramount importance. In general, patients tolerated mild to moderate facial numbness as long as the pain was well controlled and the effect was durable.

Study Limitations

There are several potential limitations to this study, including that it is a single-center experience and a retrospective (albeit case-matched) design. The nature of any retrospective study inherently limits its power and the generalizability of the study. A randomized trial comparing 2 target locations and adequately controlling for other variables (for example, dose, cause of facial pain, and prior procedures) remains the ideal method to verify differences in extent and duration of PR and the association of a complication rate for each target site. However, randomized trials are rare, costly, and logistically challenging to complete in the setting of radiosurgery for TN.

Conclusions

This study demonstrates that proximal targeting of the trigeminal nerve was reasonably safe and offered superior extent and duration of facial pain relief. The only complication identified was mild to moderate facial numbness, which was associated with smaller distances to the brainstem. Targeting selection within the DREZ should be made by carefully weighing the benefits of improved pain relief and durability with an increased risk of facial numbness.

Disclosure

Dr. Schlesinger reports receiving support of non–study-related clinical or research effort from Elekta AB.

Author contributions to the study and manuscript preparation include the following. Conception and design: Sheehan, Xu. Acquisition of data: Xu, Moldovan, Przybylowski, Sun, Lee, Yen. Analysis and interpretation of data: Sheehan, Xu, Schlesinger, Moldovan, Sun, Lee, Yen. Drafting the article: Xu, Moldovan, Przybylowski, Sun, Lee, Yen. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Sheehan. Statistical analysis: Xu. Administrative/technical/material support: Sheehan. Study supervision: Sheehan.

This article contains some figures that are displayed in color online but in black-and-white in the print edition.

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    Rogers CLShetter AGPonce FAFiedler JASmith KASpeiser BL: Gamma knife radiosurgery for trigeminal neuralgia associated with multiple sclerosis. J Neurosurg 97:5 Suppl5295322002

  • 21

    Sheehan JPan HCStroila MSteiner L: Gamma knife surgery for trigeminal neuralgia: outcomes and prognostic factors. J Neurosurg 102:4344412005

  • 22

    Sheehan JPRay DKMonteith SYen CPLesnick JKersh R: Gamma Knife radiosurgery for trigeminal neuralgia: the impact of magnetic resonance imaging–detected vascular impingement of the affected nerve. Clinical article. J Neurosurg 113:53582010

  • 23

    van der Kogel AJ: Radiation-induced damage in the central nervous system: an interpretation of target cell responses. Br J Cancer Suppl 7:2072171986

  • 24

    Xue JGoldman HWGrimm JLaCouture TChen YHughes L: Dose-volume effects on brainstem dose tolerance in radiosurgery. Clinical article. J Neurosurg 117:Suppl1891962012

  • 25

    Yen CPSchlesinger DSheehan JP: Gamma Knife® radiosurgery for trigeminal neuralgia. Expert Rev Med Devices 8:7097212011

  • 26

    Yousry IMoriggl BSchmid UDNaidich TPYousry TA: Trigeminal ganglion and its divisions: detailed anatomic MR imaging with contrast-enhanced 3D constructive interference in the steady state sequences. AJNR Am J Neuroradiol 26:112811352005

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Article Information

Address correspondence to: Jason Sheehan, M.D., Ph.D., Lars Leksell Gamma Knife Center, Department of Neurological Surgery, University of Virginia Health System, Charlottesville, VA 22908. email: jsheehan@virginia.edu.

Please include this information when citing this paper: published online December 6, 2013; DOI: 10.3171/2013.10.JNS131596.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Proximal targeting. Axial 1-mm T1-weighted MR image obtained during the procedure, illustrating the location of 50% isodose lines (yellow circle) relative to the trigeminal nerve root entry zone into the pons (upper). Distal targeting. Axial 1-mm T1-weighted MR image obtained during the procedure, illustrating the location of a 20% isodose line (green circle) touching the emergence of the pons (lower).

  • View in gallery

    Kaplan-Meier estimate of significant facial pain relief maintenance (BNI Grade I–IIIa) in relation to target location following GKRS (left), and maintenance of pain relief in those who achieved BNI Score I in relation to target location after GKRS (right).

References

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    Rogers CLShetter AGPonce FAFiedler JASmith KASpeiser BL: Gamma knife radiosurgery for trigeminal neuralgia associated with multiple sclerosis. J Neurosurg 97:5 Suppl5295322002

  • 21

    Sheehan JPan HCStroila MSteiner L: Gamma knife surgery for trigeminal neuralgia: outcomes and prognostic factors. J Neurosurg 102:4344412005

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    Sheehan JPRay DKMonteith SYen CPLesnick JKersh R: Gamma Knife radiosurgery for trigeminal neuralgia: the impact of magnetic resonance imaging–detected vascular impingement of the affected nerve. Clinical article. J Neurosurg 113:53582010

  • 23

    van der Kogel AJ: Radiation-induced damage in the central nervous system: an interpretation of target cell responses. Br J Cancer Suppl 7:2072171986

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    Xue JGoldman HWGrimm JLaCouture TChen YHughes L: Dose-volume effects on brainstem dose tolerance in radiosurgery. Clinical article. J Neurosurg 117:Suppl1891962012

  • 25

    Yen CPSchlesinger DSheehan JP: Gamma Knife® radiosurgery for trigeminal neuralgia. Expert Rev Med Devices 8:7097212011

  • 26

    Yousry IMoriggl BSchmid UDNaidich TPYousry TA: Trigeminal ganglion and its divisions: detailed anatomic MR imaging with contrast-enhanced 3D constructive interference in the steady state sequences. AJNR Am J Neuroradiol 26:112811352005

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