Cranial nerve (CN) schwannomas are intracranial tumors that are commonly managed by stereotactic radiosurgery (SRS). There is a large body of literature supporting the use of SRS for vestibular and, to a lesser extent, trigeminal schwannomas.1–4 Less common schwannoma locations, however, have not been studied in as much detail. The International Radiosurgery Research Foundation (IRRF) has recently performed multicenter studies detailing the outcomes of SRS for facial nerve and jugular foramen schwannomas.5,6
Oculomotor nerve schwannomas (CNs III, IV, and VI) are rare tumors. They are skull base neoplasms found close to the brainstem often involving the cavernous sinus, for which resection can cause significant morbidity. As for other schwannomas, SRS can be used to manage these tumors; however, only a handful of cases have been published so far,7–12 often among reports of other uncommon schwannoma locations.13–18
This paucity of current literature highlights the need to better evaluate the safety and efficacy of SRS for oculomotor cranial nerve schwannomas with regard to tumor control, clinical evolution, and the worsening or occurrence of new symptoms. The goal of this study was to collect multicenter retrospective data on tumor control, clinical evolution, and morbidity in patients treated by SRS for schwannomas of oculomotor, trochlear, and abducens cranial nerves.
Methods
Research Ethics Board Approval
This study was approved by our Research Ethics Board (Comité d’éthique de la recherche du CIUSSS de l’Estrie—CHUS). Patient consent was not necessary for this protocol.
Patient Population
All patients who underwent Gamma Knife SRS (Elekta AB) at one of the 7 participating IRRF centers were screened for eligibility. Patients were included in the study if they had undergone single-session SRS for a CN III, IV, or VI schwannoma. The diagnosis was based on clinical presentation including diplopia or ptosis as the main presenting symptom, as well as anatomical localization on the trajectory of the presumed cranial nerve of origin, or prior resection confirming histological diagnosis. There was no formal visual testing prior to or after SRS. Visual evaluation was at the discretion of each treating institution based on individual patient evaluation.
Radiosurgical Procedures
Indications for SRS treatment included primary treatment in patients who were developing new or worsening clinical symptoms and/or showing tumor progression on radiological follow-up, adjuvant treatment immediately following subtotal resection, and rescue treatment following postoperative tumor recurrence.
Radiosurgery was performed using different Gamma Knife models (B, C, 4C, and Perfexion; Elekta AB) as they became available at each participating institution. After administration of local anesthesia, an MRI-compatible stereotactic headframe was installed in all cases to perform contrast-enhanced isotropic stereotactic MRI. Treatment plans were designed using Leksell Gamma Plan software (Elekta AB) with the participation of a neurosurgeon and approved by a radiation oncologist and a medical physicist, as per the American Society for Radiation Oncology guidelines.19 There was no standardized regimen dose or isodose parameters, as procedures could vary between participating centers. A typical treatment plan is presented in Fig. 1.
Typical treatment plan and tumor response to SRS. Typical left trochlear nerve schwannoma treated by SRS in a 62-year-old man initially presenting with diplopia. At 3 years after Gamma Knife SRS, the patient experienced improvement in diplopia and tumor disappearance on imaging follow-up. Figure is available in color online only.
Variables
Baseline patient data at the time of the Gamma Knife procedure were collected, including treating institution, patient sex and age, schwannoma location and lateralization, presence or absence of diagnosis of neurofibromatosis type 2 (NF2), prior tumor management (resection, shunt, radiation therapy, or SRS), and clinical presentation (diplopia, ptosis, facial hypesthesia, trigeminal pain, visual loss, and other symptoms). Procedural data collected comprised SRS procedure date, indication for radiosurgery (primary, adjuvant after resection, or for recurrence following prior care), and dosimetric parameters (treatment volume, maximal dose, marginal dose, maximal dose received by the optic tracts, maximal dose received by the brainstem, brainstem volume receiving 12 Gy or more, isodose line, and number of isocenters). Follow-up data included imaging outcomes (transient volume increase, best initial response, tumor control, and radiation-induced increase in edema), clinical outcomes (resolution, improvement, stability, worsening or appearance of neurological symptoms, and survival), and subsequent need for further treatment (resection, shunt placement, radiation therapy, or SRS).
Statistical Analysis
Continuous variables were analyzed with descriptive statistics using the distribution’s median and range, and categorical variables are presented with frequency tables, including total number of events and valid percentages. The total was 25, except for variables for which data were missing, in which case the corresponding number is specified.
Actuarial analysis of tumor control was obtained using the Kaplan-Meier estimator. Cases were censored at the last available radiological follow-up. All times included are relative to the date of the initial SRS procedure.
Statistical significance was defined at p < 0.05. Statistical analyses were performed using IBM SPSS Statistics (version 25.0.0.0, IBM Corp.), and figures were rendered using IBM SPSS Statistics and Adobe Illustrator CS6 (Adobe Systems Inc.).
Results
Cohort Demographic and Clinical Characteristics
Twenty-five patients underwent SRS for a schwannoma of the oculomotor, trochlear, or abducens nerve at one of 7 participating IRRF centers between 1997 and 2018 (University of Pittsburgh Medical Center [n = 8], University of Virginia [n = 5], Na Homolce Hospital [n = 4], New York University Langone Medical Center [n = 3], Université de Sherbrooke [n = 2], Taipei Veterans General Hospital Neurological Institute [n = 2], and Cleveland Clinic Foundation [n = 1]). The median age at SRS was 52 years (range 11–73 years), 60% of patients were male, and 1 patient had a known diagnosis of NF2. There were 11 oculomotor nerve schwannomas, 11 trochlear nerve schwannomas, and 3 abducens nerve schwannomas. There was no significant difference in patient demographic characteristics between each oculomotor cranial nerve schwannoma location (data not shown).
At the time of the procedure, 21 patients complained of diplopia, while 8 presented with ptosis. Only 1 patient each presented with facial hypesthesia and with trigeminal neuralgia. Five patients had some degree of visual loss. Other symptoms included headaches (n = 1), proptosis (n = 1), unrelated hearing loss (n = 1), hypopituitarism (n = 1), and hemiparesis (n = 1). Only 1 patient was asymptomatic at the time of SRS treatment but had initially presented with transient diplopia that spontaneously resolved.
Four patients with CN III schwannomas underwent resection prior to SRS. None had received prior radiation therapy or radiosurgery, and no patients had prior hydrocephalus requiring shunt placement. SRS was performed as the primary management for 21 cases. Two patients with CN III schwannomas underwent SRS as adjuvant treatment immediately following subtotal resection, and 2 others received SRS as a rescue treatment following delayed postoperative tumor recurrence. Table 1 summarizes patient demographic and clinical data.
Demographic and clinical characteristics at first Gamma Knife SRS treatment
| Patient No. | Age at SRS (yrs) | Sex | Schwannoma Location | Schwannoma Side | NF2 | Clinical Symptoms at SRS | Surgery Prior to SRS | Reason for SRS Treatment |
|---|---|---|---|---|---|---|---|---|
| 1 | 70 | Male | CN VI | Lt | No | Diplopia | No | Primary |
| 2 | 62 | Male | CN IV | Lt | No | Diplopia | No | Primary |
| 3 | 30 | Female | CN III | Rt | No | Diplopia, ptosis, visual loss | Yes | Recurrence |
| 4 | 19 | Female | CN III | Lt | No | Diplopia, ptosis, visual loss | Yes | Adjuvant |
| 5 | 71 | Male | CN III | Lt | No | Diplopia, ptosis, trigeminal pain | Yes | Recurrence |
| 6 | 57 | Female | CN VI | Lt | No | Diplopia | No | Primary |
| 7 | 53 | Male | CN VI | Rt | No | Diplopia | No | Primary |
| 8 | 45 | Male | CN IV | Lt | No | Diplopia | No | Primary |
| 9 | 57 | Male | CN III | Lt | No | Diplopia, ptosis, visual loss | No | Primary |
| 10 | 40 | Female | CN III | Lt | No | Visual loss | No | Primary |
| 11 | 48 | Male | CN III | Lt | No | Diplopia | No | Primary |
| 12 | 60 | Male | CN IV | Lt | No | Asymptomatic | No | Primary |
| 13 | 22 | Male | CN III | Rt | Yes | Diplopia, ptosis | Yes | Adjuvant |
| 14 | 54 | Female | CN IV | Lt | No | Diplopia | No | Primary |
| 15 | 43 | Male | CN IV | Rt | No | Diplopia | No | Primary treatment |
| 16 | 45 | Male | CN III | Lt | No | Diplopia, ptosis | No | Primary |
| 17 | 54 | Male | CN IV | Rt | No | Diplopia | No | Primary |
| 18 | 20 | Female | CN III | Lt | No | Diplopia, ptosis | No | Primary |
| 19 | 52 | Female | CN IV | Lt | No | Diplopia | No | Primary |
| 20 | 56 | Male | CN IV | Lt | No | Diplopia | No | Primary |
| 21 | 44 | Male | CN IV | Lt | No | Facial hypesthesia | No | Primary |
| 22 | 11 | Female | CN III | Rt | No | Diplopia, ptosis | No | Primary |
| 23 | 73 | Female | CN IV | Rt | No | Unrelated hearing loss | No | Primary |
| 24 | 53 | Male | CN IV | Lt | No | Diplopia | No | Primary |
| 25 | 22 | Female | CN III | Rt | No | Diplopia | No | Primary |
| Overall | Median 52 yrs | 10 females, 15 males | 11 CN III, 11 CN IV, 3 CN VI | 17 lt, rt 8 | 1 w/ NF2 | 21 w/ diplopia, 8 w/ ptosis, 1 w/ facial hypesthesia, 1 w/ trigeminal pain, 5 w/ visual loss | 4 w/ prior resection, 21 w/ no prior intervention | 21 w/ primary treatment, 2 w/ adjuvant treatment, 2 w/ recurrence treatment |
SRS Procedure
Table 2 presents all SRS treatment parameters. The median target volume was 0.74 cm3 (range 0.01–22.4 cm3) administered using a median number of 3 isocenters (range 1–19). The median marginal dose was 12.5 Gy (range 11–15 Gy) delivered using a median isodose line of 50% (range 44%–70%). The median maximum dose received by the optic apparatus was 4 Gy (range 0.1–10.2 Gy). For the brainstem, the median maximum dose was 8 Gy (range 0.6–18.9 Gy), with a median brainstem volume receiving 12 Gy or more of 0 cm3 (range 0–0.5 cm3).
SRS treatment parameters
| Median (range) | |||||||
|---|---|---|---|---|---|---|---|
| Schwannoma Type | Treatment Vol, cm3 | Marginal Dose, Gy | Max Dose, Gy | Max Optic Tract Dose, Gy | Max Brainstem Dose, Gy | Isodose Line Used, % | No. of Isocenters |
| CN III, n = 11 or otherwise specified | 2.65 (0.01–22.4), n = 10 | 12.5 (11–15) | 24 (21.3–30) | 6.75 (4–10.2), n = 4 | 4.5 (0.6–8), n = 4 | 50 (44–58) | 5 (1–19), n = 9 |
| CN IV, n = 11 or otherwise specified | 0.085 (0.02–2.1) | 13 (12–15) | 22 (17–30) | 0.2 (0.1–0.3), n = 2 | 15.9 (13–18.9), n = 4 | 60 (50–70) | 2 (1–11) |
| CN VI, n = 3 | 0.42 (0.24–0.55) | 12.5 (12–12.5) | 24 (20.8–25) | 1 (1–9.8) | 4.4 (0.6– 13.6) | 50 (50–60) | 3 (1–10) |
| All tumors combined, n = 25 or otherwise specified | 0.74 (0.01–22.4), n = 24 | 12.5 (11–15) | 24 (17–30) | 4 (0.1–10.2), n = 9 | 8 (0.6–18.9), n = 11 | 50 (44–70) | 3 (1–19), n = 23 |
Tumor Control and Patient Survival
The median clinical and radiological follow-ups were 41 months (range 2–168 months) and 35 months (range 2–168 months), respectively (Supplementary Fig. 1). Crude tumor control was 92%, with actuarial tumor control rates of 96% at 1 year and 86% at 10 years (Fig. 2). The best initial response to SRS was seen at a median time of 30 months post-SRS and consisted of tumor disappearance in 1 patient, regression in 15 patients, and stability in 6 patients. Only 2 patients had sustained tumor progression following SRS. One of these cases was observed at 9 months post-SRS in a patient with NF2 who was then lost to follow-up. Another presented with early symptomatic growth at 3 months with deterioration of vision, and underwent resection at that time, after which he did not require any other intervention. Both of these patients had received standard SRS doses, and, although the sample size is too small to meet formal statistical significance, one of these patients had NF2 and the other did not differ clinically from other patients. One patient had an asymptomatic transient volume increase at 6 months, after which tumor stability was seen at 1 year post-SRS with no further increase in volume. One patient died at 13 years post-SRS of an unrelated cause.
Actuarial analysis of tumor control following SRS. Kaplan-Meier estimation of tumor control following SRS. Cases are censored at the last imaging follow-up. Figure is available in color online only.
Evolution of Clinical Symptoms
Following SRS, diplopia resolved in 4 patients, improved in 7 patients, and remained stable in 6 patients. Three patients had worsened diplopia after SRS, 2 of whom also had associated worsened ptosis, both in the context of tumor progression. For the other patients who had ptosis at presentation, this symptom improved in 2 patients and stabilized in another 4. Figure 3 presents detailed evolution of clinical symptoms following SRS.
Evolution of clinical symptoms following SRS. Figure is available in color online only.
Only 1 patient presented with visual deterioration, which was due to early tumor growth requiring subsequent resection. All patients who initially presented with visual loss had stable visual defects post-SRS. No change in trigeminal nerve function was seen after SRS.
Radiation-Induced Changes and Complications
There was no case of radiation necrosis or radiation-induced edema. One patient developed cystic tumor changes 42 months following SRS, for which the patient underwent no further treatment. There was no proven radiation-induced malignant transformation or new tumor formation.
Discussion
Schwannomas of the oculomotor, trochlear, and abducens nerves are rare tumors, and only limited evidence is available to guide their management. As is the case of intracranial schwannomas in more common locations, options include resection, SRS, or fractionated radiation therapy, alone or in combination. Nine studies published between 2002 and 2017 described a limited number of tumors managed by SRS, ranging from 1 to 6 cases per study.7,8,10–13,15,17,18 Eight of these studies reported long-term tumor control rates of 100%, while 1 study described a long-term tumor control of 92%. Clinical outcomes included improvement or stabilization of symptoms, including diplopia, in many cases, ranging from 38% to 100%. The rate of worsening symptoms was null in most studies, with one study describing 6% of neurological deterioration due to tumor expansion and another study identifying 3 instances of transient diplopia and 1 case of visual deterioration due to orbital tumor extension (Table 3).
Summary of published literature
| Authors & Year | No. of Patients | Median Follow-Up, Mos (range) | Marginal Dose, Gy (range) | Tumor Control | Clinical Evolution | Morbidity |
|---|---|---|---|---|---|---|
| Pollock et al., 200217* | 1 | NA | NA | 100% | NA | No |
| Petrela et al., 200911 | 2 | 24 | 13–14 | 100% | Improvement in 1, stabilization in 1 | No |
| Hayashi et al., 20107 | 4 | 27 (7–43) | 12 | 100% | Resolution of presenting diplopia in 1, worsening of preexisting vision in 1 | Transient diplopia in 3, visual deterioration in 1 w/ orbital extension |
| Choi et al., 201113* | 1 | 29 | 18 | 100% | NA | No |
| Kimball et al., 201115* | 2 | 19 | 12.5 | 100% | Stability | No |
| Inoue et al., 20158 | 1 | 12 | 12 | 100% | Resolution of diplopia | No |
| Prasad et al., 201612 | 6 | 44 (24–78) | 12.5 (12–14) | 100% | Improvement in 83% | 6% neurological deterioration due to tumor expansion |
| Puataweepong et al., 201618* | 3 | 36 (3–135) | Various, 21–25 in 5 fractions most common | 92% | Improvement in 38% | No |
| Peciu-Florianu et al., 201710 | 5 | 44 (12–54) | 12 | 100% | Resolution in 100% | No |
| Present study | 25 | 41 (2–168) | 12.5 (11–15) | 92% crude, 96% at 1 yr, 86% at 10 yrs | Improvement of diplopia in 55%, improvement of ptosis in 25% | Worsening/new diplopia in 3, ptosis in 2, visual loss in 1 |
NA = not available.
Part of nonvestibular schwannoma series; some data not specific to oculomotor schwannoma.
Tumor Control
In this study, we report actuarial tumor control rates of 96% at 1 year and 86% at 10 years, which are comparable with the 92%–100% control rates described in previous studies.7,8,10–13,15,17,18 These results also mirror some reports from prior studies pertaining to other cranial nerve schwannomas, most commonly those originating from the vestibular (10-year control of 92%),3 trigeminal (10-year control of 95%),1 facial (5-year control of 90%),6 and jugular foramen (10-year control of 82%)5 nerves. This suggests that schwannoma radiosensitivity is an intrinsic characteristic of this tumor type and may be less related to the nerve of origin.
As noted in Results, the median tumor volume treated was only 0.74 cm3 (range 0.01–22.4 cm3). Most (n = 13) of the schwannomas treated were smaller than 1 cm3, possibly related to the location of the cranial nerves of study as symptoms are more likely to appear and a diagnosis to be made with a smaller schwannoma. However, it is notable that even the larger schwannomas, such as that of 22.4 cm3, exhibited tumor regression and demonstrated either stable or improved clinical symptoms at the last clinical follow-up at 60 months. This is consistent with the experience with large vestibular schwannomas for which a good response can be consistently achieved.3
Symptom Control and Safety
In the current literature, clinical symptom control rates in oculomotor nerve schwannomas following SRS vary between 38% and 100%.7,8,11–13,15,16,18 Worsening of cranial nerve function is rare after radiosurgery, with only 2 studies each presenting a case of cranial nerve deterioration.7,12 In the present study, we were able to confirm the safety of SRS for the management of oculomotor schwannomas. Diplopia improved in 55% and remained stable in 30% of patients. For ptosis, improvement was seen in 25% and stability in 50% of patients. All patients initially presenting with visual function loss had stable symptoms post-SRS. There were only 2 patients with worsened diplopia and ptosis (both associated with tumor growth), with one of these patients also presenting with worsened vision, corresponding to a symptom worsening rate of only 8%. Furthermore, there were no instances of worsened trigeminal neuralgia or facial hypesthesia. There were also no cases of radiation necrosis or radiation-induced edema, nor were there any instances of radiation-induced malignant transformation or new tumor formation.
Due to the rare incidence of these schwannomas, there is only sparse literature reporting symptom control rates after resection.20–22 One study focusing on surgical approaches to oculomotor nerve schwannoma presented a review describing that simple observation of such tumors instead of surgical or radiosurgical treatment led to either unchanged nerve function in 33% of cases or worsening of function in 66% of patients.23 Furthermore, those who had undergone either subtotal or gross-total resection had unchanged (33%) or worsened (21%) nerve function, with only 46% having improved nerve function after surgical treatment.23 Our study demonstrates a favorable morbidity profile compared with that expected following such challenging surgical cases. SRS should therefore be considered as a first-line treatment option for oculomotor cranial nerve schwannomas, one with considerably lower risks of cranial nerve injury than microsurgery.20–23
Limitations of This Study
Schwannomas of the oculomotor, trochlear, and abducens nerves remain extremely rare, with only dozens of cases reported in the literature to date.9 This renders studying such pathologies considerably challenging. Indeed, the small number of cases described for each oculomotor cranial nerve location in this study leads to limited power of the study. Furthermore, because our cohort included patients treated as recently as 2018, clinical follow-up is heterogeneous. We addressed this limitation by performing actuarial analyses. The retrospective design of our study also induces a constitutional selection bias, which limits the possibility of extrapolating such results to a wider population. Finally, in the context of a retrospective multicenter study, each center is responsible for the quality of the data collected as such, introducing a possible source of internal variability.
Conclusions
SRS for schwannomas of the oculomotor, trochlear, and abducens nerves is effective and provides tumor control rates similar to those of other cranial nerve schwannomas. SRS offers improvement of diplopia in the majority of patients. SRS should therefore be considered as a first-line treatment option for oculomotor nerve schwannomas.
Disclosures
Dr. Lunsford: consultant for Insightec and DSMB and stock ownership in Elekta.
Author Contributions
Conception and design: Mathieu. Acquisition of data: Langlois, Faramand, Mohammed, Liščák, Kondziolka, Lee, Atik. Analysis and interpretation of data: Mathieu, Iorio-Morin. Drafting the article: Langlois. 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: Mathieu. Statistical analysis: Iorio-Morin. Study supervision: Mathieu.
Supplemental Information
Online-Only Content
Supplemental material is available with the online version of the article.
Supplementary Fig. 1. https://thejns.org/doi/suppl/10.3171/2020.8.JNS20887.
Previous Presentations
This study was presented in oral form at the 14th International Stereotactic Radiosurgery Society Congress, Rio de Janeiro, Brazil, June 9–13, 2019; and Congrès Annuel Association de Neurochirurgie du Québec, Montreal, Québec, Canada, November 8–9, 2019.
References
- 1↑
Langlois AM, Iorio-Morin C, Masson-Côté L, Mathieu D. Gamma Knife stereotactic radiosurgery for nonvestibular cranial nerve schwannomas. World Neurosurg. 2018;110:e1031–e1039.
- 2
Iorio-Morin C, Liscak R, Vladyka V, et al. Repeat stereotactic radiosurgery for progressive or recurrent vestibular schwannomas. Neurosurgery. 2019;85(4):535–542.
- 3↑
Iorio-Morin C, AlSubaie F, Mathieu D. Safety and efficacy of Gamma Knife radiosurgery for the management of Koos grade 4 vestibular schwannomas. Neurosurgery. 2016;78(4):521–530.
- 4
Kondziolka D, Lunsford LD, McLaughlin MR, Flickinger JC. Long-term outcomes after radiosurgery for acoustic neuromas. N Engl J Med. 1998;339(20):1426–1433.
- 5↑
Kano H, Meola A, Yang H-C, et al. Stereotactic radiosurgery for jugular foramen schwannomas: an international multicenter study. J Neurosurg. 2018;129(4):928–936.
- 6↑
Sheehan JP, Kano H, Xu Z, et al. Gamma Knife radiosurgery for facial nerve schwannomas: a multicenter study. J Neurosurg. 2015;123(2):387–394.
- 7↑
Hayashi M, Chernov M, Tamura N, et al. Gamma Knife surgery for abducent nerve schwannoma. Report of 4 cases. J Neurosurg. 2010;113(suppl):136–143.
- 8↑
Inoue T, Shima A, Hirai H, et al. Trochlear nerve schwannoma treated with Gamma Knife after excision: a case report and review of the literature. J Neurol Surg Rep. 2015;76(2):e248–e252.
- 9↑
Kim I-Y, Kondziolka D, Niranjan A, et al. Gamma Knife surgery for schwannomas originating from cranial nerves III, IV, and VI. J Neurosurg. 2008;109(suppl):149–153.
- 10↑
Peciu-Florianu I, Tuleasca C, Comps J-N, et al. Radiosurgery in trochlear and abducens nerve schwannomas: case series and systematic review. Acta Neurochir (Wien). 2017;159(12):2409–2418.
- 11↑
Petrela E, Hodge CJ, Hahn SS, et al. Stereotactic radiosurgery in two cases of presumed fourth cranial nerve schwannoma. J Neuroophthalmol. 2009;29(1):54–57.
- 12↑
Prasad GL, Sharma MS, Kale SS, et al. Gamma Knife radiosurgery in the treatment of abducens nerve schwannomas: a retrospective study. J Neurosurg. 2016;125(4):832–837.
- 13↑
Choi CYH, Soltys SG, Gibbs IC, et al. Stereotactic radiosurgery of cranial nonvestibular schwannomas: results of single- and multisession radiosurgery. Neurosurgery. 2011;68(5):1200–1208.
- 14
Elsharkawy M, Xu Z, Schlesinger D, Sheehan JP. Gamma Knife surgery for nonvestibular schwannomas: radiological and clinical outcomes. J Neurosurg. 2012;116(1):66–72.
- 15↑
Kimball MM, Foote KD, Bova FJ, et al. Linear accelerator radiosurgery for nonvestibular schwannomas. Neurosurgery. 2011;68(4):974–984.
- 16↑
Nishioka K, Abo D, Aoyama H, et al. Stereotactic radiotherapy for intracranial nonacoustic schwannomas including facial nerve schwannoma. Int J Radiat Oncol Biol Phys. 2009;75(5):1415–1419.
- 17↑
Pollock BE, Foote RL, Stafford SL. Stereotactic radiosurgery: the preferred management for patients with nonvestibular schwannomas? Int J Radiat Oncol Biol Phys. 2002;52(4):1002–1007.
- 18↑
Puataweepong P, Dhanachai M, Hansasuta A, et al. Clinical outcomes of intracranial nonvestibular schwannomas treated with LinacBased stereotactic radiosurgery and radiotherapy. Asian Pac J Cancer Prev. 2016;17(7):3271–3276.
- 19↑
Solberg TD, Balter JM, Benedict SH, et al. Quality and safety considerations in stereotactic radiosurgery and stereotactic body radiation therapy: executive summary. Pract Radiat Oncol. 2012;2(1):2–9.
- 20
Nonaka Y, Fukushima T, Friedman AH, et al. Surgical management of nonvascular lesions around the oculomotor nerve. World Neurosurg. 2014;81(5-6):798–809.
- 21
Acharya R, Husain S, Chhabra SS, et al. Sixth nerve schwannoma: a case report with literature review. Neurol Sci. 2003;24(2):74–79.
- 22
Ohata K, Takami T, Goto T, Ishibashi K. Schwannoma of the oculomotor nerve. Neurol India. 2006;54(4):437–439.
- 23↑
El Asri AC, Arnaout MM, Gerges MM, et al. Prognosis factor in oculomotor schwannoma: a case of endoscopic endonasal approach and systematic review of the literature. World Neurosurg. 2019;129:72–80.
