Abstract
Background
Non-vestibular schwannomas are relatively rare, with trigeminal and jugular foramen schwannomas being the most common. This is a heterogeneous group which requires detailed investigation and careful consideration to management strategy. The optimal management for these tumours remains unclear, and there are several controversies. The aim of this paper is to provide insight into the main principles defining management and surgical strategy, in order to formulate a series of recommendations.
Methods
A task force was created by the EANS skull base section along with its members and other renowned experts in the field to generate recommendations for the surgical management of these tumours on a European perspective. To achieve this, the task force performed an extensive systematic review in this field and had discussions within the group. This article is the first of a three-part series describing non-vestibular schwannomas (I, II, III, IV, VI).
Results
A summary of literature evidence was proposed after discussion within the EANS skull base section. The constituted task force dealt with the practice patterns that exist with respect to pre-operative radiological investigations, ophthalmological assessments, optimal surgical and radiotherapy strategies and follow-up management.
Conclusion
This article represents the consensually derived opinion of the task force with respect to the treatment of non-vestibular schwannomas. For each of these tumours, the management of these patients is complex, and for those which are symptomatic tumours, the paradigm is shifting towards the compromise between function preservation and progression-free survival.
Similar content being viewed by others
References
Acharya R, Husain S, Chhabra SS, Patir R, Bhalla S, Sehgal AD (2003) Sixth nerve schwannoma: a case report with literature review. Neurol Sci. https://doi.org/10.1007/s100720300076
Adachi K, Yoshida K, Miwa T, Ikeda E, Kawase T (2007) Olfactory schwannoma. Acta Neurochir (Wien). https://doi.org/10.1007/s00701-007-1158-5
Ambekar S, Sonig A, Nanda A (2012) Dorello’s canal and Gruber’s ligament: historical perspective. J Neurol Surgery, Part B Skull Base. https://doi.org/10.1055/s-0032-1329628
Anderson DR, Hoyt WF (1969) Ultrastructure of intraorbital portion of human and monkey optic nerve. Arch Ophthalmol. https://doi.org/10.1001/archopht.1969.00990020508017
El Asri AC, Arnaout MM, Gerges MM, Gazzaz M, El Mostarchid B, Schwartz TH (2019) Prognosis factor in oculomotor schwannoma: a case of endoscopic endonasal approach and systematic review of the literature. World Neurosurg. https://doi.org/10.1016/j.wneu.2019.05.170
Beppu T, Yoshida Y, Wada T, Arai H, Suzuki M, Kuroda K, Ogawa A (1997) Trochlear and abducens nerve neurinomas accompanied by a cerebellopontine angle meningioma - case report. Neurol Med Chir (Tokyo). https://doi.org/10.2176/nmc.37.416
Bohoun CA, Terakawa Y, Goto T et al (2017) Schwannoma-like tumor in the anterior cranial fossa immunonegative for Leu7 but immunopositive for Schwann/2E. Neuropathology. https://doi.org/10.1111/neup.12357
Celli P, Ferrante L, Acqui M, Mastronardi L, Fortuna A, Palma L (1992) Neurinoma of the third, fourth, and sixth cranial nerves: a survey and report of a new fourth nerve case. Surg Neurol. https://doi.org/10.1016/0090-3019(92)90172-J
Cho Y-H, Sung K-S, Song Y-J, Kim D-C, Choi S, Kim K-U (2014) Oculomotor nerve schwannoma: a case report. Brain Tumor Res Treat. https://doi.org/10.14791/btrt.2014.2.1.43
Choi CYH, Soltys SG, Gibbs IC, Harsh GR, Sakamoto GT, Patel DA, Lieberson RE, Chang SD, Adler JR (2011) Stereotactic radiosurgery of cranial nonvestibular schwannomas: results of single-and multisession radiosurgery. Neurosurgery. https://doi.org/10.1227/NEU.0b013e31820c0474
Chowdhury FH, Haque MR, Goel AH (2014) Abducent nerve schwannoma: a report of 3 cases. Neurosurg Q. https://doi.org/10.1097/WNQ.0b013e31828c7265
Civit T, Pinelli C, Klein M, Auque J, Baylac F, Hepner H (1997) Intrasellar schwannoma. Acta Neurochir (Wien). https://doi.org/10.1007/BF02747200
Elsharkawy M, Xu Z, Schlesinger D, Sheehan JP (2012) Gamma Knife surgery for nonvestibular schwannomas: radiological and clinical outcomes: clinical article. J Neurosurg. https://doi.org/10.3171/2011.8.JNS11215
Erlich SA, Tymianski M, Kiehl TR (2009) Cellular schwannoma of the abducens nerve: case report and review of the literature. Clin Neurol Neurosurg. https://doi.org/10.1016/j.clineuro.2009.01.001
Evans D, Raymond F, Barwell J, Halliday D (2012) Genetic testing and screening of individuals at risk of NF2. Clin Genet 82(5):416–424
Fadel HA, El Ahmadieh TY, Plitt AR, Neeley OJ, Johnson Z, Aoun SG, Mohamad O, Timmerman R, Weprin BE (2019) Oculomotor schwannomas: a systematic review and report of two pediatric cases treated with fractionated cyberknife stereotactic radiotherapy. World Neurosurg. https://doi.org/10.1016/j.wneu.2019.05.114
Fang C, Leavitt JA, Hodge DO, Holmes JM, Mohney BG, Chen JJ (2017) Incidence and etiologies of acquired third nerve palsy using a population-based method. JAMA Ophthalmol. https://doi.org/10.1001/jamaophthalmol.2016.4456
Farrokhi MR, Ghaffarpasand F, Taghipour M, Derakhshan N (2018) Transventricular transvelar approach to trochlear nerve schwannoma: novel technique to lesions of inferior pineal region. World Neurosurg. https://doi.org/10.1016/j.wneu.2018.03.132
Figueiredo EG, Soga Y, Amorim RLO, Oliveira AMP, Teixeira MJ (2011) The puzzling olfactory groove schwannoma: a systematic review. Skull Base. https://doi.org/10.1055/s-0030-1262945
Figueroa-Ángel V, Rodríguez-Aceves CA, Calderon-Miranda WG, Escobar-Hernandez N, Joaquim AF, Moscote-Salazar LR (2018) Subfrontal schwannoma: case report and review of literature. World Neurosurg. https://doi.org/10.1016/j.wneu.2017.10.045
Furtado SV, Hegde AS (2012) Management of oculomotor nerve schwannomas in two different locations: surgical nuances and comprehensive review. Neurosurg Rev. https://doi.org/10.1007/s10143-011-0344-3
G. M, A. H, V.V. D (1999) En bloc resection of an intracavernous oculomotor nerve schwannoma and grafting of the oculomotor nerve with sural nerve. Case report and review of the literature. J. Neurosurg.
Goel A, Muzumdar D, Raman C, Post KD, Day JD, Konovalov AN (2003) Trigeminal neuroma: analysis of surgical experience with 73 cases. Neurosurgery. https://doi.org/10.1227/01.NEU.0000053365.05795.03
Hatipoǧlu HG, Durakoǧlugil T, Ciliz D, Yüksel E (2007) Comparison of FSE T2W and 3D FIESTA sequences in the evaluation of posterior fossa cranial nerves with MR cisternography. Diagnostic Interv. Radiol.
Hayashi M, Chernov M, Tamura N, et al. (2010) Gamma Knife surgery for abducent nerve schwannoma. Report of 4 cases. J Neurosurg. https://doi.org/10.3171/2010.8.gks10947
Ho KL (1981) Schwannoma of the trochlear nerve. Case report. J Neurosurg. https://doi.org/10.3171/jns.1981.55.1.0132
Iida Y, Sakata K, Kobayashi N, Tatezuki J, Manaka H, Kawasaki T (2016) Orbital abducens nerve schwannoma: a case report and review of the literature. NMC Case Rep J. https://doi.org/10.2176/nmccrj.cr.2015-0259
Imran Zaidi SM, Naik P, Ahmed SK (2020) Abducens nerve schwannoma: first case to be treated with an expanded endonasal approach. Ear, Nose Throat J. https://doi.org/10.1177/0145561320960541
Jacquesson T, Cotton F, Attyé A, Zaouche S, Tringali S, Bosc J, Robinson P, Jouanneau E, Frindel C (2019) Probabilistic tractography to predict the position of cranial nerves displaced by skull base tumors: value for surgical strategy through a case series of 62 patients. Neurosurgery 85(1):E125–E136
Jacquesson T, Yeh F-C, Panesar S, Barrios J, Attyé A, Frindel C, Cotton F, Gardner P, Jouanneau E, Fernandez-Miranda JC (2020) Full tractography for detecting the position of cranial nerves in preoperative planning for skull base surgery: technical note. J Neurosurg 132(5):1642–1652
Jecko V, Sesay M, Liguoro D (2020) Anatomical location of the abducens nerves (VI) in the ventral approach of clival tumors. Surg Radiol Anat. https://doi.org/10.1007/s00276-020-02525-4
Joo W, Yoshioka F, Funaki T, Rhoton AL (2012) Microsurgical anatomy of the abducens nerve. Clin Anat. https://doi.org/10.1002/ca.22047
Joshi R (2012) Learning from eponyms: Jose Verocay and Verocay bodies, Antoni A and B areas, Nils Antoni and schwannomas. Indian Dermatol Online J. https://doi.org/10.4103/2229-5178.101826
Kashkouli MB, Abdolalizadeh P, Jafari S, Shahrzad S, Karimi N (2019) Is primary optic nerve sheath schwannoma a misnomer? Report of two cases and literature review Orbit (London). https://doi.org/10.1080/01676830.2018.1545239
Katoh M, Kawamoto T, Ohnishi K, Sawamura Y, Abe H (2000) Asymptomatic schwannoma of the oculomotor nerve: case report. J Clin Neurosci 7(5):458–460
Kim DS, Choi JU, Yang KH, Jung JM (2002) Optic sheath schwannomas: report of two cases. Child’s Nerv Syst. https://doi.org/10.1007/s00381-002-0663-3
Kim I-Y, Kondziolka D, Niranjan A, Flickinger JC, Lunsford LD (2018) Gamma Knife surgery for schwannomas originating from cranial nerves III, IV, and VI. J Neurosurg. https://doi.org/10.3171/jns/2008/109/12/s23
King JS (1976) Trochlear nerve sheath tumor: case report. J Neurosurg. https://doi.org/10.3171/jns.1976.44.2.0245
Kinoshita Y, Kurosaki M, Kamitani H, Watanabe T (2008) Schwannoma originating in the optic canal. Acta Neurochir (Wien). https://doi.org/10.1007/s00701-007-1452-2
Komoribayashi N, Arai H, Kojo T, Obonai C, Wakabayashi J, Ogawa A (2005) Subfrontal schwannoma: case report. Neurol. Surg.
Konovalov AN, Spallone A, Mukhamedjanov DJ, Tcherekajev VA, Makhmudov UB (1996) Trigeminal neurinomas. A series of 111 surgical cases from a single institution. Acta Neurochir (Wien). https://doi.org/10.1007/BF01412304
Krisht A, Barnett DW, Barrow DL, Bonner G (1994) The blood supply of the intracavernous cranial nerves: an anatomic study. Neurosurgery. https://doi.org/10.1227/00006123-199402000-00011
Kulkarni RG, Satalkar VY, Bhawthankar AW (1980) Neurilemmoma of optic nerve. Indian J. Ophthalmol.
Kumar R, Kothiwala A, Ghosh R (2014) Sixth nerve schwannoma. Neurol India. https://doi.org/10.4103/0028-3886.128355
Lan YH, Li YC, Chang CN, Zhang B, Lu YJ (2020) Trochlear schwannoma arising from transition zone of nerve sheath in the pineal region: case report and review of the literature. World Neurosurg. https://doi.org/10.1016/j.wneu.2020.02.019
Langlois A-M, Iorio-Morin C, Faramand A et al (2021) Outcomes after stereotactic radiosurgery for schwannomas of the oculomotor, trochlear, and abducens nerves. J Neurosurg. https://doi.org/10.3171/2020.8.jns20887
Lanotte M, Giordana MT, Forni C, Pagni CA (1992) Schwannoma of the cavernous sinus. Case report and review of the literature. J. Neurosurg. Sci.
Lee SK, Moon KS, Lee KH, Jung S (2013) Cystic abducens schwannoma without abducens paresis: possible role of cisternal structures in clinical manifestation. J Korean Neurosurg Soc. https://doi.org/10.3340/jkns.2013.53.6.374
Leunda G, Vaquero J, Cabezudo J, Garcia-Uria J, Bravo G (1982) Schwannoma of the oculomotor nerves. Report of four cases. J Neurosurg. https://doi.org/10.3171/jns.1982.57.4.0563
Li X, Li J, Li J, Wu Z (2015) Schwannoma of the 6th nerve: case report and review of the literature. Chinese Neurosurg J. https://doi.org/10.1186/s41016-015-0004-5
Liberati A, Altman DG, Tetzlaff J, Mulrow C, Gøtzsche PC, Ioannidis JPA, Clarke M, Devereaux PJ, Kleijnen J, Moher D (2009) The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate healthcare interventions: explanation and elaboration. BMJ. https://doi.org/10.1136/bmj.b2700
Liu JK, Eloy JA (2012) Expanded endoscopic endonasal transcribriform approach for resection of anterior skull base olfactory schwannoma. J Neurosurg. https://doi.org/10.3171/2012.v3.focus11300
Lo PA, Harper CG, Besser M (2001) Intracavernous schwannoma of the abducens nerve: a review of the clinical features, radiology and pathology of an unusual case. J Clin Neurosci. https://doi.org/10.1054/jocn.2000.0846
Magoon EH, Robb RM (1981) Development of myelin in human optic nerve and tract: a light and electron microscopic study. Arch Ophthalmol. https://doi.org/10.1001/archopht.1981.03930010655011
Mahadevan A, Floyd S, Wong E, Chen C, Kasper E (2011) Clinical outcome after hypofractionated stereotactic radiotherapy (HSRT) for benign skull base tumors. Comput Aided Surg. https://doi.org/10.3109/10929088.2011.565160
Mahore A, Ramdasi R, Chagla A, Tikeykar V (2019) Intraconal optic sheath schwannoma: report of two cases. Br J Neurosurg. https://doi.org/10.1080/02688697.2017.1297768
Mariniello G, De Divitiis O, Caranci F, Dones F, Maiuri F (2018) Parasellar schwannomas: extradural vs extra-intradural surgical approach. Oper Neurosurg. https://doi.org/10.1093/ons/opx174
Mascarenhas L, Magalhães Z, Honavar M, Romão H, Resende M, Resende Pereira J, Rocha Vaz A, Jooma R (2004) Schwannoma of the abducens nerve in the cavernous sinus. Acta Neurochir (Wien). https://doi.org/10.1007/s00701-003-0197-9
Masuda H, Nemoto M, Okonogi S, Node Y, Ando S, Kondo K, Harada N, Sugo N (2020) Utility of Schwann/2E and Sox10 in distinguishing CD57-negative olfactory groove schwannoma from olfactory ensheathing cell tumor: a case report and review of the literature. Neuropathology. https://doi.org/10.1111/neup.12650
Micovic MV, Zivkovic BM, Zivanovic JD, Bascarevic VLJ, Bogosavljevic V, Rasulic LG (2017) Ancient olfactory schwannoma - case report and literature review. Turk Neurosurg. https://doi.org/10.5137/1019-5149.JTN.14122-15.0
Muhammad S, Niemelä M (2019) Management of oculomotor nerve schwannoma: systematic review of literature and illustrative case. Surg Neurol Int. https://doi.org/10.25259/SNI-75-2019
Nadkarni TD, Goel A (1999) Trochlear nerve neurinoma presenting as pathological laughter. Br J Neurosurg. https://doi.org/10.1080/02688699944023
Nakamizo A, Matsuo S, Amano T (2019) Abducens nerve schwannoma: a case report and literature review. World Neurosurg. https://doi.org/10.1016/j.wneu.2019.01.123
Nakamura M, Carvalho GA, Samii M (2002) Abducens nerve schwannoma: a case report and review of the literature. Surg Neurol. https://doi.org/10.1016/S0090-3019(01)00670-X
Nathan H, Ouaknine G, Kosary IZ (1974) The abducens nerve. Anatomical variations in its course. J Neurosurg. https://doi.org/10.3171/jns.1974.41.5.0561
Nesvick CL, Perry A, Graffeo CS, Raghunathan A, Hammack JE, Van Gompel JJ (2017) Trochlear schwannoma presenting with isolated trigeminal neuralgia. World Neurosurg. https://doi.org/10.1016/j.wneu.2017.04.062
Nishioka K, Abo D, Aoyama H, Furuta Y, Onimaru R, Onodera S, Sawamura Y, Ishikawa M, Fukuda S, Shirato H (2009) Stereotactic radiotherapy for intracranial nonacoustic schwannomas including facial nerve schwannoma. Int J Radiat Oncol Biol Phys. https://doi.org/10.1016/j.ijrobp.2008.12.063
Okada Y, Shima T, Nishida M, Okita S (1997) Large sixth nerve neuroma involving the prepontine region: case report. Neurosurgery. https://doi.org/10.1097/00006123-199703000-00035
Oxman AD (2004) Grading quality of evidence and strength of recommendations. Br Med J. https://doi.org/10.1136/bmj.328.7454.1490
Park JH, Cho YH, Kim JH, Lee JK, Kim CJ (2009) Abducens nerve schwannoma: case report and review of the literature. Neurosurg Rev. https://doi.org/10.1007/s10143-009-0203-7
Peciu-Florianu I, Tuleasca C, Comps JN, Schiappacasse L, Zeverino M, Daniel RT, Levivier M (2017) Radiosurgery in trochlear and abducens nerve schwannomas: case series and systematic review. Acta Neurochir (Wien). https://doi.org/10.1007/s00701-017-3348-0
Petruzzelli MG, Margari M, Furente F, Costanza MC, Legrottaglie AR, Dicuonzo F, Margari L (2019) Recurrent painful ophthalmoplegic neuropathy and oculomotor nerve schwannoma: a pediatric case report with long-term mri follow-up and literature review. Pain Res Manag. https://doi.org/10.1155/2019/5392945
Prasad GL, Sharma MS, Kale SS, Agrawal D, Singh M, Sharma BS (2016) Gamma Knife radiosurgery in the treatment of abducens nerve schwannomas: a retrospective study. J Neurosurg. https://doi.org/10.3171/2015.8.JNS151140
Pushker N, Khurana S, Kashyap S, Sen S, Shrey D, Meel R, Chawla B, Bajaj MS (2015) Orbital schwannoma: a clinicopathologic study. Int Ophthalmol. https://doi.org/10.1007/s10792-014-9973-1
Ramey WL, Arnold SJ, Chiu A, Lemole M (2015) A rare case of optic nerve schwannoma: case report and review of the literature. Cureus. https://doi.org/10.7759/cureus.265
Sabel LHW, Teepen JLJM (1995) The enigmatic origin of olfactory schwannoma. Clin Neurol Neurosurg. https://doi.org/10.1016/0303-8467(95)00022-C
Santoreneos S, Hanieh A, Jorgensen RE (1997) Trochlear nerve schwannomas occurring in patients without neurofibromatosis: case report and review of the literature. Neurosurgery. https://doi.org/10.1097/00006123-199707000-00050
Sarma S, Sekhar LN, Schessel DA, Malis LI, Day JD (2002) Nonvestibular schwannomas of the brain: a 7-year experience. Neurosurgery. https://doi.org/10.1097/00006123-200203000-00002
Sato M, Kanai N, Fukushima Y, Matsumoto S, Tatsumi C, Kitamura K, Ozaki M, Hayakawa T (1996) Hypoglossal neurinoma extending intra- and extracranially: Case report. Surg Neurol. https://doi.org/10.1016/S0090-3019(96)80012-7
Sauvaget F, François P, Ben Ismail M, Thomas C, Velut S (2013) Anterior fossa schwannoma mimicking an olfactory groove meningioma: case report and literature review. Neurochirurgie 59(2):75–80
Sekhar LN, Lanzino G, Sen CN, Pomonis S (1992) Reconstruction of the third through sixth cranial nerves during cavernous sinus surgery. J Neurosurg. https://doi.org/10.3171/jns.1992.76.6.0935
Sharma A, Singh D, Saran R (2021) Primary optic nerve sheath schwannoma: a case report. Br J Neurosurg. https://doi.org/10.1080/02688697.2020.1869181
Shibao S, Hayashi S, Yoshida K (2014) Dumbbell-shaped abducens schwannoma: case report. Neurol Med Chir (Tokyo). https://doi.org/10.2176/nmc.cr2012-0304
Simpson RK, Harper RL, Kirkpatrick JB, Cooper B (1987) Schwannoma of the optic sheath. J Clin Neuroophthalmol. https://doi.org/10.3109/01658108709007455
Suetake K, Kurokawa Y, Uede T, Momota H, Hashi K (1998) A case of abducens neurinoma mimicking acoustic neurinoma. Comput Med Imaging Graph. https://doi.org/10.1016/S0895-6111(98)00023-8
Sun H, Sharma K, Kalakoti P et al (2017) Factors associated with abducens nerve recovery in patients undergoing surgical resection of sixth nerve schwannoma: a systematic review and case illustration. World Neurosurg. https://doi.org/10.1016/j.wneu.2017.04.146
Taha M, AlBakry A, ElSheikh M, AbdelBary T (2018) Olfactory nerve schwannoma: a case report and review of the literature. Surg J. https://doi.org/10.1055/s-0038-1669991
Tanriover N, Kemerdere R, Kafadar AM, Muhammedrezai S, Akar Z (2007) Oculomotor nerve schwannoma located in the oculomotor cistern. Surg Neurol. https://doi.org/10.1016/j.surneu.2006.06.012
Torun N, Laviv Y, Jazi KK, Mahadevan A, Bhadelia RA, Matthew A, Strominger M, Kasper EM (2018) Schwannoma of the trochlear nerve—an illustrated case series and a systematic review of management. Neurosurg Rev. https://doi.org/10.1007/s10143-016-0783-y
Tung H, Chen T, Weiss MH (1991) Sixth nerve schwannomas. Report of two cases. J Neurosurg. https://doi.org/10.3171/jns.1991.75.4.0638
Vachata P, Sameš M (2009) Abducens nerve schwannoma mimicking intrinsic brainstem tumor. Acta Neurochir (Wien). https://doi.org/10.1007/s00701-009-0302-9
Verocay J: (1910) Zur Kenntnis der ‘Neuro brome’. Beitr Pathol Anat Allg Pathol 1‐69,:
Wang M, Huang H, Zhou Y (2015) Abducens nerve schwannoma in cerebellopontine angle mimicking acoustic neuroma. J Craniofac Surg. https://doi.org/10.1097/SCS.0000000000001520
Xiao J, Ye L, Wang W, Cheng H, Li C, Luo J, Hu X, Zhang Y (2020) Microneurosurgical treatment under the guidance of neuroendoscopy for an intracranial optic nerve Schwannoma: a case report. Medicine (Baltimore). https://doi.org/10.1097/MD.0000000000020747
Y.-H. L, Y.-C. L, C.-N. C, B. Z, Y.-J. L (2020) Trochlear schwannoma arising from transition zone of nerve sheath in the pineal region: case report and review of the literature. World Neurosurg.
Yamaguchi T, Fujii H, Dziurzynski K, Delashaw JB, Watanabe E (2010) Olfactory ensheathing cell tumor: Case report. Skull Base. https://doi.org/10.1055/s-0030-1249572
Yoneoka Y, Akiyama K, Seki Y, Hasegawa G, Kakita A (2018) Frontoethmoidal schwannoma with exertional cerebrospinal fluid rhinorrhea: case report and review of literature. World Neurosurg. https://doi.org/10.1016/j.wneu.2018.01.015
Author information
Authors and Affiliations
Corresponding author
Ethics declarations
Ethics approval
All procedures performed in studies involving human participants were in accordance with the ethical standards of the local ethical committee (Geneva Ethics Committee Board no. 11-233R, NAC 11-085R) and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Consent to participate
For this retrospective type of study, formal consent is not required.
Conflict of interest
The authors declare no competing interests.
Additional information
Publisher's note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
About this article
Cite this article
Bal, J., Bruneau, M., Berhouma, M. et al. Management of non-vestibular schwannomas in adult patients: a systematic review and consensus statement on behalf of the EANS skull base section. Part I: oculomotor and other rare non-vestibular schwannomas (I, II, III, IV, VI). Acta Neurochir 164, 285–297 (2022). https://doi.org/10.1007/s00701-021-05048-y
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00701-021-05048-y