TO THE EDITOR: With great interest, we read the retrospective study by Schramm et al.1 (Schramm S, Mehta A, Auguste KI, et al. Navigated transcranial magnetic stimulation mapping of the motor cortex for preoperative diagnostics in pediatric epilepsy. J Neurosurg Pediatr. 2021;28[3]:287-294), who reviewed their database from a single institution. Preoperative motor mapping with navigated transcranial magnetic stimulation (nTMS) has been well-studied in adults and its advantages have led to the establishment of nTMS mapping as a technique for preoperative workup.2 Studies on the application of nTMS in children are mostly consistent, although its application can be more challenging due to a potential lack of compliance and increased resting motor threshold in children, which was nicely elaborated by the authors. We strongly agree with the authors that patients with known epilepsy (and receiving antiepileptic medication) should also be studied for preoperative functional evaluation, although this was considered a contraindication in some previous reports.
In addition to the well-described experience of applying nTMS in pediatric neurosurgery, we would like to add previously published reports to further complete the well-elaborated discussion by Schramm et al. In a prospective study, our group investigated the use of nTMS motor and language mapping in children undergoing surgery in motor- and/or speech-eloquent areas.3 In addition to demonstrating the feasibility of nTMS in children, we combined this technique with nTMS-based tractography for preoperative planning (i.e., defining the optimal approach to avoid eloquent areas). The motor cortex and the corticospinal tract were analyzed for motor-eloquent lesions as well as language-eloquent cortical areas, together with the complex network of language tracts for language-associated lesions in neurooncology as well as for epilepsy surgery cases. The assessment not only impacted the surgical procedure in terms of intraoperative visualization and determining the extent of resection/surgical approach, but also improved the counseling and understanding of the surgical intervention for both the parents and the child.
In addition to the experience noted above, other published studies that evaluated the use of preoperative nTMS in children could be added.4–7 Two independent case reports of a 3-year old boy with a Rolandic ganglioglioma6 and a 6-year old boy with a left perisylvian tumor7 demonstrated the feasibility of nTMS motor and language mapping in children. In an observational study of 14 children, cortical language mapping was correlated with direct cortical stimulation (DCS), and heterogeneous agreement on sensitivity and specificity but high negative predictive value was found.4 Another study aimed to examine bilateral language processing in 3 children prior to an epilepsy surgical intervention.5 In addition to studies analyzing language representation, a publication in 2013 investigated a mixed cohort of children and adults with epilepsy and demonstrated the feasibility and reliability of nTMS motor mapping with suitable accuracy compared to invasive electrical stimulation.8 All studies investigating the use of nTMS exclusively in pediatric neurosurgical cases are summarized in Table 1.
Overview of pediatric nTMS studies
| Authors & Year | No. of Children | Objective | Results |
|---|---|---|---|
| Coburger et al., 20126 | 1 | nTMS motor mapping in a 3-year-old boy w/ a Rolandic ganglioglioma compared to DCS | Successful nTMS motor mapping w/ high DCS agreement |
| Lehtinen et al., 20184 | 14 | nTMS language mapping in children w/ epilepsy compared to DCS | Feasible nTMS language mapping w/ heterogenous agreement but high negative predictive value of 95% compared to DCS |
| Rosenstock et al., 20197 | 1 | nTMS motor + language mapping + nTMS-based tractography of corticospinal tract & language network in a 6-year-old boy w/ lt perisylvian tumor | nTMS mapping + tractography supported surgical planning + intraop resection |
| Rejnö-Habte Selassie et al., 20205 | 3 | nTMS language mapping in 1 child w/ tumor & in 2 children w/ epilepsy-causing lesions | Feasible bihemispheric mapping of receptive language function in 2 of 3 children |
| Rosenstock et al., 20203 | 14 | Children w/ brain tumors & epilepsy-causing lesions in motor-/language-eloquent area, w/ the same protocol as applied as Rosenstock et al., 2019,7 study | Feasible in 10 children (71%), not feasible in 4 children: lack of compliance (n = 2), syncope (n = 1), preexisting implant (n = 1); improved counseling in all cases; modified surgical strategy in 6 cases; adapted aimed extent of resection in 6 cases |
We hope that we are adding further valuable published experiences to the presented discussion and would like to further emphasize that the algorithm presented by Schramm et al. is noteworthy for future development of nTMS in pediatric neurosurgery. The authors are to be congratulated for providing deep insight into the characteristics of nTMS motor mapping in children.
Acknowledgments
The authors acknowledge the support of the Cluster of Excellence: “Matters of Activity. Image Space Material” funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy (EXC 2025–390648296). Dr. Rosenstock is a participant in the BIH Charité Digital Clinician Scientist Program funded by the Charité–Universitätsmedizin Berlin and the Berlin Institute of Health at Charité (BIH).
References
- 1↑
Schramm S, Mehta A, Auguste KI, Tarapore PE. Navigated transcranial magnetic stimulation mapping of the motor cortex for preoperative diagnostics in pediatric epilepsy. J Neurosurg Pediatr. 2021;28(3):287–294.
- 2↑
Jeltema HR, Ohlerth AK, de Wit A, et al. Comparing navigated transcranial magnetic stimulation mapping and “gold standard” direct cortical stimulation mapping in neurosurgery: a systematic review. Neurosurg Rev. 2021;44(4):1903–1920.
- 3↑
Rosenstock T, Picht T, Schneider H, Vajkoczy P, Thomale UW. Pediatric navigated transcranial magnetic stimulation motor and language mapping combined with diffusion tensor imaging tractography: clinical experience. J Neurosurg Pediatr. 2020;26(5):583–593.
- 4↑
Lehtinen H, Makela JP, Makela T, et al. Language mapping with navigated transcranial magnetic stimulation in pediatric and adult patients undergoing epilepsy surgery: comparison with extraoperative direct cortical stimulation. Epilepsia Open. 2018;3(2):224–235.
- 5↑
Rejnö-Habte Selassie G, Pegenius G, Karlsson T, Viggedal G, Hallböök T, Elam M. Cortical mapping of receptive language processing in children using navigated transcranial magnetic stimulation. Epilepsy Behav. 2020;103(Pt A):106836.
- 6↑
Coburger J, Karhu J, Bittl M, Hopf NJ. First preoperative functional mapping via navigated transcranial magnetic stimulation in a 3-year-old boy. J Neurosurg Pediatr. 2012;9(6):660–664.
- 7↑
Rosenstock T, Picht T, Schneider H, Koch A, Thomale UW. Left perisylvian tumor surgery aided by TMS language mapping in a 6-year-old boy: case report. Childs Nerv Syst. 2019;35(1):175–181.
- 8↑
Vitikainen AM, Salli E, Lioumis P, Makela JP, Metsahonkala L. Applicability of nTMS in locating the motor cortical representation areas in patients with epilepsy. Acta Neurochir (Wien). 2013;155(3):507–518.
