Pitfalls in Trigeminal Nerve Mapping in Neurosurgery: The Mystery of the Unexpected Motor Responses

Abstract

Objective

Intraoperative neurophysiological mapping can help identify the trigeminal nerve (TN) during surgeries where it is at risk. Low-stimulating currents may only recruit sensory branch stimulation and trigger reflex responses, potentially complicating interpretation during monitoring. This report aims to address this issue by examining cases to categorize TN responses in relation to varying stimulation intensities, identify stimulation patterns, and clarify common response characteristics in surgical contexts.

Methods

Seven cerebellopontine (CP) angle surgery cases with TN exposure were studied. Concentric bipolar stimulation was applied over the TN from 0.05 to 4 mA, and responses were recorded from various muscles innervated by the cranial nerves under monitoring (V, VII, IX, X, XI, XII).

Results

Low stimulation currents (particularly below 0.5 mA) may elicit reflex responses over hypoglossal and facial innervated muscles, more often than motor responses, when the TN is stimulated.

Conclusion

A stimulation protocol starting at 0.05 mA and increasing to at least 1 mA or until compound muscle action potentials are observed in trigeminally innervated muscles is recommended for accurate TN mapping in CP angle surgery. These results may be helpful to avoid misinterpreting reflex responses in non-TN-innervated muscles

Keywords

trigeminal neuralgia - trigeminal nerve reflex - brainstem reflex - cranial nerve mapping

^* JSM and AMP contributed equally as co-first authors to this work.

Publication History

Received: 15 January 2025

Accepted: 14 March 2025

Article published online:
08 April 2025

• References

• 1 Joo W, Yoshioka F, Funaki T, Mizokami K, Rhoton Jr AL. Microsurgical anatomy of the trigeminal nerve. Clin Anat 2014; 27 (01) 61-88
• 2 Sindou M, Brinzeu A. Topography of the pain in classical trigeminal neuralgia: insights into somatotopic organization. Brain 2020; 143 (02) 531-540
• 3 Kodama K, Kothbauer KF, Deletis V. Mapping and monitoring of brainstem surgery. Handb Clin Neurol 2022; 186: 151-161
• 4 Deletis V, Seidel K, Fernández-Conejero I. Intraoperative neurophysiologic monitoring and mapping in children undergoing brainstem surgery. J Clin Neurophysiol 2024; 41 (02) 108-115
• 5 Sindou M, Brinzeu A. Technical report on intra-operative trigeminal root mapping in percutaneous lesioning for trigeminal neuralgias. Acta Neurochir (Wien) 2024; 166 (01) 434
• 6 Mirallave Pescador A, Téllez MJ, Sánchez Roldán MLÁ. et al. Methodology for eliciting the brainstem trigeminal-hypoglossal reflex in humans under general anesthesia. Clin Neurophysiol 2022; 137: 1-10
• 7 Szelényi A, Fava E. Long latency responses in tongue muscle elicited by various stimulation sites in anesthetized humans - new insights into tongue-related brainstem reflexes. Brain Stimul 2022; 15 (03) 566-575
• 8 Morota N, Ihara S, Deletis V. Intraoperative neurophysiology for surgery in and around the brainstem: role of brainstem mapping and corticobulbar tract motor-evoked potential monitoring. Childs Nerv Syst 2010; 26 (04) 513-521
• 9 Li X, Bao Y, Liang J, Chen G, Guo H, Li M. Electrophysiological mapping and assessment of facial nerve functioning during acoustic neuroma operations. Ann Transl Med 2021; 9 (05) 405
• 10 Kartush JM, Lundy LB. Facial nerve outcome in acoustic neuroma surgery. Otolaryngol Clin North Am 1992; 25 (03) 623-647
• 11 Kartush JM, Rice KS, Minahan RE, Balzer GK, Yingling CD, Seubert CN. Best practices in facial nerve monitoring. Laryngoscope 2021; 131 (Suppl. 04) S1-S42
• 12 Bernard F, Mercier P, Sindou M. Morphological and functional anatomy of the trigeminal triangular plexus as an anatomical entity: a systematic review. Surg Radiol Anat 2019; 41 (06) 625-637
• 13 Sala F. Intraoperative neurophysiology in pediatric neurosurgery: a historical perspective. Childs Nerv Syst 2023; 39 (10) 2929-2941
• 14 Deletis V, Urriza J, Ulkatan S, Fernandez-Conejero I, Lesser J, Misita D. The feasibility of recording blink reflexes under general anesthesia. Muscle Nerve 2009; 39 (05) 642-646
• 15 Ulkatan S, Jaramillo AM, Téllez MJ, Goodman RR, Deletis V. Feasibility of eliciting the H reflex in the masseter muscle in patients under general anesthesia. Clin Neurophysiol 2017; 128 (01) 123-127
• 16 de Melo DLM, Comerlato EA, Pinheiro DS, Manzano GM. The feasibility and technical aspects of trigemino-cervical reflex elicitation in humans under general anesthesia. Clin Neurophysiol 2024; 161: 173-179
• 17 Fava E, Colistra D, Fragale M, Cenzato M. A novel method of neurophysiological brainstem mapping in neurosurgery. J Neurosci Methods 2024; 405: 110096