Use of Trigeminal-Hypoglossal Reflex in Microvascular Decompression Surgery for Trigeminal Neuralgia

Introduction: Trigeminal neuralgia (TN) is a pain disorder classically characterized by recurrent paroxysms of unilateral facial pain, usually due to vascular compression of the trigeminal nerve at the root entry zone. Microvascular decompression (MVD) of the offending vessel on the nerve has been well described as an effective treatment method with optimal long-term outcomes of pain relief.
Intraoperative neurophysiological monitoring (IOMN) allows for real-time assessment of the functional integrity of neural structures and prevent injury, but is unable to monitor for effectiveness of the surgery.
We present the novel use of the trigeminal-hypoglossal reflex (THR) as an adjunct to determine adequacy of decompression and reduce the risk of postoperative complications.

Methods: 13 patients with TN underwent MVD with THR monitoring. Electrodes were placed along the trigeminal nerve and in the lateral aspect of the tongue. Stimulation of the V3 branch of the trigeminal nerve was performed and the hypoglossal muscle response recorded. Recordings were taken at the start of surgery and after decompression was performed. The absence of the trigeminal hypoglossal reflex was utilised as a marker of having achieved adequate decompression.

Results: THR was present in 12 of 13 patients at the start of surgery. All patients had absent THR after decompression was performed. There was immediate significant pain relief from an average Barrow Neurological Institute (BNI) Pain Intensity Scale of 3.77 preoperatively to 2.38 on POD1. 11 of 13 patients were weaned off analgesia by 2 months post-op and all patients by 6 months. One patient suffered a complication of cerebrospinal fluid leak and required surgical repair.

Conclusion : THR is a valuable intra-operative adjunct in MVD to achieve adequate decompression of the trigeminal nerve, translating to good postoperative pain relief in our patient cohort. Further studies in the role of THR in patients with TN without obvious neurovascular conflict may be conducted.