Internal neurolysis for trigeminal neuralgia without apparent vascular compression: Clinical outcomes and intraoperative electrophysiological conduction changes

Background: Microvascular decompression (MVD) is the standard surgical treatment for classical trigeminal neuralgia (TN) with evident neurovascular compression. Internal neurolysis (IN) offers an alternative microsurgical technique. However, the physiological basis of symptom relief remains unclear. This study analyzed surgical outcomes and intraoperative conduction changes in patients without apparent vascular compression. Methods: Among 158 patients who underwent MVD for TN between February 2022 and March 2025, 14 had no definite vascular compression on preoperative 3D Magnetic resonance cisternography/angiogram-fusion imaging or intraoperative inspection and underwent IN. Conduction changes were classified into four patterns: (1) shortened latency with increased amplitude, (2) unchanged latency with increased amplitude, (3) unchanged latency and amplitude, and (4) recovery from unmeasurable to measurable conduction. Results: The mean age was 64.9 years with an equal sex distribution. The right and left trigeminal nerves were affected in 10 and 4 patients, respectively. Nine patients had typical TN, and five had atypical features. Five patients had recurrent pain after previous MVD. Excellent outcomes (Barrow Neurological Institute [BNI] I–II) were achieved in 11 of 14 patients (78.6%), while 3 patients (21.4%) had partial pain relief (BNI III). Typical TN patients more frequently demonstrated conduction patterns 1 or 4, whereas atypical TN patients more often exhibited patterns 2 or 3. Conclusion: IN was associated with favorable clinical outcomes and intraoperative electrophysiological improvement in patients with TN without apparent vascular compression. These findings provide physiological observations accompanying clinical improvement following IN.