V1-dominant Recurrence of Trigeminal Neuralgia after Gamma Knife Radiosurgery for V2–V3 Pain in a Patient with Persistent Vertebral Artery Compression: A Case Report

Hiroaki MATSUMOTO; Yasunori YOSHIDA; Akihiro OKADA; Hiroaki MINAMI; Yasuhisa YOSHIDA; Yumiko OKADA

doi:10.2176/jns-nmc.2026-0082

Abstract

Gamma knife radiosurgery is an established minimally-invasive treatment for trigeminal neuralgia, but recurrence remains a concern, and the trigeminal division involved at relapse is rarely documented. A 63-year-old man developed recurrent trigeminal neuralgia 3 years after gamma knife radiosurgery for left V2–V3 pain, presenting this time with isolated V1 involvement. Magnetic resonance imaging revealed persistent, severe neurovascular compression of the left trigeminal root by a tortuous left vertebral artery with marked nerve flattening. Microvascular decompression achieved immediate and complete pain relief, and postoperative imaging confirmed full decompression. This case illustrates a V1-dominant recurrence pattern after gamma knife radiosurgery in the setting of persistent, deforming neurovascular compression by a tortuous vertebral artery. Although division-specific radiosurgical effects could not be confirmed, the complete resolution of pain after microvascular decompression supports the clinical importance of reassessing persistent mechanical compression when recurrent pain appears in a different trigeminal division.

Introduction

Trigeminal neuralgia (TN) is a severe neuropathic facial pain disorder characterized by recurrent, paroxysmal, electric shock–like pain in one or more trigeminal divisions.¹^,²⁾ Although carbamazepine remains the first-line therapy, surgical or radiosurgical interventions are considered when medical therapy is ineffective or poorly tolerated.²^,³⁾ Gamma knife radiosurgery (GKRS) is widely used as a minimally-invasive treatment option, particularly for elderly patients or those unwilling to undergo open surgery.⁴^,⁵⁾

Large systematic reviews have demonstrated that GKRS provides high initial rates of pain relief, but recurrence is common. In the International Stereotactic Radiosurgery Society systematic review of 6461 patients, recurrence rates after GKRS ranged from 0% to 52.2%, with a mean of 24.6%.⁴⁾ Despite the frequency of recurrence, existing radiosurgical studies define recurrence solely by global pain status using Barrow Neurological Institute (BNI) criteria and rarely specify which trigeminal division is involved at relapse.⁶⁾ As a result, whether recurrent pain returns in the same or a different division remains poorly characterized in the current literature.

This lack of division-level reporting represents an important gap in understanding the pathophysiology of radiosurgical failure. In particular, it remains unclear whether recurrence reflects persistent neurovascular compression (NVC), radiation-induced neuropathy, or differential vulnerability of fiber groups within the trigeminal root.

We report a case of TN initially involving the maxillary and mandibular divisions (V2–V3) that achieved complete remission after GKRS, but recurred 3 years later exclusively in the ophthalmic division (V1). Microvascular decompression (MVD) revealed persistent NVC by a tortuous vertebral artery (VA), and the patient experienced complete and durable pain relief after surgery. This case highlights the clinical and pathophysiological implications of a V1-dominant recurrence pattern after GKRS, a phenomenon that has not been systematically evaluated at the division level in the radiosurgical literature.

Case Presentation

A 63-year-old man presented with recurrent left-sided facial pain. Three years earlier, he had undergone GKRS at another institution for TN involving the left maxillary and mandibular divisions (V2–V3). According to the treatment-planning data obtained from the referring institution, a maximum dose of 85 Gy was delivered to the cisternal segment of the left trigeminal nerve using a single 4-mm shot, with a prescription dose of 76.5 Gy to the 90% isodose line. The 20-Gy isodose line was reconstructed on the treatment-planning image (Figure 1A). In addition, the adjacent VA was newly contoured for dose evaluation, and the maximum and mean doses to the contoured VA were 56.8 Gy and 7.6 Gy, respectively (Figure 1B). Complete pain relief was achieved within 2 months after treatment, and carbamazepine was discontinued. No facial sensory disturbance developed after GKRS.

Figure 1

Gamma knife radiosurgery treatment-planning data obtained from the referring institution.

A: Enlarged treatment-planning image showing the trigeminal target and the 20-Gy isodose line. A maximum dose of 85 Gy was delivered to the cisternal segment of the left trigeminal nerve using a single 4-mm shot, with a prescription dose of 76.5 Gy to the 90% isodose line.

B: Dose evaluation after contouring the adjacent vertebral artery (VA). The calculated maximum and mean doses to the contoured VA were 56.8 Gy and 7.6 Gy, respectively.

Three years later, the patient experienced sudden recurrence of severe, electric shock–like pain localized to the left ophthalmic division (V1). The attacks were brief, triggered by light tactile stimulation, and occurred multiple times per day. Medical therapy including carbamazepine was reintroduced but failed to provide adequate pain control. Neurological examination revealed no facial hypoesthesia and no other cranial nerve deficits. Magnetic resonance imaging (MRI) demonstrated marked neurovascular compression of the left trigeminal nerve by the left VA, which was markedly tortuous. The VA compressed the nerve from an inferior direction, resulting in pronounced flattening and distortion of the trigeminal root (Figure 2A-C). On MR angiography, the tortuous segment of the left VA was considered to correspond to the site of contact with the trigeminal nerve (Figure 2D, E). No mass lesion or demyelinating disease was identified.

Figure 2

Preoperative MRI and MR angiography findings.

A and B: Preoperative axial MRI demonstrating severe neurovascular compression of the left trigeminal nerve by a tortuous left vertebral artery (VA), resulting in marked nerve flattening and loss of normal structural definition (arrow indicates the VA).

C: Preoperative coronal MRI demonstrating marked inferior compression of the left trigeminal nerve by the tortuous VA, consistent with the severe nerve flattening observed on axial imaging (arrowheads indicate the trigeminal nerve; arrow indicates the VA).

D and E: Preoperative MRA demonstrating the overall vertebrobasilar anatomy and marked tortuosity of the left VA. The curved segment of the left VA (arrow) was considered to correspond to the site of contact with the trigeminal nerve.

Given the persistent NVC and medically refractory pain, MVD was indicated. A standard left retrosigmoid approach with a slightly more caudal craniotomy than usual was performed to optimize exposure of the VA. After cerebrospinal fluid drainage to achieve cerebellar relaxation, the lower cranial nerves were first identified from a caudal-to-rostral direction, including the glossopharyngeal, vagus, vestibulocochlear, and facial nerves. The trigeminal nerve root was then exposed. The VA was circumferentially dissected from its caudal segment toward the compression point. The VA was identified as the offending vessel, severely compressing the trigeminal nerve from below (Figure 3A). Marked flattening deformity and indentation of the nerve were observed at the site of contact. The VA was carefully mobilized using a microdissector (Figure 3B) and transposed away from the nerve. The artery was secured to the petrous bone using Teflon felt and fibrin glue, achieving complete decompression of the trigeminal root (Figure 3C). No intraoperative complications occurred.

Figure 3

Intraoperative findings and postoperative imaging.

A–C: Intraoperative photographs (* indicates the vertebral artery [VA]; arrows indicate the trigeminal nerve; † indicates the vestibulocochlear nerve).

A: The left VA severely compressing the trigeminal nerve from an inferior direction. Marked flattening deformity and indentation of the nerve are observed.

B: Mobilization of the left VA away from the trigeminal nerve using a surgical probe.

C: Transposition of the left VA away from the trigeminal nerve. The artery was secured to the petrous bone with Teflon felt and fibrin glue, resulting in decompression of the trigeminal nerve.

D: Postoperative axial MRI demonstrating successful transposition of the left VA and clear separation from the trigeminal nerve.

E: Postoperative coronal MRI confirming complete resolution of neurovascular compression, with the left VA clearly separated from the trigeminal nerve (arrowheads indicate the trigeminal nerve; arrow indicates the VA).

The patient experienced immediate and complete pain relief postoperatively. At 3 years of follow-up, he remained pain-free without medication. According to the standardized outcome assessment for MVD proposed by Kondo et al.,⁷⁾ the postoperative result was classified as E-0 for pain outcome, C-0 for complications, and T-0, indicating an excellent overall result. Postoperative MRI confirmed successful transposition of the VA and complete resolution of neurovascular compression (Figure 3D, E).

Discussion

The present case illustrates a clinical pattern that may be termed "division-shift recurrence," in which TN reappears in a different trigeminal division after initial remission following radiosurgery. Although recurrence after GKRS is well documented, most radiosurgical series define recurrence solely by global pain status using BNI criteria. Recent prospective analyses, including the study by Rosselló et al.,⁶⁾ emphasize that existing radiosurgical literature does not document which trigeminal division is involved at relapse, leaving the distribution of recurrent pain poorly characterized. This lack of division-level reporting represents a major gap in understanding the mechanisms of radiosurgical failure and may lead to under-recognition of division-shift recurrence.

GKRS provides high initial rates of pain relief and is widely used in patients who are elderly or prefer to avoid open surgery, but its long-term durability remains limited.⁴^,⁵^,⁸^-¹⁰⁾ Recurrence is often presumed to involve the same trigeminal division, although division-specific reporting is rarely provided in radiosurgical series. The present case demonstrates that recurrence may instead manifest in a different trigeminal division. This clinical pattern raises the possibility that different fiber groups within the trigeminal root may be differentially involved after GKRS and under persistent mechanical compression; however, this interpretation requires caution.

This clinical pattern should be interpreted in light of the somatotopic organization of the trigeminal root. Previous anatomical and neurophysiological studies have suggested that trigeminal fibers are not randomly arranged within the root, although the exact arrangement within the cisternal segment remains complex and may vary among individuals.¹¹⁾ Therefore, a shift in the symptomatic division after treatment may theoretically reflect differential involvement of fiber groups within the root. However, GKRS for TN is not designed to selectively irradiate fibers corresponding to individual trigeminal divisions.⁴^,⁸⁾ In the present case, additional treatment-planning data allowed visualization of the 20-Gy isodose line and estimation of the dose delivered to the adjacent VA. However, these data still did not permit precise reconstruction of the dose delivered to V1-, V2-, and V3-related fiber groups, and we cannot exclude the possibility that fibers corresponding to V1 were also included within the irradiated volume. Accordingly, the present case should be interpreted not as proof of selective radiosurgical suppression of V2–V3 fibers, but as a clinical observation that V1-dominant recurrence occurred despite prior GKRS in the setting of persistent severe mechanical compression by the VA.

One possible explanation for the absence of V1 symptoms before GKRS is that the clinically dominant hyperexcitable fibers were initially related to V2–V3, despite the presence of severe mechanical deformation of the trigeminal root. After GKRS, V2–V3 pain resolved, but the VA continued to compress and deform the nerve. Over time, persistent mechanical irritation may have induced hyperexcitability in a different subset of trigeminal fibers, resulting in V1-dominant recurrence. However, this interpretation remains speculative, and the available GKRS planning data do not allow us to determine whether the radiosurgical effect was weaker in V1-related fibers than in V2–V3-related fibers.

GKRS may relieve TN by functionally modulating the irradiated segment of the trigeminal nerve, with experimental studies showing axonal injury and partial demyelination after irradiation.⁸^,¹²⁾ However, these effects should not be interpreted as evidence of division-specific selective irradiation. Importantly, GKRS does not address the underlying NVC. The effectiveness of MVD after failed GKRS, as reported in several series,¹³^-¹⁵⁾ supports the concept that persistent mechanical compression may contribute to recurrence after radiosurgery.

Although GKRS in the present case had been performed at another institution before referral to our hospital, this case raises an important issue regarding treatment selection in TN associated with severe compression by a tortuous or dolichoectatic vertebrobasilar artery. GKRS may provide pain relief but does not resolve the underlying mechanical compression, and recurrence after GKRS remains a clinically important issue.⁴^,⁸^,⁹⁾ In the present case, dose evaluation after contouring the adjacent VA showed that the maximum and mean doses to the contoured VA were 56.8 Gy and 7.6 Gy, respectively. When a high-dose radiosurgical field is close to a major artery, potential vascular risks should be considered, although such complications are rare.¹⁶^,¹⁷⁾ Therefore, in surgically fit patients with marked nerve deformation caused by a tortuous VA, MVD with arterial transposition may be a more pathophysiologically direct treatment option.¹⁸⁾

Other mechanisms, such as arachnoid thickening, nerve atrophy, atherosclerotic plaque, or newly formed adhesions between the nerve and adjacent vessels, have also been proposed to contribute to recurrence after radiosurgery.¹⁴⁾ In the present case, the radiosurgical target was the cisternal segment, and no postoperative sensory disturbance occurred, suggesting limited structural injury. Persistent compression by a tortuous VA, accompanied by marked nerve flattening, was clearly demonstrated on MRI. Therefore, recurrence in a different trigeminal division after GKRS should prompt careful reassessment for persistent NVC. In such cases, early consideration of MVD may be warranted when structural compression is evident.

An important nuance emerges when considering the role of NVC in radiosurgical outcomes. Although recent studies on repeat radiosurgery have shown that the presence of NVC is not a significant predictor of recurrence or retreatment,⁹^,¹⁹⁾ this case suggests that the severity and persistence of NVC may be clinically important. The marked trigeminal root flattening caused by a tortuous VA suggests that substantial mechanical compression may have continued to promote ectopic activity in adjacent fiber groups, possibly contributing to the shift from V2–V3 to V1-dominant pain. The recurrence in a different trigeminal division may be interpreted as a "division-shift" phenomenon, potentially reflecting differential fiber vulnerability rather than isolated radiation-induced neuropathy. A possible explanatory model for this recurrence pattern is illustrated in Figure 4. Routine radiosurgical studies rarely assess the severity of NVC or the degree of nerve deformation. This methodological limitation likely contributes to the inconsistent finding that NVC is not a reliable predictor of radiosurgical outcomes in broader cohorts. Successful MVD in this patient further supports the clinical relevance of persistent NVC rather than isolated radiation-induced injury.

Figure 4

Hypothetical model of V1-dominant recurrence after Gamma knife radiosurgery (GKRS) in the setting of persistent vertebral artery (VA) compression.

(A) Pre-GKRS: Before GKRS, severe mechanical compression by the VA was present, while clinical pain was localized to V2–V3.

(B) Post-GKRS: After GKRS, V2–V3 pain resolved clinically, but severe mechanical compression by the VA persisted. The panel illustrates a possible reduction of V2–V3-related hyperexcitability and does not imply division-specific selective irradiation.

(C) Late recurrence: Late recurrence developed as V1-dominant pain. This model does not prove selective radiosurgical sparing of V1 fibers but illustrates a possible explanation in which persistent mechanical deformation may have contributed to preferential involvement of remaining susceptible fibers.

Conclusions

This case suggests that V1-dominant recurrence after GKRS can occur in the setting of persistent severe NVC. When recurrent pain appears in a different trigeminal division, careful reassessment for vascular compression is warranted, and MVD may represent an effective treatment when significant mechanical compression is present.

Conflicts of Interest

All authors have no conflict of interest.

Informed Consent

Informed consent was obtained from the patient.

References

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