Gamma Ray Radiosurgery for Trigeminal Neuralgia: Targeting Proximal or Distal to the Dorsal Root Entry Zone

Trigeminal neuralgia

Trigeminal neuralgia (TN) is a facial pain disorder characterized by intense and paroxysmal pain that profoundly affects quality of life and presents complex challenges in diagnosis and treatment. TN can be categorized as classical, secondary and idiopathic. Epidemiological studies show variable incidence rates and an increased prevalence in women and in the elderly, with familial cases suggesting genetic factors. The pathophysiology of TN is multifactorial and involves genetic predisposition, anatomical changes, and neurophysiological factors, leading to hyperexcitable neuronal states, central sensitization and widespread neural plasticity changes. Neurovascular compression of the trigeminal root, which undergoes major morphological changes, and focal demyelination of primary trigeminal afferents are key aetiological factors in TN. Structural and functional brain imaging studies in patients with TN demonstrated abnormalities in brain regions responsible for pain modulation and emotional processing of pain. Treatment of TN involves a multifaceted approach that considers patient-specific factors, including the type of TN, with initial pharmacotherapy followed by surgical options if necessary. First-line pharmacological treatments include carbamazepine and oxcarbazepine. Surgical interventions, including microvascular decompression and percutaneous neuroablative procedures, can be considered at an early stage if pharmacotherapy is not sufficient for pain control or has intolerable adverse effects or contraindications.

Stereotactic Radiosurgery for Trigeminal Neuralgia Caused by Vertebrobasilar Compression: A Report of Four Cases

BACKGROUND

Microvascular decompression (MVD) of the trigeminal nerve is an effective procedure for treating patients with trigeminal neuralgia (TGN). However, vertebrobasilar decompression involves technical difficulties and demonstrates a higher risk of minor trigeminal hypesthesia/hypalgesia, transient diplopia, and hearing loss. Stereotactic radiosurgery (SRS) has been an effective alternative treatment for TGN. Few studies reported the treatment results of SRS for TGN caused by vertebrobasilar compression. This report presents the treatment results of SRS using gamma knife (GK) in four TGN cases.

MATERIALS AND METHODS

GK-SRS was performed for TGN due to vertebrobasilar compression in four patients, including two males and two females, aged 67-90 years. The maximum dose of 80 Gy was delivered at the retrogasserian portion (RGP) of the ipsilateral trigeminal nerve root.

RESULTS

All four cases with TGN achieved relief in four to 10 months after GK-SRS. However, TGN recurred 41 months after GK-SRS in one of the four cases. A second GK-SRS at the root entry zone (REZ) at a maximum dose of 70 Gy relieved pain again 10 days later. TGN in another case among the four partially recurred in three years but did not deteriorate until the patient died from old age 62 months after GK-SRS. The other three cases, including the one with repeat GK-SRS, were alive with complete TGN remission at the end of follow-up of 20-52 months. GK-SRS-related adverse effects were not observed in any case.

CONCLUSIONS

GK-SRS was a safe and effective treatment in all four TGN cases due to vertebral artery (VA)-basilar artery (BA) compression, although a second treatment session was added again for pain recurrence in one of the four cases.

Dual-Target Radiosurgery for Concomitant Continuous Pain Presentation of Trigeminal Neuralgia: Radiomodulation Effect and Dose

OBJECTIVES

Patients with trigeminal neuralgia (TN) experience concomitant continuous pain (CCP) that can be difficult to treat. A dual-target approach delivering a high dose of radiation to the nerve and the contralateral thalamus can develop a fast radiomodulation effect on lowering pain. We sought to determine if this effect was dose dependent.

METHODS

We retrospectively reviewed 21 patients treated with radiosurgery in CCP and severe TN pain, with a visual analog scale (VAS) score of nine out of 10 at the time of treatment. Ten patients were treated with a high dose (>120 Gy) in the thalamus 90 Gy to the nerve, and the rest with a low dose (<120 Gy) to the thalamus and >90 Gy to the nerve.

RESULTS

Of those who received the high dose to the thalamus, six patients (60%) received 140 Gy, and four (40%) received 120 Gy, with a median dose to the trigeminal nerve of 90 and 85 Gy, respectively. The high thalamus dose showed a radiomodulation effect from day 1. The low thalamus dose did not produce radiomodulation on any of the first four days. The percentage of VAS score reduction one month after treatment was higher in the high-thalamus dose group than in the low-thalamus dose group. At three months, VAS score was 2 in the high-dose group and 4 in the low-dose group.

CONCLUSIONS

The radiomodulation effect in pain and dual-target radiosurgery is dose dependent in CCP in TN; a high dose can provide a more consistent clinical result than a lower dose.

Radioneuromodulation by Dual-Target Irradiation in Pain Crisis From Trigeminal Neuralgia

Background Radioneuromodulation (RNM) can explain the immediate pain relief experienced by a subgroup of patients after stereotactic radiosurgery (SRS) for trigeminal neuralgia (TN). In this study, our main objective was to demonstrate that a minimum of a 50% reduction in TN pain can be achieved consistently in under 72 hours by targeting the affected nerve, the contralateral centromedian nucleus, and parafascicular complex in patients experimenting a prolonged refractory pain crisis. Methodology We treated eight patients experiencing severe TN pain crisis in whom percutaneous procedures had failed or were unwanted with SRS with an intention to procure pain relief in under 72 hours. The affected trigeminal nerve was targeted using a 4-mm collimator with an 80 to 90-Gy dose; an additional target was defined in the mesial portions of the thalamus and irradiated using the 4-mm collimator with a 120 to 140-Gy dose. Results The median duration of TN was 60 months, the median duration of pain crisis was 10.7 weeks despite the best medical treatment, and the mean presenting visual analogue score (VAS) was 10 at the time of treatment. The median follow-up was 135 days (range, 65-210). Twenty-four hours after treatment, two (25%) patients had no pain (VAS 0), three (37.5%) had mild pain (VAS 1 to 3), and three (37.5%) had moderate pain (VAS 4 to 7). Forty-eight hours after treatment, all patients reported pain relief, seven (87.5%) reported >50%, and one (12.5%) patients reported 30% relief. The three-month median VAS score was 3 (range, 0 to 5). At the last follow-up, there were no adverse events to report. Conclusions Dual irradiation to the affected trigeminal nerve and contralateral mesial structures of the thalamus may provide fast pain relief for patients experiencing a prolonged pain crisis from TN, which veers away from the concept that the SRS pain relief effect is generally delayed and holds no place in the management of such patients. Although this is a small series with a limited follow-up duration, no adverse effects were noted. RNM can be defined as the capacity to alter neuronal activity through targeted delivery of a stimulus of radiation at a duration too brief to be explained by the development of a focal lesion. The immediate pain relief and its habitual oscillatory nature of lesser pain recurrence in most patients until enough time elapses for pain stabilization clinically demonstrates that the pain circuitry is altered and remains functional, thus accomplishing a neuromodulation effect even at the face of an apparent doses suspected to be ablative. Further research is needed to understand if this clinical effect is achieved with a suspected sub-ablative dose.