Connectomic Targeting of Mesencephalic Pain Pathway for Treatment of Intractable Cancer Pain

Introduction: Spinothalamic tract ablation, commonly performed in the upper cervical spine, is an established method for relieving intractable cancer pain. However, cervical targeting is fraught with risks, including central hypoventilation syndrome. Given the precious territory of lesioning, precise targeting with white matter tractography could significantly improve the safety profile. Mesencephalic targeting offers an alternative to cervical targeting but can also be associated with ocular side effects.

Methods: We report the use of multi-seed tractographic isolation of the spinothalamic tract in the midbrain for targeted radiofrequency (RF) ablation. This approach was utilized in a patient with intractable left-sided cancer pain of the chest due to thymoma and concomitant diaphragmatic paralysis, which rendered cervical tractotomy impossible. In this case, connectomic-based coordinates were lateral and posterior to conventional atlas-based coordinates. Seeds were placed in the dorsal midbrain contralateral to the painful side, the posterolateral thalamus, and S1.

Results: Using connectomic-based targeting (Fig. 1), frame-based stereotactic targeting was used to position a 2mm tip cranial RF electrode into the dorsal midbrain region. The conventional atlas-based targeting coordinates were X: 5, Y: -16, and Z: -8 from the midcommisural point, whereas connectomic-based coordinates were X: 6.5, Y: -17, and Z: -8. Stimulation at the conventional atlas-based coordinates with 100 Hz induced a flushing sensation and disruption of horizontal eye movement at a low amplitude of < 0.3 mA. In contrast, connectomic-based targeting produced a contralateral hot sensation of the trunk at 0.1 mA with no side effects up to 0.5 mA. Two RF lesions at 60°C for 60 seconds and 75°C for 90 seconds achieved complete pain relief with no side effects (Fig 2).

Conclusion : Connectomic targeting of the spinothalamic tract in the midbrain could provide a safer option for lesioning in patients with cancer-related pain.