Objective: One of the few resources for treating medically intractable pain is ablative surgery, but its indications have fallen dramatically over the last decades. One such procedure is mesencephalotomy. This study aims to determine current risks and benefits of MR-guided semidirect targeting-based stereotactic mesencephalotomy.
Methods: This was a retrospective study based on a review of the medical records of 22 patients with nociceptive (n = 5), neuropathic (n = 10), or mixed (n = 7) refractory pain treated with unilateral mesencephalotomy alone (17 patients) or associated with bilateral anterior cingulotomy (5 patients) between 2014 and 2021 in the authors' institutions. The confidence interval adopted in this study was 95%.
Results: The sample included 12 women and 10 men with ages ranging from 23 to 80 years (mean 55.1 ± 17.1 years). Using MR-guided semidirect targeting, the following structures were targeted: spinoreticulothalamic (neuropathic/mixed pain, n = 17), trigeminothalamic (nociceptive/mixed pain in the face, n = 5), and neospinothalamic (nociceptive/mixed pain in the body, n = 7) pathways. The most common response to macrostimulation was central heat/moderate discomfort. Radiofrequency thermocoagulation was made with 70°C-75°C/60 sec. A total of 86.3% (3 months) and 76.9% (12 months) of the patients achieved excellent or good results (improvement of pain > 50%), presenting with a significant mean pain relief of 80.1% at 3 months and 71.4% at 12 months postoperatively. The addition of bilateral anterior cingulotomy did not improve the results. Patients with upper limb, cervicobrachial, and face pain did significantly better than those with trunk pain. The worst results were seen in patients with neuropathic and/or trunk pain. The surgical failure (pain relief ≤ 25%) and recurrence rates were 9.1% each, apparently related to the use of lower lesioning parameters (70°C/60 sec) and to the presence of neuropathic and/or trunk pain. The morbidity rate was 8%, with both complications (vertical diplopia and confusion/agitation) happening in patients lesioned with 75°C/60 sec. There were no deaths in this series.
Conclusions: These results show that contemporary stereotactic mesencephalotomy is an effective, relatively low-risk, and probably underused procedure for treating medically intractable pain. Careful semidirect determination of the target coordinates associated with close attention to electrical macrostimulation responses certainly plays an important role in avoiding complications in most of the procedures. A higher lesioning temperature (75°C) apparently prevents recurrence, but at the cost of an increased risk of complications.
Keywords: MR; functional neurosurgery; mesencephalic tractotomy; mesencephalotomy; pain; rostral mesencephalic reticulotomy; stereotactic techniques.