Introduction: Thalamic deep brain stimulation (DBS) for the treatment of medically refractory pain has been largely abandoned on account of its inconsistent and oftentimes poor efficacy. Given the inability to discern the internal anatomic detail of the thalamus on traditional magnetic resonance imaging (MRI), it is difficult to determine whether this poor clinical response is a failure of optimal simulation or a sequela of inappropriate targeting. We hypothesized that by using diffusion tensor imaging (DTI)-based segmentation to assess the internal thalamic nuclei of patients that have undergone thalamic DBS for intractable pain, we could retrospectively determine functional lead position and correlate it with clinical outcome.
Methods: DTI-based segmentation was performed on 5 patients that underwent sensory thalamus DBS for chronic pain. Postoperative computed tomography (CT) images obtained for electrode placement were fused with preoperative MRIs that had undergone DTI-based thalamic segmentation. Sensory thalamus maps of 4 patients were transferred into standard MNI152 space via FSL tools non-linear image transformation (FNIRT) to investigate interpatient variability.
Results: The two patients that experienced significant pain relief following DBS demonstrated contact positions within the DTI-determined sensory thalamus, whereas those that did not respond to stimulation did not. One patient only experienced stimulation-induced intraoperative paresthesias when the electrode was repositioned posterior to the initial Schaltenbrand-Wahren Atlas coordinates, into what was later retrospectively confirmed to be the DTI-determined sensory thalamus. Only 4 voxels (2%) were shared by all 4 patients in common MNI space; 108 voxels (58%) were uniquely represented by single patients.
Conclusions: Given the interpatient heterogeneity of thalamic nuclei, personalized stereotactic targeting is required. DTI-based segmentation of the thalamus can be used retrospectively to confirm thalamic lead placement relative to the sensory thalamus, and may serve as a useful tool to guide thalamic DBS in the future.
Patient Care: Deep brain stimulation for medically refractory pain has largely been abandoned in the United States on account of its inconsistent and oftentimes poor efficacy. We believe that inaccurate targeting of the sensory thalamus may have played a role in these unfavorable clinical outcomes. By demonstrating correlation between lead placement in the DTI-determined sensory thalamus and clinical outcome, we exhibit the utility that functional segmentation of DBS targets not readily appreciated on traditional MRI modalities may have on thalamic DBS. Moreover, in the future these methods may help guide the stereotactic localization of thalamic and other poorly discernible DBS targets without the aid of neurophysiological assessment and microelectrode recording.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the importance of individualized segmentation-based targeting for DBS nuclei that are insufficiently appreciated on traditional MR imaging modalities, and 2) Discuss in small groups the potential advantages and disadvantages of segmentation-based targeting versus lead adjustment based on neurophysiological assessment.
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