Introduction: The lateral habenula (lHb) has been identified in the neural circuitry of refractory major depressive disorder. The major afferent pathway to the lHB, the stria medullaris (SM), has been identified as a possible target for deep brain stimulation (DBS) in treatment of refractory depression. Since SM is not readily identifiable on conventional MRI, we evaluated whether diffusion tensor imaging and MR tractography can be used to identify the SM for DBS targeting.
Methods: Five patients underwent MRI studies. Patients were imaged using a 3-Tesla Siemens Verio MRI scanner. The exam included a 3D T1-weighted axial sequence (MP-RAGE, 260x227-mm FOV, 1x1x1-mm resolution, scan time of 4 minutes) and an axial diffusion-weighted sequence (8 volumes with no diffusion weighting, 69 volumes with diffusion weighting of 1000 s/mm2 uniformly distributed in 3D space, 256x256-mm FOV, 2x2x2-mm resolution, scan time of 16 minutes). Motion and distortion correction of the raw diffusion-weighted images to match the 3D T1-weighted volume was accomplished using TORTOISE. We then used Diffusion Toolkit and TrackVis to track and visualize fibers of the SM. A spherical seed region (radius 3-4 mm) was centered on the lateral habenula. An additional “waypoint” region was drawn by hand on a coronal slice to include the ipsilateral white matter of the internal capsule between the caudate and putamen. Fiber tracts passing through both regions were identified as belonging to the SM.
Results: Fiber tracts of the SM were readily identified and spanned from the basal forebrain region to the contralateral lHB and monoaminergic nuclei of the upper brainstem (Figures 1-3).
Conclusions: Diffusion tensor imaging can be used to identify the stria medullaris for direct targeting in DBS surgery.
Patient Care: The presented work will help improve target identification in DBS surgery involving the stria medullaris and habenula.
Learning Objectives: 1) Identify the utilization of diffusion tensor imaging during DBS surgery involving the stria medullaris thalami
2) Identify the image modality parameters used to identify the stria medullaris thalami tractography on MRi