Introduction: Stereotactic radiosurgical (SRS) lesioning of the anterior limb of the internal capsule remains a treatment option for patients with treatment-resistant obsessive-compulsive disorder (OCD). However, mechanisms behind response remain unclear. To probe whether lesions placed in specific white-matter tracts were related to response, we determined the connectivity profile of responsive vs non-responsive lesions.
Methods: Bilateral lesions from 16 OCD patients who underwent SRS ventral capsulotomy were hand-traced and then warped to MNI space. Individual patient volumes were labeled "responder" or "nonresponder" based on Yale-Brown Obsessive Compulsive Scale (YBOCS) change from baseline. Composite lesion volumes were created from voxels where >50% of lesion overlap occurred.
As only post-surgical scans were available for lesion tracing, a separate cohort of 7 OCD patients was used for tractography analysis. Probabilistic tractography was performed between all Freesurfer-segmented anatomical ROIs and individually warped capsulotomy lesion volumes. The connectivity of responder and nonresponder lesions to ROIs (number of tracts) was compared for the cortical and subcortical ROI with the highest connectivity difference.
Results: The YBOCS change of responders (-23.6 ± 7.2) and nonresponders (-9.8 ± 3.5) differed significantly (p<0.001). The responder composite centroid was lateral to the midline (Left: 15.2 mm, Right: 13.9 mm), anterior to the anterior commissure (L: 12.7 mm, R: 12.8 mm), and inferior to the AC-PC plane (L: 5.3 mm, R: 5.2 mm).
Compared to nonresponders, left responder composite volumes had significantly greater connectivity to the ipsilateral caudate (p=0.011) and medial orbitofrontal sulcus (p=0.029). Right responder volumes had significantly greater connectivity to the ipsilateral putamen (p=0.009), and nonsignificantly greater connectivity to the ipsilateral gyrus rectus (p=0.311).
Conclusions: Preliminary tractography analysis of SRS capsulotomy lesions suggests that more clinically effective lesions are located within medial orbitofrontal-striatal loops, whose altered connectivity has been thought to underlie OCD symptoms. These results can help optimize lesion placement in future studies.
Patient Care: This research, although preliminary, points towards a target white-matter network associated with better outcomes for obsessive-compulsive disorder patients undergoing stereotactic radiosurgical lesioning of the internal capsule. These results suggest more generally that the use of preoperative diffusion tensor imaging may lead to improved surgical targeting and outcomes.
Learning Objectives: By the conclusion of this session, participants should be able to 1) recognize the use of diffusion-tensor imaging to understand surgical outcomes, 2) learn which white-matter tracts are more associated with better surgical outcomes for stereotactic radiosurgical lesioning of the internal capsule, and 3) discuss how imaging-based methods may be applied prospectively to obsessive-compulsive disorder patients undergoing stereotactic radiosurgery.