Introduction: Dorsal anterior cingulotomy is an effective and durable treatment option for patients with severe, refractory obsessive-compulsive disorder (OCD).[1] Little is known, however, about structural network changes produced by the lesion. We hypothesized that cingulotomy would produce changes in white matter tracts connecting key regions in the cortico-basal ganglia-thalamo-cortical circuit implicated in the pathogenesis of OCD.[2]

Methods: We acquired pre- and immediate (within 3 days) post-operative diffusion weighted imaging data from 12 patients who underwent cingulotomy for refractory OCD. Tract based spatial statistics (TBSS) were computed using FSL's FDT toolkit.[3] Using skeletonised fractional anisotropy (FA), a voxel-wise threshold free cluster enhanced comparison was made between the two time points. We also calculated mean skeletonized FA for the anterior (ALIC) and posterior (PLIC) limb of the internal capsule, and the external capsule (EC) bilaterally. A Wilcoxon signed-rank test was used to assess for statistical significance of post-operative decreases in mean FA values in the six major tracts on a patient-specific basis.

Results: The voxel wise comparison demonstrated significant decreases in the bilateral ALIC and EC, and certain areas in the frontal white matter (Figure 1). Notably, more changes were observed in right sided tracts. While the mean FA of all six major tracts decreased postoperatively, only the right ALIC and bilateral EC demonstrated a statistically significant decrease (Figure 2). The greatest change was in the right ALIC.

Conclusions: We demonstrate acute FA changes in key white matter tracts following cingulotomy. These tracts are known to connect important nodes in the associative circuit implicated in OCD, including the orbitofrontal and cingulate cortices, ventral striatum, and thalamus. These results provide a neuroanatomical basis for understanding how targeted neurosurgical procedures can therapeutically alter the circuitry underlying psychiatric disorders.

Patient Care: A better understanding of the circuitry affected by cingulotomy will aid in the development of superior surgical therapies for OCD.

Learning Objectives: By the end of this session participants should be able to: • Describe the usefulness of using diffusion imaging to study postoperative white matter changes. • Describe the general connectivity pattern disrupted by cingulotomy. • Describe the circuitry thought to underlay the pathology of OCD.

References: 1) Greenberg, B. D., Rauch, S. L., & Haber, S. N. (2009). Invasive circuitry-based neurotherapeutics: stereotactic ablation and deep brain stimulation for OCD. Neuropsychopharmacology, 35(1), 317-336. 2) Kopell, B. H., & Greenberg, B. D. (2008). Anatomy and physiology of the basal ganglia: implications for DBS in psychiatry. Neuroscience & Biobehavioral Reviews, 32(3), 408-422. 3) Smith, S. M., et. al. (2006). Tract-based spatial statistics: voxelwise analysis of multi-subject diffusion data. Neuroimage, 31(4), 1487-1505.