No abstract

The uncinate fasciculus is the largest white matter association tract connecting the prefrontal cortex and the anteromedial temporal lobe. The traditional anatomical description outlines a temporal stem that hooks around the posterior insula, a subinsular body, and 2 prefrontal stems extending to the lateral orbital gyri and the frontopolar cortex. Recent imaging studies of the white matter tracts deep to the subgenual cingulate gyrus (Brodmann area 25: BA25) suggest the presence of white matter fibers extending from BA25 to the amygdala, via a route that would run in close proximity to the uncinate fasciculus, that are of functional importance in mood disorders. We hypothesized that these fibers represent a third, medial prefrontal stem of the uncinate fasciculus. Using diffusion tensor imaging in 74 healthy volunteer humans, we seeded the uncinate fasciculus using 2 regions of interest centered over the temporal stem and the caudal body of the uncinate fasciculus in the coronal plane at the level of the anterior commissure. A medial prefrontal stem extending to the subgenual cingulate gyrus was demonstrated in 65/74 left and 70/74 right cerebral hemispheres, and had a mean fractional anisotropy value of 0.43 (95% CI 0.40-0.47). The medial subgenual stem fibers were inseparable from the caudal body and temporal stem of the main uncinate fasciculus and followed the same hookshaped morphology. A probable medial subgenual prefrontal stem of the uncinate fasciculus was demonstrated in a cohort of healthy volunteers and is of potential significance in our understanding of neuropsychiatry and mood disorders.

Background: Subcaudate tractotomy is a functional ablative procedure performed for treatment-resistant psychiatric disease, targeting the white matter tracts ventral to the head of the caudate nucleus. The white matter anatomy of this region has extensive interindividual variability, and this is thought to impact upon the treatment response to ablative and deep brain stimulation procedures. Objective: We aim to assess in detail the white matter tract anatomy and topographic variability underlying subcaudate tractotomy. Methods: 74 non-depressed adult volunteers underwent MRI including diffusion tensor imaging. Individualized regions of interest were formed in both hemispheres using native non-normalized data to simulate a subcaudate tractotomy. Tractography and analysis were performed and the exact tract locations measured including mean distances and standard deviations to assess variability. Results: The cingulum bundle, uncinate fasciculus, corticostriatal fibres, and corticothalamic fibres were consistently demonstrated. The location of the cingulum bundle was consistent across subjects, but there was extensive interindividual variability in the topographic location of the other tracts. Conclusion: We have demonstrated a detailed analysis of the white matter tracts and their anatomical variability underlying subcaudate tractotomy. This has significant implications for neurosurgical targeting.