Multi-tensor investigation of orbitofrontal cortex tracts affected in subcaudate tractotomy

Abstract

Subcaudate tractotomy (SCT) is a neurosurgical lesioning procedure that can reduce symptoms in medically intractable obsessive compulsive disorder (OCD). Due to the putative importance the orbitofrontal cortex (OFC) in symptomatology, fibers that connect the OFC, SCT lesion, and either the thalamus or brainstem were investigated with two-tensor tractography using an unscented Kalman filter approach. From this dataset, fibers were warped to Montreal Neurological Institute space, and probability maps with center-of-mass analysis were subsequently generated. In comparing fibers from the same OFC region, including medial OFC (mOFC), central OFC (cOFC), and lateral OFC (lOFC), the area of divergence for fibers connected with the thalamus versus the brainstem is posterior to the anterior commissure. At the anterior commissure, fibers connected with the thalamus run dorsal to those connected with the brainstem. As OFC fibers travel through the ventral aspect of the internal capsule, lOFC fibers are dorsal to cOFC and mOFC fibers. Using neuroanatomical comparison, tracts coursing between the OFC and thalamus are likely part of the anterior thalamic radiations, while those between the OFC and brainstem likely belong to the medial forebrain bundle. These data support the involvement of the OFC in OCD and may be relevant to creating differential lesional procedures of specific tracts or to developing deep brain stimulation programming paradigms.

Subcaudate Tractotomy White Matter Anatomy and Variability: A Diffusion Tensor Imaging Study

“…We present here a detailed assessment of the tract anatomy, anatomical variability, and locations of the white matter fibres likely disrupted by subcaudate tractotomy, using native (non-normalized) diffusion tensor imaging (DTI) data from healthy controls. This work builds upon the prior excellent work of Yang et al [3, 7], from 2014 and 2015, that was based on normalized DTI data.…”

“…Previous DTI-based studies investigating the tracts likely affected by subcaudate tractotomy have superimposed an ROI derived from scans of lesioned patients onto normalized control databases, whereby brain anatomy is warped to fit a common model [3, 7]. However, since there is extensive interindividual anatomical variability with respect to the exact location and branching patterns of the prefrontal white matter [16], such differences may not be accurately accounted for in spatially normalized data sets (compared with native data sets), due to error accumulation during spatial transformation of the underlying tract vectors [23, 24].…”

“…The resulting 3D ellipsoid ROI was thus centred between the 2 simulated ablation points within the subcaudate white matter, with dorsal extension into the ventral striatum/nucleus accumbens (as described by Yang et al [3, 7]), and medial and ventral extension to the grey-white matter junctions of the subgenual cingulate gyrus and medial orbitofrontal cortex, respectively (Fig. 2a).…”

“…Lesion mapping of the subcaudate tractotomy ablation zones from patients who have undergone this procedure implicates disruption of both grey and white matter structures including the nucleus accumbens, subgenual cingulate gyrus, orbitofrontal cortex, anterior thalamic radiation, uncinate fasciculus, medial forebrain bundle, and corticostriatal fibres [3, 7]. …”

“…There is significant overlap between the tracts implicated in successful response to BA25 DBS and those tracts likely disrupted by subcaudate tractotomy [3, 7, 12], including the uncinate fasciculi and corticostriatal fibres arising from the ventromedial and orbitofrontal cortex. Given both techniques have shown moderate response rates for treatment-resistant depression, it is feasible that they represent 2 different anatomical approaches to modulating a shared set of underlying white matter tracts.…”