Tag: Medial forebrain bundle

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Ventral amygdalofugal pathway as an integrated surgically important network

J Neurosurg 141:540–554, 2024

The ventral amygdalofugal pathway (VAFP) provides afferent and efferent connections to the amygdala and spans along some of the frequently traversed intra-axial surgical corridors as a dominant fiber bundle. This study aimed to reveal the frequently overlooked VAFP fibers by examining their courses and connections to the basal forebrain, septal region, hypothalamus, thalamus, tegmentum, and brainstem.

METHODS Ten postmortem human brains were used to display the characteristics of the VAFP, and fiber dissection results were compared with those of tractography.

RESULTS From anterior to posterior, the VAFP was separated into 5 different portions: 1) amygdala–substantia innominata; 2) amygdaloseptal (diagonal band of Broca); 3) amygdalo-thalamic; 4) amygdalo-hypothalamic, intermingling with the medial forebrain bundle and extending to the bed nucleus of stria terminalis; and 5) amygdalotegmental. The results of fiber dissections were confirmed with findings obtained from diffusion tensor tractography.

CONCLUSIONS This study supports the concept that interconnected forebrain, diencephalic, mesencephalic, and brainstem connections of the VAFP form an integrated surgically important network. The fiber dissection findings also provide the neuroanatomical basis for VAFP segmentation, which may help neurosurgeons better appreciate the complex microsurgical anatomy of the amygdalar connections. Amygdala–substantia innominata and amygdalotegmental connections are demonstrated for the first time and clarified within the structure of the VAFP.

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Topographical anatomy of the subthalamic region with special interest in the human medial forebrain bundle

J Neurosurg 141:570–580, 2024

The medial forebrain bundle (MFB) is a novel promising deep brain stimulation (DBS) target in severe affective disorders that courses through the subthalamic region according to tractography studies. Its potential therapeutic role arose in connection with the development of hypomania during stimulation of the subthalamic nucleus (STN) in Parkinson’s disease, offering an alternative explanation for the occurrence of this side effect. However, until now its course exclusively described by tractography had not yet been confirmed by any anatomical method. The aim of this study was to fill this gap as well as to provide a detailed description of the fiber tracts surrounding the STN to facilitate a better understanding of the background of side effects occurring during STN DBS.

METHODS Ten human cadaveric brains (20 hemispheres) and 100 healthy subjects (200 hemispheres) from the S500 Release of the Human Connectome Project were involved in this study. Nineteen hemispheres were dissected according to Klingler’s method. One additional hemisphere was prepared for histological examinations to validate the macroscopical results and stained with neurofibril silver impregnation according to Krutsay. The authors also aimed to reconstruct the MFB using tractography and correlated the results with their dissections and histological findings.

RESULTS The white matter connections coursing through the subthalamic region were successfully dissected. The ansa lenticularis, lenticular fasciculus, thalamic fasciculus, ipsi- and contralateral cerebellar fibers, and medial lemniscus were revealed as closely related fiber tracts to the STN. However, the existence of a distinct fiber bundle corresponding to the MFB described by tractography could not be identified. Using tractography, the authors showed that the depiction of the streamlines representing the MFB was also strongly dependent on the threshold parameters.

CONCLUSIONS According to this study’s findings, the streamlines of the MFB described by tractography arise from the limitations of the diffusion-weighted MRI fiber tracking method and actually correspond to subthalamic fiber bundles, especially the ansa lenticularis and lenticular fasciculus, which erroneously continue in the anterior limb of the internal capsule, toward the prefrontal cortex.

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Machine learning—aided personalized DTI tractographic planning for deep brain stimulation of the superolateral medial forebrain bundle using HAMLET

Acta Neurochirurgica (2019) 161:1559–1569

Growing interest exists for superolateral medial forebrain bundle (slMFB) deep brain stimulation (DBS) in psychiatric disorders. The surgical approach warrants tractographic rendition. Commercial stereotactic planning systems use deterministic tractography which suffers from inherent limitations, is dependent on manual interaction (ROI definition), and has to be regarded as subjective. We aimed to develop an objective but patient-specific tracking of the slMFB which at the same time allows the use of a commercial surgical planning system in the context of deep brain stimulation.

Methods The HAMLET (Hierarchical Harmonic Filters for Learning Tracts from Diffusion MRI) machine learning approach was introduced into the standardized workflow of slMFB DBS tractographic planning on the basis of patientspecific dMRI. Rendition of the slMFB with HAMLET serves as an objective comparison for the refinement of the deterministic tracking procedure. Our application focuses on the tractographic planning of DBS (N = 8) for major depression and OCD.

Results Previous results have shown that only fibers belonging to the ventral tegmental area to prefrontal/orbitofrontal axis should be targeted. With the proposed technique, the deterministic tracking approach, that serves as the surgical planning data, can be refined, over-sprouting fibers are eliminated, bundle thickness is reduced in the target region, and thereby probably a more accurate targeting is facilitated. The HAMLET-driven method is meant to achieve a more objective surgical fiber display of the slMFB with deterministic tractography.

Conclusions The approach allows overlying the results of patient-specific planning from two different approaches (manual deterministic and machine learningHAMLET). HAMLET shows the slMFB as a volume and thus serves as an objective tracking corridor. It helps to refine results from deterministic tracking in the surgical workspace without interfering with any part of the standard software solution. We have now included this workflow in our daily clinical experimental work on slMFB DBS for psychiatric indications.

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