gms | German Medical Science

Objective: The aim of our study was to compare the course of the medial forebrain bundle (MFB) with the courses of the fibers running through the activated tissue of effective and non-effective contacts of the electrodes in a patient with obsessive compulsive disorder (OCD).

Method: Deterministic fiber tracking of the MFB was performed by setting 2 regions of interest (ROIs) in each hemisphere: in the nucleus raphe dorsalis and in the ventral tegmental area. Fibers running through the activated tissue around each contact of the electrodes were tracked based on ROIs, which were constructed as a sphere with a diameter of 2mm centered on the midpoint of each contact. The fiber tracts running through the ROIs of the electrode contacts are referred to as "contact-fibers". The courses of the contact-fibers were documented and compared to the course of the MFB. Minimal fiber length was set at 30mm and the FA threshold at 0.12.

Results: 7 of 8 contacts were located immediately medial to the MFB. Anterior to the contacts, the contact-fibers of effective contacts, concerning the alleviation of OCD symptoms, joined the course of the MFB. Contact-fibers of ineffective contacts were located inferior to the MFB. Posteriorly, the fibers of effective contacts followed the MFB to the brain stem on a slightly more anterior path. The fibers of most ineffective contacts did not accompany the MFB to the mesencephalon. Fibertracking of all contact-fibers depicted an additional superior branch to the medial-posterior thalamus, superior to the MFB. In some cases these fibers continued their course between the posterior horns of the lateral ventricles to the splenium corporis callosi and terminated in the superior parietal lobulus.

Conclusions: The medial forebrain bundle, as defined with deterministic fiber tracking, might help to refine atlas based targeting in deep brain stimulation for obsessive compulsive disorders.