Morphometry and localization of the temporal transverse Heschl's gyrus in magnetic resonance imaging: a guide for cortical stimulation of chronic tinnitus.

Purpose: Subjective tinnitus is considered a phantom auditory phenomenon. Recent studies show that electrical or magnetic stimulation of the cortex can alleviate some tinnitus. The usual target of the stimulation is the primary auditory cortex (PAC) on Heschl's gyrus (HG). The objective of this study was to specify the anatomy of HG by magnetic resonance imaging (MRI).

Methods: Cerebral MRI of 60 patients with chronic tinnitus, carried out before neuronavigated repetitive transcranial magnetic stimulation targeting the auditory cortex, were included. 3D-T1 MRI was reformatted in Talairach-Tournoux's stereotactic space, then the following steps were performed: morphometry of HG, localization of the probabilistic center of the PAC (pcPAC) chosen at the junction between the medial third and the lateral two-thirds of HG, relative to external and cortical landmarks, and identification of its coordinates relative to the bicommissural line (AC-PC).

Results: In relation to external landmarks, the pcPAC was identified around 5 cm above the root of the helix of the ear in the direction of a point on the vertex located 4 cm behind the coronal suture, for both sides. In Talairach-Tournoux's stereotactic space with the anterior commissure as the origin, the pcPAC coordinates were x = 43, y = -20, z = 6.8 on the right side, and x = -42.5, y = -21.5, and z = 6.5 on the left. Probabilistic maps of the presence of HG pointed to a relative contraction of data in space, despite inter- and intraindividual differences.

Conclusion: The choice of our stimulation target was established in the middle of the theoretical position of the PAC. MRI allows a reliable identification of the target structure.