Objective: The functional importance of the superior temporal lobe at the level of Heschl's gyrus is well known. However, the organization and function of these cortical areas and the underlying fiber tracts connecting them remain unclear. The goal of this study was to analyze the area formed by the organization of the intersection of Heschl's gyrus-related fiber tracts, which the authors have termed the "Heschl's gyrus fiber intersection area" (HGFIA).
Methods: The subcortical connectivity of Heschl's gyrus tracts was analyzed by white matter fiber dissection and by diffusion tensor imaging tractography. The white matter tracts organized in relation to Heschl's gyrus were isolated in 8 human hemispheres from cadaveric specimens and in 8 MRI studies in 4 healthy volunteers. In addition, these tracts and their functions were described in the surgical cases of left temporal gliomas next to the HGFIA in 6 patients who were awake during surgery and underwent intraoperative electrical stimulation mapping.
Results: Five tracts were observed to pass through the HGFIA: the anterior segment of the arcuate fasciculus, the middle longitudinal fasciculus, the acoustic radiation, the inferior fronto-occipital fasciculus, and the optic radiation. In addition, U fibers originating at the level of Heschl's gyrus and heading toward the middle temporal gyrus were identified.
Conclusions: This investigation of the HGFIA, a region where 5 fiber tracts intersect in a relationship with the primary auditory area, provides new insights into the subcortical organization of Wernicke's area. This information is valuable when a temporal surgical approach is planned, in order to assess the surgical risk related to language disturbances.
Keywords: A-Arc = anterior segment of the arcuate fasciculus; AR = acoustic radiation; D1 = shortest distance between the temporal pole and the anterior limit of Heschl’s gyrus; D2 = shortest distance between the temporal pole and the anterior limit of Heschl’s gyrus at the inferior limiting sulcus of the insula; D3 = shortest distance between the limen insulae and Heschl’s gyrus at the inferior limiting sulcus of the insula; DTI = diffusion tensor imaging; DTI tractography; HGFIA = Heschl’s gyrus fiber intersection area; Heschl’s gyrus; IFOF = inferior fronto-occipital fasciculus; L-Arc = long segment of the arcuate fasciculus; MLF = middle longitudinal fasciculus; MTG = middle temporal gyrus; OR = optic radiation; ROI = region of interest; STG = superior temporal gyrus; Wernicke’s area; arcuate fasciculus; fiber dissection; middle longitudinal fasciculus.