Association fibers connecting the Broca center and the lateral superior frontal gyrus: a microsurgical and tractographic anatomy

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Recently, intraoperative mapping has disclosed that, in addition to the classic language centers (that is, the Broca and Wernicke centers), other cortical regions may also play an important role in language organization. In the prefrontal cortex, although the lateral superior frontal gyrus (LSFG) could have language-related functions, there are no detailed reports that demonstrate the anatomical connection between the LSFG and other well-known language cortices, such as the Broca center. To show the existence of the structural connection, white matter association fibers between the inferior frontal gyrus (IFG) and the LSFG were examined using fiber dissection (FD) and diffusion tensor (DT) imaging–based tractography.


Eight cadaveric cerebral hemispheres were dissected to reveal the association fibers between the IFG and LSFG. The DT imaging–based tractography studies targeting the prefrontal cortex were obtained in 53 right-handed patients who had no organic cerebral lesions.


The association fiber tract between Brodmann area 44/45 (the Broca center in the dominant hemisphere) and LSFG were detected in all specimens by FD. In the DT imaging–based tractography studies, the tract was identified in all patients bilaterally, except for the 4 in whom the tract was detected only in the left hemisphere. This tract was spread significantly wider in the left than in the right hemisphere, and left lateralization was evident in male patients.


Based on its character, this tract was named the Broca-LSFG pathway. These findings suggest a close relationship between this pathway and language organization. The structural anatomy of the Broca-LSFG pathway may explain speech disturbances induced by LSFG stimulation that are sometimes observed during intraoperative language mapping.

Abbreviations used in this paper: DT = diffusion tensor; DW = diffusion-weighted; FD = fiber dissection; IFG = inferior frontal gyrus; LI = lateralization index; LSFG = lateral superior frontal gyrus; ROI = region of interest; SLF = superior longitudinal fascicle; SMA = supplementary motor area.

Article Information

Address correspondence to: Yutaka Hayashi, M.D., Department of Neurosurgery, Kanazawa University, 13-1 Takaramachi, Kanazawa 920-8641, Japan. email:

Please include this information when citing this paper: published online November 11, 2011; DOI: 10.3171/2011.10.JNS11434.

© AANS, except where prohibited by US copyright law.



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    Magnetic resonance images and tractography studies reconstructed from DW images. The green lines in panels A–D outline the ROIs. A: Axial fractional anisotropy map at the level of the IFG. B: A T2-weighted image, in which ROIs are configured in the bilateral IFG. C: Axial fractional anisotropy map at the level of the LSFG. D: A T2-weighted image, in which ROIs are configured in the bilateral LSFG. E: Tractography study showing the fiber tracts connecting the IFG and SFG in an anterior view on a coronal T2-weighted image. Left fiber tract (F) and right fiber tract (G) in lateral views on a sagittal T2-weighted image.

  • View in gallery

    Photographs showing FD performed via a lateral approach (left hemisphere). Asterisks designate the opercular region in IFG. A: A lateral view showing the fiber tract ascending from the opercular region of the IFG to the LSFG (arrows show the posterior edge of the tract). B: A magnified image showing the SLF (triangles) that converges with the fiber tract between the IFG and LSFG. C: An upper view of the fiber tract that terminates in the lateral portion of the LSFG. CS = central sulcus.

  • View in gallery

    Tractography studies showing the targeted fiber tract between the IFG and LSFG in relation with other close fibers on a fractional anisotropy map. A: A targeted fiber tract running in proximity to the internal capsule (IC) or external capsule (EC) in an anterolateral view. B: An anterior view. C: A coronal image of the targeted fiber tract running outside both the internal and external capsule fibers. The label IFG-LSFG denotes the fiber tract between the IFG and LSFG.

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    Bar graph showing average width of the tract on DT imaging–based tractography studies; the average width of the fiber tract terminations in the IFG and SFG is given.

  • View in gallery

    Point graphs of the LI in the SFG (A) and IFG (B). The midline of the diamond denotes the average index; the upper and lower portions denote the 95% confidence interval.

  • View in gallery

    A: Illustrative anterior view of fibers in the 3 lateralization groups, based on the results of cluster analysis. The fiber tract images are as marked on the individual panels. B and C: Box plot graphs of the 3 lateralization groups of the tract of the SFG (B) and IFG (C). Boxes represent the 25th and 75th percentiles, with the medians indicated by the middle lines in the boxes. Vertical bars (whiskers) indicate the range of data, except for the outliers. The percentage of each group is also given in the figures.



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