The Frontal Aslant Tract: A Systematic Review for Neurosurgical Applications

Abstract

The frontal aslant tract (FAT) is a recently identified white matter tract connecting the supplementary motor complex and lateral superior frontal gyrus to the inferior frontal gyrus. Advancements in neuroimaging and refinements to anatomical dissection techniques of the human brain white matter contributed to the recent description of the FAT anatomical and functional connectivity and its role in the pathogenesis of several neurological, psychiatric, and neurosurgical disorders. Through the application of diffusion tractography and intraoperative electrical brain stimulation, the FAT was shown to have a role in speech and language functions (verbal fluency, initiation and inhibition of speech, sentence production, and lexical decision), working memory, visual-motor activities, orofacial movements, social community tasks, attention, and music processing. Microstructural alterations of the FAT have also been associated with neurological disorders, such as primary progressive aphasia, post-stroke aphasia, stuttering, Foix-Chavany-Marie syndrome, social communication deficit in autism spectrum disorders, and attention-deficit hyperactivity disorder. We provide a systematic review of the current literature about the FAT anatomical connectivity and functional roles. Specifically, the aim of the present study relies on providing an overview for practical neurosurgical applications for the pre-operative, intra-operative, and post-operative assessment of patients with brain tumors located around and within the FAT. Moreover, some useful tests are suggested for the neurosurgical evaluation of FAT integrity to plan a safer surgery and to reduce post-operative deficits.

Keywords: diffusion-weighted imaging; executive function skills; frontal aslant tract; language; motor coordination; neurosurgery; tractography; working memory.

Figure 1

Flow chart applied to the retrieval and selection of studies included in the systematic literature review according to PRISMA guidelines.

Figure 2

MR-diffusion tensor imaging of the frontal aslant tract (FAT) in a 23-year-old healthy female. Right (red) and left (yellow) FAT overlaid over coronal images (A), left FAT terminations in the left posterior inferior frontal gyrus overlaid over sagittal images (B), superior right and left FAT terminations, respectively, in the right and left superior frontal gyrus overlaid over axial images (C). 3D brain reconstruction of right and left FAT (D).

Figure 3

A 33-year-old woman with a WHO grade II astrocytoma located in the left cortico-subcortical region of the superior frontal gyrus. Surgical resection was performed through fluorescein-guided microsurgical technique guided by intraoperative neurophysiological monitoring and by functional MRI (fMRI)/tractography-integrated neuro-navigation system. Pre-operative symptoms included motor partial seizure affecting the right leg, followed by a generalized seizure. The patient post-operatively developed a transient mild weakness in the right leg. Preoperative axial and coronal T2-weighted MR images (A), post-operative axial T1-weighted post-gadolinium and coronal T2-weighted MR images (B), fMRI with blood oxygen level-dependent response in the left paracentral lobule evoked during voluntary movement of the right foot overlaid on sagittal T1-weighted MR images (C), and 3D relationship between the tumor and frontal aslant tract tractography reconstruction (D).

Figure 4

Graphical representation of the frontal aslant tract and its putative roles.