Frontal aslant tract projections to the inferior frontal gyrus.

Abstract

Frontal aslant tract (FAT) is a white matter bundle connecting the pre-supplementary motor area (pre-SMA) and the supplementary motor area (SMA) with the inferior frontal gyrus (IFG). The purpose of the present study was to evaluate the anatomical variability of FAT. Total number of fibres and the lateralisation index (LI) were calculated. We attempted to find factors contributing to the diversity of FAT regarding IFG terminations to the pars opercularis (IFG-Op) and to the pars triangularis (IFG-Tr). Magnetic resonance imaging of adult patients with diffusion tensor imaging (DTI) with total number of 98 hemispheres composed a cohort. V-shaped operculum was the most common (60.5%). Total number of FAT fibres had widespread and unimodal distribution (6 to 1765; median: 160). Left lateralisation was noted in 64.3% of cases and was positively correlated with total number of FAT fibres and the bundle projecting to IFG-Op (p < 0.01). LI correlated with total number of FAT fibres (r = 0.43, p < 0.01). FAT projected predominantly to IFG-Op (88.9%; 88 of 99). Only in 3 (3.1%) cases more fibres terminated in IFG-Tr than in IFG-Op. Total number of FAT fibres and number of fibres terminating at IFG-Op did not correlate with the ratio of fibre numbers: FAT/IFG-Op, FAT/IFG-Tr and IFG-Op/IFG-Tr (p > 0.05). The greater total number of fibres to IFG-Tr was, the higher were the ratios of IFG-Tr/ /FAT (r = 0.57, p < 0.01) and IFG-Tr/IFG-Op (r = 0.32, p = 0.04). Among the IFG, the major termination of FAT is IFG-Op. Whereas the IFG-Tr projection seems to be related to the expansion of the entire FAT bundle regardless of side, domination and handedness. Nevertheless, FAT features a significant anatomical variability which cannot be explained in terms of DTI findings.