Inferior temporal sulcus as a site of corticotomy: magnetic resonance imaging analysis of individual sulcus patterns

OBJECTIVE: Transcortical approaches to the inferior horn often result in quadrant hemianopsia attributable to the injury to the optic radiation. The inferior temporal sulcus (ITS) has received little attention as an entrance point for the transsulcal approach. We used the method of detecting the ITS with magnetic resonance imaging (MRI) scans and investigated the sulcus pattern of ITS, its incidence rate, and the availability of the ITS to the corticotomy for selective amygdalohippocampectomy. METHODS: The sulcus patterns of the ITS of 100 temporal lobes in 50 healthy individuals were classified according to the number of interruptions by gyral bridges, and the localization of the ITS was characterized in relation to the outer surface by means of the surface anatomy scan of MRI. RESULTS: Most of the ITS was interrupted by one to three gyral bridges (0 bridges, 8%; one bridge, 27%: two bridges, 37%; three bridges, 20%; more than four bridges or no apparent ITS, 8%). When the ITS was present, it was located 15 mm above the orbitotragus line at a point 20 mm anterior to the tragus. The number of gyral bridges was significantly larger in the left temporal lobes than in the right temporal lobes, regardless of the sex of the subject. CONCLUSION: The ITS was clearly identified in 72% of the temporal lobes by the oblique sagittal view of MRI scans; thus, in such cases, the ITS was considered to be a candidate for an entrance point of a small temporal corticotomy. The preoperative observation of the ITS in relation to the orbitotragus line by means of MRI may improve the planning of the transsulcal approaches to deeply seated mesial temporal lesions, such as hippocampal sclerosis.