Figure 9c.

Localization of the precentral sulcus intersections and hand knob. (a) Axial T1-weighted MR image shows the intersection of the superior frontal sulcus (yellow) with the precentral sulcus (blue). The central sulcus (purple) forms an epsilon-shaped hand knob. See Figure 2b and 2c for an example of an omega-shaped hand knob. (b) Parasagittal T1-weighted MR image shows the “hook” sign of the hand knob in the sagittal plane. (c) Parasagittal T1-weighted MR image lateral to b shows the intersection of the inferior frontal sulcus (red) with the precentral sulcus (blue), and the central sulcus (purple) behind it.