Fig 1. Schematic representation of the criteria used for morphologic classification and corresponding MR image of a typical example. The position of the third fissure, which segments the knob, modifying its appearance from an omega to an epsilon in the lateral, central, or medial part of the hand knob indicates a medially asymmetric epsilon, epsilon, and laterally asymmetric epsilon, respectively. To distinguish an omega from a null, the height of the knob must be greater than the thickness of the precentral gyrus measured at the base of the knob. If the height is smaller than the thickness, the HMC is classified as null. Multiplanar reformatted MR imaging axial sections were obtained from left hemispheres 50 ± 2 mm above the Talairach ACPC plane. The red area in the MR images highlights the morphologic variant.