Ischemic Infarct of the Hand Knob Gyrus: Natural History, Morphology, and Localizing Value of the Omega Sulcus – A Case Report With a Side Note on the Dynamic Forces Underlying Sulci Formation

We describe a case of right-hand weakness localizable to an ischemic infarct of the hand knob gyrus of the left primary motor cortex. The hand knob gyrus is usually delimited by an omega-shaped sulcus, which is useful in outlining the posterior border of the frontal lobe. Being a cortical infarct, a potential embolic etiology was investigated and found, in keeping with previous case series reports. This finding, along with the relatively benign nature of this type of ischemic infarction, is emphasized. Identifying the omega sulcus is important as it is a reliable landmark demarcating eloquent motor cortex, which is critically important in planning surgical removal of brain tumors. In this case report, we review the largest case series of ischemic infarcts of the hand knob gyrus. We also describe the morphology of the omega sulcus, discuss the various theories underlying the convolutions or folding of the gyri of mammalian and human brains, and speculate as to why ischemic infarcts of the hand knob gyrus carry a relatively benign outcome.