The cuneus is the medial aspect of the occipital lobe. It is defined inferiorly by the calcarine fissure, which divides the occipital lobe horizontally. The superior and anterior boundary of the cuneus is the parieto-occipital fissure, which separates the occipital lobe from the parietal lobe, running diagonally from the most superior part of the occipital lobe in an inferior/anterior direction. (Fig. 1, Fig. 2, Fig.3)
To define the boundaries initially, mask first in the sagittal view. Go to a mid-sagittal slice where the parieto-occipital fissure and the calcarine sulcus are easily identified. Mask the parieto-occipital fissure to its inferior endpoint and mask a straight line to the anterior endpoint of the calcarine sulcus. Follow the calcarine sulcus to the posterior end of the brain. If it does not connect to the posterior end of the brain, connect it to the next highest sulcus. Mask everything within these boundaries. (Fig. 4)
Once a guide has been set up, switch to the axial view. Start superiorly, where the gyrus as masked in the sagittal view first appears. To define the lateral boundary of the gyrus, move slightly (5-6 slices) inferiorly from this initial slice, and label everything medial to the first sulcus interior to the longitudinal fissure, using the height identified from the preexisting label. Continue to label the all slides superior to that and inferior as well at the same defined thickness. (Fig. 5, Fig. 6)
At the inferior portion of the cuneus, there may be a few gaps in the preexisting label made by the calcarine sulcus. Follow the preexisting label by splitting the mask into two sections, filling in everything between the label and the interhemispheric fissure. (Fig. 7, Fig. 8)
Once you have labeled all of the cuneus, switch to the sagittal view again and clean up any labels beyond the around the calcarine sulcus and the parieto-occipital fissure.