Angular Gyrus

  1. The angular gyrus is located in the parietal lobe, posterior to the supramarginal gyrus and immediately anterior to the occipital lobe. Its anterior boundary is the Jensen sulcus and its posterior boundary is the occipital lobe. Its superior boundary is the intraparietal sulcus and its inferior boundary is the superior temporal sulcus. The inferior and posterior end of the angular gyrus should form a ‘c’ shape around the posterior end of the superior temporal sulcus (STS). (Fig. 1, Fig. 2)
  2. Before masking, it is important to eyeball the boundaries of the angular gyrus on a 3D object. Begin by finding the anterior boundary of the occipital lobe, by imagining a line between the occipital notch inferiorly and the parieto-occipital fissure superiorly. This line will serve as a posterior boundary for the angular gyrus (Fig.3) . Secondly, find the STS’s posterior boundary. The angular gyrus should form a ‘c’ shape around this boundary. Finally, find anterior boundary by locating the Jensen sulcus by locating the posterior ends of sylvian fissure’s middle segment and the STS. Draw an imaginary line from both these points up to the intraparietal sulcus. Between these two lines is the Jensen sulcus. (Fig. 4)
  3. Masking of the angular gyrus is done in the axial view. Begin anteriorly, at a slice where the Jensen sulcus is clear. Mask the Jensen sulcus to its internal endpoint and draw a straight line down to the intraparietal sulcus. Follow the intraparietal sulcus to its lateral end, and fill in everything within these boundaries. (Fig. 5)
  4. Continue step 3 to the superior end of the brain. If either sulcus becomes unclear, find the final slice at which it was last clear and approximate this point on all other slices. (Fig. 6)
  5. Once the angular gyrus is masked to the superior end of the brain, find the first slice that was masked, and continue step 3 inferiorly. Moving inferiorly, the Jensen sulcus will disappear. At this point, reference the last slice where the sulcus was clear and approximate its location on the following slices. On the 3d object, this will create a straight line from the end of the Jensen sulcus to the inferior end of the angular gyrus. In addition, the intrapareital sulcus may become unclear. When this happens, reference the predetermined boundary of the occipital lobe on the 3D object for the boundary and mask between these two approximated points. (Fig. 7)
  6. Moving inferiorly, the posterior segment of the sylvian fissure will come into view. At this point, mask from the posterior segment of the sylvian fissure to the approximated anterior boundary of the occipital lobe. Continue this step until reaching the STS. (Fig. 8)