The ventral diencephalon (VDC) is not an anatomical name for a single structure but a name we've given to a group of structures that generally cannot be distinguished from each other with standard MRI images. This "miscellaneous" area includes the hypothalamus, mammillary body, subthalamic nuclei, substantia nigra, red nucleus, lateral geniculate nucleus (LGN), and medial geniculate nucleus (MGN). White matter areas such as the zona incerta, cerebral peduncle (crus cerebri), lenticular fasciculus, and the medial lemniscus are also included in this area. The optic tract is included in this area in the most anterior extent. Each structure fades in and out of the VDC at different times. Therefore, the VDC greatly varies from slice to slic
Procedure
Sulci Lines
The superior border of the VDC is defined by the hypothalamic fissure, and is the dividing line between the thalamus and the VDC. This border is marked by drawing sulci in the medial sagittal views of the thalamus and VDC. The hypothalamic fissure is seen most easily toward the midline in the sagittal view, therefore begin drawing the sulci lines on or close to the most medial sagittal slice. The fissure should be drawn as a line which cups the bottom of the thalamus beginning caudally and moving rostrally as far as possible. It is often advantageous to draw many sulci on consecutive sagittal slices, moving from medial to lateral, in order to see the full extent and curve of the fissure more accurately in the coronal view.
Segmentation
The outline for the VDC is created using contour lines and manual drawing.
The anterior VDC starts one slice posterior to the anterior commisure and should be defined by an isointensity contour line.
The superior border is the hypothalamic fissure and the thalamus. This contour should exclude the anterior commissure, fornix, or any surrounding white matter and by convention should extend only a little wider than the optic chiasm (when present). The VDC should never extend to the pallidum.
In most cases the same contour line used for the thalamus will work for the lateral borders of the VDC. The contour line should provide most of the lateral border of the VCD, though some manual editing with the draw function may be required. If the best fit contour shows the internal capsule, or cerebral peduncle cutting dramatically into the VDC manually edit the contour to include that portion of the internal capsule, or cerebral peduncle in the volume of the VDC.
This outline is labeled "VentralDC."