Inferior and superior colliculus

The inferior colliculus (iCo) is an oval-shaped grey matter mound located in the caudal half of the mesencephalic tectum. The superior colliculus (sCo) is a gray matter mound located in the rostral half of the mesencephalic tectum (Fig. ​(Fig.1717).

A The superior and inferior colliculus (sCO and iCO) in the midbrain and border the CSF which facilitates delineations. B Magnification, asterisks indicate the structrures of interest

The iCo and sCo are delineated on the R2* map or T2*-weighted image. In the R2* map for the sCo and iCo are hyperintense. In T2* weighted images contrasts are inverted. The iCo is located near the tectum of the midbrain, caudal to the sCo on the dorsal aspect of the mesencephalon, lateral—in its dorsal aspect- to the periaqueductal gray (PAG), and ventrally to the cuneiform nucleus. The iCo is laterally bordered by the ventricular system. The sCo is visible in the midbrain, rostral to the iCo, lateral to the PAG and bounded laterally by the cerebrospinal fluid (CSF). Both structures appear on T₂* maps as a hypointense structure and a hyperintense structure on R2* maps. Both structures are visible on T2* maps; however, the CSF contrast is better on the R2* maps.

To start, the center of the RN is identified, and the cursor is placed there. At this point, the sCo and iCo will appear on the sagittal image at the roof of the mesencephalic tectum. The structures are small, and well defined; therefore, no additional information on arbitrary decisions is provided. The delineation is driven by shape consistency. The cursor is then moved to the center of the sCo in the sagittal image, subsequently performing the delineation in the axial plane. First move in a dorsal direction, complete the delineation in the ventral direction. Shape consistency should be checked in the coronal as well as the sagittal plane. The iCo is delineated in the same manner. In Fig. 18 delineations of the sCo and iCo are illustrated at various anatomical levels.

a The inferior colliculus can easily be located due to the characteristic location at the mesencephalic tectum. b The superior colliculus can easily be located due to the characteristic location at the mesencephalic tectum above the inferior colliculus (sagittal view)