Coronal Section of the Brainstem Showing Ocular Motor Nuclei and Anatomy of the Vestibular Nucleus (with SCC Inputs)

(A) Seen here is a coronal view of the brainstem showing the locations of the ocular motor nuclei (IIIrd, IVth, VIth) as well as the nuclei of VII and VIII (vestibular and cochlear). The vestibular nucleus (VN) is divided into the inferior, lateral, medial, and superior subnuclei, and the medial vestibular nucleus (MVN) also plays a role in horizontal gaze-holding along with the nucleus prepositus hypoglossi (NPH). (B) Because the afferents from the horizontal and posterior semicircular canals (SCC) mainly go to the MVN, while the afferents from the anterior SCC go to both MVN and SVN (superior), the anterior SCC central pathways can be relatively spared with MVN damage. This pattern (+ head impulse testing in the planes of horizontal and posterior SCC, and negative head impulse in the plane of the ipsilateral anterior SCC) can have clinical relevance in the acute vestibular syndrome as a vestibular nucleus lesion should be considered. In contrast, the superior division of the vestibular nerve innervates anterior and horizontal SCC, while the inferior division innervates posterior SCC; therefore, anterior and horizontal SCC involvement with posterior SCC sparing is pattern seen commonly with vestibular neuritis.