Figure 61: Vascular Distribution and Anatomy (Including 6th, 7th, 8th Nerves, MLF) of the Pons

In this axial section of the pons, the proximity of the 7th (VII) and 8th (VIII) fascicles can be appreciated, and a lateral inferior pontine syndrome (anterior inferior cerebellar artery, AICA territory), which could involve both of these fascicles, could cause acute prolonged vertigo accompanied by an abnormal ipsilateral head impulse test (HIT, fascicle of CN8) and ipsilateral lower motor neuron facial palsy (fascicle of CN7). Although a ‘central' acute vestibular syndrome typically has a normal HIT, exceptions exist where an abnormal HIT can be due to a stroke. Commonly a ‘central' abnormal HIT can be seen with lesions affecting the root entry zone of CN8, or those involving the vestibular nucleus or with labyrinthine ischemia (AICA territory). A lesion involving the middle cerebellar peduncle (MCP) itself can also result in acute prolonged vertigo, but if the fascicle of CN8 is spared, HIT will be normal. A dorsal midline lesion can cause unilateral or bilateral internuclear ophthalmoplegia (INO) due to medial longitudinal fasciculus injury (usually stroke or multiple sclerosis). Dorsal pontine injury can also cause a horizontal gaze palsy (VI or 6th nucleus) or a gaze palsy + INO, causing a one-and-a-half syndrome (+/- 7th NP). Finally, the central tegmental tract (CTT) is in this vicinity as well, making oculopalatal tremor a finding to look for months after suffering a pontine lesion (e.g., hemorrhagic cavernoma).