Medial Pontine Syndrome and Lateral Pontine Syndrome

by Craig Canby, PhD

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    00:00 The medial region or area of the pons can be damaged due to vascular insult. If it’s the medial structures of the pons, this would be medial pontine syndrome. This is going to be due to a lesion of the basilar artery that travels over the pons and gives rise to numerous pontine vessels to help supply them.

    00:28 Structures that are damaged in the medial pontine syndrome, there will be three. The corticospinal tract, the descending pathway is damaged. The medial lemniscus pathway, ascending tract is damaged.

    00:46 You’ll have damage to abducens nerve fibers, so you have a cranial nerve involvement as well.

    00:54 So two pathways and one cranial nerve being involved. We can see a couple of this very readily.

    01:02 At this level section, here’s your medial lemniscus here in blue. Then here you have your corticospinal components here in red. The abducens fibers are not visible at this axial level. We would have to be distal or inferior to this level. If injury to each one of these structures, what would we see or what would you see? First, the corticospinal tract symptoms. This would result in contralateral hemiparesis of upper and lower extremities. The medial lemniscus system is conveying vibration, conscious proprioception, and fine touch. If this pathway is lesioned, then you’ll have a contralateral loss of those functions.

    01:57 With abducens fiber injury, you will essentially inhibit or cause paralysis of the lateral rectus, the muscle that moves the eyeball laterally or moves it so that it abducts. If you can’t do that any longer, the eye will move medially and that is medial strabismus. You can also have injury or lesion of the lateral structural components of the pons. This would result in lateral pontine syndrome. This is also due to vascular insult, so it's a vascular lesion. A couple of vessels can produce this. The basilar artery is a culprit.

    02:56 The anterior inferior cerebellar arteries can also produce this lesion. Several structures are damaged or lesioned in this particular syndrome. One of which would be the spinothalamic tract components.

    03:17 Communications or a tract connection with the cerebellum is lesioned. Vestibular and cochlear nuclei are also damaged. The facial nucleus is an involved structure. It’s damaged. Descending hypothalamic fibers are also injured in this syndrome. There’s a lesion of the trigeminal nucleus, so we do have some cranial nerve components that are damaged or lesioned in this syndrome. We do have some tracts that are damaged as well. Injury to the spinothalamic tract would result in a loss of pain and temperature from the contralateral side of the body. This would be distal to the face. A lesion of the cerebellar tract would cause ipsilateral ataxia. Vestibular and cochlear nuclei involvement would result in ipsilateral hearing impairment. There’d be vertigo and nystagmus as well. Involvement of the facial nerve, a lesion of this cranial nerve would result again in ipsilateral paralysis, ipsilateral loss of gustation from the anterior two-thirds of the tongue. You would lose your excitatory or secretory excitation over lacrimal and salivary gland secretions. So those are inhibited. There will be an impaired corneal reflex as a result of injury to this cranial nerve nucleus. A lesion of the descending hypothalamic fibers, these are sympathetic fibers, descending would cause ipsilateral Horner’s syndrome. Involvement of the trigeminal nucleus would cause ipsilateral loss of pain and temperature from the face. Trigeminal nerve innervates muscles of mastication. So a lesion of this nucleus would result in their weakness. The jaw, as a result, will deviate toward the side of the lesion as a result of the weakness of the muscles of mastication.

    About the Lecture

    The lecture Medial Pontine Syndrome and Lateral Pontine Syndrome by Craig Canby, PhD is from the course Brain Stem. It contains the following chapters:

    • Medial Pontine Syndrome
    • Lateral Pontine Syndrome

    Included Quiz Questions

    1. VI
    2. III
    3. XII
    4. IX
    5. IV
    1. Anterior inferior cerebellar artery (AICA)
    2. Middle cerebral artery (MCA)
    3. Posterior inferior cerebellar artery (PICA)
    4. Posterior cerebral artery (PCA)
    5. Anterior spinal artery (ASA)
    1. Contralateral loss of sweat gland secretion
    2. Loss of gustation from the anterior two-thirds of the tongue
    3. Ipsilateral facial paralysis
    4. Ipsilateral loss of salivary gland secretion
    5. Ipsilateral loss of lacrimal gland secretion
    1. Ptosis
    2. Diplopia
    3. Excessive sweating
    4. Mydriasis
    5. Loss of corneal reflex

    Author of lecture Medial Pontine Syndrome and Lateral Pontine Syndrome

     Craig Canby, PhD

    Craig Canby, PhD

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