Neuro-Pathology - Pontine Lesions

In my last post, I discussed the anatomy of the Pons and I discussed the nerves and the nucleus in the pons. Today, I will be looking at the Pontine lesions, and in the conclusion of the last post, I mentioned the lesions that I will be discussing.

I will be discussing Pontine Lesions, where I will be talking about Ventral Pontine Syndrome (Millard Gubler Syndrome) where I will look at the structures of the pons and the lesion at the ventral aspect of the pons which is the base of the pon and these structures includes the pontine nuclei, the middle cerebellar peduncle, and the corticospinal fibers. The Foville Syndrome which affects the ventral aspect of the pons and the tegmentum, Ventromedial pontine syndrome (Raymond Syndrome), Lateral Pontine Syndrome, and locked-in Syndrome. -

Starting with the Ventral Pontine Syndrome (Millard-Gubler Syndrome) which happens with certain lesions or occlusions around the pons such as an occlusion in the facial nerve fasciculus leading to ipsilateral facial nerve palsy where facial expression would not be possible thereby causing drooping of the side of the face. Also, the facial nerve is crucial in salivation and lacrimation and so when there is a lesion that affects the facial nerve fasciculus, it will lead to a lack of salivation and lacrimation ipsilaterally. The facial nerve also supplies the anterior two-thirds of the tongue and when there is an occlusion of the nerve, it would lead to an ipsilateral loss of taste in the area of the two-thirds of the tongue. The facial nerve supplies lots of areas, including the tympanic membrane and the external ear and it is important in touch, pain, pressure, and temperature sensations, and occlusion will lead to ipsilateral loss of touch, pain, pressure, and temperature sensations in the external ears. If the abducens nerve which supplies the lateral rectus is damaged with Ventral Pontine syndrome, it would affect the movement of the eyeball preventing it from being pulled laterally, and if the oculomotor nerve is not affected, then it would cause the eye to deviate medially known as ipsilateral rectus palsy. If the upper motor neurons which are around the pontine nuclei towards the medulla go to synapses with the lower motor neurons at the anterior gray horn. There is a corticospinal fiber that can be occluded leading to a contralateral hemiplegia.

Foville Syndrome involves the basilar part of the pons and extends into the tegmentum. In the tegmentum, the paramedian pontine reticular formation nuclei are responsible for sending sending information on eye movement when the head moves to the cranial nerve 6, cranial nerve 4, and cranial nerve 3. When there is a lesion of the paremedian pontine reticular formation nucleus there will be loss of stimulation to the lateral rectus inhibiting the eyes from following the gave of the head which is known as an ipsilateral gaze palsy.

Ventromedial pontine syndrome (Raymond Syndrome) is a lesion that involves the ventral region of the pons where the facial nerve fasciculus and the corticospinal fibers are affected. The Corticospinal fiber lesion would lead to a contralateral hemiplegia since the fibers will cross to supply their regions. The facial nerve fasciculus occlusion would cause Ipsilateral facial nerve palsy.

Lateral Pontine Lesion (Marie-foix syndrome) which is a lesion of the lateral aspect of the pons which has to do with occlusion of the corticospinal cortical nucleus fibers which affects the contralateral lower motor neuron causing contralateral hemiplegia. It also damages the spinal lemniscus which carries pain, temperature, crude touch, and pressure sensations that synapse with neurons in the dorsal horn and go to the thalamus. So when there is a lesion on the spinal lemniscus, it would lead to a contralateral loss of pain, crude touch, temperature, and pressure sensations. It can also affect the middle cerebellar peduncles which connect the pons to the cerebellum which is responsible for posture, coordination, and equilibrium, and a lesion would lead to ipsilateral ataxia. If it goes more dorsally in the pons, it can affect the spinal nucleus of the trigeminal system causing loss of pain, temperature, and proprio reception from the face, as well as it can affect cochlear nuclear leading to deafness.

Locked-in syndrome is a bilateral pontine lesion affecting the ventral aspect of the pons as well as the nucleus of the 6th nerve. If it affects the cortico-spinal fibers, it leads to a loss of the bilateral paralysis of the upper extremities and the lower extremities causing quadriplegia, it would also lead to a lack of speech known as Aphonia. One final thing, if the abducens nerve is damaged as well as the oculomotor nerve causing an inability to move the eyes and loss of interaction with other nerves as a result of damage to medial longitudinal fasciculus leading to internuclear abdominoplasty where both abducens nerves are damaged. ^,

Image 1 || Wikimedia Commons || Lower pons horizontal