Medial Pontine Syndrome

Medial pontine syndrome results from occlusion of paramedian branches of the basilar artery (Figure IV-5-16).

At a minimum, this lesion affects the exiting fibers of the abducens nerve and the corticospinal tract. The medial lemniscus may be affected if the lesion is deeper into the pons, and the facial nerve may be affected if the lesion extends laterally.

The long tract signs will be the same as in medial medullary syndrome, involving the corticospinal and medial lemniscus, but the abducens nerve and the facial nerve lesions localize the lesion to the caudal pons.

Corticospinal tract lesions produce contralateral spastic hemiparesis of both limbs.

Medial lemniscus lesions produce a contralateral deficit of proprioception and touch, pressure, and vibratory sensations in the limbs and body.

Lesions of the abducens nerve exiting the caudal pons produce an internal strabismus of the ipsi-lateral eye (from paralysis of the lateral rectus). This results in diplopia on attempted lateral gaze to the affected side.

Lesions of the facial nerve exiting the caudal pons produce complete weakness of the muscles of facial expression on the side of the lesion.

Lesions of the facial nerve may also include an alteration of taste from the anterior two thirds of the tongue, loss of lacrimation (eye dry and red), and loss of the motor limb of the corneal blink reflex.

If a lesion extends dorsally to include the abducens nucleus (which includes the horizontal gaze center in the PPRJF), there may be a lateral gaze paralysis in which both eyes are forcefully directed to the side contralateral to the lesion.

Figure IV-5-16. Medial Pontine Syndrome
Table IV-5-6, Medial Pontine Syndrome

Structure

Sign

Medial lemniscus Fibers of VI

Contralateral spastic hemiparesis of the body Contralateral loss ofposition and vibration on the body Medial strabismus

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