Book Review And Study Questions For Chapter 3

Tic douloureux (trigeminal neuralgia) is a lancinating pain that originates from the territories of the trigeminal nerve, primarily its V2 or V3 territories. The trigger zone is frequently around the corner of the mouth. There is a geniculate neuralgia (related to the ear) and a glossopharyngeal neuralgia(related to the throat or palate),but neither of these originates from the surface of the face near the oral cavity. The hypoglossal nerve is the motor for the tongue and the vagus is the motor for most of the pharynx and larynx, visceromotor for much of the gut, and contains viscerosensory fibers from the gut.(p.45)

The glossopharyngeal nerve contains the afferent limb of the gag reflex and, through its innervation of the stylopharyngeus muscle, is an important part of the efferent limb of this reflex. The nucleus ambiguus, the location of the motorneurons serving the stylopharyngeus, also contributes to the innervation of muscle served by the vagus nerve and, therefore, to the efferent limb of the gag reflex. The trigeminal and facial nerves participate in the afferent and efferent limbs (respectively) of the corneal reflex. The accessory nerve innervates the ipsilateral trapezius and sternocleidomastoid muscles, and the hypoglossal nerve innervates the ipsilateral genioglossus muscle.(p.46–47)

The combination of pain in the throat on swallowing and apparent lack of a trigger zone points to glossopharyngeal neuralgia; this reflects the distribution of the ninth nerve fibers in the oral cavity. Geniculate neuralgia is experienced in the territory of the facial nerve (face, around eye, cheek, radiating to ear) and trigeminal neuralgia is experienced in the territory of the trigeminal nerve on the face, mainly around the corner of the mouth, and both of these have trigger zones. Post herpetic neuralgia (commonly called shingles) may be experienced by patients following an infection with the herpes zoster virus. Occipital neuralgia is an entrapment condition in which the pain is in the area of the occiput; a trigger zone is usually present.(p.47)

The Wallenberg (lateral medullary) syndrome is a lesion of the lateral portions of the medulla that is localized to the territory of the posterior inferior cerebellar artery. This territory includes the nucleus ambiguus, along with other important structures. In addition to the dysphagia and hoarseness(and some dysarthria),an alternating hemi anesthesia is frequently seen in patients with this syndrome. Although other cranial nerve deficits may be seen in the other brainstem syndromes, dysarthria, dysphagia, and hoarseness are not prominent features in these situations.(p.50)

The internal acoustic meatus contains the vestibulocochlear nerve, the facial nerve, and the labyrinthine artery, branch of the anterior inferior cerebellar artery. A vestibularschwannoma located in the meatus would likely affect the cial nerve and result in facial weakness. The vagus and glossopharyngeal nerves exit the skull via the jugular foramen(along with the accessory nerve).The cerebellar arteries originate within the skull and distribute to structures within the skull.(p.46,275)

About 10%–15% of all intracranial aneurysms are found on the vertebrobasilar system. The majority of these are found at the bifurcation of the basilar artery into the posteriorcerebral arteries; this point is also called the basilar tip or the basilar head. This type of lesion may compromise the integrity of the oculomotor nerve with corresponding deficits. Aneurysms at the other locations on the vertebrobasilar system are rare.(p.43–44)

The oculomotor nerve (III) exits from the medial aspect of the midbrain into the interpeduncular fossa/cistern. It traverses this space, and courses through the lateral wall of the cavernous sinus to eventually enter (along with the trochlear[IV] and abducens [VI] nerves) the superior orbital fissure. Cranial nerves IV, VI, and V1 (the ophthalmic portion of the trigeminal nerve),along with III, pass through the cavernoussinus. Cranial nerve II (optic) is quite rostral to the interpeduncular fossa.(p.43–44,49)

The afferent limb of the corneal reflex is via the ophthalmic division of the trigeminal nerve (V); the cell body of origin is in the trigeminal ganglion and the central terminations in the pars caudalis of the spinal trigeminal nucleus. The efferent limb originates in the motor nucleus of the facial nerve (VII) and distributes to the facial muscles around the eye. None of the other choices contains fibers related to the corneal reflex.(p.44)

The Claude syndrome is a lesion in the midbraintegmentum involving the red nucleus, cerebellothalamic fibers, and the fibers of the oculomotor nerve. This results insignificant loss of movement of the eye on the side of the lesion. The Raymond syndrome (also called the Foville syndrome) involves the abducens root, but this would not represent eye movement deficits nearly as great as damage to the root of the oculomotor nerve. The Wallenberg syndrome lesion includes the vestibular nuclei which may, in some cases, result in nystagmus. Although certainly a disability, this may resolve with time. Although other cranial nerve deficits are seen in the Déjérine and Gubler syndromes, they do not involve eye movement.(p.49,50)

Vestibular schwannomas larger than 2.0 cm in diameter may impinge on the root of the trigeminal nerve and cause numbness on the same side of the face. Although the other deficits listed are not seen in these patients, diplopia (involvement of oculomotor, abducens or trochlear nerves, singularlyor in combination) may be present, but in fewer than 10% of these individuals.(p.46,275)

The combination of a loss of most ocular movement and a dilated pupil in the same eye point to a lesion of the oculomotor nerve. Lesions of the other cranial nerves would result is a loss of some, but not most, eye movement and the pupil would be unaffected. The oculomotor nerve passes through the interpeduncular cistern, not the ambient.(p.44)

As it exits the anterior (ventral) surface of the mid-brain, the oculomotor nerve passes between the superior cerebellar artery (which is caudal to the nerve root) and the P1 segment of the posterior cerebral artery (which is rostral to the nerve root).The trigeminal root is adjacent to more distal portions of the superior cerebellar artery; the labyrinthine artery accompanies the vestibulocochlear nerve as it enters the internal acoustic meatus; and the ophthalmic artery accompanies the optic nerve along part of its extent. The abducens nerve passes rostrally adjacent to the basilar artery in the prepontinecistern.(p.43–44)

An inability to abduct the left eye, in the face of no other deficits, indicates a lesion in the root of the abducens nerve on the left (the side of the lesion).Lesions at all of the other locations will result in abducens paralysis and other deficits such as an INO on the contralateral side or a contralateral hemiplegia (see p.46,49).

Especially large aneurysms in this area may impinge on optic structures, most frequently the chiasm, with a loss of parts of the visual fields in both eyes. In addition, rupture of an aneurysm in this location may also result in visual deficits or in deficits related to damage to the hypothalamus. A partial loss of eye movement or diplopia indicates damage to cranial nerves III, IV, or VI; structures not located in this area. Facial pain is most commonly related to the Vth (trigeminal neuralgia) or VIIth (geniculate neuralgia, hemifacial spasm) cranial nerves, and a constricted pupil would result from a loss of sympathetic input.(p.42)

This woman has a right internuclear ophthalmoplegia resulting from a lesion of the abducens internuclear fibers in the right MLF. Lesions of the abducens nucleus would result in an INO plus weakness of the lateral rectus muscle on the side of the lesion. Damage to the oculomotor nucleus would result in a profound loss of eye movements on the side of the lesion (see p.46,49).

Branches of the superior cerebellar artery are most frequently involved in cases of trigeminal neuralgia that are presumably of vascular origin. The posterior cerebral artery and its larger branches serve the midbrain-diencephalic junction or join the medial surface of the hemisphere. The basilar artery serves the basilar pons and the anterior inferior cerebellar artery serves the caudal midbrain, inner ear, and the inferior surface of the cerebellar surface. The basal vein drains the medial portions of the hemisphere and passes through the ambient cistern to enter the great cerebral vein (of Galen).(p.45)

In this patient the pontine lesion is on the right side. This results in a paralysis of the right lateral rectus (abducenslower motor neurons) and the right and left medial recti (dam-age to the axons of interneurons in the medial longitudinal fasciculus on both sides).The surviving muscle is the left lateral rectus.(p.49,50)

Difficulty speaking (dysarthria) may result from damage to the brainstem centers that influence the throat muscles or in some cases the facial muscles. Dysarthric speech may also be seen in patients with damage to the hypoglossal root or nucleus. In this situation altered speech is due to the fact that one half of the tongue is paralyzed during attempted movement. The combination of all medially located lesions, some dysarthria, and a left-sided hemiparesis clearly points to a lesion in the medial medulla on the right side. The other choices either are on the wrong side or do not involve cranial nerves that innervate structures in the oral cavity.(p.48,50)