D R . N I S H T H A J A I N

S E N I O R R E S I D E N T ,

D E P A R T M E N T O F N E U R O L O G Y ,

G M C , K O T A .

CRANIAL NERVES XI AND XII

The Spinal Accessory Nerve

The spinal accessory (SA) nerve - two nerves that run

together in a common bundle for a short distance.

The smaller cranial portion (ramus internus) is a

special visceral efferent (SVE) accessory to the vagus.

The cranial root runs to the jugular foramen and unites

with the spinal portion, traveling with it for only a few

millimeters to form the main trunk of CN XI.

The cranial root communicates with the jugular ganglion of

the vagus, and then exits through the jugular foramen

separately from the spinal portion.

It passes through the ganglion nodosum and then blends

with the vagus.

Distributed principally with the recurrent laryngeal nerve to

sixth branchial arch muscles in the larynx except there is

no XI contribution to the cricothyroid muscle.

The major part of CN XI is the spinal portion (ramus

externus).

The fibers of the spinal root arise from SVE motor cells in

the SA nuclei in the ventral horn from C2 to C5, or even C6.

The supranuclear innervation of CN XI arises from the

lower portion of the precentral gyrus.

The bulk of current evidence indicates that both the SCM

and trapezius receive bilateral supranuclear innervation.

The input to the SCM motor neuron pool - ipsilateral and

that to the trapezius motor neuron pool - contralateral.

Somatotopic arrangement present : cord levels C1 and C2 innervate the ipsilateral sternocleidomastoid muscle, and levels C3 and C4 innervate primarily the ipsilateraltrapezius.

The corticobulbar fibers to the sternocleidomastoid are located in the brainstem tegmentum, whereas fibers to the trapezius are located in the ventral brainstem.

Thus, a ventral pontine lesion can cause supranuclearparesis of the trapezius with sparing of the sternocleidomastoid muscle.

To assess SCM power, have the patient turn the head fully

to one side and hold it there, then try to turn the head back

to midline, avoiding any tilting or leaning motion.

The muscle usually stands out well, and its contraction can

be seen and felt.

Significant weakness of rotation can be detected if the

patient tries to counteract firm resistance.

The two sternocleidomastoid muscles can be examined

simultaneously by having the patient flex his neck while the

examiner exerts pressure on the forehead, or by having the

patient turn the head from side to side.

Flexion of the head against resistance may cause deviation

of the head toward the paralyzed side.

With unilateral paralysis, the involved muscle is flat and

does not contract or become tense when attempting to turn

the head contralaterally or to flex the neck against

resistance.

Weakness of both SCMs causes difficulty in anteroflexion

of the neck, and the head may assume an extended

position.

With trapezius atrophy the outline of the neck changes,

with depression or drooping of the shoulder contour and

flattening of the trapezius ridge.

The strength of the trapezius is traditionally tested by

having the patient shrug the shoulders against resistance.

To examine the middle and lower trapezius, place the

patient's abducted arm horizontally, palm up, and attempt

to push the elbow forward.

Weakness of the trapezius disrupts the normal scapulohumeral

rhythm and impairs arm abduction.

Impairment of upper trapezius function causes weakness of

abduction beyond 90 degrees.

Weakness of the middle trapezius muscle causes winging of the

scapula.

The winging due to trapezius weakness is more apparent on

lateral abduction in contrast to the winging seen with serratus

anterior weakness, which is greatest with the arm held in front.

When the trapezius is weak, the arm hangs lower on the

affected side, and the fingertips touch the thigh at a lower

level than on the normal side.

Placing the palms together with the arms extended

anteriorly and slightly below horizontal shows the fingers on

the affected side extending beyond those of the normal

side.

The two trapezius muscles can be examined

simultaneously by having the patient extend his neck

against resistance.

Bilateral paralysis causes weakness of neck extension.

The patient cannot raise his chin, and the head may tend to

fall forward (dropped head syndrome).

The shoulders look square or have a drooping, sagging

appearance due to atrophy of both muscles.

Weakness of the muscles supplied by CN XI may be

caused by supranuclear, nuclear, or infranuclear lesions.

Supranuclear involvement usually causes at worst

moderate loss of function since innervation is partially

bilateral.

In hemiplegia there is usually no head deviation, but

testing may reveal slight, weakness of the SCM, with

difficulty turning the face toward the involved limbs.

There may be depression of the shoulder resulting from

trapezius weakness on the affected side.

Irritative supranuclear lesions may cause head turning

away from the discharging hemisphere.

This turning of the head (or head and eyes) may occur as

part of a contraversive, ipsiversive, or jacksonian seizure,

and is often the first manifestation of the seizure.

Extrapyramidal lesions may also involve the

sternocleidomastoid and trapezius muscles, causing

rigidity, akinesis, or hyperkinesis.

Lesions of the lower brainstem or upper cervical spinal cord

may cause dissociated weakness of the SCM and

trapezius muscles depending on the exact location.

Nuclear involvement of the SA nerve may occur in motor

neuron disease, syringobulbia, and syringomyelia.

In nuclear lesions, the weakness is frequently accompanied

by atrophy and fasciculations.

Localisation

Weakness of the trapezius on one side associated with

weakness of the sternocleidomastoid on the other side

(dissociated weakness) indicates an upper motor neuron

lesion ipsilateral to the weak sternocleidomastoid.

Weakness of the trapezius on one side with sparing of the

sternocleidomastoid muscles indicates a ventral brainstem

lesion, a lower cervical cord lesion, or a lower spinal

accessory root lesion.

Weakness of the sternocleidomastoid with trapezius

sparing indicates a lesion of the lower brainstem

tegmentum or upper cervical accessory roots.

Weakness of the sternocleidomastoid and the trapezius

muscles on the same side indicates a contralateral

brainstem lesion, an ipsilateral high cervical cord lesion, or

an accessory nerve lesion before the nerve divides into its

sternocleidomastoid and trapezius branches.

The Hypoglossal Nerve

The hypoglossal nerve (CN XII) - a pure motor nerve,

supply the tongue.

The branches of the hypoglossal nerve are the meningeal,

descending, thyrohyoid, and muscular.

The meningeal branches send filaments derived from

communicating branches with C1 and C2 to the dura of the

posterior fossa.

The descending ramus sends a branch to the omohyoid,

and then joins a descending communicating branch from

C2 and C3 to form the ansa hypoglossi which supplies the

omohyoid, sternohyoid, and sternothyroid muscles.

The thyrohyoid branch supplies the thyrohyoid muscle.

The descending and thyrohyoid branches carry

hypoglossal fibers but are derived mainly from the cervical

plexus.

CN XII supplies the intrinsic muscles, all of the extrinsic

muscles of the tongue except the palatoglossus, and

possibly the geniohyoid muscle.

The cerebral center regulating tongue movements lies in

the lower portion of the precentral gyrus near and within the

sylvian fissure.

Supranuclear control to the genioglossus muscle is

primarily crossed; supply to the other muscles is bilateral

but predominantly crossed.

The clinical examination of hypoglossal nerve function

consists of evaluating the strength, bulk, and dexterity of

the tongue—looking especially for weakness, atrophy,

abnormal movements (particularly fasciculations), and

impairment of rapid movements.

After noting the position and appearance of the tongue at

rest in the mouth, the patient is asked to protrude it, move it

in and out, from side to side, and upward and downward,

both slowly and rapidly.

Motor power can be tested by having the patient press the

tip against each cheek as the examiner tries to dislodge it

with finger pressure.

The normal tongue is powerful and cannot be moved.

When unilateral weakness is present, the tongue deviates

toward the weak side on protrusion because of the action

of the normal genioglossus.

The patient cannot push the tongue against the cheek on

the normal side, but is able to push it against the cheek on

the side toward which it deviates.

Unilateral weakness may cause few symptoms; speech

and swallowing are little affected.

With severe bilateral weakness the tongue cannot be

protruded or moved laterally; the first stage of swallowing is

impaired, and there is difficulty with articulation, especially

in pronouncing linguals.

Rarely, the tongue tending to slip back into the throat may

cause respiratory difficulty.

Supranuclear Lesions

Lesions of the corticobulbar tract anywhere in its course

from the lower precentral gyrus to the hypoglossal nuclei

may result in tongue paralysis.

A lesion of the corticobulbar fibers above their decussation

result in weakness of the contralateral half of the tongue.

A supranuclear lesion is not accompanied by atrophy or

fibrillations of the tongue.

Sudden isolated dysarthria may occur with lacunar infarcts

affecting the contralateral corona radiata or internal

capsule, which interrupt in isolation the cortico-lingual

pathways to the tongue (central monoparesis of the

tongue).

The main decussation of supranuclear projections to the

hypoglossal nucleus in the brainstem is located close to the

pontomedullary junction.

Pontine lesions at the ventral paramedian base close to the

midline affect the contralateral cortico-hypoglossal

projections, whereas lateral lesions at the pontine base

affect ipsilateral projections.

Nuclear Lesions and Intramedullary

Cranial Nerve XII Lesions

Unilateral lesions of the hypoglossal nucleus or nerve result

in paresis, atrophy, furrowing, fibrillations, and

fasciculations that affect the corresponding half of the

tongue.

Because of the close proximity of the two hypoglossal

nuclei, dorsal medullary lesions (e.g., multiple sclerosis,

syringobulbia) often result in bilateral lower motor neuron

lesions of the tongue.

A rare but characteristic syndrome that affects the

hypoglossal nerve in its intramedullary course is the medial

medullary syndrome (Dejerine's anterior bulbar syndrome).

This syndrome results from occlusion of the anterior spinal

artery or its parent vertebral artery.

The anterior spinal artery supplies the ipsilateral pyramid,

medial lemniscus, and hypoglossal nerve; its occlusion

therefore results in three main signs:

Ipsilateral paresis, atrophy, and fibrillations of the tongue

(due to affection of cranial nerve XII).

Contralateral hemiplegia (due to involvement of the

pyramid) with sparing of the face.

Contralateral loss of position and vibratory sensation (due

to involvement of the medial lemniscus).

Peripheral Lesions of Cranial Nerve XII

With neck lesions, the cervical sympathetic chain may be

involved, resulting in an ipsilateral Horner syndrome

(miosis, anhidrosis, and ptosis).

Isolated hypoglossal nerve palsy has been described due

to compression by a kinked vertebral artery (hypoglossal-

vertebral entrapment syndrome).

Skull metastases to the clivus may cause bilateral

hypoglossal nerve palsies.

Combined abducens nerve and hypoglossal nerve palsies

are rare. This ominous combination may be seen with

nasopharyngeal carcinoma (Godtfredsen's syndrome) and

with other clival lesions, especially tumors (three-fourths of

which are malignant).

Lesions, usually tumors or chronic inflammatory lesions, of

the occipital condyle may cause occipital pain associated

with an ipsilateral hypoglossal nerve injury (occipital

condyle syndrome).

The hypoglossal nerve may be injured in isolation in the

neck or in its more distal course near the tongue.

The causes of this peripheral involvement include

carotid aneurysms,

aneurysms of a persistent hypoglossal artery,

vascular entrapment,

spontaneous dissection of the extracranial internal carotid

artery,

local infections,

tuberculosis of the atlantoaxial joint,

rheumatoid arthritis,

surgical (e.g., carotid endarterectomy) or

accidental trauma,

birth injuries,

neck radiation, and

tumors of the retroparotid or retropharyngeal spaces, neck,

salivary glands, and base of the tongue.

Unilateral or bilateral hypoglossal neuropathy may occur in

patients with hereditary neuropathy with liability to pressure

palsy.

Referrences

Dejong’s the neurologic examination, 6th edition.

Localisation in clinical neurology, 5th edition.

Bradley’s neurology, 6th edition.