Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_2548_Библиотеки_им_академика_М_И_Перельмана
.pdf
328
https://t.me/med1917
16
Nervous system
hand (or cover the eye with your own hand) and then
ask him to look with his open eye straight into your
own confronting eye (his left into your right and vice
versa). First, put the pinhead into the middle of the
visual field and check that the patient sees it as bright
red. Swap to the other eye and compare the perceived
brightness of red reported by the patient for his two
eyes. Loss of perceived redness in one eye (red desaturation) raises the possibility of a mild optic neuropathy.
A patient who is already known to have poor acuity in
one eye may have a central scotoma, in which case the
pinhead either will not be seen in the centre of the field
or will be perceived black. A small central scotoma can
be defined by moving the pinhead outwards in four
different directions until the patient sees its redness.
Next, put the pinhead into each of the four quadrants
of vision close to the centre and check that the patient
sees it as bright red. This may detect a paracentral scotoma and is also a good way of detecting temporal field
defects caused by optic chiasm lesions such as pituitary
tumours. Then finally, while ensuring that the patient
maintains fixation into your eye, compare the periphery of his field with your own by moving the pin from
outside the field in towards the centre at various points
around the periphery, with the pin midway between
you and the patient. The patient has to report not
when he first sees the pin or your hand but when the
pinhead colour changes from black to red.
The pupils
Examination of the pupils and their responses to
light and accommodation provides information not
only about specific neurological syndromes which
affect the pupils, such as Adie’s syndrome, but
also information about the integrity of the anterior
visual pathways (particularly the optic nerves), the
brainstem and the efferent parasympathetic and
sympathetic pathways to the pupillary sphincter and
dilator muscles, respectively.
Pupil constriction is a parasympathetic function.
Afferent optic pathways project to the pretectal
nucleus, at the level of the superior colliculus, in the
midbrain. The pretectal nucleus projects to both ipsilateral (uncrossed) and contralateral (crossed) Edinger–
Westphal nuclei, adjacent to the oculomotor nucleus, in
the midbrain, leading to direct and consensual pupillary
responses, respectively. Pre- ganglionic parasympathetic
axons travel in the oculomotor nerve to the ciliary ganglion in the orbit. Post- ganglionic axons innervate the
pupillary sphincter. Lesions of the Edinger–Westphal
nucleus or the pupilloconstrictor nerve fibres in the
oculomotor (third) cranial nerve or in the orbit lead to
dilatation of the pupil (mydriasis) unless there is simultaneously a lesion of the sympathetic innervation of the
pupil. In either case, there is a failure of constriction of
the pupil to light. In general, compression of the third
cranial nerve (classically by a posterior communicating
artery aneurysm) affects the pupilloconstrictor fibres
(located on the dorsal surface of the oculomotor nerve
and separately supplied by pial blood vessels), termed a
‘surgical’ oculomotor palsy. A microvascular ischaemic
lesion of the third nerve may spare the pupilloconstrictor fibres, giving rise to a pupil- sparing third nerve
lesion, termed a ‘medical’ oculomotor palsy. Microvascular lesions of the oculomotor nucleus may spare
the Edinger–Westphal nucleus with the same result. A
mid- sized unreactive pupil caused by a lesion of both
parasympathetic and sympathetic supplies is seen in
aneurysms of the internal carotid artery within the cavernous sinus, along with other features of a cavernous
sinus syndrome.
Pupil dilation is achieved by sympathetic innervation of pupillodilator muscle fibres. The first-order
neurons are in the hypothalamus. They project down
through the brainstem and cervical spinal cord to the
ciliospinal centre in the lower cervical and upper thoracic spinal cord, from where second- order neurons
project via the T1 nerve root and sympathetic chain to
the superior cervical ganglion. Third- order axons run
up the internal carotid artery as far as the cavernous
sinus and from there through the orbit to the pupil.
There is also sympathetic innervation of the superior
tarsal muscle by the same route. A lesion of the sympathetic supply to the pupil at any point between
the hypothalamus and the orbit will give rise to the
two main features of Horner’s syndrome: constriction
(miosis) of the pupil (which will still react to light by
further constricting) and partial ptosis (drooping of
the upper eyelid but less marked that in a complete
oculomotor (III) palsy).
Examination of the pupils
First, in normal illumination, establish whether the
pupils are of equal size. If they are not, bear in mind
that there are two possibilities: either one is smaller
than it should be or the other is larger. Be careful not
to jump to the wrong conclusion.
Ideally, the reactions of the pupils to light should be
tested in moderately low illumination. Use a bright
torch, not an ophthalmoscope. Shine the light into one
eye and observe the response of the pupil (the direct
response), the normal response being constriction
of the pupil, which is sustained until the light is
removed. Repeat the test, this time looking at the
contralateral pupil, which will normally constrict (the
consensual response). Then test the other eye. Next,
test accommodation (constriction of the pupils when
focusing on a near object). Ask the patient to look into
the distance, then at your finger held at a distance and
to keep looking as you advance your finger to a distance
of about 20 cm from the patient’s face. Advancing
your finger in a wavy line allows you to check that the
patient is looking at the finger. Observe the adduction
of the eyes and the constriction of the pupils. Then ask
the patient to look into the distance again.
Afferent pupillary defect
A patient with a severe lesion of the anterior visual
system in one eye (an ophthalmological disorder or
an optic nerve disorder, such as severe optic neuritis
or an ischaemic optic neuropathy) will have an
afferent pupillary defect (i.e. a failure of constriction
SECTION THREE
Aqueduct
III nerve nucleus
Spinothalamic
lemniscus
nigra
peduncle
Paramedian
Posterolateral
WWW.BOOKBAZ.IR
https://t.me/med1917
Nervous system
329
of either pupil to light shone into the affected eye).
If the visual system on the other side is unaffected,
light shone into the normal eye will lead to a normal
direct pupillary response and there will also be a
consensual response in the visually impaired eye,
assuming the efferent pathway is intact.
Relative afferent pupillary defect
A patient with a mild lesion of the anterior visual
apparatus on one side will exhibit a direct pupillary
response to light, but it will be less vigorous than the
consensual response to light shone into the other eye.
In this situation, the swinging torch test may reveal
a relative afferent pupillary defect. If a patient has a
mild optic nerve lesion in the left eye, then acuity and
colour vision may be only mildly impaired and the
field normal. Shine the torch into the affected left eye
and note the seemingly normal response. After 2 seconds, move the torch briskly to shine into the normal
right eye. The right pupil will already be constricted
as a result of the consensual response. It will stay constricted and, if anything, will constrict a little further.
After 2 seconds, move the torch briskly back to the
left eye. Because of the subtle afferent defect, the sig-
strictor (Edinger–Westphal) nuclei will be reduced,
resulting in an apparently paradoxical dilation of the
left pupil despite light being shone into it. If you keep
swinging the torch back and forth from one eye to
the other, the relative afferent pupillary defect will
continue to be observed, although the defect is best
seen within the first few attempts.
Afferent and relative afferent pupillary defects
are important because they are objective. A person
who gives the impression of having functional visual
impairment in one eye, but who has an afferent
pupillary defect, must have an organic problem. In
contrast, a person who reports uniocular blindness
and has normal pupillary responses to light will not
be blind.
tendon reflexes. An acute Adie pupil is enlarged,
does not react to light and there is a slow constriction to accommodation. Redilation of the pupil
after accommodation is delayed such that, temporarily, the normal pupil may be larger than the
affected one.
Argyll Robertson pupils: these are small, irregular,
unequal pupils, which do not react to light but do to
accommodation. They were previously commonly
seen in advanced syphilis. Without the irregularity
but with the other features, diabetic small vessel
disease is currently the most common cause.
The pupils in coma: this is important but covered
elsewhere (see Chapter 9).
Fundoscopy
Fundoscopy is described in Chapter 21. The neurological examination focuses on papilloedema, optic
atrophy, pigmentary retinal degeneration and vascular disease.
The oculomotor (III), trochlear (IV) and
abducens (VI) nerves—eye movements
Abnormalities of eye movements may result from
disorders of the cerebral hemispheres; brainstem;
cerebellum; cranial nerves III, IV and VI; the neuromuscular junctions between oculomotor nerves and
eye muscles; the eye muscles themselves; and from
lesions affecting the structure and contents of the
orbits. Their importance in neurological and general
physical examination is therefore obvious.
The nucleus for the third cranial nerve is in the midbrain (Fig. 16.2). The nerve emerges ventrally (anteri-
orly), medial to the cerebral peduncle, passing forward
through the cavernous sinus to the superior orbital fissure. In the orbit, the superior ramus supplies superior
Efferent pupillary defect (part of a third cranial
nerve lesion)
A lesion of the pupilloconstrictor nerve fibres in the
oculomotor nerve will lead to dilation of the ipsilateral
pupil (owing to the unrestrained effect of the intact
sympathetic supply). Further, there will be failure of
constriction of the pupil to light, although the consensual response in the other eye will be preserved. Light
shone into the contralateral eye will elicit a normal
direct response but no consensual response.
Other common pupillary abnormalities of
neurological relevance
Simple (physiological) anisocoria (inequality of
pupil size): this is common. The pupillary inequality is not marked and the reactions to light and
accommodation are normal.
Tonic pupil: this is seen in Holmes Adie syndrome,
a relatively benign polyneuropathy composed of a
lesion of the ciliary ganglion and a degree of loss of
territory
territory
Basal
territory
Figure 16.2 A diagram of the midbrain. Note the dorsally positioned
third nerve nuclei. Vascular territories are shown on the left.
Cerebral
tract
Medial
Red
nucleus
Substantia
330
territory
Paramedian
VI
Cochlear
lemniscus
nuclei and fibres
https://t.me/med1917
16
Nervous system
vascular
territory
VIIn
IV
ventricle
VIn
Posterolateral
vascular
territory
Basal
vascular
Figure 16.3 A diagram of the fifth, sixth and seventh nerve nuclei in
the pons. Note how the nerve fibres of VII loop round the nucleus of VI.
nucleus
Medial
longitudinal
fasciculus
nucleus
Medial
nucleus
V tract
and
nucleus
VII
Pontine motor
rectus and levator palpebrae superioris. The inferior
ramus supplies inferior rectus, inferior oblique and medial rectus, and parasympathetic fibres from the inferior ramus pass to the ciliary ganglion and thence to the
ciliary muscle and the pupil sphincter.
The fourth nerve nucleus lies just caudal to the third
nerve nucleus in the brainstem. The nerve fibres of the
fourth nerve decussate. The nerve starts on the dorsal
aspect of the brainstem and passes around the brainstem
through the cavernous sinus and superior orbital fissure
to the superior oblique muscle. Consequent upon
the decussation of fibres, the right trochlear nucleus
innervates the left superior oblique and vice versa.
The sixth nerve nucleus is beneath the floor of the
fourth ventricle in the pons (Fig. 16.3). Nerve fibres
run forward (ventrally) through the pons emerging at
its lower border, then up the skull base and forward
through the cavernous sinus to the superior orbital
fissure and into the orbit to supply the lateral rectus
muscle. The nerve is long, thin and very susceptible
to dysfunction, most notably in the setting of raised
intracranial pressure of any aetiology, which may give
rise to either unilateral or bilateral sixth nerve lesions.
This is referred to as a ‘false localizing sign’, since a
focal mass lesion causing raised intracranial pressure
may be remote from the sixth nerves and their nuclei
or there may be no focal cause of the raised pressure
at all (e.g. idiopathic intracranial hypertension).
Table 16.4 and Figure 16.4 outline the actions of
each eye muscle.
Terminology in eye movements
Horizontal movement of the eye outwards (laterally) is termed abduction and inwards (medially) is
termed adduction. Vertical movement upwards is
termed elevation and downwards is depression. The
eye is also capable of diagonal movements (version) at
Vestibular
nuclei
Middle
cerebellar
peduncle
Spinothalamic
tract
Table 16.4 Actions of the eye muscles
Action
Nerve Muscle
Abducens; VI Lateral
With eye
abducted
Abduction Abduction
With eye
adducted
rectus
Oculomotor; III Inferior
rectus
Oculomotor; III Inferior
oblique
Oculomotor; III Medial
Depression Depression;
extorsion
Extorsion;
Elevation
elevation
Adduction Adduction
rectus
Oculomotor; III Superior
rectus
Trochlear; IV Superior
oblique
The eye is offset laterally in relation to the apex of the orbit, which accounts for
why the superior and inferior rectus muscles have only purely vertical actions
when the eye is abducted. Adduction of the eye turns the superior and inferior
oblique muscles into a pure depressor and elevator, respectively.
6XSHULRU
UHFWXV
5LJKW /HIW
/DWHUDO
UHFWXV
,QIHULRU
UHFWXV
Figure 16.4 A diagram showing which muscles elevate and
depress the abducted and adducted eye.
Elevation Elevation;
Intorsion;
depression
,QIHULRU
REOLTXH
0HGLDO
UHFWXV
6XSHULRU
REOLTXH
intorsion
Depression
any intermediate angle. Rotary movements are those
in which the eye twists on its anterior–posterior axis.
Intorsion is rotation such that the upper part of the eye
moves medially and the lower part of the eye moves
laterally. Extorsion is the opposite. Convergence refers
to adduction of both eyes to fixate on a near object.
Lateral rotation of the head causes reflex movement
of the eyes in the opposite direction (adduction of one
eye, abduction of the other). A squint (the eyes point
in different directions) is described as convergent or
divergent strabismus, depending on whether the eyes
point towards or away from each other. Saccades are
abrupt, rapid, small movements of both eyes, such
as those needed to shift fixation from one object to
another. Nystagmus denotes rhythmic oscillations of
one or (more usually) both eyes. In pendular nystagmus, the movement is slow in both directions. In jerk
nystagmus, there is a slow phase in one direction and a
fast phase in the opposite direction. By convention, the
direction of nystagmus is the direction of the fast phase,
but the defect is in fact the slow phase and is either an
abnormal deviation of the eyes or a failure of the eyes
to maintain position, and the fast phase is a compensatory saccade aimed at restoring the correct position of
the eyes. Some types of nystagmus are outlined below.
SECTION THREE
WWW.BOOKBAZ.IR
https://t.me/med1917
Nervous system
331
$
Figure 16.5 A severe right third nerve lesion with complete ptosis (A). With the paralysed eyelid raised, paresis of adduction is seen on
attempted left gaze (B). In this patient the pupil is spared, as is commonly seen in ischaemic lesions, but not in compressive lesions. The
other features of a third nerve lesion are paresis of elevation of the eye and intorsion of the eye on attempting to look down, owing to the
action of the superior oblique muscle on an eye that cannot be adducted. (Reproduced from Forbes and Jackson, Color Atlas and Text of
Clinical Medicine, Mosby, 2002.)
Examination of eye movements
As with every other component of examination, the
detail in which the eye movements are examined
depends on whether there are relevant symptoms
and whether abnormal signs are likely to be present.
Ask the patient to keep his head still (assist him by
putting your left hand on his head to steady it) and
then to look at your right index finger held directly
in front of his eyes at about half a metre distance.
In the primary position of gaze, look for any visible
abnormality of the alignment of the two eyes (an
affected patient may or may not complain of double
vision) and any pendular or vestibular nystagmus (see
below). Now move your finger to the right, then left,
and then up and down. The pursuit eye movements,
which are elicited, should precisely follow your finger
at the appropriate constant velocity. Eye movements,
which are ‘broken up’ into a series of short saccades,
indicate a brainstem or cerebellar lesion affecting eye
movement control. Patients with diplopia usually
will experience their diplopia at some point (or at all
times) during this simple test. However, in patients
with a complaint of diplopia it is important not just
to test vertical eye movements from the primary position of gaze, but to test movements to the right and
up and down and then to the left and up and down.
During pursuit eye movement examination, gazeevoked and vestibular nystagmus will be observable
(see below). When looking for nystagmus, it is important not to get the patient to look too far in any direction because, at the extremes of gaze, nystagmus can
be normal as the patient struggles to deviate his eyes
beyond what is possible. Look for nystagmus at about
30° away from the primary position of gaze.
%
curvature of the cornea), cataracts or lens dislocation (e.g. in Marfan’s syndrome and homocystinuria).
However, persistence of diplopia when one eye is
covered, particularly in the absence of objective ophthalmoparesis, may suggest a non- organic cause. In
patients who have obvious, easily visible paresis of
movement of one or both eyes, the reason for diplopia is self- evident.
Diplopia develops with even very subtle misalignment of the eyes, which cannot be seen on simple
inspection. In this situation, if the ophthalmoparesis
affects just one eye, it is possible to deduce which eye
muscles are underactive by diplopia testing. The true
image is the one generated by the eye with normal
movements. The false image is the one generated by
the eye with the paretic muscle or muscles. For example, if a patient develops double vision on looking to
the right, with horizontal separation of the images, the
false image will be the one further out to the right.
This is true whether it is the right eye, which does not
abduct adequately (right lateral rectus weakness) or
if it is the left eye, which does not adduct adequately
(left medial rectus weakness). If this does not seem
immediately clear, consider the extreme case: one eye
moves, the other does not. An image (an examiner’s
finger or a white pinhead) moves to the patient’s
right. The image remains in the middle of the field of
the eye, which moves but moves progressively to the
right of the field of the eye, which does not. The same
rule applies in all directions of gaze. Diplopia is always
maximal in the direction in which the weak muscle
has its purest action (see Table 16.4).
The severity of the diplopia should be assessed in
eight positions: looking to left and right, up and down,
and obliquely up and down to the left and obliquely
Diplopia testing
If a patient complains of double vision, first establish
that it is true diplopia and not monocular diplopia.
Monocular diplopia normally suggests a problem
with the orbital globe, such as the cornea (e.g. keratoconus, cone-shaped cornea; or astigmatism, abnormal
up and down to the right. To work out which muscle
is underactive, where the diplopia is maximal, cover
each eye in turn and get the patient to tell you which
of the two images disappears. Inconsistent answers are
common, however, and the assistance of an ophthalmologist or optometrist is frequently desirable. The
332
https://t.me/med1917
16
Nervous system
Table 16.5 The effects of lesions of the oculomotor (III), trochlear (IV) and abducens (VI) nerves
Affected nerve Signs Comment
Oculomotor
Trochlear Paresis of superior oblique Extorsion of the eye owing to unopposed action of inferior oblique leads to
Abducens Paresis of lateral rectus Horizontal diplopia to ipsilateral lateral gaze
*
Figure 16.5 shows a patient with a severe oculomotor palsy.
*
Paresis of adduction (medial
rectus)
Paresis of elevation (superior
rectus and inferior oblique)
Paresis of depression (inferior
rectus)
Ptosis owing to paresis of
levator palpebrae superioris
Dilated, unreactive pupil This feature is not present in pupil- sparing lesions (microvascular lesions of
The eye becomes abducted because of unopposed action of lateral rectus, and
slightly depressed because of action of superior oblique.
The pure depressor action of superior oblique cannot be tested because the eye
cannot be adducted.
Intorsion of the eye on attempted down gaze indicates intact trochlear nerve
and superior oblique function.
With complete ptosis, of course, there is no diplopia.
nucleus or nerve).
diplopia such that a vertical line looks V- shaped.
The patient compensates with a head tilt to the side opposite the lesion, intact
intorsion on that side tending to correct the diplopia. This is the basis of the
Bielschowsky head tilt test when double vision is improved by tilting the head away
from the affected side and worsened by tilting the head towards the affected side.
features of lesions of the third, fourth and sixth cranial
nerves are summarized in Table 16.5. It is important
to assess for diplopia in sustained directional gaze,
particularly if a neuromuscular transmission disorder
(e.g. myasthenia) is considered, as otherwise fatigable
ophthalmoparesis may be missed.
In assessing patients who have double vision, it is
best first to establish which muscles appear to be weak
and then try to decide what the nature of the problem
is likely to be, taking into consideration all the physical signs. Thus, impairment of eye movements in one
eye in combination with proptosis of that eye may
occur because of mechanical restriction of eye movements by an intraorbital lesion. Weakness of muscles
in both eyes with different patterns of involvement of
the muscles in the two eyes is likely to be caused by
a disorder of the muscles themselves (orbital myositis, thyroid eye disease) or by ocular or generalized
myasthenia. The pupils will not be involved. Bilateral,
asymmetrical combinations of cranial nerve lesions
are relatively uncommon (neoplastic infiltration, cranial polyneuritis). Bilateral sixth cranial nerve lesions
are common, usually but not exclusively as a feature
of raised intracranial pressure. Multiple oculomotor
neuropathies in one eye direct attention to the superior orbital fissure and the cavernous sinus (Box 16.2).
Horizontal gaze paresis; internuclear
ophthalmoparesis
Neural control of voluntary lateral gaze to the right
starts in the left cerebral hemisphere, such that a large
left cerebral hemisphere lesion may be associated
with failure of right gaze and a tendency for the eyes
to deviate to the left (the side of the lesion). Output
Box 16.2
1. Lesion of the cavernous sinus (e.g. internal carotid
— potential involvement of cranial nerves III, IV, VI, V1
— cavernous sinus thrombosis combines the above with
2. Lesion of the superior orbital fissure (e.g. Tolosa Hunt
— potential involvement of III, IV, VI and V1 (ophthalmic
— extension into the orbit may lead to involvement of the
runs to the right paramedian pontine reticular formation (PPRF); hence, a right- sided pontine lesion may
involve a right gaze paresis. Output from the right
PPRF goes to the right sixth nerve nucleus, resulting
in right eye abduction, and across, via the left medial
longitudinal fasciculus (MLF), to the left third nerve
nucleus, resulting in simultaneous left eye adduction.
Attempted right gaze in the setting of a left MLF
lesion results in abduction of the right eye, but failure
of adduction of the left eye—an internuclear ophthalmoparesis (INO) (Fig. 16.6). Bilateral MLF lesions
give rise to bilateral INO, in which case, with lateral
gaze in either direction, only the abducting eye moves
normally. Nystagmus is commonly seen in the abducting eye. The pathway for adducting both eyes for near
vision is separate and sometimes in bilateral INO,
Cranial nerve involvement in lesions of the
cavernous sinus and superior orbital fissure
aneurysm, internal carotid artery dissection,
meningioma):
(ophthalmic division), V2 (maxillary division) and
sympathetic pupillodilator nerve fibres
proptosis, chemosis, papilloedema and visual failure
syndrome):
division)
optic nerve
$WWHPSWHGODWHUDOJD]HWROHIW
WWW.BOOKBAZ.IR
https://t.me/med1917
/HIW5LJKW
:HDNDGGXFWLRQ 1\VWDJPXV
$
&RPPDQG
0HGLDO
UHFWXV
0/)
9HVWLEXODU
QXFOHL
%
Figure 16.6 (A) A right internuclear ophthalmoparesis. (B) A diagram
of the pathways for horizontal gaze. The command for left gaze
originates in the right cerebral hemisphere. Descending nerve fibres
decussate to reach the left pons. Lesion 1 produces a left horizontal
gaze paresis. Lesion 2 produces a right internuclear ophthalmoparesis.
Lesion 3 produces the ‘one and a half’ syndrome: a left gaze paresis
and left internuclear ophthalmoparesis (failure of adduction of the
left eye on right gaze)—only abduction of the right eye on right gaze
remains. NPH, nucleus prepositus hypoglossi; MLF, medial longitudinal
fasciculus; PPRF, paramedian pontine reticular formation.
5/
,,,
335)
9,
13+
/DWHUDO
UHFWXV
preservation of adduction of the eyes for near vision
(convergence) can be demonstrated, proving that the
problem is not bilateral medial rectus weakness.
Vertical gaze paresis
The neural control of upgaze and downgaze is complex. Ultimately, output for upgaze is via components
of the third nerve nucleus mainly to the superior rectus and inferior oblique muscles bilaterally. The output for downgaze is from the third and fourth nerve
nuclei to the inferior rectus and superior oblique
muscles, respectively. In general, defects of upgaze or
downgaze localize rather poorly, but lesions, such as
pineal tumours, which compress the midbrain and
bilateral descending connections from the hemispheres, often cause upgaze paresis. For example,
Parinaud’s syndrome, from compression of the dorsal midbrain, owing to a pineal tumour, for example,
causes restriction of upgaze, convergence- retraction
nystagmus and pupillary light- near dissociation
(pupils accommodate but respond poorly to light).
Rare midbrain ischaemic strokes owing to occlusion
SECTION THREE
Nervous system
of a perforating vessel from the top of the basilar
artery include downgaze paresis among the clinical
manifestations.
Non- paralytic strabismus
Clinicians need to be able to recognize developmental
non- paralytic strabismus. Decompensation of a longstanding squint may be a cause of acquired diplopia.
The alternating cover test and unilateral cover test
(cover–uncover test) are useful for detecting ocular
deviation, when the misaligned eye will deviate
inwards or outwards, on covering. This is particularly
useful in detecting phorias (or latent strabismus),
when ocular deviation is only evident when binocular
vision is prevented, compared with tropias (exotropia
or isotropia), when misalignment is evident during
binocular vision, but often further exacerbated by the
cover test.
Testing saccadic eye movements
Getting a patient to follow a moving finger tests pursuit
eye movements. It takes very little time to test saccadic
eye movements and useful signs may be detected. First,
simply ask the patient to keep his head still and look
to the left, to the right, up and down. Then hold your
hands up in front of the patient, one in the primary
position of gaze, the other to the side, with palms facing the patient, fists closed. Ask the patient to keep
his head still. Open the fist of the hand in front of the
patient and ask him to look at it. Then close that fist
and open the other and ask the patient to switch his
gaze to the hand at the side. By alternating which hand
is open you can get the patient to refixate briskly to
and fro. Then check the other side. These manoeuvres
test saccadic movements; in disease, saccades may be
slowed or interrupted. A mild INO will be best seen
during saccadic horizontal eye movements, with relative delay of adduction of eye on the affected side.
Because detecting a mild INO requires observing a difference in the velocity of movement of the two eyes, it
is difficult to appreciate if the examiner fixates on one
or the other eye; perhaps, unintuitively, it is best to look
at the bridge of the patient’s nose to see the movement
of the two eyes at the same time.
Supranuclear gaze pareses
Reflex eye movements related to head movements
are generated and organized by vestibular, cerebellar
and brainstem systems, whereas voluntary gaze is
initiated in the cerebral hemispheres. A patient’s
gaze paresis is therefore supranuclear if reflex eye
movements are intact. In a patient with selective
paresis of downgaze, if brisk backward rotation of
the head (extension of the neck) produced reflex
depression of both eyes, a supranuclear lesion would
be inferred. In practice, this is often not easily
achieved because the relatively common disorder
giving supranuclear downgaze paresis is progressive
supranuclear palsy, a condition in which there is also
axial rigidity affecting neck movements.
333
334
https://t.me/med1917
16
Nervous system
Peripheral vestibular nystagmus
Peripheral vestibular nystagmus occurs with lesions
of the labyrinth or vestibular nerve. Normally there is
tonic input to the brainstem vestibular nuclei from the
periphery. Loss of this tonic input leads to deviation of
the eyes towards the affected side (slow phase) with
fast- phase nystagmus directed to the opposite side. In
mild lesions, the nystagmus is only seen when the eyes
look in the direction of the fast phase. In more severe
lesions, the nystagmus is seen with the eyes in the primary position of gaze or even when looking away from
the direction of the fast phase. Usually the nystagmus is
of high frequency and relatively low amplitude.
Gaze paretic nystagmus
Gaze paretic nystagmus is a gaze- evoked nystagmus in
which the eyes are not able to maintain a position away
from their primary position, so the slow phase is a drift
back to the primary position, whereas the fast phase
is in the direction of gaze. In the primary position, the
eyes are still. The nystagmus may be of large amplitude
and low frequency. Drug- induced nystagmus (alcohol, benzodiazepines, antiepileptic medication) is of
this sort and is seen in all directions of gaze. Structural
brainstem or cerebellar lesions may cause asymmetric gaze paretic nystagmus. In cerebellar hemisphere
lesions, the nystagmus may be unidirectional with the
fast phase towards the side of the lesion.
Upbeat nystagmus (fast phase upwards) may occur
with lesions at various locations in the brainstem and
with cerebellar vermis lesions. Downbeat nystagmus
is characteristic of cervicomedullary junction lesions,
such as Chiari malformations, but may also be seen
with cerebellar degenerations.
Congenital nystagmus
The rule here is that the nystagmus is horizontal,
even when the patient looks up or down. On left
gaze, it is left beating, and on right gaze, it is right
beating. There may be a null point at which the nystagmus is least conspicuous, but it is not necessarily in the primary position, and the eyes may not be
completely still. Congenital nystagmus is damped by
convergence.
Pendular nystagmus
Pendular nystagmus may be seen as a complication
of congenital or acquired very poor vision. It is also
seen in pontine lesions (e.g. multiple sclerosis).
The trigeminal (V) nerve
The trigeminal nerve is a mixed motor and sensory
nerve. The nerve trunk emerges from the pons as
sensory and motor roots.
Sensory component of the trigeminal nerve
The primary sensory neurons are in the trigeminal
ganglion, just behind the cavernous sinus at the apex
of the petrous bone. Central projections run in the
Ophthalmic (V1)
C2
Trigeminal
Maxillary (V
Mandibular (V
Figure 16.7 Areas of cutaneous innervation of the head and neck
by the three divisions of the trigeminal nerve and the upper cervical
nerve roots.
)
2
)
3
C3
C4
trigeminal nerve into the pons. Figure 16.7 shows
the cutaneous distribution of the three divisions of
the trigeminal nerve: ophthalmic (V1), maxillary
(V2) and mandibular (V3). These nerves also mediate general sensation inside the mouth and nose
and proprioception. The ophthalmic nerve passes
through the cavernous sinus and superior orbital
fissure. The maxillary nerve also passes through the
cavernous sinus, but leaves the inside of the skull
through the foramen rotundum. The mandibular
nerve passes through the foramen ovale.
Afferents mediating touch sensation pass to the
principal sensory nucleus of the trigeminal nerve in
the pons. Pain and temperature afferents go into the
spinal tract and pass caudally into the medulla and
into the spinal nucleus of the trigeminal nerve, which
extends down from the medulla as low as the upper
cervical spinal cord. Thus, lesions in the medulla can
give rise to dissociated sensory loss in the trigeminal
territory (loss of pinprick sensation with preserved
light touch sensation). Afferents mediating masticatory muscle proprioception pass to the more rostral
mesencephalic nucleus.
The afferent and efferent components of the jaw
reflex are mediated by the sensory and motor components of the trigeminal nerve via the trigeminal
mesencephalic nucleus.
Motor component of the trigeminal nerve
Motor nerve fibres from the motor nucleus in the
pons run in the motor root of the trigeminal nerve,
bypassing the trigeminal ganglion to enter the mandibular nerve. They supply the muscles of mastication: masseter, temporalis and the medial and lateral
pterygoids.
SECTION THREE
WWW.BOOKBAZ.IR
https://t.me/med1917
Nervous system
335
Trigeminal territory sensory loss
Patients with impaired sensation on one side of the
face may have a trigeminal nerve lesion, a trigeminal
nucleus lesion or a lesion of central trigeminal sensory pathways. Not uncommonly, unilateral facial
sensory symptoms remain unexplained, which does
not necessarily make them ‘non- organic’. Much
is made of distinguishing between patients whose
distribution of sensory loss is anatomical and those
in whom it is not. Sensory loss, which ends at the
jaw line and at the hairline, would be regarded as
non- anatomical; however, too much dogma may be
unwise—patients are often not very careful reporters of exactly where their sensory symptoms are
located. Clearly defined symptoms of reduced sensation render examination almost redundant, but
the area of hypoaesthesia can be delineated in the
same way as sensory loss anywhere else using a pin
and testing from a numb area outwards towards
where sensation is normal.
The corneal reflex
A sensory stimulus applied to the cornea causes a
reflex blink, which cannot be suppressed; its absence
on one side establishes unequivocally the presence
of a trigeminal lesion. Patients with an anaesthetic
cornea are at risk of corneal injury, so it is important
to identify affected individuals by testing patients
who very clearly have symptoms and other signs
of a trigeminal lesion. It is also an important test
in coma. The test is uncomfortable and should not
be part of a ‘routine’ neurological examination. The
presence of a normal corneal reflex does not mean
that there is no lesion of the trigeminal nerve or its
connections.
Explain to the patient what is going to happen. Ask
him to look in such a direction that the eyes are wide
open. Using the corner of a clean tissue, touch the
centre of the patient’s cornea, approaching from the
side. The normal response is a brisk blink. Some use
cotton wool, but there is a risk of strands getting stuck
in the eye because of the blink. In coma, a drop of saline
applied to the cornea is a good stimulus. Remember
that if there is ipsilateral facial paralysis (e.g. Bell’s
palsy), the reflex will be absent on the affected side,
but will be readily seen on the other side.
Testing the motor component of the trigeminal
nerve
Look for wasting of the temporalis and masseter
muscles. Feel for contraction of the masseter muscles
when the patient clenches his jaw. Ask the patient
to open his mouth; the lateral pterygoid muscles
on each side draw the mandible forward, such that
a severe lesion of the trigeminal nerve will lead to
deviation of the jaw towards the side of the lesion
owing to weakness of the pterygoid muscles on the
affected side. The pterygoid muscles may be further
tested by asking the patient to push his open jaw
sideways against your hand.
The facial (VII) nerve
The facial nerve is principally a motor nerve, supply-
ing facial muscles on one side, but it also has small
general somatic sensory and major gustatory sensory
components, as well as important parasympathetic
functions.
The facial nerve nucleus is in the caudal pons, lying
ventrolateral to the sixth cranial nerve nucleus (see
Fig. 16.3). It receives upper motor neuron input from
both cerebral hemispheres. Lower motor neuron
fibres from the facial nucleus first pass round the
sixth nerve nucleus and then emerge from the pons
to form the facial nerve. From here, it travels laterally,
adjacent to the eighth cranial nerve, to the internal
auditory meatus, thence to the facial canal, which
has a relatively long and tortuous course through
the skull, emerging at the stylomastoid foramen. The
nerve then passes forward into the parotid gland and
divides into branches, which supply all the facial
muscles and the platysma muscle on one side. In the
facial canal, a branch of the facial nerve supplies the
stapedius muscle.
The nerve cell bodies of the sensory components
of the facial nerve are in the geniculate ganglion in
the facial canal. Gustatory sensory afferents from the
anterior two- thirds of the tongue travel in the lingual
nerve and then via the chorda tympani nerve to join
the facial nerve in the facial canal. Central projections reach the medulla via the nervus intermedius
between the facial and eighth cranial nerve.
The peripheral projections of the small general
somatic sensory contribution innervate the tympanic
membrane, external auditory meatus and tragus of
the ear. This accounts for the herpetic vesicles seen in
the ear in patients with the Ramsay Hunt syndrome
of facial paralysis caused by herpes zoster affecting
the facial nerve.
Secretomotor parasympathetic efferents leave the
pontomedullary junction in the nervus intermedius,
which joins the facial nerve in the internal auditory
meatus. Some of the parasympathetic nerves leave the
facial nerve at the geniculate ganglion in the greater
petrosal nerve, and via the pterygopalantine ganglion,
eventually mediating tear secretion from the lachrymal glands. Others leave via the chorda tympani
nerve to reach submandibular and sublingual salivary
glands, via the submandibular ganglion (note that
the parotid salivary gland is innervated by the glossopharyngeal nerve via the greater auricular nerve).
These complexities are relevant to clinical neurology because a facial nerve lesion, depending on its
location, may be associated with loss of taste, hyperacusis (if the stapedius is paralysed) and, in chronic
lesions, gustatory lachrymation ‘crocodile tears’ (i.e.
inappropriate tear production when salivary glands
should be activated), attributed to aberrant reinnervation of salivary and lachrymal glands. Other
aberrant reinnervation syndromes, relevant to recovering facial nerve palsies, include facial synkinesis
336
https://t.me/med1917
16
Nervous system
(voluntary contraction of one facial muscle leads to
contraction of an ipsilateral facial muscle—such as
eye winking on smiling) or hemifacial spasm (spontaneous unilateral twitching, which usually responds
to botulinum toxin treatment).
Facial weakness occurs because of muscle disorders
(invariably bilateral weakness), myasthenia (invariably
bilateral, but may be asymmetrical early on), polyneuropathies (e.g. Guillain- Barré syndrome or vasculitis,
unilateral or bilateral), facial nerve or nuclear lesions
(most commonly unilateral), motor neuronopathies
(usually bilateral) or upper motor neuron disorders
(usually unilateral, but occasionally bilateral).
A lower motor neuron lesion affecting the whole
of the facial nerve nucleus or the whole of the facial
nerve will cause weakness of all muscles of one side
of the face. A unilateral upper motor neuron lesion,
however, will cause weakness of the lower half of
the face with sparing of the upper half of the face
because there is bilateral representation of the upper
half of the face in the motor cortex.
Testing the facial nerve
Look for asymmetry of the face. Ask the patient to
raise his eyebrows (to look astonished), to blink and
then to screw both eyes up, firmly closed. On a weak
side, the eyelashes will be less buried by the eyelids.
Attempt to raise the patient’s eyebrows while his
eyes are closed and screwed up; mild weakness may
be detected. With severe lower motor neuron facial
weakness, the patient will not be able to close the
affected eye. Attempted eye closure will be accompanied by elevation of the eyes (Bell’s phenomenon).
Ask the patient to blow his cheeks out, to show his
teeth (or gums) and then to grimace. Observe the
patient’s spontaneous smiles. (In some upper motor
neuron disorders of facial muscle control, voluntary
movement of the lower face is lost, but smiling is
relatively preserved and vice versa ‘emotional versus
volitional’.) Ask the patient to purse his lips together
and attempt to open them using your fingers. These
tests usually suffice to pick up facial weakness and to
distinguish between upper and lower motor neuron
disorders.
The cochlear and vestibular (VIII) nerves
The cochlear and vestibular nerves convey afferents
from the cochlea and the vestibular apparatus, respectively, via the internal auditory meatus to the pontomedullary junction in close proximity to the facial
nerve, reaching cochlear and vestibular nuclei in the
brainstem. Acute sensorineural deafness and acute
vestibular neuritis reflect separate pathologies selectively affecting each of these nerves.
Testing the cochlear and vestibular nerves
The assessment of deafness is covered in detail else-
where (see Chapter 22). At the bedside, a crude
assessment of hearing can be achieved by rubbing
your index finger and thumb together close to the
patient’s ear or by whispering numbers close to his
ear, with the contralateral ear occluded. Rinne’s test
is good for distinguishing between conduction and
sensorineural deafness, as long as you use the appropriate tuning fork (frequency 512 Hz—not the lower
frequency tuning fork (128 Hz) used for testing vibration sense). Rinne’s test is performed by placing the
tuning fork on the mastoid, until the sound is no longer heard, and then placing the tuning fork a few centimetres from the auditory canal.
Conduction deafness is sometimes of neurological
significance if an infective or neoplastic middle ear
lesion has spread to affect the middle or posterior
cranial fossa structures.
Unilateral sensorineural deafness is an important
feature of ‘cerebellopontine angle lesions’, such as
acoustic neuroma or meningioma, along with variable combinations of facial weakness (facial nerve),
facial sensory symptoms (trigeminal nerve), nystagmus (brainstem and vestibular nerve), ataxia (brainstem and cerebellum) and ultimately long- tract signs
(brainstem) and raised intracranial pressure.
Bilateral sensorineural deafness may be a feature
of certain multisystem neurological disorders, particularly mitochondrial disorders.
Two important tests of vestibular function assess
much of the vestibular system (the semicircular
canals of the labyrinths, the vestibular nerves and
the vestibular nuclei of the brainstem). These are
the Dix- Hallpike test for positioning vertigo and
nystagmus and the head thrust test. They should be
performed in patients with vertigo.
The Dix- Hallpike test is described in Chapter
22. Far and away the most common cause of posi-
tioning vertigo is the condition benign paroxysmal
positional vertigo, a labyrinthine disorder, and it is
by far the most common cause of an abnormal DixHallpike test. Vestibular neuritis is usually associated
with nystagmus that does not require a change in
head position to elicit it, but in this condition vertigo
and nystagmus are usually exacerbated by positioning tests. Brainstem disorders may also be the cause
of positioning vertigo and nystagmus. Typically,
peripheral disorders are associated with a latent
period between head movement and onset of vertigo and nystagmus, intense vertigo and a reduction
of the vertigo and nystagmus with repeated testing,
whereas central positioning nystagmus may be associated with rather mild vertigo, but with nystagmus
that does not diminish with repeated testing.
The head thrust test (head impulse test) detects a
failure of the afferent component of the vestibuloocular reflex. In a normal individual, fixating on an
object straight ahead, an abrupt rotation of the head
to one side or the other will not disrupt ocular fixation. In a patient with an acute unilateral peripheral
vestibulopathy (vestibular neuritis), a head thrust
rotating the front of the head towards the side of
the lesion will result in the eyes turning with the
SECTION THREE
3RVWHURODWHUDO
3,&$
'RUVDOYDJDO
VROLWDULXV
6\PSDWKHWLF
3\UDPLG
QXFOHXV
WWW.BOOKBAZ.IR
https://t.me/med1917
Nervous system
337
head momentarily and a noticeable saccade to bring
the eyes back to restore fixation. This test is useful
in distinguishing acute vertigo caused by vestibular
neuritis from vertigo caused by a brainstem stroke or
transient ischaemic attack. With the patient’s gaze
fixed on the examiner’s nose, the examiner then
abruptly turns the patient’s head successively about
30° to the right and left.
The glossopharyngeal (IX) nerve
Anatomical and functional relationships exist
between the glossopharyngeal nerve, the vagus nerve
and the cranial component of the accessory nerve. The
nucleus ambiguus in the medulla (Fig. 16.8) contains
the motor neurons, which innervate striated muscle
of the palate, pharynx, larynx and upper oesophagus;
fibres running partly in the glossopharyngeal nerve,
mainly in the vagus nerve and partly in the cranial
portion of the accessory nerve. Situated more dorsally
in the medulla, the dorsal motor nucleus of the vagus
and the inferior salivatory nucleus (whose fibres join
the glossopharyngeal nerve) contain preganglionic
parasympathetic neurons, which control glands and
smooth muscle. Special visceral afferents (i.e. taste
fibres from the intermediate nerve and the glossopharyngeal nerve) enter the solitary tract to end in the
nucleus of the solitary tract in the medulla. General
somatic sensory afferents in the glossopharyngeal and
vagus nerves join trigeminal sensory nuclei.
The glossopharyngeal nerve rootlets emerge from
the medulla just rostral to those of the vagus nerve.
The glossopharyngeal nerve leaves the skull via the
jugular foramen (together with the vagus and accessory nerves). It mediates somatic sensation of the
QXFOHL
1XFOHXV
DPELJXXV
WUDFW
FHUHEHOODU
SHGXQFOH
6SLQRWKDODPLF
,QIHULRU
ROLYDU\
,QIHULRU
9WUDFW
DQG
QXFOHXV
1XFOHXV
WUDFWXV
WUDFW
QXFOHXV
9HVWLEXODU
0HGLDO
$6$
WHUULWRU\
;,,
QXFOHXV
OHPQLVFXV
WHUULWRU\
%DVDO
3,&$
WHUULWRU\
Figure 16.8 A diagram of cranial nerve nuclei and tracts in the
medulla. Vascular territories are shown on the left. ASA, anterior
spinal artery; PICA, posterior inferior cerebellar artery.
3DUDPHGLDQ
palate and pharynx and gustatory sensation from the
posterior third of the tongue; it has parasympathetic
autonomic secretomotor fibres, which reach the
parotid gland (via the otic ganglion); and supplies
the stylopharyngeus muscle (which cannot be tested
clinically).
Testing the glossopharyngeal nerve
The glossopharyngeal nerve is not tested in routine
neurological examinations. With particular clinical
indications to test it, such as a symptom of pharyngeal
sensory impairment, pharyngeal neuropathic pain
or a lesion of the vagus nerve, pharyngeal sensation
can be tested using an orange stick to touch lightly
the mucosa of the posterior pharyngeal wall. This
requires tolerance and cooperation on the part of the
patient. Some normal individuals will gag even at
the approach of a tongue depressor or orange stick.
In stuporous or comatose patients, testing the gag
reflex may be useful. The afferent component of this
reflex involves the glossopharyngeal nerves.
The vagus (X) nerve
The rootlets of the vagus nerve emerge from the
medulla just below those of the glossopharyngeal
nerve. Both nerves leave the base of the skull through
the jugular foramen. The vagus nerve passes down
the neck adjacent to the internal carotid artery and
internal jugular vein. Motor efferent fibres supply
pharyngeal muscles. The superior laryngeal nerve
supplies the cricopharyngeus muscle of the larynx
and conveys sensation from the larynx. Lower down
in the thorax, the recurrent laryngeal nerve passes
back up the neck to supply the laryngeal muscles
other than the cricopharyngeus. The visceral afferent
and efferent fibres of the vagus nerve downstream of
the recurrent laryngeal nerves are not amenable to
clinical neurological examination.
Testing the vagus nerve
A patient with a proximal unilateral lesion of the
vagus nerve may complain of dysphagia and nasal
regurgitation of swallowed fluids. There will be
weakness of the muscles of the soft palate on the
affected side. Attempted voluntary elevation of the
soft palate (ask the patient to say ‘Ahh’, preferably
fairly high pitched) reveals the weakness of elevation
of the palate on the affected side, along with deviation of the uvula to the unaffected side, because
of the unopposed action of the palatal muscles on
that side. In addition, ipsilateral vocal cord paresis
will lead to dysphonia. Bilateral lesions of the vagus
nerves will invariably be associated with dysphagia.
(Bilateral palatal weakness is not commonly caused
by bilateral vagus lesions but rather by more diffuse
disorders, such as polyneuropathy or myasthenia gravis.) The effects of bilateral lesions of innervation of
the larynx vary depending on whether there is weakness mainly of vocal cord abduction or adduction or
Соседние файлы в папке Библиотека им академика М.И. Перельмана