CS - Examination of the cranial nerves Flashcards
What are the different sections you need to cover in a cranial nerve exam?
- Introduction
- General inspection
- Sense of smell - (olfactory nerve CN I)
- Close inspection of eyes
- Visual acuity (optic nerve CN II) - Distance + near vision
- Visual fields by confrontation (CN II)
- Fundoscopy (CN II)
- Light reflexes (direct and consensual CN II - afferent and CN III efferent)
- Near response (CN II and III)
- Eye movements (optic - II, oculomotor - III, trochlear - IV and abducens (VI)
- Cutaneous facial sensation (sensory root trigeminal V)
- Muscles of mastication (motor root of CN V)
- Muscles of facial expression (facial nerve CN VII motor component)
- Taste and salivation (sensory and parasympathetic components of facial nerve)
- Examination of ear
- Vestibulocochlear (CN VIII - auditory component and air conduction)
- Vestibular function (vertigo)
- Throat (pharynx and larynx, glossopharyngeal (IX) and Vagus (X) - motor sensory and parasympathetic functions)
- Head movements (Accessory nerve (XI)
- Mouth + tongue (hypoglossal (XII)
- Speech (CN X and XII)
- Conclusion
What would you cover in General Inspection?
General Inspection;
Facial asymmetry (CN VII);
- Bell’s palsy CNVII
- Herpes zoster rash CN V
Position of head;
- Head tilt - may indicate a nerve lesion, e.g away from side of the lesion to compensate in a fourth nerve lesion
- Head turn - occurs in visual defects due to stroke (e.g right homonymous hemianopia -> right head turn)
Around the bed (e.g wheelchair or walking aid, glasses and/or case, hearing aid). Patient wearing glasses (CN II) or hearing aid (CN VIII) ?
How would you inspect Sense of Smell - (Olfactory nerve CN I)?
Sense of Smell - (Olfactory nerve CN I);
- Ask patient if they have had any changes in smell (CN I) or taste (CN VII) recently ?
- If no, no further testing is necessary
- If yes, ask if patient has a cold or blocked nose or had an injury to head
- If yes, change in sense of smell, but no cold, occlude one nostril at a time and ask patient to smell and identify strong odours such as coffee, chocolate, soap and orange peel
It is more important that the patient can detect different odours than be able to name them. Do not use irritant odours like ammonia which are detected via trigeminal nerve endings in the nasal mucosa. Patients with anosmia will still respond to pungent, irritant odours such as ammonia.
In head injury, anosmia may occur resulting of shearing of the olfactory neurons against the cribriform plate of the ethmoid bone
What would you cover in a Close Inspection of the Eyes?
Close Inspection of the Eyes
Note the resting position of the eyes (primary gaze);
- Is there a squint ?
Look closely for abnormal position of eyes;
Look closely for abnormal eyelid position (e.g ptosis - upper eyelid droops over the eye) or pupil abnormality;
- Ptosis can be complete or partial (easy to miss a mild degree of it)
- Commoner causes of ptosis are microvascular. In CN III palsy ptosis is complete and in Horner’s syndrome we have partial ptosis
Observe nystagmus at rest;
What is Ptosis and what are the main causes of it and what muscles are involved?
Ptosis = drooping of eyelid
Commoner causes of ptosis are microvascular. In CN III palsy ptosis is complete and in Horner’s syndrome we have partial ptosis
Rarer causes include: congenital, myasthenia gravis (when ptosis is variable)
Levator palebrae superioris acts to elevate and retract the upper eyelid and is supplied by the 3rd nerve.
There is also sympathetic innervation to Muller’s muscle (a supportive muscle which inserts onto the tarsal plate) which adds in lid retraction
What are the features of Horner’s syndrome?
Horner’s Syndrome;
- Small pupil (mitosis)
- Partial ptosis
- Enophthalmos (posterior displacement of the eyeball within the orbit)
- Reduced or absent sweating (anhidrosis) on affected side of face
What are the features of a Sympathetic Palsy?
There is also sympathetic innervation to Muller’s muscle (a supportive muscle which inserts onto the tarsal plate) which adds in lid retraction
In a Sympathetic Palsy the lesion may be anywhere in the course of the sympathetic supply - keep in mind an apical bronchial adenocarcinoma (Pancoast’s tumour) in a smoker
What would you cover in Visual Acuity (Optic nerve CN II) ?
Visual Acuity (Optic nerve CN II) - Test Distance and Near Vision;
Acuity (use Snellen chart of some other distance measuring device at the appropriate distance);
1). Test unaided, with patient’s distance correction snd then with a pinhole
2). Usng a Snellen chart, stand the patient six meters away from the chart and ask them to read from the top of the chart, with the fellow eye fully covered with the palm of the patient’s hand or an occluder.
3). If your patient cannot read the top line at six metres bring them forward to one metre and ask them to read the top line.
4). If the patient cannot read the top line at one metre, then assess with hand movements, then counting fingers and then light perception as necessary.
5). If you tested at a distance of 6 metres then record the visual acuity as ‘6/x’, in which 6 indicates the distance at which the test is performed and x denotes the number of the line of the smallest text that was seen.
Near Acuity;
1. Place the chart at a comfortable reading distance, approximately 40cm. (This should also be the distance the near test has been calibrated for).
2. Ask the patient to read the smallest text that they can see comfortably
3. Record this as N* (where * is the smallest text the patient can read comfortably)
How would you test the Visual Fields by Confrontation (CN II)?
Visual Fields by Confrontation (CN II)
- Setup: Sit directly in front of your patient, at the same height, with your knees almost touching
- Test binocular visual field:
a. Present your open palms in the 2 upper quadrants halfway between you and the patient
b. Ask the patient “while looking at my nose, can you tell me how many hands I am holding up”
c. Present your open palms in the 2 lower quadrants and repeat the question
d. Now waggle the fingers of one hand
e. As the patient “Point to the hand which is waving”
f. Repeat this 2 or 3 times to ensure a consistent response - Uniocular visual field assessment
a. Hold up 1 or 2 fingers in front of the patient and confirm their vision is good enough to see ‘counting fingers’ and that they understand the test
b. Emphasise they should keep looking at your open eye and not the fingers
c. With the patient’s left eye covered and your right eye closed, ask the patient to fix on your open eye. Then, explain to the patient that you are going to hold up different numbers of fingers. Ask them to tell you how many fingers they see.
d. Place your fist in the middle of one quadrant and ‘flash’ either 1 or 2 fingers halfway between you and the patient
e. Test all 4 quadrants of one eye twice randomly presenting one or two fingers and not simply alternating
f. Repeat this for the fellow eye
Remind the patient throughout the visual field examination to look at your open eye and not at the fingers.
The commonest error here is not keeping the examining hand halfway between examiner and patient.
A more in depth visual field assessment can be carried out to explore the meridia (horizontal and vertical) and also the blindspot using a red pin. However, the above points 1 to 3 are substantial enough for your stage in training.
What would you do in Fundoscopy (CN II) ?
Observe the optic discs of both eyes. (Retina reflex)
Important observations to make are of the;
- Colour – This should be yellowy-pink in appearance. If the disc is pale, this could signify optic atrophy
- Contour – The margin of the disc should be clearly defined. If it is not, this could be due to raised intracranial pressure, in which the sign is papilloedema.
- Cup – A normal optic cup:disc ratio is 0.3. If it is larger than this, it signifies a cupped disc, such as in the case of glaucoma.
How would you test Light Reflexes (Direct and Consensual) (CN II afferent and CN III efferent) ?
Light Reflexes (Direct and Consensual) (CN II afferent and CN III efferent);
Examine pupils for size and shape;
- Check pupil size is equal in both eyes. Record the size of the pupils in mm (can use a pupil gauge to estimate the size).
- Are the pupils regular in contour? (irregularity occurs for example with posterior synechiae in uveitis)
Are there any ‘holes’ in the iris? (Iridotomy is a treatment for glaucoma)
- Initially observe the pupil diameter in light and dark conditions. This highlights whether any difference in pupil size (anisocoria) is physiological or due to an efferent palsy.
- If the difference is due to physiological anisocoria, the difference between light and dark conditions will be much the same.
- If due to a sympathetic palsy, anisocoria will be most evident in the dark and with a parasympathetic palsy, anisocoria will be greater in bright light.
Direct and indirect light reflexes;
It is a crossed reflex. The afferent limb of the reflex is mediated via the optic nerve (CN II).
The efferent limb is the parasympathetic component of the oculomotor nerve on both sides. The parasympathetic supply to the pupil hitch-hikes on the outside of CN III and arise in the Edinger–Westphal nucleus of the midbrain.
Direct response;
Shine light from the pen torch in one eye and observe the response in the same eye (pupillary constriction).
Indirect/Consensual Response;
Shine the light in one eye and observe the response in the fellow eye (pupillary constriction).
Repeat the process for the direct and consensual responses in the fellow eye.
Check for a relative afferent pupillary defect (RAPD);
- Shine light on one eye for 2-3 seconds, then rapidly move to the fellow eye.
- A normal response is either no change in size OR a brief constriction followed by return to the same size. This is called ‘hippus’.
- A pupil exhibiting an RAPD will however paradoxically dilate when the light moves towards it.
How would you test Near Response (CN II and III)?
A. Instruct patient to look at a far object in the distance
B. Looks into distance then focuses on a near fixation target
C. Observe for convergence and pupillary constriction
The near response is a triad consisting of:
1. Convergence
2. Pupillary constriction
3. Accommodation
Two of these can be directly observed.
Ask your patient to look into the distance at a target and then look at a fixation object placed vertically 40cm in front of them. Observe the normal reaction of papillary constriction and convergence (adduction).
The afferent limb of this reflex is mediated through the optic nerve (CN II) and the efferent limb through the oculomotor nerve (CN III). CN III controls medial rectus bilaterally and gives a bilateral parasympathetic supply (from the Edinger Westphal nucleus) to the sphincter pupillae muscle.
The final component is accommodation (which cannot be directly observed). This is also mediated by a parasympathetic supply to the ciliary muscle, which acts to change the conformation/shape of the lens to adjust for near vision.
How would you test Eye Moments (Optic - II, Oculomotor - III, Trochlear - IV, Abducens - VI)?
Eye Moments (Optic - II, Oculomotor - III, Trochlear - IV, Abducens - VI);
Test slow pursuit eye movements;
- Start at the centre point of fixation and move laterally to each temporal field in turn
- Then move from the centre to the corner of each quadrant of the binocular field
Ask the patient to let you know if they see “double” or more than one of the fixation target at any point throughout the examination
Note the position of the patient’s head and the position of the eyes. Hold the fixation target vertically about 60cm away from the patient, in the centre of their gaze. Encourage the patient to keep their head still throughout and only follow the fixation target with their eyes. Ask them to tell you if they see ‘double’ at any point. Move fixation target from the centre to the temporal sides of the binocular field in turn and then to each of the corners of the 4 quadrants of the binocular field
* Move the target out to the left temporal field and then to the right temporal field
* Move the target slowly from the centre out to the four corners of the binocular field in turn
* Move the target up and down from the centre
Also observe for nystagmus
Inputs from the frontal and occipital lobes, and the cerebellum and vestibular nuclei are integrated in the brainstem so that both eyes move together
What are 2 important eye related structures found in the brainstem?
Important structures in the brainstem are the;
Horizontal gaze centre in the pons
The medial longitudinal fasciculus (MLF) which runs between the nuclei of III and IV in the midbrain and VI in the pons.
What muscles does the Oculomotor nerve supply ?
Levator palebrae superiors and all of the extra-ocular muscles of the eye with exception to Superior Oblique (CN IV) and Lateral Rectus (CN VI)
Remember SO4 LR6!
What are the functions of each muscles of the eye?
Primary actions of the extraocular muscles:
- Lateral rectus abducts the eye.
- Medial rectus adducts the eye.
- Superior rectus and inferior oblique elevate the eye.
- Inferior rectus and superior oblique depress the eye.
- Superior oblique depresses, abducts and intorts the eye. The depressive action of superior oblique is most effective when the visual axis is aligned with the axis of ‘pull’ of the muscle. Therefore, superior oblique contributes most to depression when the eye is adducted, hence this is the position in which it is tested.
(Hence difficulty in superior oblique lesion in seeing step when walk downstairs.) - Inferior oblique elevates. abducts and extorts pupil.
Elevation is most effective when the eye is turned medially.
Also test eye movements to pursuit. (The site of control is the occipital lobe.) This is done by asking the patient to track a moving target in vertical and horizontal directions. (Smooth visual pursuit)
How would you test for Nystagmus?
Nystagmus is an involuntary rhythmic oscillation. There is usually a slow phase and fast correction in the opposite direction. It is conventional to describe nystagmus in the direction of the fast (correction) phase. It is usually asymptomatic as the patient is unaware of it. Nystagmus can be:
- Physiological - (as when looking out of a moving train window)
- Peripheral - due to abnormalities of vestibular system, the eighth nerve or nucleus
- Central - due to abnormalities of central vestibular connections or the cerebellum
- Retinal – due to damage to retina and a resultant inability to fix on an image
Testing for nystagmus:
Note the presence of any nystagmus in the primary (resting) position of gaze (this should have been done with close inspection of the eyes). While examining for eye movements, briefly pause at each position and look carefully for nystagmus.
What is Ocular Paresis and the signs of it?
Clinical signs of ocular paresis;
III - Ptosis, eye deviated ‘down-and-out’, pupil may be dilated or constricted depending on cause of CNIII palsy, i.e. whether a sympathetic or parasympathetic palsy.
IV - Impaired depression of the fully adducted eye, head may be tilted to the opposite side to avoid diplopia when reading or looking down to walk downstairs.
VI- Impaired abduction
How does the parasympathetic supple travel to the eye and how may a defect in it manifest?
The parasympathetic supply to the pupil “hitch hikes a ride” and is carried on the outside of the oculomotor nerve. Compression of the outside of the nerve and subsequent fixed dilation of the pupil may be one of the first signs of a “surgical” cause of an oculomotor palsy e.g: posterior communicating artery aneurysm or raised intracranial pressure and downward depression of the brain compressing the third nerve against the free edge of the tentorium cerebelli.
How would you test Cutaneous Facial Sensation (sensory root of Trigeminal CN V)?
Cutaneous Facial Sensation (sensory root of Trigeminal CN V);
A. Ask patient to close his eyes
B. Check light touch in all 3 divisions, comparing side to side
C Check pinprick with neuropin in all 3 divisions, comparing side to side ((know how to do and offer in OSCE, don’t need to perform)
First demonstrate light touch on sternum. Ask your patient to close his eyes and to say “yes” each time he feels the test. Lightly touch, over the forehead, the medial aspects of the cheeks and the chin with your finger or cotton wool. Compare side to side and ask patient if notices a difference. These 3 areas correspond to the ophthalmic, the maxillary and mandibular branches of the trigeminal. Omit pinprick testing of the face and tongue. But offer this test in an OSCE.
Can also do Corneal Reflex Test (CN V and CN VII)
How would you carry out a Corneal Reflex test?
Corneal Reflex Tests CN V and CN VII;
This will be inhibited in contact lens wearers. To elicit the reflex, ask them to remove their lenses.
The afferent route is via the ophthalmic division of CN V and the efferent route is carried by the facial nerve (CN VII). Gently touch the cornea with a wisp of cotton wool. It is a crossed reflex and there should be synchronous blinking of both eyes. Know how to do the test - be able to describe it. You will not be required to perform the corneal reflex on a simulated patient in your session nor your St Andrews’ OSCE. However remember to OFFER to do the test in your OSCE.
Offering this test when examining cranial nerve VII is also appropriate.
How would you test the Muscles of Mastication (motor root of CN V)
Muscles of Mastication (motor root of CN V);
A. Inspect for wasting
B. Palpate – ask to clench teeth and palpate for size of masseter and temporalis
C. Check protraction and side to side movement
D. Open jaw against resistance
F. Jaw jerk
The muscles of mastication, the pterygoids, temporalis and masseters are supplied by the mandibular division of the trigeminal. The medial and lateral pterygoid muscles give rise to side to side movement of the lower jaw. The pterygoids of one side are able to protrude the lower jaw and rotate the chin to the opposite side.
Inspect for wasting of the muscles of mastication.
Ask patient to push lower jaw forward and also make movements from side to side.
Ask patient to clench his teeth together while you palpate the bulk of masseter and temporalis muscles. Assess the pterygoids by resisting the patient’s attempts to open their mouth.
In unilateral lesions of the motor division of CNV, the lower jaw deviates to the paralysed side.
The jaw jerk
The afferent limb of this brainstem reflex is mediated through proprioception endings within the muscles of mastication. These endings are stimulated when the muscles are stretched when hit. These proprioceptive fibres travel in the trigeminal nerve to the mesencephalic nucleus in the midbrain. Fibres then project to the pons to the motor nucleus of V lying in the upper pons. This motor nucleus supplies the motor root of CN V. The efferent limb arises from this nucleus and travels in the mandibular division of the trigeminal back to the muscles of mastication.
Ask your patient to open their mouth slightly. Rest your thumb on the apex of the jaw and tap your finger gently with a tendon hammer. The normal response is reflex closing of the mouth due to contraction of masseter and temporalis muscles. The reflex is often absent or minimal and an absent reflex is not significant. It is pathologically brisk when there are bilateral upper motor neurone lesions affecting the corticobulbar pathways. E.g.: infarction within the internal capsule.
How would you test the Muscles of Facial Expression (Facial nerve CN VII - motor component)?
Muscles of Facial Expression (Facial nerve CN VII - motor component);
A. Inspect face for asymmetry - mouth drooping, nasolabial fold, a more widely opened eye, forehead wrinkles
B. Test muscle power
C. Compare with involuntary movements – spontaneous smile
D. Corneal reflex (CN V and VII) - remember to mention this and know how to do it but don’t actually perform
Inspect for facial asymmetry. Look in particular for drooping of the mouth, loss of the nasolabial fold and a more widely open eye.
Motor Power - Muscles of facial expression
Demonstrate to your patient what you would like him to do for each test.
Ask patient to: -
* grimace and show me your teeth (platysma and dilator muscles)
* say “me-me-me” (uses lips and front of mouth)
* puff out your cheeks and don’t let me squeeze the air out (orbicularis oris, NOT buccinator!)
* screw up eyes tight and don’t let me open your eyes (orbicularis oculi)
* look upwards to wrinkle forehead (follow horizontal finger) (frontalis)
Compare involuntary movements with voluntary
* watch for any spontaneous smile
How would you differentiate upper and lower motor neurone lesions of facial nerve (CN VII) in facial asymmetry ?
The key is to remember the unusual anatomical fact that there is a bilateral supply from both cortices to both facial motor nuclei in the pons for control of the forehead (frontalis). But only a unilateral crossed supply to the area of the nucleus that controls the muscles of the lower part of the face. (e.g. buccinator and orbicularis oris.)
In an upper motor neurone lesion of the facial nerve the occipitofrontalis and orbicularis oculi muscles are largely spared. In UMNL, although the UMN pathway is damaged somewhere from the cortex to the nucleus, there is still innervation of the facial nucleus from the contralateral cortex for that part of the nucleus that controls the forehead. The patient is therefore able to have some movement of the forehead. (Usually seen as bilateral wrinkles.) An example would be a stroke.
In a lower motor neurone lesion, the lower and upper part of the face (forehead) are completely paralysed (i.e. the whole half of the face including the forehead), because the final common pathway (the lower motor neurone) to move the muscles is discontinued. An example would be a Bell’s palsy. Bell’s palsy is used to describe swelling of the facial nerve in the facial canal. There may also be hyperacusis as stapedius muscle may also be affected. Its function is to dampen the ossicular chain and so if affected, sounds may be echoing and distorted.
Note also that in a severe lower motor neurone lesion you may see the eyeball turned upwards when the patient tries to close his eyes. This is rather confusingly called “Bell’s phenomenon.”
Ramsay Hunt syndrome describes a lower motor neurone lesion of the 7th where there is herpes zoster infection of the geniculate ganglion. There are usually associated vesicular eruptions in the external auditory canal.
One problem (rare) is when there are bilateral CNVII lesions and there is no obvious facial asymmetry. However in that case you would establish that there is very little movement of the facial muscles on clinical examination.
