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!
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.
