Cranial nerves exam

Question 1

List the cranial nerves.

Answer 1

CN I = Olfactory 
CN II = Optic
CN III = Oculomotor 
CN IV = Trochlear 
CN V = Trigeminal 
CN VI = Abducens 
CN VII = Facial 
CN VIII = Vestibulocochlear
CN IX = Glossopharyngeal 
CN X = Vagus 
CN XI = Spinal (Accessory)
CN XII = Hypoglossal

Question 2

How do you test CN I?

Answer 2

Sense of smell

• formally test one nostril at a time with samples that give characteristic smells
• if these are unavailable, you can ask the patient if they have noticed any change in their sense of smell or taste

Question 3

How do you test CN II?

Answer 3

1. Visual acuity:
   - always test each eye separately
   - assess using a snellen chart
   - stand the patient 6 metres away and assess one eye a a time by covering the other
   - record for each eye how far down the chart they can read
   - if no snellen chart is available, you can do a basic screening by asking the patient to read something like your ID badge
2. Visual fields:
   - ask the patient to look at your face and ask if any of it is missing
   - examine one eye at a time by asking the patient to cover their eye with their hand
   - cover your opposite eye
   - ask the patient to look directly into your pupil
   - for each quadrant in turn, place your moving finger held way between you and the patient,. at the edge of your visual field
   - ask the patient if they can see your finger moving
   - ask the patient to tell you when the finger stops moving

Question 4

How do you test pupillary reflexes? What CN is this testing?

Answer 4

• testing CN II and III
  1. ask the patient to look directly behind you
  2. inspect the pupils - are they equal and regularly shaped?
  3. warn the patient you are about to shine a light in their eyes (bring the light in from the outside)
  4. for each pupil assess:
• directly light response: does the pupil constrict when you shine a light directly into it?
• consensual light response: does the other pupil constrict as well?
• the speed of constriction: is one pupil more sluggish than the other
  5. to assess accommodation:
• hold you finger ~30cm from the patient’s face and ask them to focus on it
• move you finger closer to their face and ask them to keep focusing
• each eye should constrict as you move your finger closer

Question 5

How do you test eye movements? What CN does this assess?

Answer 5

• assesses CN III, IV and VI
  1. hold your finger (or a brightly coloured pin) equidistant between you and the patient
  2. ask them to focus on it and follow it as you move it in a H-shape
  3. ask if there is any pain or double vision at each point

Question 6

How do you assess CN V?

Answer 6

1. facial sensation
   - using a piece of cotton wool, touch the patient’s sternum as a reference
   - ask them to close their eyes and say ‘yes’ when they feel you touch them
   - test skin in the distribution of each branch and ask whether it feels the same on both sides
2. facial movement (muscles of mastication)
   - palpate over the temples (temporals) and mandibular angle (master)
   - ask the patient to clench their jaw and feel for contraction of the muscles
   - ask the patient to open their jaw against resistance (pterygoids)

Question 7

How do you assess CN VII?

Answer 7

Muscles of facial expression:

• ask the patient to perform the following movements and assess for symmetry:
  1. ‘raise your eyebrows’
  2. ‘close you eyes tightly’ - oppose this movement
  3. ‘give me a big smile’
  4. ‘blow out your cheeks’ - oppose this movement

Question 8

How do you assess CN VIII?

Answer 8

1. basic testing: whisper a number one each ear and ask them to repeat it back to you (with or without blocking the other ear canal through pressure on the trigs)
   - alternatively, finger rub test: inability to hear a strong finger rub is highly likely to represent hearing loss
2. Weber’s test (low sensitivity): place a vibrating 512 Hz tuning fork in the middle of the patient’s forehead
   - ask them to say whether they can hear it in both ears and whether one side is louder
3. Rinne’s test (more sensitive and specific): place the vibrating tuning fork (512 Hz) on the patient’s mastoid process
   - ask them o tell you when they can no longer hear the tuning fork
   - when the patient tells you, take the tuning fork and move it so that the prongs of the tuning fork are at the entrance of the ear and ask again if they can hear it

Question 9

What result in Weber’s and Rinne’s test would indicate no hearing loss?

Answer 9

Weber’s: both ears equal

Rinne’s: Air > Bone

Question 10

What result in Weber’s and Rinne’s test would indicate conductive hearing loss?

Answer 10

Weber’s: louder in affected ear

Rinne’s: bone louder than air

Question 11

What result in Weber’s and Rinne’s test would indicate sensorineural hearing loss?

Answer 11

Weber’s: louder in unaffected ear

Rinne’s: air louder than bone

Question 12

How you you assess CN IX and X?

Answer 12

Pharyngeal and palatal muscles

• ask the patient to cough
• ask the patient to open their mouth and say ‘aah’ whilst looking at their pharynx with a pen torch
• assess for asymmetry

Question 13

Which way does the uvula deviate in a CN X lesion?

Answer 13

Away from the lesion

Question 14

How do you assess CN XI?

Answer 14

• ask the patient to shrug their shoulders (trapezius) - try and push them down
• place the back or side of your hand on the patient’s check - ask them to turn their face towards your hand against resistance (SCM)
• remember that tuning the patient’s head to the right assesses their left SCM and vice versa

Question 15

How do you assess CN XII?

Answer 15

Tongue movement

• ask the patient to open their mouth, look for wasting and fasciculations
• ask them to stick out their tongue - if their is a CN XII lesion, tongue will deviate towards the lesion
• ask patient to push the tip of their tongue in each cheek and use your fingers to push against the tongue by pressing on their cheeks, assessing strength