Cranial Nerve Evaluation

Question 1

When we do a CN evaluation, do we evaluate the function of every nerve?

Answer 1

Not necessarily. For a specific concern, may test “adjacent” nerves. For example, for a patient with compromised CNVI, test nerves V and VII.

For general concerns, like HA or personality changes, it is prudent to test all nerves

Question 2

Search the archives of your memory from Undergrad and tell me what each of the 12 CNs are

Answer 2

I: Oflactory
II: Optic
III: Oculomotor
IV: Trochlear
V: Trigeminal
VI: Abducens
VII: Facial
VIII: Auditory (Acoustic)
IX: Glossopharyngeal
X: Vagus
XI: Accessory
XII: Hypoglossal

Question 3

How do we test CNI: Olfactory?

Answer 3

The patient closes their eyes. Occlude 1 nostril, and ask patient to identify a smell. Change nostrils, and ask them to identify a different smell. If not changing smell, ask patient to compare intensity between nostrils.

Question 4

What are some common causes of reduced olfactory function?

Answer 4

Rhinitis due to allergies. Common cold. Trauma to nose. Trauma to fontal lobe, or frontal lobe lesions. Early Alzheimer disease.

Question 5

How do we test CNII: Optic?

Answer 5

It’s in our eye exam! Visual acuities, visual fields, ONH examination during fundoscopy

Question 6

How do we test CNIII: Oculomotor?

Answer 6

It’s in our eye exam! Pupils & EOMs

Question 7

How do we test CNIV: Trochlear?

Answer 7

It’s in our eye exam! EOMs

Question 8

How do we test CNVI: Abducens?

Answer 8

It’s in our eye exam! EOMs

Question 9

How do we test the motor portion CNV: Trigeminal?

Answer 9

Do the muscles of mastication work equally well on both sides of the face? Have patient clench jaw and test strength by pulling apart on the jaw. Palpate cheek muscles for even tone.

Question 10

How do we test the sensory portion CNV: Trigeminal?

Answer 10

Is the ability to sense light touch (cotton wisp) and pain (broken swab) equal on both sides? Ask them to locate the wisp, and to tell you dull vs sharp with the broken swab. Check for symmetry and test all 3 divisions.

Question 11

What are the 3 sensory divisions of the Trigeminal nerve?

Answer 11

1) Ophthalmic: upper lids, forehead, cornea, top of nose
2) Maxillary: lateral nose surfaces, cheeks, lower lids
3) Mandibular: jaw, side of face (up by ear).

Question 12

What are some common causes for impaired strength or sensation in CNV: Trigeminal?

Answer 12

Herpes simplex or zoster infection. Cavernous sinus lesion.

Question 13

How do we test the motor portion of CNVII: Facial?

Answer 13

Do the facial muscles work equally well on both sides? Ask the patient to wrinkle their forehead, smile, frown, raise eyebrows, and purse their lips.

Then test strength of orbicularis muscles by having the patient squeeze their eyes shut and trying to open them. This test is sensitive for early loss of function.

Question 14

How do we test the sensory portion of CNVII: Facial?

Answer 14

We don’t typically. Not covered in this lecture.

Question 15

What are some common causes for impaired strength in CNVII: Facial?

Answer 15

Bell’s Palsy. Acoustic neuroma

Question 16

How do we test CNVIII: Acoustic?

Answer 16

Compare hearing ability on each side with finger rubbing or a tuning fork.

If hearing loss is present, differentiate between conduction and sensorineural via the Weber and Rinne tests.

Question 17

Describe the Weber test

Answer 17

Activate fork and place tuning fork on top of patient’s head, holding fork by the handle. Ask patient to localize the sound. Sound should be centered between ears. Neurological loss will cause sounds to be localized to “good” ear. Conduction loss will cause sound to be localized to the “bad” ear.

Question 18

Describe the Rinne Test

Answer 18

Activate tuning fork and place it in the mastoid process. When patient can no longer hear the sound, move the fork to in front of the external ear. Note how long it takes the patient to stop hearing the fork each time. Air conduction should be better than bone conduction, and both should be equal AU.

If bone conduction is not equal AU, expect nerve damage on shorter-hearing-time side. If air conduction is not > bone conduction, or air conduction is not equal AU, expect something blocking sound waves (eg cerumen, or tympanic membrane problems).

Question 19

We test CNs IX Glossopharyngeal and X Vagus together. How do we do this?

Answer 19

Ask about difficulty swallowing or changes in voice. Check gag reflex by touching posterior 1/3 of tongue, soft palate, or posterior pharyngeal wall with cotton swab. Then, depress tongue and have patient say “ahhh”. Observe elevation of soft palate and uvula.

Question 20

When evaluating CN IX, you see the uvula deviate to the right. Which side is abnormal? What conditions can cause these kinds of asymmetries?

Answer 20

The left is abnormal. The uvula will deviate toward the normal side.

Lack of symmetry can indicate space-occupying-lesions or vertebral artery aneurysms

Question 21

How do we test CNXI: Accessory?

Answer 21

Test strength of sternocleidomastoid (SCM) and trapezius muscles. SCM = turning head left and right against the doctor’s hand. Trapezius = patient shrugs against doctor pushing down on shoulders

Question 22

How do we test CNXII: Hypoglossal?

Answer 22

Ask patient to stick tongue out straight and look for a deviation, which will be toward the affected side.

Have the patient push their tongue against the inside of their cheek while you push inward from the outside of the cheek. You’re looking for symmetry of strength left and right.