Cranial nerve examination
| Cranial nerve examination |
The cranial nerve exam is part of the neurological examination. It is used to identify problems with the cranial nerves by physical examination.
Olfactory nerve
Smell is tested in each nostril separately by placing stimuli under one nostril and occluding the opposing nostril. The stimuli used should be non-irritating and identifiable. Some example stimuli include cinnamon, cloves and toothpaste. Bilateral loss can occur with rhinitis, smoking or aging. Unilateral loss indicates a possible nerve lesion or deviated septum. This test is usually skipped on a cranial nerve exam.
Optic nerve
Visual acuity is tested in each eye separately. Ensure the patient's vision is corrected with eyeglasses or a pinhole. The patient is asked to read progressively smaller lines on the near card.
Visual fields are assess by asking the patient to cover one eye while the examiner covers the opposite eye. The examiner wiggles the finger in each of the four quadrants and asks the patient to state when the finger is seen in the periphery. The examiner's visual fields should be normal, since it is used as the baseline.
Pupillary light reflex The patient stares into the distance as the examiner shines the penlight obliquely into each pupil. Papillary constriction should be noted on the eye examined (direct response) and on the opposite eye (consensual response). The swinging flashlight test involves moving the light between the two pupils. Normally both direct and consensual responses are ellicited when the light shines on an eye, and some dilation will occur during the swing between.
Extraocular Movements: Oculomotor nerve, Trochlear nerve, Abducens nerve
First, inspect for ptosis, eye position and nystagmus. The pupil size should be measured, its shape and any asymmetry should be noted. A commonly used abbreviation to describe normal pupils is PERRLA (pupils equal, round and reactive to light and accommodation).
The examiner tests ocular movements by standing one meter in front of the patient and asking the patient to follow a target with eyes only, and not the head. The targets is moved in an "H" shape and the patient is asked to report any diplopia. Then, the target is held at the lateral ends of the patient's visual field. Nystagmus should be noted. One or two beats is a normal finding. The accommodation reflex is tested by moving the target towards the patient's nose. As the eyes converge, the pupils should constrict. The optokinetic nystagmus test is optional and involves asking the patient to look at a moving strip of horizontal lines. Nystagmus is normally observed.
Trigeminal nerve
Light touch is tested in each of the three divisions of the trigeminal nerve and on each side of the face using a cotton wisp or tissue paper. The ophthalmic division is tested by touching the forehead, the maxillary division is tested by touching the cheeks, and the mandibular division is tested by touching the chin. Be careful not to test the mandibular division too laterally, as the mandible is innervated by the [[[great auricular nerve]]] (C2 and C3). A common mistake is to use a stroking motion, which will trigger pain and temperature nerves. Instead, a point stimulus should be applied. For pain and temperature repeat the same steps as light touch but use a sharp object and a cold tuning fork respectively.
Coronal reflex is conducted along with the facial nerve section of the test. Note the sensory innervation of the cornea is provided by the trigeminal nerve while the motor innervation for blinking the eye is provided by the facial nerve.-
Muscles of mastication (temporalis, masster) should be inspected for atrophy. Palpate the temporalis and masseter as the patient clenches the jaw. The pterygoids can be tested by asking the patient to keep the mouth open against resistance, and move from side to side against resistance. A jaw jerk reflex can be tested by placing a finger over the patient's chin and then tapping the finger with a reflex hammer. Normally the jaw moves minimally.
Facial Nerve
Inspect for facial assymmetry and involuntary movements.
- Motor
Vestibulocochlear
- Hearing: Wisper numbers in one ear and ask the patient to repeat the numbers. Make sure to cover the opposite ear. Conduct the Rinne test and Weber test.
- Vestibular Function
Glossopharyngeal and Vagus
- Gag response
- Palatal articulation "KA"
- Guttural articulation "GO"
Accessory nerve
- Shrug shoulders
- Turn head from side to side
Hypoglossal
- Inspect for tongue atrophy, fasciculations or asymmetry
References
- The Neurological Exam
- The Essentials of Clinical Examination Handbook, University of Toronto Medical Society