Answer
The following is a summary of the common lesions of cranial nerves , the resultant defects and the usual clinical tests applied to defect the effects of the relevant injuries:
Olfactory CN I: Lesions result in defects in sense of smell. This injury is usually diagnosed by testing
patient's ability to smell aromatic substances like coffee, vanilla and oil of cloves
Optic CN II; Injury to this nerve results in blindness partial or complete blindness. Diagnostic tests
include tests of peripheral vision, and of visual acuity, plus opthalmoscopic examination of
the retinas.
Oculomotor CN III: Lesions cause double vision, drooping eyelids, inability to move eyes in some
directions, and a tendency to rotate eyes laterally.
Trochlear CN IV: Injury of this nerve result in double vision, and weakened ability to look downward. .
Patient tends to tuck ciin in and and tilt head downwards. Test: Ask patient to tilt head
towards one shoulder: the affected eye shows upward deviation when the head is tilted
towards the side of the injury. This is known as Bielschowsky's head tilt test.
Trigeminal CN V ( 1,2,3)
V1: Ophthalmic branch: Result of injury is loss of sensations in upper face. Tests include
blinking reflex, and response to light touch on eyeballs.
V 2: Maxillary branch. Injury results in loss of sensation from middle face: Diagnostic tests
include include tests
of pain, of touch, temperature, pin pricks, and responses to hot and cold objects.
V3. Mandibular branch: Some effects include loss of sensations from lower face, and impaired
chewing. Tests: Palpation of masseter and temporalis muscles while
patient is chewing. Test ability to move mandible from side to side
and ability to open mouth against resistance.
Abducens CN VI: Lesions result in inability to turn eyes out laterally. At rest, eye turns medially. Test eyes
for ability to turn laterally.
Work Step by Step
Facial nerve CN VII: Injury causes loss of control of facial muscles and sagging of face. Taste of sense for
sweet is also distorted. Diagnose injury by testing anterior two-thirds of tongue for
ability to taste sugar, vinegar, and quinine. Another test is the response of lacrimal
glands to ammonia (NH3) fumes. Patient should also be asked to smile, frown, raise
eyebrows, and close his/her eyes.
Vestibulo-cochlear CN VIII. Damage results in nerve deafness, nausea , dizziness, loss of balance
and nystagmus
(oscillating of eyes from side to side). Usual diagnostic tests include the
nyatagmus test, hearing test, balance tests plus the test of the ability to walk a
straight line.
Glossopharyngeal CN IX. Injury to this nerve results in loss of taste for bitter and sour substances; also,
swallowing is impaired. Usual diagnostic tests include tests of the gag reflex , of
swallowing, and of coughing. Speech tests are also appropriate. In addition, taste
tests of bitter, and sour should also be conducted on the posterior one third of
the tongue.
Vagus CN X. Lesions may result in hoarseness, loss of voice and impairment of swallowing and GI motility.
Tests include checking for weak , hoarse voice, swallowing problems, checking the
gag reflex, checking and ability to cough forcibly.
Accessory CN XI. Accessory : Movements of head neck and shoulders impaired. Difficulty in shrugging
shoulder on injured side. . Head tends to turn to damaged side because of
sternocleidomastoid damage.To diagnose, test ability to to rotate head, and
to shrug shoulders against resistance.
Hypoglossal CN XII. Signs of injury are impaired speech and of swallowing, inabilityto protrude tongue
directly forward; deviation of tongue toward injured side. Note deviations as
subject tries to protrude and withdraw tongue. Test ability to protrude tongue
against pressure.
