How are the 12 cranial nerves (CN) tested?

From the Guidelines

The 12 cranial nerves are tested through specific clinical examinations that assess their function, including tests such as identifying scents, visual acuity testing, examining pupillary responses, testing facial sensation, and evaluating hearing and balance. The tests for each cranial nerve are as follows:

• CN I (olfactory) is tested by having the patient identify different scents with each nostril.
• CN II (optic) is evaluated through visual acuity testing, visual field assessment, and fundoscopic examination.
• CN III, IV, and VI (oculomotor, trochlear, and abducens) are tested together by examining pupillary responses, eye movements in all directions, and checking for ptosis.
• CN V (trigeminal) is assessed by testing facial sensation in all three divisions and jaw strength during biting.
• CN VII (facial) is evaluated by having the patient make facial expressions like smiling, frowning, and closing eyes tightly.
• CN VIII (vestibulocochlear) is tested through hearing assessment with whispered words or tuning forks, and balance evaluation.
• CN IX and X (glossopharyngeal and vagus) are examined by checking the gag reflex, palate elevation, and voice quality.
• CN XI (accessory) is tested by having the patient shrug shoulders against resistance and turn their head against resistance.
• CN XII (hypoglossal) is assessed by observing tongue movement and checking for any deviation or atrophy, as recommended by the American College of Radiology Appropriateness Criteria 1. These tests are essential for neurological examination and help identify specific cranial nerve dysfunction that may indicate various neurological conditions affecting the brain, brainstem, or the nerves themselves, and imaging modalities such as MRI may be used to further evaluate cranial neuropathy 1.

From the Research

Cranial Nerves and Their Testing

The 12 cranial nerves (CN) are tested through various clinical examination techniques. Here's a list of the cranial nerves and how they are each tested:

• CN I (Olfactory): Tested by assessing the patient's ability to smell different odors 2
• CN II (Optic): Tested by evaluating visual acuity and visual fields 2
• CN III (Oculomotor): Tested by assessing eye movements and pupillary reflexes 2
• CN IV (Trochlear): Tested by evaluating eye movements, particularly the superior oblique muscle 2
• CN V (Trigeminal): Tested by assessing facial sensation and motor function, including the corneal reflex 2
• CN VI (Abducens): Tested by evaluating eye movements, particularly the lateral rectus muscle 2
• CN VII (Facial): Tested by assessing facial motor function, including taste and hearing 2
• CN VIII (Vestibulocochlear): Tested by evaluating hearing and balance 2
• CN IX (Glossopharyngeal): Tested by assessing swallowing and taste 2
• CN X (Vagus): Tested by evaluating swallowing, voice, and gag reflex 2
• CN XI (Spinal Accessory): Tested by assessing shoulder movement and strength 2
• CN XII (Hypoglossal): Tested by evaluating tongue movement and strength 2

Clinical Significance

Examination of the cranial nerves is an essential part of a complete neurological examination, as it can help diagnose specific lesions and conditions 2. Despite the development of modern imaging modalities, clinical examination techniques remain crucial for assessing cranial nerve function.