What is the approach to a patient presenting for a cranial nerve examination?

Cranial Nerve Examination: Systematic Clinical Approach

Perform a systematic examination of all 12 cranial nerves in sequence (CN I-XII), testing specific functions for each nerve, with particular attention to identifying patterns of multiple nerve involvement that localize lesions to specific anatomic regions. 1

Anatomic Framework for Examination

The 12 cranial nerves emerge from the brainstem and provide specialized sensory and motor innervation to the head and neck region, following long circuitous routes that make them vulnerable to pathology at multiple anatomic points. 1 Due to close proximity of cranial nerve nuclei, segments, and exit sites, single lesions frequently cause multiple cranial neuropathies, making pattern recognition essential. 1

Individual nerve fibers, particularly autonomic fibers, may travel with multiple cranial nerves from their nuclei to final destinations, meaning loss of specific function can indicate involvement of more than one cranial nerve. 1

Systematic Examination by Nerve

CN I (Olfactory)

• Test each nostril separately for ability to identify common odors 2

CN II (Optic)

• Assess visual acuity, visual fields, pupillary light reflexes, and fundoscopic examination 2

CN III, IV, VI (Oculomotor, Trochlear, Abducens)

• Examine extraocular movements in all directions of gaze 2
• Assess pupillary size, symmetry, and reactivity 2
• Check for ptosis 2

CN V (Trigeminal)

• Test facial sensation in all three divisions (ophthalmic, maxillary, mandibular) 3
• Assess masticatory muscle strength by palpating temporalis and masseter during jaw clenching 2
• Evaluate corneal reflex 2
• Clinical presentation includes facial pain, sensory loss in trigeminal distribution, or masticatory muscle weakness 1

CN VII (Facial)

• Test facial expression muscles by having patient raise eyebrows, close eyes tightly, smile, and puff cheeks 2
• Assess taste on anterior two-thirds of tongue if indicated 1
• Distinguish upper motor neuron (forehead spared) from lower motor neuron (complete facial weakness) patterns 4

CN VIII (Vestibulocochlear)

• Test hearing acuity with finger rub or whisper test 2
• Perform Weber and Rinne tests if hearing loss detected 2
• Assess for nystagmus and balance 2

CN IX (Glossopharyngeal)

• Evaluate palatal elevation symmetry by having patient say "ah" - the uvula deviates away from the affected side 5
• Test gag reflex (sensory component) 2
• Assess for oropharyngeal pain 3
• Clinical presentation includes palate weakness and oropharyngeal pain 3

CN X (Vagus)

• Assess palatal elevation (motor component of gag reflex) 2
• Evaluate voice quality for hoarseness suggesting vocal cord paralysis 3
• The uvula deviates toward the unaffected side when the vagus nerve is damaged due to unopposed muscle contraction 5
• Vocal cord paralysis requires imaging from skull base to mid-chest due to the long course of CN X 3, 5

CN XI (Accessory)

• Test sternocleidomastoid strength by having patient turn head against resistance 2
• Assess trapezius strength by having patient shrug shoulders against resistance 2
• Clinical presentation includes weakness or paralysis of sternocleidomastoid and trapezius muscles 3

CN XII (Hypoglossal)

• Observe tongue at rest for atrophy or fasciculations 2
• Have patient protrude tongue - it deviates toward the affected side 1, 5
• Test tongue strength by having patient push tongue against cheek 2

Recognition of Named Cranial Nerve Syndromes

Multiple cranial nerve involvement suggests specific anatomic localization patterns that guide diagnosis: 1

• Gradenigo syndrome: CN V and VI involvement at the petrous apex 1
• Vernet syndrome: CN IX, X, and XI involvement at the jugular foramen 1
• Collet-Sicard syndrome: CN IX, X, XI, and XII involvement from lesions just below the skull base or large lesions affecting both jugular foramen and hypoglossal canal 1

Critical Clinical Pitfalls

Autonomic nerve fibers traveling with multiple cranial nerves mean single functional deficits may reflect multiple nerve involvement, requiring comprehensive examination of all potentially affected nerves. 1

Perineural tumor spread can evade detection even with careful examination; maintain high suspicion with subtle findings like asymmetric facial musculature, particularly with CN V and CN VII. 3, 1

Incomplete evaluation of CN X that does not extend to mid-chest imaging misses recurrent laryngeal nerve pathology. 1

When to Pursue Advanced Imaging

Contrast-enhanced MRI at 3.0T is the gold standard for evaluating any identified cranial neuropathy, preferred over 1.5T due to superior signal-to-noise ratios and spatial resolution. 1, 5

Intravenous contrast is imperative for comprehensive evaluation of cranial neuropathy. 1, 5

Complete evaluation must include imaging of the entire nerve course from brainstem nuclei to end organs. 1, 5

Specific imaging recommendations by nerve presentation:

• CN V involvement: MRI head and orbit/face/neck with and without IV contrast (rating 8/9) 3
• CN VII involvement: MRI head and orbit/face/neck with and without IV contrast (rating 8/9) 3
• CN IX involvement: MRI head and orbit/face/neck with and without IV contrast (rating 8/9) 3
• CN X involvement (vocal cord paralysis): MRI orbit/face/neck with and without IV contrast (rating 8/9) OR CT neck with IV contrast (rating 8/9) 3
• CN XI involvement: MRI head and orbit/face/neck with and without IV contrast (rating 8/9) 3
• CN XII involvement: MRI head and orbit/face/neck with and without IV contrast (rating 8/9) 3

Examination Efficiency

Cranial nerve testing can be performed quickly and efficiently without complicated or potentially unavailable equipment, making it feasible for routine musculoskeletal and neurological practice. 4