How do you test the 7th (seventh) cranial nerve, also known as the facial nerve?

Clinical Examination of the Facial Nerve (CN VII)

Test the 7th cranial nerve by asking the patient to perform specific facial movements that assess the motor function of facial expression muscles, including raising eyebrows, closing eyes tightly, showing teeth, and puffing out cheeks, while observing for asymmetry or weakness.

Motor Function Assessment

The facial nerve controls all muscles of facial expression, and testing should systematically evaluate different facial regions 1:

• Forehead/Frontalis muscle: Ask the patient to raise both eyebrows and look for symmetry of forehead wrinkling 2
• Orbicularis oculi: Instruct the patient to close their eyes tightly while you attempt to gently open them, assessing for weakness 3
• Mid-face muscles: Have the patient show their teeth or smile broadly, observing for asymmetry of the nasolabial folds 2
• Lower face/Orbicularis oris: Ask the patient to puff out their cheeks and hold air against resistance, checking for air escape 4
• Platysma: Request the patient to grimace or pull down the corners of their mouth 2

Distinguishing Central vs. Peripheral Lesions

A critical distinction must be made based on the pattern of weakness 3:

• Peripheral (lower motor neuron) lesions: Affect both upper and lower face on the same side, causing complete hemifacial weakness including inability to wrinkle forehead 3, 4
• Central (upper motor neuron) lesions: Spare the forehead due to bilateral cortical innervation of the upper facial muscles, affecting only the lower face 3

Additional Sensory and Autonomic Testing

Beyond motor function, the facial nerve has sensory and parasympathetic components that can be assessed 2:

• Taste sensation: Test the anterior two-thirds of the tongue for sweet, salty, sour, and bitter tastes (nervus intermedius component) 5, 2
• Hyperacusis: Ask about increased sensitivity to sounds, which indicates stapedius muscle dysfunction 3
• Lacrimation: Observe for decreased tearing on the affected side 3

Common Clinical Presentations

The most common cause of facial nerve dysfunction is Bell's palsy (idiopathic facial paralysis), accounting for 70% of cases 3:

• Unilateral facial weakness affecting both upper and lower face 3
• May be accompanied by hyperacusis, altered taste, and disordered lacrimation 3
• Ramsay Hunt syndrome (herpes zoster oticus with facial neuropathy) is another important cause to consider 3

When Imaging is Indicated

Most Bell's palsy cases do not require imaging, but specific circumstances warrant investigation 1:

• MRI with contrast is the imaging modality of choice when symptoms are atypical or persist beyond 2 months 1
• Imaging should be considered for suspected structural lesions including schwannomas, meningiomas, cholesteatomas, paragangliomas, or parotid tumors 1
• CT is useful for trauma cases to evaluate temporal bone fractures and bony facial canal involvement 1, 6

Critical Pitfalls to Avoid

• Do not confuse facial nerve palsy with hypoglossal nerve dysfunction—the latter causes tongue deviation, not facial weakness 7
• Delayed presentation of traumatic facial nerve paralysis can occur days after head injury, so maintain high suspicion in trauma patients 6
• Enhancement of the geniculate, tympanic, and mastoid portions of the facial nerve may be normal and should not automatically be interpreted as pathologic 1