Assessing Facial Nerve Integrity: Puff Out Both Cheeks
The correct maneuver to assess facial nerve (cranial nerve VII) integrity is to have the patient puff out both cheeks. This tests the buccinator muscle and other muscles of facial expression, which are innervated by the facial nerve 1.
Why This Is the Correct Answer
The facial nerve (CN VII) provides motor innervation to all muscles of facial expression 1, 2. When testing this nerve, you need to evaluate its ability to control these muscles bilaterally. Having the patient puff out their cheeks tests:
- Buccinator muscle function (primary muscle tested)
- Orbicularis oris (lip seal maintenance)
- Overall facial muscle symmetry and strength
This maneuver is particularly useful because weakness or paralysis will cause air to leak from the affected side, making asymmetry immediately apparent 3.
Why the Other Options Are Incorrect
Clenching teeth: Tests the trigeminal nerve (CN V), specifically the motor branch innervating the masseter and temporalis muscles 1
Extruding the tongue: Tests the hypoglossal nerve (CN XII), which provides motor innervation to intrinsic and extrinsic tongue muscles 1
Producing a big yawn: This is a complex movement involving multiple cranial nerves and is not a standardized test for any single cranial nerve
Clinical Context: Hypertension and Facial Nerve Assessment
In your hypertensive patient on hydrochlorothiazide, facial nerve assessment remains the same regardless of their cardiovascular status. However, be aware that:
- Thiazide diuretics like hydrochlorothiazide can cause electrolyte imbalances (hypokalemia, hyponatremia) 4, 5, though these do not directly affect facial nerve function
- If facial weakness is present, consider secondary causes beyond Bell's palsy, including stroke (particularly brainstem lesions affecting CN VII nuclei in the pons) 6, 1
Additional Facial Nerve Testing
Beyond puffing cheeks, comprehensive CN VII examination should include:
- Raising eyebrows (tests frontalis muscle - note: instruct "raise your eyebrows" NOT "wrinkle your forehead" as 54.9% of patients incorrectly frown when given the latter instruction) 3
- Closing eyes tightly (tests orbicularis oculi)
- Showing teeth/smiling (tests lower facial muscles)
- Puffing out cheeks (tests buccinator and lip seal)
Critical Distinction: Upper vs. Lower Motor Neuron Lesions
When facial weakness is detected:
- Peripheral CN VII lesion (Bell's palsy): Affects BOTH upper and lower face on the same side 2, 7
- Central lesion (stroke): Spares forehead/eyebrow elevation due to bilateral cortical innervation of upper facial muscles, but affects lower face 1
This distinction is crucial in the hypertensive patient, as it helps differentiate between benign Bell's palsy (which may not require imaging unless atypical) 6, 2 and stroke (which requires immediate intervention).