What could be the cause of progressive facial asymmetry in a 4-year-old girl with mild enhancement of the right facial nerve at the labyrinthine segment and cystic anterior extension of the left parotid gland on MRI with contrast?

Progressive Facial Asymmetry with Facial Nerve Enhancement and Parotid Cyst

This child requires urgent referral to pediatric otolaryngology or neurotology for comprehensive evaluation and likely surgical consultation, as the combination of progressive facial weakness with labyrinthine segment enhancement suggests a compressive or infiltrative facial nerve lesion that may require intervention. 1

Most Likely Diagnoses Based on MRI Findings

The mild enhancement of the right facial nerve at the labyrinthine segment combined with progressive facial asymmetry points to several critical possibilities:

Primary Considerations for Right Facial Nerve Enhancement

Facial nerve schwannoma is the leading concern given the progressive nature over one year and enhancement at the labyrinthine segment. 1 This tumor typically causes gradual facial weakness and shows enhancement on contrast MRI. 2

Inflammatory or infectious neuritis can cause facial nerve enhancement, though the one-year progressive course makes this less likely than a structural lesion. 1

Perineural tumor spread must be excluded, particularly given the parotid finding on the contralateral side, though the cystic nature makes primary parotid malignancy less likely. 2

The Left Parotid Cystic Lesion

The cystic anterior extension of the left parotid is likely unrelated to the right-sided facial weakness but requires separate evaluation. This could represent a benign cystic lesion, lymphatic malformation, or first branchial cleft cyst. 3

Critical Next Steps in Workup

Immediate Clinical Assessment Required

Complete cranial nerve examination must document function of all cranial nerves (V, VI, VII, VIII, IX, X, XI, XII) to exclude skull base pathology or multiple nerve involvement. 4, 1 Specifically assess:

• Forehead involvement: Ask the child to raise eyebrows and wrinkle forehead. Forehead weakness confirms peripheral (facial nerve) pathology rather than central cause. 4, 1
• Eye closure completeness: Evaluate for lagophthalmos (incomplete eye closure), which requires immediate eye protection. 4, 1
• Smile symmetry and mouth movement: Document the degree of lower facial weakness. 4
• Taste sensation: Test the anterior two-thirds of the tongue on both sides. 4
• Hyperacusis: Ask about increased sensitivity to sound. 4

Essential Imaging Studies

High-resolution temporal bone CT is now indicated to evaluate for structural abnormalities, osseous erosion, foraminal expansion, or fracture patterns that may not be visible on MRI. 1 This complements the MRI findings and helps surgical planning. 2

The existing MRI with contrast showing labyrinthine enhancement is concerning and warrants action, not dismissal. 1

Electrodiagnostic Testing

Electroneurography (ENoG) and electromyography (EMG) should be performed if complete or near-complete facial paralysis is present. 1 Testing at 3-14 days after onset of complete paralysis can predict prognosis, with >90% amplitude reduction on ENoG indicating severe nerve injury requiring surgical consultation. 1

Urgent Eye Protection Measures

Implement corneal protection immediately if any lagophthalmos is present to prevent permanent corneal damage: 4, 1

• Lubricating ophthalmic drops during the day
• Ophthalmic ointment at night
• Eye taping or patching during sleep
• Sunglasses for outdoor protection

Why the Provider's Dismissiveness is Problematic

Progressive facial weakness with imaging abnormalities in a child is never normal and demands investigation. 1 The one-year progression from expression-only asymmetry to visible asymmetry with minor movements indicates worsening nerve function. 4

The enhancement at the labyrinthine segment is an objective finding that suggests active pathology—inflammation, compression, or tumor. 2, 1 This is not a normal variant and cannot be dismissed without further workup.

Specific Referral and Management Algorithm

1. Urgent pediatric otolaryngology or neurotology referral (within 1-2 weeks, not months) for evaluation of the facial nerve enhancement. 1

2. High-resolution temporal bone CT to complement the MRI findings and evaluate for structural causes. 1

3. Consider electrodiagnostic testing if facial weakness is severe or complete. 1

4. Separate evaluation of the left parotid cystic lesion by pediatric otolaryngology, though this is likely unrelated to the right facial weakness. 3

5. Surgical decompression may be indicated if severe nerve compression is identified and ENoG shows >90% reduction. 1

Common Pitfalls to Avoid

Do not assume this is Bell's palsy. Bell's palsy has rapid onset (<72 hours), not progressive worsening over one year. 4 Bell's palsy is also a diagnosis of exclusion that should not be made when imaging shows abnormalities. 4

Do not ignore unilateral facial nerve enhancement in a child. This finding demands explanation, particularly with progressive clinical symptoms. 2, 1

Do not delay referral. Progressive facial nerve dysfunction in a child with imaging abnormalities requires specialist evaluation to prevent permanent nerve damage. 1