What is the differential diagnosis and further workup needed for a 4-year-old female with progressive facial asymmetry, mostly apparent with facial expression, and normal imaging studies, including noncontrast head computed tomography (CT), noncontrast brain magnetic resonance imaging (MRI), and contrast MRI of the brain, brainstem, face, and orbits, who has cystic anterior extension of the left parotid and mild unilateral labyrinthine enhancement of the right facial nerve, with physical exam findings of left facial weakness and abnormal facial expression?

Progressive Facial Asymmetry in a 4-Year-Old: Differential Diagnosis and Workup

This child requires immediate pediatric neurology and neurotology consultation for evaluation of a facial nerve schwannoma or inflammatory neuritis, given the unilateral labyrinthine enhancement of the right facial nerve on contrast MRI. 1, 2

Critical Interpretation of Imaging Findings

The unilateral labyrinthine enhancement of the right facial nerve is pathological and demands urgent specialist assessment, as this is a common location for facial nerve schwannomas presenting with progressive facial weakness. 1 The labyrinthine segment enhancement, combined with progressive facial asymmetry over one year, strongly suggests either:

• Facial nerve schwannoma (most concerning given location and progressive course) 1
• Inflammatory facial neuritis (less likely given chronicity) 1
• Neurofibromatosis type 2-related tumor (must be excluded) 1

The cystic anterior extension of the left parotid is likely incidental, but the discordance between right-sided nerve enhancement and left-sided facial weakness requires careful clinical correlation—this may represent bilateral pathology or compensatory posturing. 2

Primary Differential Diagnoses

Most Likely Diagnoses (Based on Imaging)

1. Facial Nerve Schwannoma

• The labyrinthine segment enhancement is highly suggestive of this diagnosis 1
• Progressive facial asymmetry over one year fits the natural history 1
• Requires contrast-enhanced MRI for detection, which was appropriately obtained 1
• Treatment options include observation with serial imaging, stereotactic radiosurgery (0.1% risk of persistent deficit), or microsurgical resection (10% risk of persistent deficit) 1

2. Inflammatory Facial Neuritis

• Can cause asymmetric enhancement but typically more acute presentation 1
• Less likely given the one-year progressive course 2

3. Atypical Bell's Palsy

• Contrast imaging was appropriate to exclude other causes 1
• Progressive course over one year makes this less likely 3

Must-Exclude Diagnoses

4. Intracranial Mass/Tumor

• New progressive facial asymmetry may be the first sign of intracranial pathology requiring urgent attention 1, 2
• Contrast MRI was essential and appropriately obtained, as non-contrast studies miss isodense tumors and subtle masses 1

5. Meningeal Infiltration or Perineural Tumor Spread

• Facial nerve is one of the two most commonly involved nerves in perineural spread 1
• Requires contrast enhancement for detection 1

6. Strabismus with Compensatory Head Posture

• Can mimic structural facial asymmetry 2, 3
• Requires comprehensive ophthalmological assessment to exclude 2

Structural/Developmental Causes (Lower Priority Given Imaging)

7. Hemifacial Microsomia

• Progressive with growth, showing increasing asymmetry over time 2, 4
• However, imaging would typically show mandibular hypoplasia, which was not reported 4

8. Localized Scleroderma

• Can cause facial asymmetry with skin atrophy and muscle spasm 5
• Less likely given imaging findings 5

Immediate Required Workup

Urgent Specialty Referrals (Within 1-2 Weeks)

Pediatric Neurotology/Neurosurgery Consultation

• Immediate referral for confirmed pathological enhancement of the facial nerve 2
• Surgical planning for potential biopsy or resection if neoplastic features present 2
• Discussion of observation versus intervention based on facial nerve function 1

Pediatric Neurology Consultation

• Evaluation for intracranial or neurological causes 2, 3
• Assessment for neurofibromatosis type 2 or other syndromic associations 1

Pediatric Ophthalmology Consultation

• Visual acuity testing, binocular alignment assessment, and extraocular muscle function evaluation 2, 3
• Fundoscopic examination to rule out papilledema or other ophthalmological conditions 2
• Evaluation for compensatory head posture from strabismus 2, 3

Additional Clinical Assessments

Complete Facial Nerve Assessment

• Document House-Brackmann scale grade to establish baseline severity 1, 2
• Assess forehead movement, eye closure completeness, and mouth symmetry at rest and with movement 1
• Check for synkinesis, contracture, or hemifacial spasm 1

Comprehensive Cranial Nerve Examination

• Complete assessment beyond just facial nerve 2
• Motor and sensory function testing throughout 2
• Cerebellar function evaluation 2

Detailed Facial Asymmetry Documentation

• Evaluate midline vertical alignment through glabella, nasal dorsum, philtrum, and menton 2
• Check for left-right differences in facial width, orbital level, and alar base position 2
• Assess for cheek flattening or slanting of midface, which suggests more extensive pathology 2

Laboratory and Electrodiagnostic Testing

Consider Electrodiagnostic Testing

• Electroneuronography (ENoG) and electromyography (EMG) may be considered if complete paralysis develops 2
• Typically reserved for acute scenarios but may help characterize nerve function 2

Genetic Testing

• Consider NF2 gene testing if facial nerve schwannoma confirmed, especially if bilateral involvement or family history 1

Imaging Follow-Up Protocol

Serial MRI Monitoring

• For small facial nerve schwannomas with preserved function: MRI every 6-12 months is reasonable initial approach 1
• High-resolution MRI protocols with thin-cut (3mm) axial and coronal sections with gadolinium enhancement 2
• Repeat imaging necessary if symptoms progress or change 1, 2

Clinical Monitoring Schedule

• Repeat clinical assessment every 4-6 weeks until specialist evaluation complete 1
• Close monitoring essential as conditions may show increasing asymmetry with growth 2, 3

Critical Pitfalls to Avoid

Do Not Assume Benign Structural Asymmetry

• New-onset progressive hemifacial asymmetry should be considered potentially serious requiring prompt evaluation 2
• Even asymmetry only present with smiling requires full workup 1

Do Not Delay Evaluation

• Facial asymmetry may be the first sign of intracranial process requiring urgent attention 1, 2
• The one-year progressive course makes urgent evaluation even more critical 2

Distinguish True Anatomical from Functional Asymmetry

• Strabismus with compensatory head posture can mimic structural facial asymmetry 2, 3
• This is why ophthalmology evaluation is mandatory 2, 3

Do Not Rely on Non-Contrast Imaging Alone

• Tumors affecting facial nerve, meningeal infiltration, and vascular malformations require contrast for detection 1
• Non-contrast studies miss critical pathologies 1

Family Education Points

Red Flag Symptoms Requiring Urgent Reevaluation

• Clinical changes including regression of motor skills 2
• Loss of strength or new neurological symptoms 2
• Any concerns with respiration or swallowing 2
• Rapid progression of asymmetry 2

Expected Timeline

• Specialist evaluation should occur within 1-2 weeks given imaging findings 1, 2
• Treatment decisions depend on size, location, and functional status of any identified lesion 1
• For observation approach: serial imaging every 6-12 months 1