In a 4‑year‑old child, magnetic resonance imaging shows mild contrast enhancement of the labyrinthine segment of the right facial nerve and a cystic‑appearing lesion projecting anteriorly from the left parotid gland, with no facial weakness, ear symptoms, or palpable neck mass; what is the most likely diagnosis and appropriate management?

Mild Labyrinthine Facial Nerve Enhancement and Parotid Cystic Lesion in a 4-Year-Old

Most Likely Diagnosis

In an asymptomatic 4-year-old child, mild enhancement of the labyrinthine segment of the right facial nerve is most likely a normal variant rather than pathology, while the cystic lesion in the left parotid gland likely represents a benign congenital or developmental lesion such as a first branchial cleft cyst or lymphatic malformation. 1, 2

Facial Nerve Enhancement: Normal vs. Pathological

Understanding Normal Enhancement Patterns

• Mild enhancement of the labyrinthine segment can be a normal finding on high-resolution MRI sequences, particularly on 3T scanners where 84% of normal facial nerves show labyrinthine enhancement and 60% show canalicular enhancement. 1

• The facial nerve has a rich arteriovenous plexus that causes physiologic enhancement, with normal enhancement commonly seen in the geniculate ganglion (96.9-100%), tympanic segment (88.4-98%), and mastoid segment (66.6-100%). 3, 1, 4

• Enhancement intensity is key: Mild to moderate enhancement in the labyrinthine segment is typically normal, while intense (+3) enhancement in this location suggests pathology. 4

Criteria for Pathological Enhancement

Three specific criteria indicate pathological facial nerve enhancement rather than normal variant 4:

• Enhancement extending outside the facial canal (into cerebellopontine angle or parotid)
• Enhancement extending to the eighth cranial nerve
• Intense enhancement specifically in the labyrinthine and/or mastoid segments

Clinical Context is Critical

The absence of facial weakness, ear symptoms, or other cranial neuropathies strongly favors this being a normal variant rather than pathology. 2, 5, 6

• Bell's palsy and other facial nerve pathologies present with rapid onset (<72 hours) of ipsilateral facial weakness involving the forehead. 6

• Facial nerve tumors in children (69.2% present with facial palsy) would typically cause progressive symptoms. 7

• Enhancement intensity does not correlate with clinical severity or prognosis in facial nerve pathology, so the presence of mild enhancement without symptoms is reassuring. 8

Parotid Cystic Lesion Evaluation

Differential Diagnosis

The cystic anterior projection from the left parotid in a 4-year-old child most likely represents 2:

• First branchial cleft cyst (most common congenital cystic parotid lesion in children)
• Lymphatic malformation (low-flow vascular malformation)
• Ranula extending from sublingual space
• Less likely: cystic parotid neoplasm (rare in children, typically solid)

Imaging Characteristics

• Ultrasound is the initial imaging modality of choice for pediatric neck masses, effectively differentiating solid from cystic lesions and characterizing vascular flow with color Doppler. 2

• MRI provides superior soft tissue characterization and is appropriate when already obtained, showing cystic lesions as T2-hyperintense with thin walls. 2

Recommended Management Algorithm

Immediate Steps

1. Perform complete cranial nerve examination focusing on:

   • Forehead wrinkling (raise eyebrows)
   • Eye closure completeness (assess for lagophthalmos)
   • Smile symmetry
   • Cheek puffing
   • All other cranial nerves (V, VI, VIII, IX, X, XI, XII) 5, 6

2. Assess for any facial asymmetry at rest or with movement that parents may not have noticed. 5

3. Examine the parotid region for palpable mass, overlying skin changes, or tenderness. 2

If Examination is Completely Normal

• Reassurance is appropriate given that mild labyrinthine enhancement is a normal variant in up to 84% of children on high-resolution MRI. 1

• Clinical follow-up in 3-6 months to reassess for any development of facial weakness or parotid mass. 5, 6

• No immediate intervention required for the parotid cystic lesion if asymptomatic and examination is normal. 2

Red Flags Requiring Urgent Referral

Refer immediately to pediatric otolaryngology if any of the following develop 2, 5, 6:

• Any degree of facial weakness (even subtle asymmetry)
• Progressive symptoms (worsening over days to weeks)
• Other cranial nerve involvement (hearing loss, dysphagia, tongue deviation)
• Palpable or enlarging parotid mass
• Recurrent facial symptoms

If Facial Weakness is Present

• Urgent temporal bone CT to evaluate for structural abnormalities, fractures, or bone erosion. 2, 5

• Electrodiagnostic testing (ENoG/EMG) at 3-14 days if complete paralysis, with >90% amplitude reduction indicating severe injury requiring surgical consultation. 5

• Immediate eye protection measures: lubricating drops, ointment, taping, sunglasses to prevent corneal damage. 5, 6

Common Pitfalls to Avoid

• Do not assume enhancement equals pathology: Normal facial nerve enhancement is common on modern high-resolution MRI, particularly at 3T. 1, 4

• Do not ignore asymmetry: While 69% of normal patients show right-left asymmetry in enhancement, clinical correlation is essential. 4

• Do not overlook other cranial nerves: Multiple cranial nerve involvement excludes Bell's palsy and indicates serious skull base pathology. 2, 6

• Do not delay eye protection: If any facial weakness develops, corneal protection must be implemented immediately to prevent permanent damage. 5, 6

• Do not assume all parotid cysts are benign: While most are in children, clinical follow-up ensures no growth or development of concerning features. 2