Infant With an Asymmetrical Smile

A 4-month-old female infant presented for a well-child visit. Her parents were concerned about the left side of her face. Since birth, she had an asymmetrical smile, and her left eye could not be closed and had excessive tear production. She was otherwise healthy and met all developmental milestones.

The infant was born at 38 weeks of gestation by uncomplicated spontaneous vaginal delivery to a multiparous mother. Labor was induced due to the mother's chronic hypertension and uncontrolled type 2 diabetes that required insulin. With oxytocin augmentation, labor lasted 13 hours, with less than 1 hour of pushing. During birth, the infant aspirated meconium, which required deep suctioning and positive pressure ventilation for 8 minutes. Apgar scores were 6, 7, and 9 (at 1, 5, and 10 minutes, respectively), and birth weight was 3,530 g (76th percentile). Initially, she had difficulty feeding but had been eating well and gaining weight appropriately for the past few months.

On examination, the infant had a flat left nasolabial fold, did not fully close the left eye when closing the right eye, and had asymmetrical forehead wrinkling (Figure 1). Her extraocular movements were intact, and her pupils were equal and reactive to light. Magnetic resonance imaging of the brain showed no abnormality.

Based on the patient's history and physical examination, which one of the following is the most likely diagnosis?

• A. Congenital facial nerve palsy.
• B. Dacryostenosis.
• C. Neonatal stroke.
• D. Oculomotor nerve palsy.

The answer is A: congenital facial nerve palsy. This palsy occurs in approximately 2 out of 1,000 live births in the United States and is typically recognized at birth or shortly thereafter. It presents as lack of motion on one or both sides of the face leading to asymmetrical smiling, inability to fully close the eye on the affected side, and difficulty raising the eyebrow. Feeding difficulties often occur during the neonatal period.^1,2

The most common etiology of congenital facial nerve palsy is perinatal trauma from pressure on the infant's face during labor and delivery. Other causes include congenital anomalies and genetic abnormalities. Some cases are idiopathic. Risk factors associated with a traumatic palsy include primiparity, birth weight greater than 3,500 g, use of forceps, cesarean delivery, and prematurity.

Most cases spontaneously resolve within the first 2 months of life, but severe or persistent cases can be treated with physical therapy and surgical interventions, such as lid loading surgery and microneurovascular muscle transfer.^1–3 When the condition persists for more than 2 months, clinicians should consider other rare but serious causes such as hypoplasia of brainstem motor nuclei, genetic malformations, and Arnold-Chiari syndrome.

Dacryostenosis results from nasolacrimal duct obstruction and can be congenital or acquired. It presents as persistent tear production and yellow crusting of the lid margin. Most cases resolve with conservative management by 6 to 10 months of age; otherwise, surgical intervention may be required. Dacryostenosis does not impair facial movement.⁴

Neonatal strokes occur between birth and 28 days of life, with an incidence of 9.6 per 100,000 live births per year in the United States. They can present with seizures, apnea, focal weakness, and hemiparesis. Imaging reveals arterial territory infarction, hemorrhage, or periventricular venous infarction. The infant in this case had negative findings on magnetic resonance imaging and both upper and lower left facial palsy, which is consistent with lower motor neuron impairment.^5,6