The observation that one side of a baby’s face appears larger or different than the other can be unsettling for any parent. Facial asymmetry in infants is a common phenomenon where facial features are not perfectly mirrored on both sides. While this difference can sometimes indicate a medical condition, it is often a temporary developmental variation or a consequence of external forces. The degree of asymmetry varies widely, from subtle differences in cheek fullness to a noticeable shift in the jawline. Understanding the reasons behind this observation helps determine if an evaluation is needed, though many cases resolve without intervention.
Common and Benign Causes of Infant Facial Asymmetry
The most frequent reasons for a baby’s face to appear uneven are typically benign, stemming from external pressures or muscle preferences. Positional plagiocephaly, often called “flat head syndrome,” occurs when repeated pressure on one area of the soft skull causes flattening. This pressure results from a consistent sleeping position, where the infant favors resting their head in the same orientation. This distortion can make one side of the face seem fuller or cause the eye socket to appear slightly different.
Torticollis, or a tight neck muscle, frequently contributes to this positional preference. Congenital muscular torticollis involves a shortened sternocleidomastoid muscle, causing the head to tilt and the chin to rotate. This restricted range of motion encourages the baby to lie in a single position, leading to a misshapen skull and subsequent mild facial asymmetry. Torticollis, along with intrauterine positioning constraints, is a leading cause of craniofacial asymmetry at birth.
Normal developmental variation also accounts for minor differences, as perfect facial symmetry is uncommon in humans. Another specific benign cause is neonatal asymmetric crying facies (NACF), where the face is symmetrical at rest but shows asymmetry when the baby cries. This is usually due to the underdevelopment of the depressor anguli oris muscle, which pulls down the corner of the mouth only on the unaffected side. If related to birth trauma, NACF often improves spontaneously; otherwise, the asymmetry is permanent but harmless.
Underlying Medical Conditions Affecting Facial Symmetry
Less common causes of facial asymmetry relate to underlying medical conditions involving structural, nerve, or vascular development. Hemifacial microsomia (HFM) is a congenital condition where tissues on one side of the face are underdeveloped, affecting structures like the ear, jaw, and soft tissues. HFM is the second most common facial birth defect, causing the affected side of the face to appear smaller, often involving jaw undergrowth and nerves controlling facial movement.
Issues with the facial nerve (cranial nerve VII) can also cause asymmetry, resulting in weakness or paralysis on one side. Congenital facial nerve paralysis may occur due to birth trauma, such as a difficult delivery, or developmental issues. When the nerve is affected, the baby may have difficulty closing one eye, drooling, or inability to smile on the affected side. Acquired conditions like Bell’s palsy, often caused by a viral infection, can also lead to facial nerve paralysis later in infancy.
Craniosynostosis is a rare condition where one or more fibrous sutures between the skull bones prematurely fuse. When this happens unilaterally, the skull cannot expand perpendicular to the fused suture, leading to an abnormal head shape and facial asymmetry. This manifests as a flattening of the forehead, an elevation of the eye socket, and a rotation of the nose on the affected side.
Pediatric Evaluation and Diagnostic Steps
When facial asymmetry is noticed, the first step is a thorough physical examination by a clinician. The clinician observes the baby’s face at rest and during movement, such as crying, to determine if the asymmetry is static or dynamic. The assessment checks for differences in the height of the eyes or ears, jaw deviation, or visible skull flattening.
A detailed medical history is collected, focusing on the onset of asymmetry, the nature of the delivery, and any head-turning preference. For positional causes, the pediatrician assesses the baby’s neck range of motion to check for torticollis. If a complex condition like hemifacial microsomia or craniosynostosis is suspected, imaging studies are necessary.
Specific imaging, such as X-rays or a Computed Tomography (CT) scan, assesses the facial skeleton and skull sutures for premature fusion or underdevelopment. A Magnetic Resonance Imaging (MRI) scan may be ordered to evaluate intracranial pathology or soft tissues and nerves. Depending on the suspected cause, the child may be referred to specialists, including craniofacial surgeons, neurologists, or geneticists, for diagnosis and care.
Management and Treatment Options
Treatment for infant facial asymmetry ranges from simple positional changes to complex surgical intervention. For common positional asymmetry, management focuses on counteracting external pressure. This includes frequent repositioning during sleep and wake times, ensuring the baby spends time off the flattened area.
If asymmetry is linked to torticollis, physical therapy is the primary course of action, involving specific stretching and strengthening exercises for the neck muscles. Early intervention, ideally starting before three months of age, significantly improves outcomes for congenital muscular torticollis. For moderate or severe positional plagiocephaly affecting facial features, a cranial orthotic helmet may be prescribed to redirect skull growth.
Medically significant causes require more involved treatment and a specialized team. Craniosynostosis typically requires surgery to open the fused suture, allowing the brain space to grow and correcting the skull shape. Congenital defects like hemifacial microsomia may be managed through reconstructive surgical procedures, often timed for later childhood or adolescence. Facial nerve paralysis may require nerve grafting or muscle transfer if spontaneous recovery does not occur.