Neonatal asymmetric crying facies: a new look at an old problem.

Neonatal asymmetric crying facies, described 75 years ago, is a clinical phenotype resembling unilateral partial peripheral facial nerve paralysis, with an incidence of approximately 1 per 160 live births. The cause is either facial nerve compression or faulty facial muscle and/or nerve development. Spontaneous resolution is expected with the former, but not necessarily with the latter etiology. Approximately 10% of the developmental cases have associated major malformations. Mandibular asymmetry and maxillary-mandibular asynclitism (non-parallelism of the gums) are frequently overlooked visual clues to nerve compression. Ultrasound imaging of facial muscles and electrodiagnostic testing may be useful for differential diagnosis and management.