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Summary:
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. Clin Pediatr. 2005;44:109-119
Introduction
Unilateral neonatal facial asymmetry, an age-old problem, is a generic heading for several clinical phenotypes. In 1929, Bonar and Owens published an extensive literature review of congenital facial paralysis and concluded, "one finds little clarity about the condition."1 A review of the literature since then indicates that despite some controversial issues and unanswered questions, there is a much clearer understanding today of the phenotype that is the focus of this report. Pape and Pickering named this phenotype "asymmetric crying facies" in 1972.2 Other names have been proposed, but we favor "neonatal asymmetric crying facies" (NACF) because it indicates that the condition is present at birth, and it allows for multiple etiologies. The clinical hallmark of NACF is a symmetric appearance of the oral aperture and lips at rest, but significant depression of one side of the lower lip with crying. A review of pertinent facial muscle and nerve anatomy and function is helpful.
Facial Muscle and Nerve Anatomy and Function
Downward movement of the lower lip with crying is produced by four sets of muscles (Figure 1). The depressor anguli oris muscle (DAOM) extends upward from the mandible to the corner of the mouth and inserts into the orbicularis oris muscle (OuM), which encircles the mouth. The DAOM pulls the corner of the mouth downward, slightly laterally and everts it. The depressor labii inferioris muscle (DLIM), which is slightly anterior to the DAOM, extends upward from the mandible to the lower lip and depresses it. The mcntalis muscle extends downward from the mandible at the level of the incisor teeth to the chin, and raises and protrudes the lower...