Asymmetrical Crying Face (ACF), also known as Congenital Unilateral Lower Lip Palsy (CULLP), is a condition where parents observe noticeable drooping or lack of movement on one side of the baby’s lower lip when the child cries. The face appears entirely symmetrical and normal when the baby is resting, which distinguishes ACF from other types of facial paralysis. ACF is a minor congenital anomaly, and understanding its cause and progression can provide reassurance.
Identifying Asymmetrical Crying Face
The diagnosis of ACF is visual, confirmed by observing the infant’s face during intense movement, such as crying or grimacing. The key structure involved is the Depressor Anguli Oris (DAO) muscle, which pulls the corner of the mouth downward. When the DAO muscle on one side is weak or undeveloped, the functional DAO on the opposite side pulls the mouth strongly toward the normal side, creating the lopsided appearance.
ACF is limited to the lower lip, distinguishing it from more extensive facial nerve injuries. The infant can still close both eyes completely, wrinkle their forehead symmetrically, and maintain normal nasolabial folds. This condition is relatively uncommon, occurring in an estimated one out of every 160 live births.
Understanding the Root Causes
The underlying reason for ACF falls into two categories: congenital muscular hypoplasia and neurological issues. Muscular hypoplasia is the most frequent cause, involving the incomplete development of the Depressor Anguli Oris muscle. This is an isolated finding, meaning the muscle itself is structurally deficient.
The second category involves neurological issues, specifically injury to the marginal mandibular branch of the facial nerve (Cranial Nerve VII). This nerve branch supplies the lower lip muscles and can be compressed during the birthing process, often due to pressure or the use of delivery instruments. This results in acquired ACF, a temporary paralysis due to birth trauma.
Differentiating between these two causes is important because the prognosis and medical workup differ. ACF caused by muscular hypoplasia is a structural anomaly, while ACF caused by nerve compression is a temporary paralysis.
Typical Resolution and Long-Term Outlook
ACF often goes away, particularly for cases linked to birth trauma. ACF resulting from temporary nerve compression has an excellent prognosis and spontaneously resolves in the vast majority of cases, often within the first few weeks or months of life as the nerve recovers.
For cases due to congenital muscular hypoplasia, the asymmetry is permanent, but the cosmetic effect becomes less noticeable with age. This improvement is attributed to the infant crying less frequently and the development of compensating facial muscles. It does not affect feeding, speech, or overall development.
If the asymmetry persists into childhood and remains a cosmetic concern, surgical options are available. Procedures can involve weakening the corresponding muscle on the unaffected side or transferring a small muscle from under the chin to the affected side. For most isolated cases, the facial difference is minor and becomes less prominent over time, requiring no intervention.
Associated Conditions Requiring Medical Screening
While most instances of ACF are isolated and benign, the condition can rarely indicate a larger, systemic congenital syndrome. When ACF is caused by muscular hypoplasia, there is a risk of associated major congenital anomalies, most frequently involving the cardiovascular system. Comprehensive medical screening is recommended following an ACF diagnosis.
The association of ACF with congenital heart defects is known as cardiofacial syndrome (Cayler syndrome), frequently linked to a genetic deletion on chromosome 22q11. If a baby presents with ACF alongside other findings, such as heart defects, genitourinary issues, or a visibly deformed ear, immediate consultation with a pediatrician and specialist evaluation is mandatory. If ACF is determined to be the sole finding after a thorough physical examination, the risk of a major associated anomaly is low.