A 4-hour-old girl is examined in the newborn nursery. The patient was born vaginally after an uncomplicated pregnancy and delivery. She began breastfeeding after delivery. Physical examination shows a unilateral cleft lip on the left side with an intact palate. The rest of the physical examination is unremarkable. This patient's abnormal findings most likely resulted from which of the following intrauterine processes?
Show Explanatory Sources
The lip and palate form during early gestation through a series of structural changes and fusions involving 5 structures: frontonasal prominence, paired maxillary prominences, and paired mandibular prominences. Upper lip development involves the following steps:
The frontonasal prominence (overlies the forebrain) gives rise to the lateral and medial nasal prominences. The medial nasal prominences fuse and give rise to a midline structure, the intermaxillary segment.
The intermaxillary segment fuses with the left and right maxillary prominences beneath the nose to form the upper lip. Failed fusion on either side leads to a unilateral cleft lip, as seen in this patient; failed fusion of both sides creates a bilateral cleft lip.
Although cleft lip can occur in isolation, as in this child, the presence of a cleft lip increases the risk for cleft palate. For example, fusion of the intermaxillary segment and maxillary prominences also contributes to the development of the anterior portion of the hard palate (primary palate), and an anterior cleft palate may be an associated finding in some patients. A cleft palate can also develop from failed fusion of the palatine shelves, which are thin sheets of tissue derived from the maxillary prominences that grow medially, fuse, and form the posterior (secondary) palate (Choice C).
(Choice A) Failed fusion of the medial nasal prominences to form the intermaxillary segment is associated with severe midline defects, such as holoprosencephaly.
(Choice D) The orbits normally arise from the sides of the face and rotate medially. Hyperplasia of the frontonasal prominence can result in hypertelorism (wide-set eyes), in addition to a broad forehead and wide nasal bridge.
(Choice E) Hypoplasia of the mandibular prominence causes micrognathia. In Pierre Robin sequence, severe micrognathia results in posterior displacement of the tongue, which can prevent fusion of the palatine shelves due to mechanical obstruction, causing cleft palate. Mandibular hypoplasia does not contribute to cleft lip development.
Educational objective:
Cleft lip occurs due to failed fusion of the left or right maxillary prominence with the intermaxillary segment in early gestation. Cleft palate occurs primarily when the palatine shelves fail to fuse. Cleft lip and palate can occur together or in isolation.