Cleft lip and palate and isolated cleft palate are the most common congenital anomalies of the face and skull, affecting approximately one in 700 newborns in the U.S. Of those children born with a cleft, a cleft of both the lip and palate affects about 50%, isolated cleft palate alone affects about 30% and a cleft of the lip alone affects about 20%.
Patients with clefts of the palate only (isolated cleft palate) have different inheritance patterns and characteristics from patients with cleft lip and palate or cleft lip alone. Therefore, isolated cleft palate will be discussed separately.
A basic understanding of the anatomy of the lip will help in understanding where clefts in the lip are found and how they vary from the normal anatomy.
A baby’s upper lip, nose and roof of the mouth (palate) have completed formation by only 10 weeks into the pregnancy. The philtrum is the normal feature found in the middle portion of the upper lip seen above. The lip forms from three parts – the center part and the left and right side parts.
The left and right parts of the lip grow toward the center as the face is formed early during the pregnancy. Normally the side portions meet and fuse with the center portion. The places where the center and side portions of the lip fuse become the philtral columns. These are the raised ridges extending the vertical length of the lip up to the nose. The Cupid’s bow is the normal shape of the lip where the red and white portions of the lip meet. The philtral columns meet the red portion of the lip at the peaks of Cupid’s bow, as illustrated in the figure above.
During formation of the lip, if one side doesn’t reach and connect with the center part of the lip, a unilateral cleft of the lip occurs.
In the image on the right side of the figure above, the baby has a left unilateral cleft lip. The philtral column and the peak of the Cupid’s bow are absent on the left side (the side of the cleft) because the cleft occurs through these structures. If both the left and right side fail to meet the center part of the lip a bilateral cleft lip forms.
In bilateral cleft lip, both the left and right philtral columns and the peaks of the Cupid’s bow are absent. In both unilateral and bilateral cleft lip, the majority of patients will have some involvement of the gums and palate.
Unilateral cleft lip makes up nine out of 10 of all patients with cleft lip. Unilateral cleft lip is twice as common on the left side as it is on the right. Bilateral cleft lip is present in only one out of 10 patients with cleft lip. There is a spectrum of severity of clefts of the lip.