Cleft lip and clip palate is an "umbrella term" for a heterogeneous collection of orofacial clefts. It includes clefting of the upper lip, the maxillary alveolus (dental arch), and the hard or soft palate, in various combinations. The anatomic combinations include:
cleft lip [CL]
cleft lip and alveolus [CLA]
cleft lip, alveolus, and palate [CLAP]
cleft lip and palate (with an intact alveolus) [CLP]
cleft palate [CP]
Laterality
Embryologically, the upper lip may become clefted in the center (a median cleft lip) or on one or both sides (a paramedian cleft lip). The paramedian form is more common, and the median cleft lip is exceedingly rare. Most classification schemes consider only paramedian cleft lip to fall under the CL/P grouping, although this has been the subject of some controversy. (Many consider the median cleft lip to be better grouped under the Tessier classification for atypical orofacial clefts, with median cleft lip representing a Tessier 0 cleft.) The typical paramedian cleft lip may affect one side (unilateral) or both sides (bilateral). A unilateral cleft lip is much more common.
Clefting of the maxillary alveolus tends to accompany the cleft of the lip, and thus may affect the center (with a median cleft lip) or one or both sides (in unilateral or bilateral paramedian cleft lip, respectively).
Cleft palate does not have laterality in the same sense that the cleft lip does. Rather, there are certain morphologic forms of cleft palate (described succinctly by the Veau classification, as explained in detail below). An isolated cleft of the palate (whether Veau-I soft palate only or Veau-II hard and soft palate) is a "midline" cleft. A Veau-III cleft may be considered "unilateral," as it is contiguous with a unilateral cleft lip. A Veau-IV cleft may be considered "midline" or "bilateral" as it is contiguous with a bilateral cleft lip. Due to the confusion regarding laterality of the palate, usage of the terms "midline," "unilateral," and "bilateral" should be discouraged in favor of more accurate morphologic descriptions.
Severity of cleft lip
The clefting of the lip may be complete, incomplete, or lesser-form, with the lesser-form clefts being further subdivided into minor-form, microform, and mini-microform. A bilateral cleft lip may feature the same degree of clefting on each side (and thus be symmetric bilateral cleft lip) or may differ from side-to-side (asymmetric bilateral cleft lip). The severity of the cleft lip informs the choice for operative repair.
Morphology of cleft palate
The clefting of the palate is most usefully described by the Veau classification: Veau-I cleft palate: A midline cleft of the velum (soft palate), with the intact hard palate. Veau-II cleft palate: A midline cleft of the velum (soft palate) and secondary hard palate (posterior to the incisive foramen), with intact primary palate (anterior to the incisive foramen) Veau-III cleft palate: A cleft of the velum (soft palate), extending unilaterally through the secondary hard palate, past the incisive foramen, and through the primary hard palate and alveolus. The vomer (the bony part of the nasal septum) remains attached to the palatal shelf on the greater segment (non-cleft side). Veau-IV cleft palate: A cleft of the velum (soft palate), extending in the midline through the secondary hard palate up to the incisive foramen and then bilaterally through the primary hard palate and alveolus on each side. The vomer (the bony part of the nasal septum) remains in the midline and is attached to the premaxilla.
In addition to these four types, there exists a submucous cleft palate. In the submucous cleft palate, the palate appears grossly intact, without an obvious cleft. However, deep to the intact mucosa, there may be a separation of the levator palatini muscles, and thus palatal function is affected. Subtle signs of submucous cleft palate may include the zona pellucida (a pale coloring of the midline of the palate, indicative of a submucous bony defect), notching of the hard palate at its posterior edge, and bifid uvula. Some clinicians make the distinction between overt submucous cleft palate (in which these signs are present) and occult submucous cleft palate, in which case they may not be appreciable, but the levator musculature is in fact clefted.