**2. Normal anatomy**

*"All cleft surgery is merely applied embryology."*

—Victor Veau [1]

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

The pathologic origins of a cleft lip are traceable to distinct embryological events. The fusion failure during gestational weeks 4–7 of facial primordia: the central frontonasal prominence and two lateral maxillary prominences result in a typical cleft lip of a newborn. Advances in developmental science have promoted our knowledge and understanding of this phenom‐ enon, helping to guide diagnosis and surgical reconstruction; however, craniofacial embryol‐ ogy is beyond the scope of this chapter.

It is important to note that cleft lip and palate is considered a distinct entity from isolated cleft palate, the difference chiefly characterized by the location of the cleft palate anterior or posterior to incisive foramen, respectively. Soft‐tissue and bony deficiencies are variable with accompany‐ ing nasal distortion (**Figure 1**). Surgical management hinges upon the accurate identification of involved structures and methodical attention to detail in surgical techniques in reconstruction.

**Figure 1.** (A) A child with a microform or "forme fruste" cleft lip, demonstrating vermilion notching, scar‐like depression. (B) A child with a complete unilateral cleft lip, demonstrating tissue hypoplasia and asymmetry.

#### **2.1. Normal anatomy of the lip**

The layers of the lip include the skin, a thin layer of subcutaneous tissue, orbicularis oris and other facial muscles, and mucosa. The vermillion is a unique tissue consisting of modified mucosa, and the white roll is a ridge at the junction of the vermillion and the lip skin. The lips are divided into four aesthetic subunits: the philtrum, two lateral wings (from the philtral columns to the nasolabial folds), and the entire lower lip.

Muscles of the upper lip include orbicularis oris, levator labii superioris alaeque nasi, zygomaticus major and minor, levator labii superioris, and nasalis. The orbicularis oris con‐ sists of superficial and deep layers. The deep fibers run circumferentially between modioli and function as the primary sphincter in feeding. The superficial fibers originate from the ipsi‐ lateral modiolus and run obliquely toward midline, interdigitating with the other muscles of facial expression and inserting into the dermis. The superficial fibers are further distinguished into either superior fibers (pars peripheralis) or inferior fibers (pars marginalis) of the upper lip. The pars marginalis courses along the vermillion border connect with the contralateral pars marginalis fibers at midline and inserts into the region of the vermilion tubercle. The pars peripheralis has a flat‐fan shape diffusing out from each modiolus, and inserting into the skin of the contralateral philtral ridge [2]. Two other distinct fibers of the pars peripheralis have also been identified using micro‐computed tomography [3]. One bundle terminates at the tis‐ sue below the ipsilateral anterior nasal spine, in continuation with depressor septi. The other bundle crosses midline and continues with the alar portion of nasalis muscle. The decussation of fibers creates the philtral columns, and lack of insertion at the midline creates the philtral depression.

Superficial layers of the levator labii superioris alaeque nasi, zygomaticus minor, and levator labii superioris cross the nasolabial groove and migrate toward the superficial orbicularis. The levator labii superioris alaeque nasi originates from the upper face, enters the upper lip superior and lateral to the ipsilateral philtral column, and descends on the medial side of the column. A bundle of fibers terminate in the dermis of the lateral aspect of the ipsilateral philtral column. Another bundle of short and long fibers terminates in the skin of the vermil‐ lion border; however, the long fibers interlock with the pars marginalis before their insertion. Thus the lip peak of the vermillion border, which creates cupid's bow, is due to a balance of muscular tension between the pars marginalis and levator labii superioris alaeque nasi.

Superficial reticular fibers of the levator labii superioris alaeque nasi, zygomaticus major and minor, levator labii superioris, and orbicularis oris insert into the medial philtrum ridge. The intersection of these fibers and the contralateral orbicularis oris forms the philtral column. The bulging appearance of the region lateral to the philtral column, however, results from a greater number of muscle insertions into the lateral skin than to the philtral dimple [4] (**Figure 2A**).

**Figure 2.** (A) A schematic representation of the orbicularis oris, demonstrating symmetry and continuity. (B) A schematic representation of the orbicularis oris affected by a cleft, demonstrating asymmetry and discontinuity.

#### **2.2. Normal anatomy of the nose**

The pathologic origins of a cleft lip are traceable to distinct embryological events. The fusion failure during gestational weeks 4–7 of facial primordia: the central frontonasal prominence and two lateral maxillary prominences result in a typical cleft lip of a newborn. Advances in developmental science have promoted our knowledge and understanding of this phenom‐ enon, helping to guide diagnosis and surgical reconstruction; however, craniofacial embryol‐

It is important to note that cleft lip and palate is considered a distinct entity from isolated cleft palate, the difference chiefly characterized by the location of the cleft palate anterior or posterior to incisive foramen, respectively. Soft‐tissue and bony deficiencies are variable with accompany‐ ing nasal distortion (**Figure 1**). Surgical management hinges upon the accurate identification of involved structures and methodical attention to detail in surgical techniques in reconstruction.

The layers of the lip include the skin, a thin layer of subcutaneous tissue, orbicularis oris and other facial muscles, and mucosa. The vermillion is a unique tissue consisting of modified mucosa, and the white roll is a ridge at the junction of the vermillion and the lip skin. The lips are divided into four aesthetic subunits: the philtrum, two lateral wings (from the philtral

**Figure 1.** (A) A child with a microform or "forme fruste" cleft lip, demonstrating vermilion notching, scar‐like depression.

(B) A child with a complete unilateral cleft lip, demonstrating tissue hypoplasia and asymmetry.

Muscles of the upper lip include orbicularis oris, levator labii superioris alaeque nasi, zygomaticus major and minor, levator labii superioris, and nasalis. The orbicularis oris con‐ sists of superficial and deep layers. The deep fibers run circumferentially between modioli and function as the primary sphincter in feeding. The superficial fibers originate from the ipsi‐ lateral modiolus and run obliquely toward midline, interdigitating with the other muscles of facial expression and inserting into the dermis. The superficial fibers are further distinguished into either superior fibers (pars peripheralis) or inferior fibers (pars marginalis) of the upper lip. The pars marginalis courses along the vermillion border connect with the contralateral pars marginalis fibers at midline and inserts into the region of the vermilion tubercle. The pars peripheralis has a flat‐fan shape diffusing out from each modiolus, and inserting into the skin of the contralateral philtral ridge [2]. Two other distinct fibers of the pars peripheralis have

ogy is beyond the scope of this chapter.

74 Designing Strategies for Cleft Lip and Palate Care

**2.1. Normal anatomy of the lip**

columns to the nasolabial folds), and the entire lower lip.

The nose can be divided into anatomical thirds. The proximal third consists of the paired nasal bones and bony septum (vomer, perpendicular plate of ethmoid, nasal crest of maxilla and palatine bone). Upper lateral cartilages and cartilaginous septum comprise the middle third. Lower lateral cartilages, the tip, and caudal cartilaginous septum form the lower third of the nose. The lower lateral cartilages consist of the medial, middle, and lateral crura (**Figure 3A**). The scroll area refers to the overlapping of lateral crura with the caudal edge of upper lateral cartilages. The nasalis muscle originates at the incisive fossa and inserts into four different regions. The transverse part courses past the alar base around the lateral side of the nose, and ascends medially to join procerus and the contralateral transverse fibers at midline. Fibers that course around the alar rim and above the lower lateral cartilages are the alar portion of nasalis. The columella and basal parts insert in the membranous sep‐ tum, medial crura, and nostril sill skin. The columellar part of nasalis is synonymous with depressor septi.

**Figure 3.** (A) A schematic representation of the lower lateral cartilages demonstrating symmetry. (B) A schematic representation of the lower lateral cartilages demonstrating asymmetry: a short medial crus, an obtuse genu, and a lateral crus that is longer and drawn into an S‐shaped fold on the cleft side.

The facial artery is the main blood supply to the upper and lower lips. The facial artery travels through the cheek beneath zygomaticus major and superficial to buccinator muscles, giving rise to the inferior and superior labial arteries. Once the superior labial artery emerges from the zygomaticus major, it may dive into the substance of the orbicularis oris, giving rise to the ipsilateral columellar artery. After giving rise to the superior labial artery, the facial artery terminates as the angular artery. The lateral nasal artery is a branch of the angular artery.
