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Facial Plastic and Reconstructive Anatomy and Embryology with Radiologic Correlates
Key Points
- 1.
Formation of the head and neck structures is intimately related to the development of the pharyngeal arches, with each arch carrying an artery, nerve, cartilaginous bar, and muscle.
- 2.
Palate formation requires midline fusion of the medial nasal prominences and palatal shelves. Incomplete fusion results in a spectrum of cleft palate deformities.
- 3.
The superficial muscular aponeurotic system (SMAS) represents a discrete fascial layer that separates the subcutaneous fat from the underlying parotidomasseteric fascia and facial nerve.
- 4.
When operating on the face, if dissection is kept superficial to the superficially situated musculature, the facial nerve should not be harmed.
- 5.
When completing a facial fracture repair, it is often necessary to reestablish the vertical buttresses with rigid fixation.
Pearls
- 1.
The forehead is composed of five anatomic layers, described by the mnemonic “SCALP.” Identification of these layers is important for both cosmetic and reconstructive procedures in this region.
- 2.
The galea aponeurosis can serve as a tension-bearing layer during scalp reconstruction.
- 3.
The majority of facial mimetic muscles are superficially situated and receive facial nerve innervation from their deep surface.
- 4.
With progressive age, descent of the suborbicularis orbital fat pad (SOOF) structures leads to deepening of the nasolabial crease.
Questions
Applied Embryology
1
What are the pharyngeal arches? How are they significant to head and neck development?
Formation of the head and neck structures is intimately related to the development of the pharyngeal arches, with each arch carrying an artery, nerve, cartilaginous bar, and muscle. The formation of these arches begins at approximately 20 days of gestation, and by 28 days, five arches are visible. Each arch is lined by ectoderm and inside houses mesoderm and neural crest cells, which form an artery, nerve, cartilaginous bar, and muscle. Of note, the first arch cartilage develops into the maxillary process and mandible and carries the mandibular branch of the trigeminal nerve, the internal maxillary artery, and the muscles of mastication. The second arch carries CN 7 (facial nerve), the stapedial artery, and the muscles of facial expression.
2
What primitive structures contribute to the formation of the face?
At the end of the fourth embryonic week, neural crest–derived facial prominences appear from the first pair of pharyngeal arches. Maxillary prominences are found laterally. The frontal nasal prominences develop into the forehead and frontal nasal process. On either side of the frontal nasal prominences are local thickenings that form nasal placodes. These placodes invaginate to form nasal pits and ultimately ridges of tissue that can be divided into lateral nasal prominence and medial nasal prominence ( Table 58.1 and Fig. 58.1 ).
Table 58.1
Structures That Contribute to the Formation of the Face
(From Wang TD and Milczuk HA: Cleft lip and palate. In: Lesperance MM, Flint PW, eds: Cummings – Pediatric Otolaryngology , Philadelphia, 2015, Saunders Elsevier.)
| PROMINENCE | STRUCTURES FORMED |
|---|---|
| Frontonasal | Forehead, bridge of the nose, medial and lateral nasal prominences |
| Maxillary | Cheeks, lateral portion of the upper lip |
| Medial nasal | Philtrum of the upper lip, crest, and tip of the nose |
| Lateral nasal | Alae of the nose |
| Mandibular | Lower lip |
3
How and when is the upper lip formed?
At approximately 6 weeks postconception, the paired maxillary prominences grow medially and contact the paired medial nasal prominences. As fusion of these structures occurs, the upper lip is formed. Ultimately, the maxillary prominences form the lateral lip and the medial nasal prominences form the philtrum, medial upper lip, columella, and nasal tip.
4
Discuss the embryology of the nose.
In the 7-week embryo, five facial prominences contribute to the formation of the nose: the frontal nasal prominence, the paired medial nasal prominences, and the paired lateral nasal prominences. The frontal nasal prominence forms the nasal bridge, the medial nasal prominences fuse and form the nasal tip and columella, and the lateral nasal prominence forms the nasal alae.
5
How is the primary palate (intermaxillary segment) formed?
Formation of the palate begins concurrently with the formation of the upper lip and nose at the end of the fifth week. In addition to contributing to the nose and upper lip, fusion of the two medial nasal prominences forms the intermaxillary segment. The primary palate includes the hard palate anterior to the incisive foramen.
6
What is the secondary palate, and how is it formed?
The secondary palate refers to the portions of the palate posterior to the incisive foramen. It is formed by the medial migration and midline fusion of the two palatine shelves around the seventh week. These shelves are extensions of the maxillary prominences. Midline fusion proceeds from anterior to posterior, ending with creation of the uvula.
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