The Human Face
Today’s society holds a high importance on physical beauty. Particularly the anatomy of the face affects our everyday life. Facial anomalies are not uncommon and every medical professional ought to have a basic knowledge about the facial development in utero, how it can go wrong and what treatment options are available for the people suffering from these severe conditions.
The development of the face starts with the oral (or anterior) portion of the alimentary canal, the stomatodeum. It is surrounded by the three different swellings of the face divulging from the cells of the neural crest. These three facial swellings are known as the frontonasal prominence, maxillary prominence and mandibular prominence. Both the maxillary and mandibular prominence develop from the first pharyngeal arch whereas the frontonasal prominence is formed from the mesenchyme.
Two ectodermal layers start to take shape just lateral of the frontonasal prominence and become the two nasal placodes. Nasal pits further develop from the placodes by invaginating at the centre which then leaves ridges of tissue bilaterally over the pits. These tissue ridge are called the lateral and medial nasal prominences. The intermaxillary segment is formed by fusion of the medial nasal prominences in the midline.
Anatomy and Supply
The various features found on the human face have different embryological origins:
- The upper lip develops from the maxillary prominence and the medial nasal prominence.
- The lower lip derives from the mandibular prominence which is a direct result of the development of the first pharyngeal arch.
- The lacrimal sac and the nasolacrimal duct are the mature structures of the nasolacrimal groove that separates the lateral nasal prominence and the maxillary prominence.
- The nose consists of a triad of embryonic structures including the frontonasal prominence, the medial nasal prominence and the lateral nasal prominence.
- Unlike the nose, the cheeks stem forms a single structure known as the maxillary prominence which arises from the first pharyngeal arch, just like the mandibular prominence.
- The intermaxillary segment ends up as the philtrum, the primary palate and the upper jaw containing the central and lateral incisors.
The face is richly perfused by a subdermal plexus formed mainly by musculocutaneous arteries coming from the superficial temporal and facial arteries. The facial artery branches off the external carotid artery, winds around the inferior border of the mandible and ascends along the side of the nose. The superficial temporal artery derives from the external carotid artery too and gives off numerous branches which supply different parts of the face including the transverse facial artery and the middle temporal artery. The venous blood of the face drains from the subdermal plexus to the deep venous plexus via communicating veins.
The three divisions of the trigeminal nerve are responsible for the somatic sensation of the entire face according to the three embryological origins. The ophthalmic nerve (V1) which comes from the frontonasal prominence supplies the anterior scalp, forehead and nasal dorsum. Deriving from the maxillary prominence the maxillary nerve (V2) provides mainly the anterior cheek, the lateral face, the upper lip, the side of the nosa and the lower eyelid. The mandibular nerve (V3) originates from the mandibular prominence and supplies the lower lip, the chin and posterior cheek. In contrast, the posterior scalp, the lower border of the mandible and the neck are not innervated by the trigeminal nerve but direct branches of the cervical plexus (C2).
The pathological traits of facial growth are many and quite frequent. Lasting complications include facial disfigurement, difficulties hearing, speaking, eating, swallowing and breathing. The most common and well known facial anomalies, known as facial clefts, are listed below:
- Cleft lip - a partial or complete lack of fusion of the maxillary prominence with the lateral nasal prominence on one or both sides. Depending on the severity of the lack of fusion, this can result in a partial or complete, unilateral or bilateral cleft lip.
- Cleft palate - Cleft palates are divided into primary and secondary depending on whether they are in front of or behind the incisive foramen respectively. The primary (or anterior) cleft deformities include lateral cleft lip, upper cleft jaw and a cleft between the primary and secondary palates. Behind the incisive foramen the clefts can either be of the secondary palate or known as a cleft uvula. Cleft palates result from a lack of fusion between the palatine shelves. Rarely, a cleft will run from the lip to the secondary palate.
- Oblique facial clefts - When the maxillary prominence fails to merge with the lateral nasal prominence the nasolacrimal duct is exposed.
- Median (or midline) cleft: This type of anomaly occurs with the incomplete fusion of the two medial nasal prominences in the midline. This particular defect can have much more serious consequences that the others it is associated with cognitive disabilities and brain abnormalities.
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