S6 Face - Learning Objectives
1. Describe the superficial anatomy of the face.
The face is the anterior-most region of the head, bounded superiorly by the frontal region, laterally by the auricular regions, and inferiorly by the inferior margin of the mandible (jaw). The face contains five openings: two palpebral (eye) fissures, two nares (nostrils), and one oral fissure. The majority of the muscles of the face act upon these openings. The anatomy particular to the palpebral fissures will be specifically addressed in Session 10 (Orbit & Cavernous Sinus).
The nose (and nasal cavity) is superior to the mouth (and oral cavity). The dorsum (bridge) of the nose extends infero-anteriorly to the apex (tip) of the nose, and this is flanked on either side by the ala of the nose, which partially surround the nares. The nares are separated by the nasal septum. The external, skin-covered portion of the nasal septum is the nasal columella.
The nasal region is separated from the oral region by the upper lip. The upper and lower lips surround the oral fissure. Lips have three areas defined by their surface tissue: skin, vermillion zone, and mucosa. The oral fissure is the gap between the upper and lower lips, which is flanked at each side by the angles of the mouth.
Skin folds may be visible between adjacent musculature. When present, nasolabial folds extend from lateral to the nose and curve toward the angles of the mouth. They are often referred to as ‘smile lines,’ and often deepen with age. When present, the mentolabial fold is a horizontal cleft between the lower lip and the chin.
2. Describe the distribution (and relative depths) of facial fasciae.
The skin of the face rests upon a layer of fibro-adipose tissue of various depths. The fibro-adipose tissue is rich with dense connective tissues, thus allowing the facial muscles to move and shape the skin of the face. Deep to the fibro-adipose layer is the superficial musculo-aponeurotic system (SMAS), a fascial layer that either invests or covers the muscles of facial expression to a variable extent.
The SMAS (and associated layers) extends from the platysma mm. of the cervical region to the epicranial aponeurosis of the cranium (anteriorly). Above the zygomatic arch, co-planar to the SMAS is the temporoparietal fascia. Temporoparietal fascia covers the temporal region superficial to the temporal fascia (deep, investing fascia of the temporalis m.). Deep to the SMAS is the parotid-masseteric fascia. Parotid-masseteric fascia covers the the parotid gland and masseter, covering the parotid duct, and branches of both the facial n. and mandibular n. (V3). Branches of the facial n. (CN VII) are predominantly found deep to the temporoparietal & parotid-masseteric fasciae.
Succinctly, the layers of tissue of the face (superficial to deep) include the:
- Fibro-adipose tissue (subcutaneous layer)
- Superficial musculo-aponeurotic system (SMAS), muscles of facial expression, and temporoparietal fascia (superior to zygomatic arch)
- Parotid-masseteric fascia (inferior to zygomatic arch, superficial to buccal fat pad)
- Facial n. divisions (in parotid gland)
- Buccopharyngeal fascia (deep to buccal fat pad); Muscles of mastication
3. What are the most clinically relevant fascial spaces of the face (superior to the mandible)?
The infra-orbital (= canine) fascial space is deep to the “quadratus labii superioris m.” group, which consists of the levator labii superioris alaeque nasi m., levator labii superioris m., and the zygomaticus major & minor mm. The buccal fascial space is continuous anteriorly with the infra-orbital space. Odontogenic infections of the ipsilateral canine or first premolar may spread to this space, causing infra-orbital edema. Left untreated, infection may spread to either the buccal space, and/or to the orbital vasculature, and the cavernous sinuses beyond. The angular a. & v. and the infra-orbital n. (of V2) are found in this space. The buccal space is continuous with the (sub)masseteric space posteriorly and the pterygomandibular space posteromedially. These spaces represent a potential route of metastasis from the teeth to the retropharyngeal space and associated spaces.
4. Describe the various groups of facial muscles. How are these groups distributed about the face? What are functions and innervations of the facial muscles?
Muscles of the superficial head fall into two major groups: epicranial and craniofacial. Epicranial muscles are few, primarily act upon the scalp, and are best represented by the occipitofrontalis m.: a muscle with two bellies (frontal and occipital) connected by an intermediate epicranial aponeurosis. Craniofacial muscles are located in the facial region and are often referred to as muscles of facial expression, as they move the skin of the face.
5. Describe the superficial vasculature (arteries and veins) of the face.
The superficial temporal v. typically accompanies the superficial temporal a. and the auriculotemporal n. superior to the parotid gland. The superficial temporal v. typically unites with the maxillary v. to form the retromandibular v. The retromandibular v. may divide into anterior and posterior divisions. The anterior division of the retromandibular v. typically unites with the facial v. before joining the internal jugular v. The posterior division of the retromandibular v. typically unites with the posterior auricular v. to form the external jugular v.
The superior thyroid a., the lingual a., and the facial a. are typically the first three anteriorly oriented branches of the external carotid a. The facial a. traverses the submandibular triangle before emerging over the body of the mandible (anterior to the masseter m.), accompanied by the facial v., deep to the branches of the facial n. The artery ascends and supplies structures of the face.
The facial a. has several branches. Major branches include the: inferior labial br., superior labial br., and the nasal br. The labial branches adjacent to the modiolus of the mouth and run courses between the orbicularis oris m. and the mucous membrane. The labial branches often anastomose with their contralateral counterparts. The lateral nasal br. often arises lateral to the nose, and anastomoses with its contralateral counterpart. In some cases, the lateral nasal br. may arise from the superior labial br. The angular a. is the terminal branch of the facial a. that courses toward the medial canthus of the eye.
The facial v. and its branches mirror the distribution of the facial a. and its branches. The angular v. is valveless and receives the supra-orbital v. and supratrochlear v. to drain the forehead and regions medial to the eye. The deep facial v., which drains the pterygoid plexus of veins and deep face, is valveless, and joins the facial v. anterior to the masseter m. Anastomoses between facial v. branches may allow infections a direct route into the cavernous sinus. For example, anastomoses between the angular v. and the superior and inferior ophthalmic vv. may allow infections from the ‘danger area of the face’ a direct route into the cavernous sinus. Likewise, infections may move through the deep facial v. through the pterygoid plexus of veins into the cavernous sinus.
6. Describe the distribution (and name the branches) of the facial n. (CN VII) distal to the stylomastoid foramen.
The facial n. exits the stylomastoid foramen, then divides into two divisions: the temporofacial division (superiorly) and the cervicofacial division (inferiorly). These divisions and their branches course through the parotid gland. The temporofacial division typically gives rise to the temporal brs., zygomatic brs., and a portion of the buccal brs. The cervicofacial division typically gives rise to a portion of the buccal brs., marginal mandibular br., and the cervical br.
7. Describe the dermatomes of the face & head. Which divisions of the trigeminal n. (CN V) serve these dermatomes, and what are the major terminal cutaneous nerves of the face?
The trigeminal n. (CN V) is responsible for innervating muscles of mastication (efferent) and sensation of the skin of the face (afferent). The trigeminal n. has three divisions: ophthalmic n. (V1), maxillary n. (V2), and mandibular n. (V3). The complete courses and functions of these divisions will be discussed elsewhere, but there are five nerves of these divisions afferently serving the skin of the face: the supra-orbital n. & supratrochlear [supratrochlear will discussed in more detail in Session 10] (V1), the infra-orbital n. (V2), the mental n. (V3), and the cutaneous portion of the auriculotemporal n. (V3).
The supra-orbital n. is the terminal continuation of the frontal n. through the supra-orbital notch or foramen, which afferently serves the conjunctiva, mucosa of the frontal sinus, and skin of the superior palpebra, forehead, and epicranial scalp. The supra-orbital n. is a branch of the ophthalmic n. (V1). Variations of crania include those with supra-orbital notches and those with supra-orbital foramen. Either of these structures, when present, are found along the superior rim of the orbit, nearly halfway between the midpoint of the superior rim and the medial rim of the orbit.
The infra-orbital n. is the branch of the maxillary n. (V2) which exits the infra-orbital foramen of the maxilla. The infra-orbital foramen is below the orbit, approximately in-line with (or just lateral) to the supra-orbital foramen (or notch) above. The infra-orbital n. afferently supplies the mucosa of the maxillary sinus and gingiva, and skin of the: inferior palpebra, the lateral nose, upper lip, and cheek.
The mental n. is the terminal continuation of the inferior alveolar n., a branch of the mandibular n. (V3), which passes through the mental foramen of the mandible to afferently serve the mandibular gingiva, and skin of the: lower lip and chin.
The auriculotemporal n. is also a branch of the mandibular n. (V3). The auriculotemporal n. serves many functions, but germane to this session, it afferently serves the skin of the: tragus of the ear, the external auditory meatus, and the area anterosuperior to the ear. The cutaneous portion of the auriculotemporal n. may be found accompanying the superficial temporal a. and v. superiorly from the parotid gland.
8. What is facial nerve (Bell’s) palsy? How might one distinguish between Bell’s palsy and a cerebrovascular accident (CVA)?
Facial n. (Bell’s) palsy is the ipsilateral paralysis of facial mm. due to a neuropathy of the facial n.
Many of the upper motor neurons of the temporofacial division originate bilaterally in the cerebral cortex, whereas the upper motor neurons for the cervicofacial division are sourced in the contralateral cerebral cortex. A cerebrovascular accident (CVA, or a stroke) may typically present with contralateral facial muscle paralysis of the lower face, whereas facial n. (Bell’s) palsy typically presents with total ipsilateral facial muscle paralysis. Thus, an individual suffering a CVA may be able to elevate the skin of their brow (wrinkle the forehead), whereas an individual with a facial n. palsy cannot elevate the skin of their brow.