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Atlas of facial ultrasound

ATLAS OF FACIAL ULTRASOUND

Ultrasound in 5 minutes series Cedum ®; read the concise article about the ultrasound anatomy of the face; best read on the PC. The face is an external part of viscerocranium (visceral cranium), which is a part of the head. Shape of the face is created by the internal bony and cartilagineous deep skeleton, the facial viscera and elements of an integument. Respectively the variety of individual facial features are based not only on the diversity of the shape of the bony skeleton, but also on differences of shapes, thickeness and changeable locations of individual elements of facial soft tissues and organs.

The structure of the face is founded concentrically in a form of multiple layers. From the most outer one they are the following: the skin (syn. dermis), the subucutaneous tissue (syn. hypodermis), the superficial fascia and its conjoint structures forming superficial musculoaponeurotic structure (syn. SMAS), the subfascial fat pads and its accompanying elements, the deep fascia and its conjoint structures, the deepest conective tissues and fat pads, the layer of bones and cartilages. Moreover some of the layers may split and form additional spaces containing additional organs. All of the layers, their internal structures and their margins are generally clearly visible in ultrasound without the blurring sign. They are also pierced by multiple nerves and vessels; the latter are clearly recognisable in ultrasound Doppler modalities.

Areas of the face consists of the forehead, the nose, cheeks, temporal fossas, lips, mental and sumental areas. The largest zones are the cheeks, which borders are the orbits, the orbital-cheek crease, the zygomatic arch, the preauricular crease, the mandibular crease, the labio-mandibular crease, the naso-labial crease, the naso-facial sulcus. The cheek can be further subdivided into infraorbital, zygomatic, naso-labial, buccal and parotido-masseteric units. Parts of the lips consists of the labial skin, the vermilion (syn. the red lip), the labial oral mucosa.

Skin of the face (syn. dermis) is generally thiner than on other parts of the body, but respectively within the face itself there are zones with even thiner skin, like on eyelids and their surrounding areas, as well as with significantly thicker skin like on the tip of the nose. Apart from anatomical areas thickness of the skin depends also on the sex and the age; the men have more often thicker skin, the elderly have thiner. One can also observe in color-Doppler and microvasculature modalities (MVF) of ultrasound different intensities of vascularisation of dermis; i.e. high density of dermis vascularisation is visible within the vermilion of lips.

The subcutaneous tissue (syn. hypodermis) consists of conective tissue fibers, which weave in a neat manner forming the scaffolding of this layer, and the fatty component / lobules. Conective tissue fibers may concentrate even in a more sophisticated fashion forming in some areas retaining ligaments playing an important role in preserving the beauty of an individual. Retaining ligaments linking the fascia and the skin are called „false”; those linking deeper bone with the fascia are called „true” retaining ligaments.

Thickness of the subcutaneous tissue differs depending on the area. On the cheeks is generally thicker and forms more prominent subcutaneous fat pads, which may be compartmentalized, like into the malar fat pad, the nasolabial fat pad or the jowl fat pad. The malar fat pad plays an important role in rejuvenation procedures. Loosely hanging jowl pad respectively can provoke a fat ptosis and create characteristic face deformation of an elderly age. On the eyelids and just around them the thickness of the hypodermis is very minute or even absent.

Knowledge of thickness of particular layers of the facial integument is key before proceding any cosmetic procedures. Too deep implementation of a chemical agent or a physical phenomenon, as laser, may for example paralyse the orbicular oculi muscle and precipitate bags under eyes. Apart from differences in thickness the density of hypodermis also varies. The intensly dense in conective fibers subcutaneous tissue may be observed on the nose, the zygomatic arch, lips and on the chin.

The fat component of hypdermis serves as the protective shock absorbing cushion, the store of energy, the element of the metabolic and endocrine system, as well as the creator of an individual’s facial lines.

Under the hypodermis lies the superficial fascia, which with other elements like inserting tendon fibers of expression muscles create on the face functional system called SMAS (syn. superficial musculoaponeurotic system). SMAS covers the face, extends upwards to the orbicularis oculi muscle, the frontalis muscle, the galea aponeurotica and the temporo-parietal fascia (syn. superficial temporal fascia), as well downwards to the neck, where it blends with the platysma. SMAS distributes forces of expression muscles and plays an important role in creating the shape of the face and in the mimicry.

The mimic muscles that blend with or at least partialy and directly insert into the SMAS are the frontalis, the orbicularis oculi, the levator labi superioris alaeque nasi, the levator labii superioris, the zygomaticus minor, the risorius, the depressor labii inferioris, the depressor anguli oris, the platysma. Most of them constitute the superficial muscular group of facial muscles; more to be read further. Mimic muscles that converge at the angle of the mouth create a tendineous and muscular node tightly attached to the skin, which is named modiolus.

Next deeper layer of the facial integument is the deep fascia, which in different parts of the viscerocranium may split into two laminae, that encompass some particular tissues or organs. For example in the temporal fossa they hide a fat pad. Respectively on the cheek they encompass the parotid gland, the masseter muscle and within so-called buccal space they contain the accesory parotid gland, the parotid duct (syn. Stensen’s duct), the Bichat’s buccal fat pad, the facial and the buccal artery, the facial vein.

The buccal fat pad (syn. Bichat fat pad) is a deep pad interlocated between the musculi masseter and buccinator. In adults it provides fullness and contour of the face; in infant it plays a role in suckling and mastication. It is clearly visible in ultrasound of the cheek. Its extension may reach the temporal fossa as the deep temporal fat pad, which faciliates gliding the temporalis muscle under the zygomatic arch.

Muscles of the face itself are divided into the deep and the superficial groups. The deep group consists of the masseter muscle, the buccinator, the levator anguli oris and the temporalis muscle. The remaining face muscles belong to the superficial group. The main function of the masseter and the temporalis muscles is providing the biting force and the mastication. Respectively the main function of the buccinator is providing a scaffolding structure of the cheeks and walls of the oral cavity. The buccinator is pierced by the parotid duct. Just underneath the layer of the buccinator, the oral mucosa is observed.

Within the area of the face one can find many exocrine glands of which the largest is the parotid; very often it posseses a buccal protrusion or simply accesory salivary gland lying on the external surface of the masseter muscle. Other salivary glands include two submandibular glands, two sublingual glands and many tiny submucosal glands. Within the upper lateral aspects of the orbits one finds the lacrimal glands. All the glands are characterised by an internal microgranular pattern on ultrasound. Some of them, particulary the parotids, additionally may have visible pattern of internal delicate fibers. Within parotids usually lymph nodes are also found.

Healhty bones of the face, as bones in other parts of the body, have smooth surface and give a strong echo in ultrasound. Throughout the face we can find variety of bony hallmarks like supraorbital, infraorbital, mental foramina or ridges and creases in particular areas, such as orbits and zygomatic fossae. In contrast, cartilages of the nose are transparent for ultrasound and remain echolucent.

The face receives most of the arterial blood supply from multiple branches of external carotid arteries (ECA) on both sides. Minority of the blood inflow comes from the branches of the internal carotid arteries (ICA); nonetheless very important to be understood during cosmetic medicine procedures. Most of the vessels that lie within the soft tissues of the viscerocranium are clearly visible by means of the modern ultrasound equipment.

The highest branch of each ECA, and being its direct continuation, is the superficial temporal artery (STA). It is visible in the ultrasound ascending within the parotid gland, between the auditory meatus and the head of mandible, further above the zygomatic arch superficially splitting into frontal / anterior and occipital / posterior branches; the anterior branch supplies the forehead and the neighboring area. Inferiorly, some of important branches of the STA supplying the face include from the highest: the middle temporal artery (MTA) supplying temporal muscles; the transverse facial artery (TFA) emerging on the face at the anterior border of the parotis, accompanying the parotid duct and lying within the depth of the SMAS on the cheek. An important cutaneous perforator of TFA emerging in the preauricular zone gives the important blood supply for the preauricular and buccal areas. During plastic surgery procedures of a scalp or facial flap mobilisation and incisions in the preauricular area the caution must be taken to avoid injury of STA, accompanying vein or the auriculotemporal nerve.

The next important and lower branch of each ECA is the maxillar artery (MA), which divide into many branches, some of them supplying the face and the viscerocranium. The deep temporal artery (DTA) traverse into the deeper layers of temporal fossa. The infraorbital artery (IOA) being the continuation of the main trunk of MA, crossing through the bottom of the orbit emerges onto the face together with the infraorbital nerve bundle (V2) through the infraorbital foramen and give vasculature for the lower eyelid, the nose, the superior lip and the cheek. The buccal artery emerges onto the face by piercing through the buccinator muscle just anteriorly to the anterior edge of the masseter and it supplies blood for the cheek. The mental artery, which is the continuation of the interior alveolar / dental artery, emerges onto the face through the mental foramen on the mandible and supplies the region of the chin and the lower lip.

The next lower branch of the ECA is the facial artery (FA). It has two parts: cervical and facial. Within the cervical part it runs by or crosses the submandibular gland. The facial part begins, where the FA curls around the mandible between the masseter and depressor anguli oris muscles; then in a tortuous manner the artery runs medialy to the nasolabial sulcus and traverses towards the inner canthus, where it ends as the angular artery. Branches of the FA within the cervical part include: ascending palatine artery (APA), tonsilar artery (TA), glandular branches, submentalis artery (SMA). Branches of the FA within the facial part include: premasseteric artery (PMA), inferior labial artery (ILA), superior labial artery (SLA), inferior alar artery (IAA), lateral nasal artery (LNA), angular artery (AA). The last one anastomoses with branches of the supratrochlear artery from the basin of the internal carotid artery.

Soon available atlas of facial anatomy in ultrasound. Content for ultrasound courses by dr Tomasz Szczepanski.

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Autor: Tomasz Szczepański MD