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INTRODUCTION In modern eras, statistical community-based studies show that facial traumas, usually inflicting damage to the superficial musculoaponeurotic system SMAS and leaving the pat

INTRODUCTION

In modern eras, statistical community-based studies show that facial traumas, usually inflicting damage to the superficial musculoaponeurotic system (SMAS) and leaving the patients with disfiguring scars, has been becoming more prevalent in traffic, occupational and domestic accidents along with socioeconomic developments Besides, the aging process also decreases the skin elasticity and therefore leads to the appearance of striae, wrinkles and fat disposition beneath the facial SMAS

In this day and age, plastic surgery has been being extensively developed and researched all around the world Furthermore, surgeons’ aptitude has ameliorated more than ever before, and they have achieved many great feats in restoring aesthetics and physical functions to the patients However, intervention to facial structures can be occasionally limited and sometimes iatrogenic damage such as facial paralysis, rupture of the parotid duct, etc., can be attributed to surgeons’ restricted knowledge and expertise, especially about the aspect of clinical anatomical landmarks of the SMAS

There has been many in-depth studies on the SMAS and its relation to important facial structures such as the parotid duct, the facial nerve, the superficial temporal artery, etc., but their results are contradictory still On the other hand, SMAS studies are scarce in Vietnam and the SMAS is simply depicted as a superficial facial fascia

Based on the aforementioned arguments, I’ve decided to

conduct a “Study on the anatomical characteristics of the facial SMAS and its relation to the facial nerve on Vietnamese adults”

with two main objectives: (1) To investigate the anatomical characteristics of the SMAS and (2) to identify the gross and microsco Figure relation of the facial nerve branches to the SMAS

New contributions of the study:

1 It always has SMAS layer in each side of face and devides that side into three parts: upper, middle and lower part Its shape likes number 3 with the upper vacancy is orbicularis oculi and the lower one is orbicularis oris, the area of SMAS is affected by size of the superficial muscles such as frontalis, orbicularis oculi and orbicularis oris We noticed the thickeness of the upper temporal septum, anguli oculi lateralis, zygomatic, masseteric and mandibular ligaments, which tighten SMAS

2 At the place ligaments attach, there always have the branches

of facial nerve run into the ligaments, such as frontal branch runs under temporal septum, orbital branch runs into anguli oculi lateralis, buccal branches run into zygomatic ligament, masseter and mandibular branch runs into mandibular ligament, these are the protective mechanism of the branches of facial nerrve, that is why surgician need to be careful when performing process in the SMAS

papers (comprising 12, 108 papers in Vietnamese and English respectively)

CHAPTER 1 LITERATURE REVIEW 1.1.2 Basic principles of the facial layers

Figure 1.2 The facial layers

* Source: from Mendelson B.C (2009) [22]

1.1.3 Basic structures of five facial layers

1.1.3.3 Superficial musculoaponeurotic system (SMAS)

The SMAS, first described in 1976, the muscular part of this system is predominant in several regions in the third layer while in other parts of the face the aponeurotic part dominates Fibrous tissues

of the three outer layers are the SMAS, being the deepest layer of this single unified unit In the midface and the lower third of the face, this mixed structure still persists despite being ambiguous [6], [41] The third layer exists in a multilayered form, in which the flat part comprises the superficial layer covering the anterior aspect of the face: frontalis muscle makes up the upper third and the orbicularis muscle form the middle third of the face, while the platysma muscle, extending from the lower third to the lateral face [43], [44]

1.1.3.4 Fascial spaces

The anatomical complexity of this fourth layer will become much more comprehensible if we understand the arrangement of these structures, which follow this principle [7]: they all lie above the bones

as this layer originally forms the virtual spaces and the immobolized region; the virtual spaces are functional regions, each of which has distinct borders and has minimal coupling; internal arrangement of the retaining ligaments further reinforces the borders of the virtual spaces and facilitates the identification of different regions; the muscles lie within the deep fascial layers and attach to the underlying bones at the borders; there is always a continuous line, being an extension of the retaining ligaments, running along the circumference of the bone cavities

1.1.3.5 Deep fascia

Has the same structure as the periosteum, but instead is a mobile membrane which lies over the supraperiosteal fat It runs beneath the origin of the deep muscles and the retaining ligaments

1.2 Concepts and studies on the structure of retaining ligaments, ligamentous attachments and septa of the face

1.2.1 McGregor’s patch

The term ”McGregor’s patch”, zygomatic ligaments or zygomatic cutaneous ligaments were all synonyms that were used in the past In 1959, ”McGregor’s patch” was described as ” an area of fibrous attachment between the anterior margin of the parotid fascia and the dermis of the skin of the cheek” [47] When the

”McGregor’s patch” is found, there are 3 important anatomical structures which go through the parotideomasseteric fascia: the transverse facial artery, the parotid duct and the zygomatic branch of the facial nerve [49]

1.2.3 The masseteric retaining ligaments

Özdemir R et al hypothesized that the fibrous attachments can originate from the anterior border of the masseter, 1-2 cm posterior to the anterior border or even in the middle part of the muscle The variability of the origins of the masseteric retaining ligaments may relate to the corresponding structure of the intermingling region between the masseteric fascia and the size of the parotid fascia [7], [15], [19]

1.2.4 Zygomatic retaining ligaments

Funas D.W described the zygomatic retaining ligaments as tough fibres which originate from the inferior border of the zygomatic arch and then extend to the anterior aspect of the junction between the arch and the body of the zygoma [3], [6]

1.2.5 Orbicularis retaining ligaments

Muzaffar A.R et al recorded the presence of a septum-like structure of the ligaments, whose origin is the periosteum of the lateral border of inferior orbital rim which lies closely to orbital septum

These fibres then attach deeply to the orbicularis oculi and have unclear borders [57]

1.2.6 Temporalis retaining ligaments

Knize D.M documented and described a 6-mm-wide region having fibrous attachments locating medially to the superior temporal line at the level of the galea aponeurotica and the periosteum is attached to the underlying bones; they also named a stout ligament found cranially to the superior orbital rim and at the distal end of the ligamentous attachments region to be the ”orbicularis retaining ligaments” [9], [59] Moss C.J et al have studied and classified the types of the ligamentous attachments of the temporal region into: septa, ligamentous attachments and the thickened region surrounding the orbital rim namely the thickening of the periorbital septum [10]

1.2.7 Mandibular ligaments

The mandibular retaining ligaments originate from the anterior third of the mandibular body and have fibres which perforate the inferior aspect of the depressor anguli oris muscle to tether directly to the skin Furnas D.W also documented these fibres consist of two layers laying 2-3 mm apart and traveling parallel to each other and were observed approximately 1 cm above the mandibular body [3]

1.4 Studies on the relation of the facial nerve to the facial layers 1.4.2 Characteristics of the facial nerve branching pattern

According to Davis R.A et al classification [80], there are 6 patterns: type I absence of an anastomosis between the temporofacial division and cervicofacial division; type II anastomosis among the branches of the temporofacial division only; type III single anastomosis among the branches of the temporofacial division and

cervicofacial division; type IV combination of type II and III Also called “multi loops” due to the presence of multiple anastomoses of different branches; type V: double anastomosis between the temporofacial division and cervicofacial division; type VI multiple complex anastomosis between the two divisions

Figure 1.24 Six basic types of the branching pattern of the facial nerve according to the classification of Davis R.A et al

* Source: from Myint K (1992) [67]

1.4.2.1 Temporal branch

Being the uppermost branch of the temporofacial nerve, it traverses the superior margin at the point where the temporal hairline descends and intersects the zygomatic arch It also emerges 2 cm above the tragus and then traverses the zygomatic arch; runs beneath the facial fasciae, caudally to the arch The temporal branch divides into 3 branches: the auricular, the frontal and the orbicularis branches [70]

1.4.2.2 Mandibular branch

The mandibular branch is located behind the facial artery, and 20% of the cases were observed to have this branch traveling along the inferior border of the mandibular body but it’s never found 1 cm below the inferior border It’s rarely damaged during cervical surgery,

parotid gland removal surgery, mandibular angle osteotomy, facelift surgery and other submandibular surgeries [80], [85], [96]

1.5 Domestic studies on the SMAS, ligaments and facial nerve

In Vietnam, the terminology of retaining ligaments, attachments, septa, and superficial musculoaponeurotic layer are unsatisfactorily defined and not many studies have been conducted on these structures [31], [81], [83]

CHAPTER 2 SUBJECTS AND METHODS 2.1 Subjects

We performed facial dissections on 30 Vietnamese adult cadavers, which have been treated with formaldehyde Selection criteria of participants:

1 Vietnamese adult cadavers are above 18 year old

2 The participants have not been operated any ENT surgeries

3 The participants don’t have any deformation or any tumor on the face and neck region

4 The participants do not have any abnormal structure on the otolaryngology region

Facial dissection was performed on skin layers, ligaments and facial nerves 20 tissues with the size of 1cm2 were collected for histological analysis The sampling location was depended on anatomical location of branches of the facial nerves related to SMAS

2.3 Research method

2.3.1 Macroscopic analysis of the facial layers, ligaments, cavities and the facial nerve

We dissected the nerve VII with facial ligaments, and measure the dimensions of the SMAS

2.3.1.2 Macroscopic indicators

+ Qualitative analysis:

Description of the insertion of ligament of anguli oculi lateralis, zygomatic ligament, masseteric ligament, mandibular ligament Identification of the facial nerves with the facial layers and ligaments; hence choose the appropriate histological analysis location

+ Quantitative analysis:

- Measurement the depth of the skin, subcutaneous layer: eyelids, parotid gland, temporal region, frontal, mental, nasal tip Measurement dimensions of SMAS layers

2.3.2 Microscopic analysis of the facial layers, ligaments, cavities and the facial nerve

We collect 20 tissues, the size of 1cm2 and sliced into each sampling of 3-4micrometers which stained by H-E, H-SG method

CHAPTER 3 RESULTS 3.1 Anatomical characteristics of the SMAS and the borders between regions

3.1.3 The superficial musculoaponeurotic system

3.1.3.2 The SMAS

* Shape of the SMAS

There are two main types, if the area of the orbicularis oculi and orbicularis oris muscle are large, then the area of the SMAS in the middle layer is decreased as well as the superior and inferior notches are deeper (point P and I don’t coincide) (see Figure 3.5)

Figure 3.5 SMAS type 1

* Source: sample of specimen H No 1162013

- If the area of orbicularis oculi and orbicularis oris muscle are small, the area of the SMAS will be increased, as well as the 2 superior and inferior notches are shallower (point P & I coincide) (F 3.6)

Figure 3.6 SMAS type 2

* Source: sample of specimen L No 862011

*Dimensions of the SMAS

Table 3.7 Dimensions of the SMAS Dimensions (mm) Right-sided

(n=15)

Left-sided (n=15)

- Comment: The width of the SMAS: the upper facial part (IJ)

40 - 45mm, the middle facial part (HG) 100 - 110mm; the lower facial part (FE) 60 - 65mm The height of the SMAS: the upper part (ID) 60

- 70mm; the middle part (IO) 75 - 80mm; the lower part (CO) 20 - 25mm Distance from tragus to anguli oculi lateralis (HI) is about 60mm, it is shorter than distance from tragus to angle of the mouth (HE) 70 - 80mm

3.1.4 The Superficial Musculoaponeurotic System

3.1.4.1 Ligaments, fibrous tissue

* Ligaments of anguli oculi lateralis

We noticed that in 30 samples, there are connective tissue which link SMAS to the fifth layer from the anguli oculi lateralis

Figure 3.8 Angulus oculis latoralis and zygomatic ligament

* Source: sample T code 952012

* Zygomatic ligament

In 30 samples, from tragus along to the upper border of zygoma, there are connective tissue which link to hypodermis

Figure 3.11 Zygomatic ligament (Mc Gregor’s patch)

* Source: sample H code 1162013

* Masseteric Ligament

In 30 samples, there are connective tissue running along the anterior border of masseter to hypodermis with ramus marginalis mandibulae nervi facialis

Figure 3.12 Masseteric ligaments

* Source: Sample H code 1092013

* Mandibular ligament

We noticed that in 30 samples, there are connective tissue attached from the anterior border of masseter to the body of mandible, and link to subcutaneous tissue, which relate to ramus marginalis mandibulae nervi facialis

Figure 3.13 Mandibular ligament

* Source: Sample T code 952012

3.2 The relationship between SMAS and branches of facial nerve 3.2.2 Investigating the macro and microanatomy correlation between SMAS and the branches of facial nerve

3.2.2.1 Investigating the path way of frontal branch

* Frontal branch runs into ligaments of angulus oculi lateralis

The investigated area includes SMAS, frontal branch and orbicularis oculi (the square in Figure 3.33)

Fig 3.32 Frontal branch runs into lig of angulus oculi lateralis

* Source: sample T code 972012

Fig 3.33 The frontal branch runs into lig of anguli oculi lateralis

* Source: sample T code 1072013 in the right

We discovered that frontal branch runs into ligaments of anguli oculi lateralis and relates to vessels

* Frontal branch runs into frontalis

The investigated area includes SMAS, frontal branch and frontalis (the square in Figure 3.35)