Anatomic evaluation of the normal variants of the arteries of face using color Doppler ultrasonography: Implications for facial aesthetic procedures

Knowledge of normal facial vascular variations could prevent catastrophic complications of cosmetic procedures as well as providing a guide for surgical planning. Color Doppler ultrasound is a safe and noninvasive method for real time vascular evaluation.


| INTRODUC TI ON
Interest for aesthetic procedures in the facial region has been growing in the recent years. 1 Although most of these procedures are minimally invasive, serious complications are catastrophic, mostly happening due to arterial invasions like occlusions by particles, leading to tissue necrosis. 2 Therefore, a comprehensive knowledge of the individuals' facial arterial map is critical for planning of these interventions and could improve the results and also prevent complications. 3 Among the blood suppliers of the face, the facial artery is playing the most essential role since it has a rich blood flow and many branches in different depths of the facial region. 4,5 The facial artery arises from the external carotid artery, runs along the masseter muscle, then moving gradually anteriorly, gives off the two labial arteries near the angle of the mouth. The terminal part of the facial artery is the angular artery which ascends to the medial angle of the eye and anastomoses with branches of the ophthalmic artery.
The transverse facial artery arises from the superficial temporal artery before it leaves the parotid gland. It crosses the parotid, passing masseter superficially and transversely. 6 The supratrochlear and supraorbital arteries originate from the ophthalmic artery and provide the blood supply of the glabella and forehead. 7 The existing normal anatomic variations of the facial artery and its branches is shown in previous studies and needs proper consideration and management during facial procedures. 8 These variations are more apparent in angular and infraorbital branches of this artery according to previous studies. 9 Radiologic imaging modalities have been used to evaluate facial artery and its branches. 10 Color Doppler ultrasonography (US) is one the available and noninvasive radiologic method to evaluate the anatomic mapping, normal variations, and also the flow of artery and could provide details of the probable arterial variations and effectively prevent unpredictable vessel damage during interventions. [11][12][13] Iran is one of the countries with highest prevalence of cosmetic and aesthetic procedures and the trends has been growing in the past decades. 14,15 Since most of these procedures are taking place in the facial region, placing the facial artery and its branches besides the other arteries of face at risk of invasion and serious vascular complications, we aimed to assess the normal variations of the facial artery in a normal sample of Iranian population via color Doppler US.

| Study design and population
We designed this case series study taking place in the dermatology Razi hospital as a referral research, educational, and therapeutic dermatologic center affiliated with Tehran University of Medical Sciences, Tehran, Iran, from January to December 2020. We recruited 43 normal participants aged 20-60 years old presenting for dermal filler injection through a convenient sampling method. We assessed the facial arteries and its branches in addition to angular, supraorbital, supratrochlear, and transverse facial arteries at both side of the face by color Doppler US. The exclusion criteria were history of facial surgery and trauma, history of filler injection in the face, and current smoking.

| Study variables
Patients' age, sex, and body mass index (BMI) were recorded as important demographic characteristics. To achieve the study aims, an expert radiologist in dermatologic field evaluated 86 facial artery and its branches in addition to angular, supraorbital, supratrochlear, and transverse facial arteries. B-mode and color Doppler US via SuperSonic Aixplorer MACH 20 machine and its linear superficial probe with 18 MHz frequencies was used for the evaluation of the arteries. The distance between the arteries of face and reference lines, and depth of arteries were the main assessed items by the radiologist.
A schematic map of reference line for the evaluation of arteries of the face included in this study is provided in Figure 1

Conclusions:
Color Doppler ultrasound could be used to map the arteries of face to prevent vascular complications and safely guide cosmetic procedures.

K E Y W O R D S
aesthetic procedure, anatomical variation, arteries of face, color Doppler ultrasound, filler injection facial artery was measured as it crossed the anterior border of the masseter, and the distance measured from this point to the lateral canthus. The supratrochlear and supraorbital arteries were assessed in a straight line parallel to superior orbital rim and distance from mid glabella. We used superior orbital rim as reference line because it is a potential danger zone for filler injection. Supratrochlear and supraorbital arteries are branches of ophthalmic artery traverse through corrugator, then through the frontalis and orbicularis muscles to enter the subcutaneous plan 15-25 mm above the orbital rim for supratrochlear artery and 20-40 mm above the orbital rim for supraorbital artery. 16,17 Moreover, the distance from reference line was evaluated by locating each artery at the center of the ultrasound image and marked the center of probe with white face marker and then used flexible ruler on the participant skin and measured its distance from the defined landmark ( Figure 2). The US examination cross-sectional images are provided in Figure 3 for more details.

| Statistical analysis
Regarding the descriptive presentation of results, the quantitative variables were reported as mean and standard deviation (SD) and the qualitative variables were described in frequency and percentage in this study. Chi-squared, independent samples T-test, and Pearson correlation tests were utilized to investigate the association between variables. p-values less than 0.05 were assumed statistically significant. All statistical analyses were conducted by the SPSS Statistics software (SPSS for Windows, Version 16.0, SPSS Inc.).

| Facial artery
The number of absent facial artery was zero in level one, three spectively. In comparison, the estimated depths and distances were not statistically different in level one. In level two, both of these measures were significantly higher in the left side. In the level three assessment, only the measured distance was statistically different between the two sides of face (Table 1, Figure S1).

| Angular artery
The angular artery was absent in 10 (11.62%) participants. The measured depth of the angular artery in the right side of the face was 12 (Table 1).

| Sex and BMI
The comparison of the depths and distances from the reference lines of the assessed arteries between two sexes revealed only a significantly greater value of facial artery distance in level 1 in males (p-value: 0.001) (Table 2, Figure S2). Investigating the association between the assessed measures in this study and the BMI of participants, the association between the depth of facial artery in level 2  Previous comparable studies evaluated the anatomical map of only some of these arteries. One of these studies used 13 MHz ultrasound probe showed that the transverse facial artery is present in 75.5% of cases, especially in those with absent facial artery, 12 which are comparable to our study with 68.6% presence of this artery. One of the other arteries of interest in similar publications was the angular artery which was successfully mapped and tracked in a study by color Doppler US, showing that angular artery was absent in 10% of cases at left side, similar to our study with 11.62% absence. 11  Except for the facial and angular arteries, this study mapped the other three important arteries of face including the transverse facial, supratrochlear, and supraorbital arteries which the findings were comparable to similar studies. As a small supplying artery in the midface area, the transverse facial artery arises lateral to the zygomatic major muscle placed below the zygoma bone, and in accompany with angular and infraorbital arteries provide the blood supply of the midface region. 24 In the current study, the transverse facial artery was absent in about one-third of the patients which were comparable to a study that used 13 MHz ultrasound probe showing the transverse facial artery was present in 75.5% of cases, especially in those with absent facial artery, 12 while another study that used computed tomography head angiographies found this artery to be present in 96% of the cases, including a single artery in 95.3% of the cases and a double artery in 4.7% of them. 25 The buccal fat pad, which is located in the anterior of the masseter muscle, is one of the most important and prevalent sites in the face that loose the fat tissue during aging and weight loss, so far as one of the most demanding locations for the application of fillers or fat transfers for tissue augmentation. Due to the fact that the transverse facial artery runs through this area, it is important to determine the precise location (including its depth and passage) in order to avoid complications associated with injections. 26 As a result of the anastomose between the transverse facial artery and the facial artery, there is a potential risk of blindness if filler is injected into the transverse facial artery. 1,27 Also, it is important to pay attention to transverse facial artery during midface flaps and facelift surgeries. 28 Based on anatomical studies, the transverse facial artery has two branches, including a superior emerging branch and a deep emerging branch that supplies the parotid gland, the parotid duct, and the masseter muscle. 6,29 Since the superior emerging branch is located within the subcutaneous tissue, care should be taken when filling the superficial fat of the lateral and medial cheeks. Therefore, using a blunt cannula in this area is one of the best strategies during filler injection.
The supraorbital and supratrochlear arteries, as branches of the ophthalmic artery, residing the upper edge of the orbital rim in the forehead area, are among major concerns for aestheticians since many procedures take place in the forehead in cosmetic interventions. 24 A similar study investigated the anatomy of the supratrochlear artery by doppler ultrasonography and its results suggested that due to specific measured epidermis-artery distance and arteryperiost distance of this artery, injections in the glabellar region at the eyebrow level suggested to be intradermal injections and subcutaneous and supraperiosteal injections should be avoided as much as possible. 30 In the current study, we measured deep branches of these arteries lying in the corrugator muscle at superior orbital rim to find the variance of depth of deep branch of these arteries at this level to find the safe zone for superficial injection at this region.
Upper part of forehead was not examined because of the small size of vessels and difficulty of finding superficial arteries due to easily compressible lumen of small vessel even by minimal probe pressure.

ACK N OWLED G M ENTS
Authors would like thank all who contributed to this study.

CO N FLI C T O F I NTE R E S T
The authors declare no conflicts of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

E TH I C A L A PPROVA L
This study was approved by the ethical committee in research at Tehran University of Medical Sciences (Ethical code: IR.TUMS. MEDICINE.REC.1400.110).

PATI ENT CO N S ENT
All participants provided informed consent prior to participation in this study. The patient exhibited in the ultrasonography images, provided informed consent for publication of the examination images.