INTRODUCTION

The facial artery is the main artery of the muscles and skin of the face (^{Pilsl et al., 2016}). The facial artery is a branch of the external carotid artery and arises at the level of the greater cornu of the hyoid bone superior to the lingual artery (^{Kumar et al., 2014}). Anatomical textbooks describe the facial artery coursing upwards over the body of the mandible, passing along the cheek, to the lateral side of the nose and terminating at the medial aspect of the eye (^{Koh et al., 2003}; ^{Loukas et al., 2006}; ^{Lohn et al., 2011}; ^{Drake et al., 2015}; Pilsl et al.). The facial artery has been described as giving off a superior and inferior labial branches as well as a lateral nasal branch, which terminates as the angular artery (Drake et al.). Recent literature has noted additional branches which are not described in textbooks (Koh et al.; Loukas et al.; Lohn et al.; Pilsl et al.). Additional branches include the inferior and superior alar branches, or sometimes referred to as septal and alar branches (Koh et al.; Loukas et al.; Lohn et al.; Pilsl et al.).

Variations of the facial artery exist in the origin, course, branching pattern and termination but these have not been clearly described (Pilsl et al.). The artery has been observed to have anomalous origins with the lingual artery from a linguofacial trunk, as well as having an intraparotid origin (^{Midy et al., 1986}; Koh et al.; ^{Nayak et al., 2006}; Vadgaonkar et al., 2012; ^{Cardinot et al., 2014}).

Termination of the facial artery is variable in the literature (Loukas et al.; Lohn et al.; Pilsl et al.). Early terminations which have been recorded include the facial artery terminating as the submental artery, labial arteries or the alar arteries (Vadgaonkar et al., 2012; Cardinot et al.).There have been reports of the facial artery splitting into an anterior and posterior branch, viz. a duplex artery (Koh et al.; Loukas et al.; Pilsl et al.) or the facial artery terminating prior to reaching the inferior lip, being referred to as an abortive artery. In these cases the arterial supply of the facial artery is then taken over by other arterial branches in the face, such as the transverse facial artery and nasal branch of the ophthalmic artery (^{Bergman et al., 1988}; Vadgaonkar et al., 2012; Cardinot et al.).

Various studies have classified the facial arteries’ branching pattern and termination, but few have reported on the variable origin (^{Troupis et al., 2015}; ^{Mangalgiri et al., 2015}). In addition, few studies have reported on the differences of the facial artery anatomy between sex and laterality. Knowledge of the facial artery patterns’ of distribution is essential in procedures using musculomucosal and island flaps, as well as aesthetic dermatology, especially in female patients who opt for cosmetic surgery (Loukas et al.; Pilsl et al.).

MATERIAL AND METHOD

This study comprised of a sample size of twenty embalmed adult cadaveric heads and necks (11 males and 9 females). The specimens were obtained from the Department of Clinical Anatomy, School of Laboratory Medicine and Medical Sciences at the Nelson R Mandela School of Medicine campus and the Westville campuses of the University of KwaZulu Natal. Ethical clearance was obtained from Biomedical Research Ethics Committee (BREC) of the University of KwaZulu-Natal (BE503/18). The mean age of the cadavers was 79 years old with the age range of between 55-97 years of age.

The skin was reflected and the subcutaneous fat and fascial layers were removed in order to reveal the facial artery. The facial artery was found in the anterior triangle of the neck, within the submandibular triangle. The artery was observed in relation to the submandibular salivary gland, passing either behind it, or laterally over the gland. In order to observe the facial artery origin, the tendon of the posterior digastric muscle was incised and reflected. This muscle tendon was used as a landmark for the origin of the facial artery, which was consistently found deep to this tendon. This however, excluded cases in which there was variation of the origin present.

RESULTS AND DISCUSSION

Twenty embalmed adult cadaveric head and neck specimens were utilised and dissected in the study. However, one of the specimens had a previous surgery on the right side of the face, which made gathering data on the right facial artery not possible. Therefore, the final study sample consisted of 39 facial arteries (20 left and 19 right). The standard anatomic definitions of the facial artery do not include many of the possible variations which have been found in this study and previous studies.

Origin: The description of the origin of the facial artery was based on its origin from the parent trunk (external carotid artery) and the level at which the artery originated. In 84.62 % (89.47 % right, 80 % left) of cases the facial artery followed the standard anatomical description i.e. it arose from the parent trunk (Fig. 1a). Many authors noted variations in origin, such as the facial artery originating with the lingual artery from a common trunk viz. the linguofacial trunk (^{Ozgur et al., 2008}; Troupis et al.), and an intraparotid origin (^{Mangalgiri et al., 2015}). Although the current study did not find any intraparotid origins, it did observe origins from the linguofacial trunk (Fig. 1b) in 12.82 % of the specimens [Right 2/19 (10.53 %); Left 3/20 (15 %)]. In addition, the current study observed that the male specimens showed a higher number of variations in origin when compared to the female specimens [Male: 3/21 (14.29 %); Female: 2/18 (11.11 %)]. A variation noted by the study, was a case in which the facial artery originated higher up, below the mandible on the left side of a male specimen [1/ 20 (5 %)]. Such a variation was not noted in previous studies. Statistical analysis showed that the presence or absence of a linguofacial trunk on the right (p=0.937) and the left (p=0.592) was not dependent on sex.

Fig. 1 Origin observations of the facial artery [Standard anatomical origin (A); Linguofacial trunk origin (B)]. ECA. External carotid artery; FA. Facial artery; LA. Lingual artery; DT. Digastric tendon; LFT. Lingofacial trunk. 

Branching: The branching patterns of this study were classified into six types based on the origin of the branches (Fig. 2; Table I).

Fig. 2 Schematic of branching pattern classifications used in the current study. 

Table I Classification of branching patterns of facial artery. 

^{Key: FA - Facial artery; IL - Inferior labial; SL- Superior labial; IA- Inferior alar; SA - Superior alar; LN - Lateral nasal; AA - Angular artery}.

Type 1, each of the branches arose separately from the facial artery, as in the standard anatomic definition (Fig. 3). This occurred in 25/39 (64.10 %) overall [Right: 11/19 (57.89 %); Left 17/20 (85 %); Male: 15/21 (71.43 %); Female: 13/ 18 (72.22 %)].

Fig. 3 Standard anatomical branching pattern (Type 1). FA. Facial artery; IL. Inferior labial artery; SL. Superior labial artery; IA. Inferior alar artery; SA. Superior alar artery; LN. Lateral nasal artery; AA. Angular artery. 

Type 2, the superior labial branch gave off the inferior alar branch. This occurred in 7/39 (17.95 %) overall [Right: 7/ 19 (36.84 %); Left: 0/20 (0 %); Male: 4/21 (19.05 %); Female: 3/18 (16.67 %)].

Type 3, the superior and inferior labial branches originated from a common trunk and the facial artery had early termination. This occurred in 1/39 (2.56 %) overall [Right: 0/19 (0 %); Left: 1/20 (5 %); Male: 1/21 (4.76 %); Female: 0/18 (0 %)].

Type 4, the superior and inferior alar branches came from a common trunk and no superior labial and inferior labial branches were present. This occurred in 1/39 (2.56 %) in a female specimen on the left.

Type 5, the facial artery was rudimentary, which is when the artery terminated after giving off an inferior labial artery, but before reaching the upper lip. This occurred in 1/39 (2.56 %) in a male specimen on the right.

Type 6, the facial artery was abortive, which is when the facial artery gives off no facial branches. This occurred in 1/39 (2.56 %) in a female specimen on the left.

Types 1 and 2 were further divided into subtypes, as this study found that although the branches originated from the facial artery in a common manner, their termination and/or the branches present displayed variations (Table I).

Most anatomical textbooks describe the facial branches of the facial artery as arising independently of one another (Drake et al.), which is in agreement with Type 1 of this study. Loukas et al. described five main types of variations based on the patterns observed in their research with regards to the distribution of the branches of the facial artery. The study further described sub-types of each based on the sub-variations within each group. Lohn et al. described six main types of distribution patterns of the facial artery with regards to the final branch of the facial artery. In Lohn et al.’s study, the branching patterns of the six types were further classified into four patterns. Pilsl et al. classified the facial artery into four types based on the course of the artery, the branches present and the terminal branch.

Previous studies have noted branches, such as the superior and inferior alar branches, which are not mentioned in the standard anatomical description of the facial artery (Loukas et al.; Lohn et al.; Pilsl et al.). Each study used their own classifications to categorise these variant branches. Furthermore, their investigations of the facial artery have not comprehensively described the various branches, nor their relation to sex or laterality.

In the current study, the authors used the term inferior alar branch for the facial artery branch, which supplied the inferior part of the nose and septum. The term superior alar branch was used in describing the facial artery branch, which supplied the superior portion of the alar of the nose. A variation where the facial artery gave off an anterior and posterior branch to form a duplex artery was not observed in the current study as in others previously (Koh et al.; Loukas et al.; Lohn et al.). However, the current study observed one case where the superior labial artery on the right side gave rise to the right inferior alar artery, after which crossed over to the left to supply the left inferior alar branch.

This was not noted in any studies previously (Fig. 4). The current study classified this pattern as Subtype 2C. It was observed that there were overall more variations on the left side of the face [Right: 16/19 (84.21 %); Left: 18/20 (90 %)], and variations were more common in the female specimens [Male: 18/21 (85.71 %); Female: 16/18 (88.89 %)]. This finding is relevant as the facial artery could be in danger during cosmetic procedures such as neurotoxin injections and aesthetic enhancements which have become popular amongst females (^{Lazzeri et al., 2012}; ^{Yang et al., 2014}).

Fig. 4 Sub-type 2-C viewed from the right (A) and left (B). FA. Facial artery; IL. Inferior labial artery; SL. Superior labial artery; IA. Inferior alar artery; RIA. Right inferior alar artery; LIA. Left Inferior alar artery; SA. Superior alar artery. 

Termination: Anatomical textbooks describe the termination of the facial artery as the angular artery, located at the medial aspect of the eye (Drake et al.). Many variations in the termination of the facial artery have been described in the literature (Midy et al.; Koh et al.; Loukas et al.; Lohn et al.; Pilsl et al.). The results of the current study showed that the facial artery terminated as the angular artery in only 20.51 % [8/39; Right 3/19 (Females 1/19; Males: 2/19) Left 5/20 (Females 2/20; Males 3/20)] of the specimens observed. The specimens showed variant termination as the inferior labial artery [2/39; 5.13 %; Right 1/19 (Males 1/10, Females 0/9); Left 1/19 (Males 1/11, Females 0/9)], superior labial artery [4/ 39; 10.26 %; Right 0/19; Left 4/20 (Females 3/9; Males 1/ 11)], inferior alar artery [4/39; 10.26 % Right 4/19 (Females 3/9; Males 1/10)], superior alar artery [18/39; 46.15 %; Right 9/19 (Females 4/9; Males 5/10); Left 9/20 (Females 3/9; Males 6/11)] and lateral nasal artery [2/39; 5.13 %; Right 2/19 (Females 1/9; Males 1/10)]. The observed terminations of the facial arteries and their prevalence (%) according to laterality are summarised in Tables II and III.

Cases of abortive arteries have been reported in the literature (Midy et al.; Loukas et al.; Lohn et al.). The current study observed a single abortive artery during dissections on the left side of a female specimen. The current study also observed a rudimentary artery on the right side of a male specimen. A rudimentary artery is a variation where the facial artery one terminates having given off only an inferior labial branch, it has no other significant branches in the face (Loukas et al.). The findings of this study illustrated the need for knowledge of the possible variations as these could cause complications in the cosmetic procedures, should surgeons not be aware of the variations which exist.

Table II Termination of the Facial artery according to laterality. 

Table III P-values for associations between termination and sex on the right and left side. 

CONCLUSION

The current study observed a number of variations of the facial artery amongst individual specimens and according to sex and laterality. Procedures to repair oral defects would make use of musculomucosal, myocutaneous and submental artery island flaps, which require the facial artery blood supply (^{Pribaz et al., 2000}). The information on the facial artery variations in this study can help mitigate the risk of damage to the facial artery during cosmetic procedures such as neurotoxin injections (Lazzeri et al.).