The number of minimally invasive procedures to reduce the signs of facial aging has increased dramatically, in 2017 reaching more than 2.6 million treatments in the United States alone. This represents an increase of 3 percent versus the previous year, and an increase of 312 percent compared to 2000 according to procedural statistics from the American Society of Plastic Surgeons.1The same upward trend was observed for the number of adverse events resulting from minimally invasive facial injections leading to tissue loss, blindness, stroke, and even death.2,3Major adverse events are related to the inadvertent introduction of filler material into the arterial circulation, which is then transported to regions that are particularly vulnerable to ischemia caused by perfusion from the most distal end branches of a distributing artery without collateral supply.
Extracranial and Intracranial Arterial Anastomoses
The head and neck receive their blood supply predominantly from branches of the internal and external carotid arteries.4Typically, the external carotid artery supplies structures within the viscerocranium (i.e., the face and the oral and nasal cavities) (Figs. 1and2), whereas the internal carotid artery supplies the structures of the neurocranium (i.e., the brain and the bony cranial vault) (Figs. 1and2). Collateral blood supply is achieved by multiple connections between the external carotid artery and the internal carotid artery, resulting in identifiable vascular territories (Table 1).5Interestingly, a prospective interventional study assessed the contribution of the ipsilateral external carotid artery to the cerebral perfusion in patients with internal carotid artery occlusion using the grade of the filling of the ophthalmic artery and its consecutive branches (middle cerebral and anterior cerebral arteries, and the carotid siphon) as a marker for the collateral flow.6The study concluded that in patients with symptomatic internal carotid artery occlusion, focal brain regions may strongly depend on the contribution to cerebral perfusion of the external carotid artery ipsilateral to the side of the internal carotid artery occlusion by means of a patent pathway from the ophthalmic artery. These findings highlight the importance of the ophthalmic artery as an anastomotic arterial pathway for extracranial to intracranial perfusion.
The ophthalmic artery is the first intracranial branch of the internal carotid artery and provides blood supply to the eye and the periorbita. The branching pattern of the ophthalmic artery is complicated and unique not only to the individual but also to the eyes of the same person.7In total, 13 branches of the ophthalmic artery can be counted, of which the central retinal and the medial and lateral posterior ciliary arteries provide blood supply to the retina. Other branches of the ophthalmic artery are the lacrimal artery, muscular branches to the extraocular muscles, posterior and anterior ethmoidal arteries, inferior and superior palpebral arteries, supratrochlear artery, supraorbital artery, and dorsal nasal artery.811
The ophthalmic artery can be subdivided into three parts: an intracranial part, an intracanalicular (inside the optic canal) part, and an intraorbital (inside the bony orbit) part. The intraorbital ophthalmic artery can further be subdivided into three segments: the first segment, which is located lateral to the optic nerve; the second segment, oriented medially in an almost horizontal course and crossing the optic nerve (83 percent superior to the optic nerve; 17 percent inferior12); and the third intraorbital segment of the ophthalmic artery, running parallel to the medial wall of the bony orbit and terminating in the medial aspect of the orbit as it connects with the dorsal nasal artery of the contralateral side.8,10,13,14
Central Retinal Artery
The central retinal artery is the first branch of the second segment of the intraorbital segment of the ophthalmic artery, has a diameter between 0.1 and 0.6 mm, and has a variable length between 7 and 20 mm. The central retinal artery pierces the dura and the arachnoid mater of the optic nerve at its medial and/or inferior aspect and runs accompanied by the central retinal vein in the center of the optic nerve. At the location where the central retinal artery pierces the dura and the arachnoid mater to enter the optic nerve, the artery is prone to occlusion as, at this point, it has the narrowest diameter along its course.7,11At the retina, the artery divides into a total of four branches (superior and inferior nasal and temporal branches) and supplies the inner layer of the retina.911,1416Experimental central retinal artery occlusion in elderly, atherosclerotic, and hypertensive rhesus monkeys showed that the retina suffered no detectable damage for up to 97 minutes; however, after that, worsening irreversible damage occurred.17Perfusion of the retina is 0.52 cc/minute per milligram of tissue, which is comparable to that of the brain (0.48 cc/minute per milligram of tissue). The retina, however, receives additional collateral blood supply from the posterior ciliary arteries (sometimes up to five) and/or from the variable cilioretinal arteries,1820which provide oxygenation to the photoreceptors and to the retinal pigment epithelium located within the capillary-free outer retina.21,22This dual blood supply suggests that the time to an irreversible injection-related visual compromise caused by accidental intraarterial injection of soft-tissue fillers might potentially be more than 90 minutes. Investigations have shown that a central retinal artery occlusion is rarely complete when investigated by fluorescein angiography.2325Thus, a definitive declaration regarding time to irreversible injection-related visual compromise cannot be given, but 90 minutes appears to be a reasonable benchmark,2629suggesting that early intervention can potentially save retinal tissue and visual function.
With regard to the proposed30,31injection of hyaluronidase into the retrobulbar or peribulbar region for the treatment of injection-related visual compromise, it is reasonable to perform from an anatomical standpoint if the chance of preventing irreversible blindness in a previously healthy patient is increased. It seems plausible, therefore, to introduce hyaluronidase in proximity to the narrowest location of the central retinal artery (the penetration site of the central retinal artery into the optic nerve). This location is outside the optic nerve and thus in the retrobulbar area surrounded by the intraorbital soft tissues. Application of hyaluronidase in this area might be effective, as it has been shown to counteract intraarterial hyaluronic acid when applied extraarterially.32The hyaluronidase injection procedure is performed by palpating the lateral inferior orbital rim (maximum, 1 cm medial to the lateral canthus). The injector (25-gauge needle with 38 mm or 25-gauge cannula with 38 mm/50 mm) is placed in contact with the lateral inferior orbital margin and then advanced into the orbit in close proximity to the orbital floor. The injector penetrates the skin, subcutaneous fat, orbicularis oculi muscle, and the orbital septum before traversing the temporal (inferior) intraorbital fat pad. The direction of advancement is slightly angled medial and superior because of the conic shape of the bony orbit. At a depth of 30 to 45 mm (depending on the patients physiognomy), a bolus of hyaluronidase is placed in a retrobulbar position inferior to the optic nerve.
Facial Artery (Mandibular Segment)
The facial artery, previously termed external maxillary artery,4branches off the external carotid artery either as a separate branch or as a common branch (the linguofacial trunk) together with the lingual artery. It runs close to the submandibular gland and deep to the investing layer of the deep cervical fascia (Fig. 3). At the angle of the mandible, the facial artery crosses the bone in 100 percent of observed cases anterior to the accompanying vein,33deep to platysma muscle and deep to the marginal mandibular branch of the facial nerve (Fig. 4andTable 2). At this position, the artery is protected by deep fat, which is not connected with the buccal fat pad (of Bichat) or to the fat within the buccal space.3
Facial Artery (Buccal Segment)
After crossing the mandible, the facial artery enters the buccal space, which is bound by the buccinator muscle (deep), the platysma (superficial), modiolus (anterior), facial vein canal (posterior),34mandibular ligament and platysma adherent to the mandible (inferior), and the transverse facial septum (superior)33(Fig. 5). In the buccal space, the facial artery gives off the inferior labial artery and/or the horizontal labiomental artery, which supplies the chin and the lower lip.35The depth of the artery in this location is dependent on the amount of fat in the subcutaneous fat compartments36,37and inside the buccal space.
Three-dimensional reconstruction of a contrast-enhanced cranial computed tomographic scan of the head. The facial artery (FA) and the ophthalmic artery (OA) are indicated. Note the vast facial arterial network and its connections to the ophthalmic artery circulation.
At the modiolus, the artery can be identified in 100 percent of the cases to be in close proximity to the angle of the mouth, where it is connected to the modiolus by a muscular band emerging from the buccinator muscle. This muscular band attaches the artery in its position 1.5 cm posterior to the corner of the mouth (Fig. 6). The artery is thus located between the buccinator muscle (deep) and the modiolar part of the platysma38and the converging muscles of facial expression [i.e., levator anguli oris, zygomaticus major, levator labii superioris, and depressor anguli oris muscles (superficial).
Left facial dissection of a fresh cephalic specimen. The facial artery (FA) is shown to be attached to the modiolus (circle) by a muscular band (arrows) of the buccinator muscle (BM).DAO, depressor anguli oris muscle;FVC, facial vein canal;ZMM, zygomaticus major muscle.
Facial Artery (Lips)
Inferior and superior to the modiolus, the facial artery gives off the inferior and superior labial arteries. A previous study has shown that the course of the labial arteries is not consistent and varies between three positions: submucosal between the oral mucosa and the orbicularis oris muscle (78.1 percent), intramuscular between the two layers of the orbicularis oris muscle, and subcutaneous between the skin and the orbicularis oris muscle (2.1 percent) (Table 2).39This may be explained by the different time-dependent embryologic development, where muscle precursor cells have to form after the arteries have taken their final position, resulting in variability of the arteries in relation to the musculature.40,41
Angular Artery (Nasolabial Sulcus)
The common understanding is that the facial artery is called the angular artery after it gives off the superior labial artery, although various definitions have been published.4245The angular artery runs in the depth of the nasolabial sulcus in proximity to the dermis. A correct prediction of the precise position of the angular artery cannot be made, as the two-dimensional position varies highly between individuals and even between the left and right sides of the same individual (Figs. 7 through 9).44,46With regard to the three-dimensional location, dissection findings showed that within the nasolabial sulcus, the angular artery was more likely to be identified within close relationship to the skin rather than in proximity to the bone (Table 2).
The course of the angular artery between the ala of the nose and the medial canthus is highly variable in both two- and three-dimensional orientations. A recent study of 12 hemifacial fresh cadaveric dissections identified the angular artery running within the deep pyriform space47bound superficially and superiorly by the levator labii superioris alaeque nasi muscle. As it approaches the medial canthus, the angular artery gives off connecting branches to the lateral side of the nose (medially) and connects to the infraorbital artery, as it emerges from the infraorbital foramen.44
Angular Artery (Nose)
The two-dimensional vasculature of the nose has been recently summarized, and three main arterial patterns have been identified, depending on the arterial source: facial, dorsal nasal, and infraorbital.46The nose is highly vascularized, receiving its blood supply not only from the arteries stated above, but also from the superior labial and the columellar arteries, and from arteries and branches originating from the contralateral side (Fig. 9). Of great importance, however, is the three-dimensional course of the arteries. Based on current dissections, preliminary findings suggest that the majority of the arteries lie in the subcutaneous plane, rendering the deep supraperiosteal plane relatively avascular. This is of crucial importance, as nonsurgical rhinoplasty procedures have increased in popularity and are performed using the supraperiosteal or supraperichondrial plane (Table 2).4850
Three-dimensional reconstruction of a contrast-enhanced cranial computed tomographic scan. The arterial network of the glabella (red circle) and the nose (blue circle) is shown after the left facial artery was injected.FA, facial artery;OA, ophthalmic artery;STA, supratrochlear artery;DNA, dorsal nasal artery.
Dorsal Nasal Artery
The dorsal nasal artery is the bilateral terminal branch of the ophthalmic artery. The artery emerges from the orbit and pierces the orbital septum superior to the medial canthal ligament. It runs deep to the orbicularis oculi muscle inferiorly and connects to the contralateral dorsal nasal artery at the origin of the procerus muscle. The dorsal nasal artery has direct connections to the angular artery, to the medial superior and inferior palpebral arteries (both located deep to the orbicularis oculi muscle), to the dorsal nasal arteries (bilateral), and to the supratrochlear artery. The dorsal nasal artery, however, has no direct connections to the supraorbital artery but rather has indirect connections by means of the supratrochlear artery.
Glabellar Arterial Connections
In the glabellar region, multiple connections exist between the left and right dorsal nasal artery, supratrochlear artery, and supraorbital artery (Fig. 9). These connections are subject to high variability in the two-dimensional plane, rendering the glabella a high-risk area for an injection-related visual compromise.3In current dissections, no major arteries were identified deep to the procerus muscle, suggesting that the deep plane may be a safer area versus the subcutaneous layer. Anatomy alone is not sufficient to explain the high incidence of injection-related visual compromise of this region. Considering the fact that most of the injections in this region are performed using a sharp needle, an explanatory model may be constructed. Previous studies have clearly and independent of each other shown51,52that use of a needle significantly distributes the soft-tissue filler into all layers pierced by the tip of the needle along its course to its final position. The material runs retrograde inside the injection canal and can be identified in the subdermal plane even if the needle tip is in contact with bone. Therefore, despite a negative aspiration procedure, because of a through-and-through phenomenon (both sides of an arterial wall are penetrated), the application of soft-tissue fillers could result in an injection-related visual compromise (Table 2).
Like the dorsal nasal artery, the supratrochlear artery (Figs. 9and10) is a terminal branch of the ophthalmic artery and emerges from the supratrochlear notch (or foramen) at the medial superior corner of the bony orbit.53The supratrochlear artery is here in contact with the bone and pierces along its superiorly directed course the corrugator supercilii muscle and the inferior frontal septum entering the subfrontal fat.54The latter is located between the frontalis muscles (superficial) and a fascia covering the deep surface of the frontalis muscle.55When reaching the middle frontal septum, which can be found 1.5 0.17 cm (range, 1.3 to 1.7 cm) in the midline and 3.0 0.24 cm (range, 2.7 to 3.3 cm) laterally when measured from the superior orbital rim,55the artery pierces the frontalis muscle (Figs. 10and11) and its overlying fascia and can be found in the subcutaneous plane.
Virtual model of the face showing the superior (SFS), middle (MFS), and inferior (IFS) frontal septum and the frontalis muscle. The supraorbital and supratrochlear neurovascular structures become more superficial once passing the middle frontal septum.STA, supratrochlear artery;SOA, supraorbital artery
The supraorbital artery emerges from the supraorbital foramen or notch 1 to 3 mm medial to the vertical midpupillary line (Figs. 10and11). The artery emerges in contact with the bone and is located lateral to the supratrochlear vasculature. It has a variable course, and can either pierce the corrugator supercilii muscle (medial course) or have no contact with it (lateral course).53The artery is accompanied by the supraorbital nerve and its vein and becomes more superficial as it pierces the inferior frontal septum, where it gives off a variable number of branches (sometimes larger in diameter) that supply the frontal periosteum.55This neurovascular bundle has continuous fibrous connections to the periosteum and to the subcutaneous plane. These connections extend three-dimensionally and form the boundaries of the superficial5557and the deep forehead compartments.55After it pierces the frontalis muscle at the level of the middle frontal septum (Figs. 10and11), it runs inside the boundaries between the superficial lateral and central forehead compartments. There, the artery gives off a branch that connects to the anterior branch of the superficial temporal artery.
Superficial Temporal and Deep Temporal Arteries
The superficial temporal artery is the most cranial branch of the external carotid artery and emerges from deeper layers into the superficial temporal fascia58in 100 percent of the observed cases 1 cm anterior and 1 cm superior from the apex of the tragus. Throughout its course in the temporal region, the artery can be identified inside the superficial temporal fascia (layer 3), which is continuous with the midfacial superficial musculoaponeurotic system and the galea aponeurotica of the scalp.59After crossing the temporal crest, the artery changes planes and can be found in the subcutaneous plane (layer 2) in the forehead (Fig. 12), where it connects with branches of the supraorbital artery. In contrast, the middle zygomaticotemporal vein is identified inside the superficial temporal fat pad (layer 6) and changes planes at the lower temporal compartment and runs deep to the orbicularis oculi muscle (layer 4) toward the forehead, where it is called sentinel vein (Fig. 12).6062
Three-dimensional reconstruction of a contrast-enhanced cranial computed tomographic scan. The superficial temporal artery (main trunk) and its anterior (AB) and posterior branches (PB) are shown. The medial zygomaticotemporal vein (MZTV) and the sentinel vein (SV) are located deep to the arteries.
In the depth of the temporal fossa and in close relationship with the periosteum, the anterior and posterior deep temporal arteries can be identified. When measured to the lateral orbital rim, they have a longitudinal course with 1.5 to 2 cm posterior (lateral) for the anterior deep temporal artery and 2.5 to 3.0 cm for the posterior deep temporal artery (Fig. 13). Performing the deep injection technique in the temple, the proposed one up and one down technique (when measured from the point of fusion between the temporal crest and the superior orbital rim) might thus be a good landmark to place the product anterior to the (anterior/posterior) deep temporal arteries (Table 2).63
Virtual model of the face showing the location of the anterior and posterior deep temporal arteries inside the temporal fossa.ADTA, anterior deep temporal artery;PDTA, posterior deep temporal artery.
The facial arterial vasculature varies highly between individuals and even between the left and right sides of the face in the same person. Minimally invasive applications of soft-tissue fillers should thus be performed with care and knowledge to avoid injection-related visual compromise. The latter is considered the worst of all possible outcomes, and its pathophysiology is related to the connection of the vascular territories between the internal and the external carotid arteries with ultimate compromise of the retinal arterial blood flow.
Given the high number of soft-tissue filler injections performed worldwide, the number of severe adverse events remains relatively low. Reasons for this are the constantly developing technology (i.e., introduction of blunt-tip cannulas, antidotes such as hyaluronidase and sodium thiosulfate, injection algorithms, consensus recommendations, and adverse events management centers).
Initially, guidelines for safe injection procedures were developed eminence-based but with increasing knowledge and experience transitioned toward evidence-based. Increasing interest in facial anatomy contributed significantly to this development, and anatomy is to date a crucial pillar in the daily life of aesthetic providers. Based on the current understanding of the facial arterial anatomy, the two-dimensional and the three-dimensional location of the facial arteries can be predicted, and minimally invasive injections of soft-tissue fillers can be guided accordingly (Table 2).
In the forehead, the arteries transition from supraperiosteal to subcutaneous locations at the middle frontal septum (i.e., between the lower and the upper forehead), identifying the supraperiosteal plane as a safer plane for the placement of soft-tissue fillers (Table 2). In the temple, the anterior branch of the supratrochlear artery runs inside the superficial temporal fascia, designating the subcutaneous fatty layer as a safer layer, whereas the deep injection technique places the product in contact with the bony temporal fossa, deep to the branches of the facial nerve and deep to the superficial temporal artery. Here, the one up and one down technique has been shown to provide aesthetically appealing and safe results (Table 2). The glabella is a high-risk area because of its rich vasculature, which is ultimately connected to the ophthalmic arterial circulation. Safer locations for the application of soft-tissue fillers have been identified to be the supraperiosteal plane, but also intradermally, as here the product is placed superficial to the majority of the arteries (located in the subcutaneous plane) when treating the static glabellar lines (Table 2).
The midface can be separated into a medial and a lateral midface. In the latter, the arteries are located deep but sparing the zygomatic arch and the angle of the mandible. In the latter two locations, injections can be performed in contact with bone (Table 2). In the medial infraorbital area (i.e., tear trough) and in the lateral area (i.e., malar region), applications can be performed deep and in contact with the bone, as here no major arteries can be identified (Table 2). At the dorsum of the nose, the arteries can be easily detected in the subcutaneous plane. Thus, injections deep to the nasalis muscle can be considered a safer location. Similarly, in the nasolabial sulcus, the artery runs in the subcutaneous plane, enabling health care professionals to treat here using the deep approach [i.e., in contact with the bone (canine fossa)] or intradermally if needed.
In the lower face, the arteries are located deep to the platysma, rendering the subcutaneous plane a safer layer. This applies to the upper and lower lips as well, where the safest location seems to be the subcutaneous plane (Table 2). A summary for daily clinical use is provided inTable 2.
Most trepidation associated with soft-tissue filler injections centers on the potential for vascular events. An intimate knowledge of the facial arterial anatomy can help injectors mitigate the risk of such serious circumstances and deliver superior aesthetic outcomes safely.
The imaging part of this study received funding from Q-Med AB, Sweden (grant no. 15092016) and MERZ Pharmaceuticals GmbH (grant no. 13072015). Nirusha Lachman received financial support from the Obaid Vascularized Composite Tissue Award. The authors would like to thank Konstantin Frank, Michael P. Smith, Konstantin C. Koban, and Thilo L. Schenck for support during the data acquisition; the team of the Sectra Visualization Table from Linkping, Sweden, during the data visualization; and the team at Nestl Skin Health SHIELD, the Chamberlain Group, and BioDigital for the ideation and development of the facial model.Table 2was generated in collaboration with Jeremy Green, Hassan Galadari, Marina Landau, Tatjana Pavicic, Gabriela Casabona, Sabrina Fabi, Steve Dayan, Andre Braz, Gary Monheit, Torsten Walker, John Rogers, Valeria Lopez, Fabio Ingallina, Carlo Di Gregorio, Giovanni Salti, Jeff Downie, Andreas Nikolis, Stephanie Lam, Luiz Eduardo Avelar, and Alessandra Haddad.