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Reconstructive Surgery and Regenerative Medicine Research Centre. Institute of Life Sciences, Swansea University Medical School. Swansea, United KingdomWelsh Centre for Burns and Plastic Surgery, Morriston Hospital, Swansea, United Kingdom
Corresponding author: Professor Iain S. Whitaker MA Cantab PhD FRCS Plast FAcadTM, Reconstructive Surgery & Regenerative Medicine Research Centre, Institute of Life Sciences, Swansea University Medical School, Swansea SA2 8PP, United Kingdom, Tel: 01792205678
Reconstructive Surgery and Regenerative Medicine Research Centre. Institute of Life Sciences, Swansea University Medical School. Swansea, United KingdomWelsh Centre for Burns and Plastic Surgery, Morriston Hospital, Swansea, United Kingdom
Vascular complications from soft tissue fillers can have catastrophic consequences for patients. Adverse events are rare but increasing and appear may be the result of intravascular injection. A comprehensive understanding of 2-dimensional anatomy (distribution) and 3-dimensional anatomy (depth) of facial vasculature is fundamental for the safe delivery of non-surgical cosmetic procedures. The purpose of this review is to provide an illustrated approach to examine surgical anatomy specific to the facial vascular system and the anatomical considerations clinicians need to give in specific danger during injectable cosmetic procedures. A grounding in safety and anatomy will help the new injector mitigate the risk of vascular complications.
Non-surgical injectable procedures to improve facial attractiveness are a challenge complicated by different ethnicity and a demanding and diverse society.
Internet access and social media platforms are responsible for the rapid globalization of the perception of beauty in all ages. Snapchat and Facetune dysmorphia especially prevalent in Millennials show no geographical boundary and transcend cultural differences.
The societal and cultural pursuit of perfection is increasing and appears to be a key determinant in the rapidly increasing popularity of injectable cosmetic procedures.
Hyaluronic acid (HA) filler products for injection have been globally available since 1996 with the first report of vascular complications described within the literature in 2002.
The Aesthetic Plastic Surgery National Databank Statistics for 2018 recorded a total of 810,240 HA filler for non-surgical cosmetic procedures in the United States with the reported adverse events increased by 130% from 2015 to 2019.
The most serious adverse event relates to embolization of soft tissue filler in the arterial circulation which travels to regions most vulnerable to ischaemia because of limited collateral perfusion e.g. the glabellar region.
The aim of this narrative review is to provide and illustrated approach to examining facial anatomy specific to the facial vascular system critical to delivery of lower risk injectable cosmetic procedures and to define the anatomical structures and risk zones critical to avoid complications. By providing the visual and descriptive basis for a grounding in safety and anatomy this article contributes mitigating the risk of vascular complications for the new injector.
Methods
The methodology for this narrative review included the identification of data from meta- analyses, randomized control studies, and case reports of adverse events following HA filler injections for non-surgical cosmetic procedures. A review of current publications was performed to determine the relationship between vascular compromise, anatomical danger zones, the use of HA dermal fillers, and protocols for complication. A search strategy was developed and applied to search the Embase (1980-2020) and MEDLINE (1946-2020) databases for relevant literature. A concept table was generated to define the research question according to the patient, intervention, comparator, outcome and study design (PICOS) principle and also apply inclusion and exclusion criteria (Table 1). The search strategy is shown in (Table 2).
Table 1Concept table.
PICOS element
Inclusion criteria
Exclusion criteria
Problem
Humans Animals
In vitro experiments
Intervention
Hyaluronic acid fillers
Non-hyaluronic acid fillers Other injectables
Comparison/control
-
-
Outcome
Vascular (arterial and venous) events and complications including thrombus formation, embolization, occlusion, compression and vasospasm
Plastic surgery intervention Infection Swelling Nodule formation
Study design
English language texts Case Studies Randomised controlled trials Review articles Meta-analysis Studies dated 2010-2020
Non-English language texts Studies dates prior to 2010
Table 2MeSH (Medical Subject Headings) terms and search strategy.
Vascular
And
Complications
And
Injectables
Vascular* OR Arterial OR Artery OR Vein OR Venous Or Vessel* OR Anatom*
Complicat* OR Adverse effect OR Thrombosis OR Thrombus OR *embolic OR Embolous OR Necrosis OR Necroti* OR Occlusion Or Occlude* OR Clot OR Blind* OR Danger* OR Compress* Or Spasm
Injectable* OR Injection* OR Filler OR HA OR Hyaluron* OR Implant OR HA Filler
Anatomical consideration of vascular risk in the face
The facial arterial blood supply is highly variable in 2-D pattern (distribution) and 3-D (depth) between faces and contralateral sides of the same face.
The arterial supply of the face originates from the two branches of common carotid arteries. The external carotid artery (ECA) generally perfuses the structures within the viscerocranium while the internal carotid artery (ICA) the neurocranium.
Multiple anastomoses exist to ensure a collateral supply with strong ipsilateral contributions between the ECA and ICA through the ophthalmic artery pathway for intra- and extracranial perfusion. ECA and tributaries are the main arterial supply for the face (Figure 1) while the major contribution of forehead arises from the ophthalmic artery branch of the ICA.
Deep and superficial fascial vascular plexuses exit connected by perforators over the entire face. The anterior zones of the face have a cutaneous supply related to musculocutaneous perforators with the lateral arterial supply from arising from fasciocutaneous perforators. Predicting 3-D anatomical depth and 2-D anatomical distribution allows practitioners to develop techniques to help mitigate vascular adverse events.
The face generally consists of five concentric anatomical layers from superficial to deep: skin (layer 1), superficial fat (layer 2), muscle (layer three), deep fat (layer four) and bone (layer five) (Figure 2). Layer 4 is also referred to as a layer of spaces/gliding planes and containing retaining ligaments as described by Mendelson.
There are only three exceptions to the five layers of the face concept, the temple (10 layers) the tear trough (three layers) and the preauricular region (seven layers). There is a statistical predictable consistency of the 3-D depth of vessels within these layers.
The nose and glabella form most reported cases of blindness although moderate risk sites include the nasolabial folds, forehead, periocular region, temple, and cheek.
The assessment of a patient for HA filler injection can be guided by the respective anatomical subunit. Each anatomical subunit differs in risk, injection technique and product rheology. The main objective remains consistent – to avoid high risk procedures while providing the patient with their ideal aesthetic outcome. We offer consideration of these factors in the following six facial anatomical subunits: (1) forehead and glabella complex; (2) temple; (3) cheeks and nasolabial fold; (4) nose (5) lips and perioral region; and (6) chin and jawline.
Forehead and glabella complex
The forehead has distinct anatomical boundaries: superiorly at the hairline, the superior boarder of the orbit inferiorly and the laterally the superior temporal fusion line.
The forehead consists of five distinct layers and the vascular architecture of the region is well documented.
The ophthalmic artery (OA)
The OA is the first intracranial branch of the ICA arising within the middle cranial fossa perfusing the eye and surrounding periorbital region. This artery is the major arterial anastomosis between the ICA and ECA.
The central retinal artery is a significant branch for vascular complications supplying the retina. The superficial branches of OA supply the skin of the forehead: supratrochlear, supraorbital and dorsal nasal artery.
The supratrochlear artery (STr)
The STr artery is a terminal branch of the OA which exits the orbit 17-22mm lateral to the midline. The STr artery traverses the margin of the orbit emerging deep from a supratrochlear notch or foramen before transitioning more superficially as it ascends cranially (Figure 3).
At the orbital margin the STr artery perforates or is superficial to corrugator supercilii and deep to both orbicularis oculi and frontalis muscles. The vessel ascends to reach the middle frontal septum at approximately 13-17mm in midline where it transitions superficially through frontalis and orbicularis oculi to the overlying fascia in the subcutaneous plane.
An ultrasound-based investigation by Cotofana et al has shown that the deep branch of the STr artery changes plane from deep to superficial to the frontalis muscle at a mean distance of 14mm (range, 10.0-19.0mm in males, 4.0-27.0mm in females) when measured from the superior orbital rim.
The average entire volume of the STr artery from the glabella to the orbital apex is 0.085ml (range 0.04–0.12ml), and injection volume should not exceed this volume at critical injection points.
The SOA is another terminal branch of the OA and exits the orbit via a supraorbital notch or foramina around 32mm laterally to the midline corresponding to a line vertical from the medial limbus of the eye.
The SOA emerges deep, ascends cranially with variable distribution. The medial course perforates the corrugator supercilii but the lateral course does not contact the muscle.
The SOA ascends in the inferior frontal septum and at the junction with the middle frontal septum gives perforators to supply the periosteum. In the same ultrasound-based investigation of the STr artery by Cotofana et al, the deep branch of SOA changed plane from deep to superficial to the frontalis muscle at a mean distance of 13 mm (range, 7.0-19.0 mm) in males and at 14 mm (range, 4.0-24.0 mm) in females when measured from the superior orbital rim.
The SOA has both deep and superficial branches that anastomose with the superficial temporal artery both medially and laterally.
The superficial temporal artery (STA)
The STA is a terminal branch and most cranial tributary of the ECA possessing complex anastomoses within the forehead. STA connections with the supratrochlear, supraorbital, dorsal nasal (DNA) and angular arteries (AA) generally in the region lateral inferior and middle third of the forehead. The frontal branch of STA is located over frontalis approximately 15mm superior and 14mm posterior to the peak of the brow having multiple anastomoses with the contralateral branch.
The midline can possess the central artery from the DNA and paracentral arteries branches from the angular artery. The glabella represents a high-risk area for potential anastomoses between branches of ICA and the ECA with direct pathways to the vascular supply of the eye.
The temple has distinct boundaries: the superior temporal fusion line forms a curved boundary both superiorly and anteriorly, the frontal process of zygomatic bone anteriorly and inferiorly the arch of the zygoma before transitioning to the midface. There are 10, often contested, distinct layers in the temple and specific vascular distribution can be found in respective layers.
This vessel can be classified into 3 groups by anatomical relationship and bifurcation from the source vessels. The originate is approximately 11.3 mm in front of the midpoint of the apex of the tragus, with most trunks located less than 20.0 mm above the zygomatic arch.
The rich plexus of anastomose between ECA and ICA represent a high risk for vascular complications through the eyelid vessels. The mean diameter of the zygomatico-orbital artery is 1.2 ± 0.2 mm and has an average depth of 5.61mm and 8.50cm long.
The LA is the second and the largest branch of the OA. It enters the orbit and traverses along the superior edge of the lateral rectus muscle. It supplies the eyelids, lacrimal gland, and conjunctiva. The lacrimal artery is a branch of the OA system and gives 2 branches: zygomaticofacial artery and zygomaticotemporal artery.
The zygomaticotemporal artery (ZA)
The zygomaticotemporal artery (ZA) exits a small foramen in the lateral wall of the orbit and contributes to the blood supply of the temple. The ZA perforates the orbicularis oculi muscle in a variable 2-D pattern forming a rich plexus in lateral orbital and temple region.
The superficial temporal artery (STA)
At the superior border of the zygomatic arch the STA gives off the middle temporal artery. Ascending cranially over the zygomatic arch the vessel bifurcates into frontal and parietal branches on average 3cm superior to apex of the tragus showing a mean deviation of 87 degrees. The vessels perfuse the forehead-temple part of the zygomatic complex and ear.
The mean diameter of the frontal branch is approximately 2mm and always situated 10mm anterior and 10mm superior from the apex of the tragus and lies within the superficial temporal fascia.
The STA traverses the temporal fusion line and changes planes to a subcutaneous plane anastomosing with the tributaries of the ICA of the forehead. The STA is often visible and palpable following a tortuous course.
The middle temporal arteries (MTA)
The MTA branches from the STA above the zygomatic arch before transition deep to perfuse the deep temporal fascia and gives multiple branches that supply the temporalis muscle. The MTA anastomoses with the anterior and posterior deep temporal arteries.
Deep temporal arteries (DTA)
Deep in the temporal fossa the anterior deep and posterior deep temporal arteries run cranially at 1.5-2cm and 2.5-3.0cm from the lateral orbital rim and perfuse the temporalis muscle.
The main blood supply for the cheeks originates from the transverse facial artery and the facial artery. The buccal artery, a branch of the maxillary artery, contributes to the blood supply in the buccal region of the cheek.
The upper portion of the cheek over the zygoma is supplied by the ZFA arising deep on the zygoma through a foramen. A branch of the lacrimal artery representing potential danger zone back the OA and vision disturbance via an anastomosis between ECA and ICA or direct intravascular injection in the region. The ZFA is a small vessel with a diameter of 0.3mm.
The TFA has its origin in the parotid gland as a branch from the superficial temporal artery. At the origin the TFA has a mean diameter of around 1mm (+/- 0.4mm) and follows a transverse course parallel approximately 2cm below the zygomatic arch.
The TFA is divided into superior and inferior trunks in the gland and then crosses the masseter. It has been classified into four types according to branching patterns. The TFA has a significant role in the blood supply to the lateral face.
This artery can anastomose with the facial and infraorbital artery and supplies the parotid gland and duct, facial nerve, facial musculature, and the skin in the lateral and medial face.
The infraorbital artery (IAO)
The IAO is a terminal branch of the maxillary artery and on exiting the maxilla via the infraorbital foramen, approximate 9.1mm below the orbital rim, it divides into multiple branches.
There are three main branches of the IOA involved in the perfusion of the infraorbital and midface and upper lip region (Figure 4) with the average diameter of all IOA branches being 0.5mm.
The ZMB becomes superficial around 17 mm medial to the edge of the zygomatic arch, and travels in the infraorbital fat pad before perfusing skin of the cheek.
3
Vestibular artery branch (VB) also known as the labial branch.
The VB supplies the vestibule and oral mucosa of the upper jaw. It has a diameter of 0.7mm and was found to be too narrow to disrupt when cannula technique is performed.
The FA has an extremely tortuous course that provides excess vessel length allowing open the oral cavity and expression without extension that would constrict the bore and restrict blood flow.
Evaluation of the facial artery on computed tomographic angiography using 64-slice multidetector computed tomography: implications for facial reconstruction in plastic surgery.
Adapted from Furukawa M, Mathes DW, Anzai Y. Evaluation of the facial artery on computed tomographic angiography using 64-slice multidetector computed tomography: implications for facial reconstruction in plastic surgery. Plast Reconstr Surg 2013; 131: 526–535.
An intermediate course that terminates at the superior labial artery (Figure 5. 2).
3
The short course which terminates before the superior labial artery (Figure 5. 3).
4
The duplex course that shows a dominant lateral angular branch (Figure 5. 4).
The FA courses the lower border of the mandible and curves upwards to the lateral aspect at the pre-masseteric notch beneath platysma. Deep in the buccal space ascending with tortuous course and approximately 2.14mm diameter.
Evaluation of the facial artery on computed tomographic angiography using 64-slice multidetector computed tomography: implications for facial reconstruction in plastic surgery.
The FA is fixed by a muscular band from buccinator approximately 15mm posterior to the commissures close to the modiolus and between buccinator and platysma and the converging muscles of facial expression.
The AA is a small tributary of the FA traversing a tortuous 2-D path in the dermis of the NLF presenting medial (42.9%), lateral (23.2%), or crossing the NLF (33.9%) (Figure 6).
New anatomical insights on the course and branching patterns of the facial artery: clinical implications of injectable treatments to the nasolabial fold and nasojugal groove.
The AA may occasionally follow a deeper course along the roof of the deep pyriform space. Injection deep on bone in this region reduces the risk of adverse vascular events.
As AA ascends it anastomoses with vascular branches of the lateral nose and medial branches of the infraorbital artery forming a complex rich plexus of collateral supply.
Medial (above left, 42.9%), lateral (above right, 23.2%) and crossing the variations (below left and right, 33.9%).
Adapted from Yang H-M, Lee J-G, Hu K-S, et al. New anatomical insights on the course and branching patterns of the facial artery: clinical implications of injectable treatments to the nasolabial fold and nasojugal groove. Plast Reconstr Surg 2014; 133: 1077–1082.
After transitioning the NLF there are four branching patterns of the AA (Figure 7).
1
This distribution pattern originates cranially at the branch of LNA adjacent to the ala of the nose (Figure 7, Type I).
2
This is the detouring pattern in which the AA traverses continuously from the detouring branch of the FA and ascends cranially to the nasojugal groove and medial canthal areas (Figure 7, Type II).
3
An alternative pattern in which the AA originates only from the OA and demonstrating a reverse blood flow direction (Figure 7, Type III).
Adapted from Kim YS, Choi DY, Gil YC, Hu KS, Tansatit T, Kim HJ. The anatomical origin and course of the angular artery regarding its clinical implications. Dermatologic Surgery. 2014 Oct 1;40(10):1070-6.
The nose is a highly vascular structure with complex anastomoses between the ICA and ECA. The literature now indicates that soft tissue filler injections for non-surgical rhinoplasty is the primary cause of vision loss.
The 5 layers of the nose include skin, superficial fat, muscle and fascia (superficial musculoaponeurotic layer [SMAS]), areolar tissue and cartilage/bone.
The superficial blood supply of the nose is located above the nasal SMAS (Figure 8) and is composed of a complex multidirectional anastomotic system of the ECA and the ICA.
The vasculature of the nose has three main arterial distribution patterns in the 2-D plane. The source of the blood supply identifies the patterns according to facial, dorsal nasal, or infraorbital.
The complex plexus of vessels that supply the highly vascular nose also include superior labial, columellar and the superior and inferior alar arteries as well as a contralateral supply.
The DNA traverses out of the orbit through the orbital septum and runs approximately 5mm superiorly to the medial canthal ligament. Deep to orbicularis oculi anastomosing with the contralateral DNA on nasal bone at the origin of procerus muscle. The DNA has multiple plexus of anastomoses with angular, palpebral and supratrochlear arteries.
The lateral nasal artery (LNA)
The LNA is the main blood supply to the tip with DNA the main blood supply to the upper portion of the nose. The vessel has an internal diameter of approximately 0.5mm and branches from the AA several times along the lateral border of the nose.
The lip can be classified into four zones – cutaneous portion, intramuscular portion containing orbicularis oris, red vermillion (dry oral mucosae) and the mucosal lip (wet oral mucosa) in respect to arterial position (Figure 9). The blood supply includes the following arteries.
Figure 9Classification of the lip into four zones.
The SLA branches around the level of the commissure having an average external diameter of 1.6mm (0.6-2.8mm) and lumen diameter of 0.85mm+/-0.34mm diminishing to 0.56+/-0.21mm at the midline.
The SLA traverses in the subcutaneous layer between orbicularis oris and the skin before transitioning deep to anastomose with the contralateral vessel forming a rich arterial plexus (Figure 10). In Caucasians the SLA was found submucosal in 78.1%, intramuscular in 17.6% and subcutaneous in 2.6% but transitioned between planes once 16% and twice 13% taking a more consistent course than the ILA.
The SLA provides multiple small caliber superficial and deep perforator septal and columella vessels ascending to supply the upper cutaneous lip tissue forming a rich nasal tip plexus. Similar position of this vessel has also been confirmed in Asian lip morphology by ultrasonographic evidence.
At origin of ILA the diameter is 1.6mm and runs towards midline and forms a rich plexus with the contralateral ILA, labiomental, mental and submental arteries.
In Caucasian, the ILA travels inferior to the vermillion border with a distribution pattern identified to course submucosally 78.1 % intramuscular 17.3% and subcutaneously 1.7% but transitioned between these planes once 9% and twice 23%.
The variable 2-D and 3-D distribution/depth pattern of these labial arteries is determined by embryogenesis. The vessels formation precedes the formation of the precursor cells for orbicularis oris muscle which forms around the preexisting perioral vasculature.
Many previous studies have suggested guideline for lower risk injection depth of soft tissue fillers for lip augmentation recommending intimate knowledge of lip topography is fundamental to prevent complications with superficial injection.
Within the buccal space the FA give a rise to the HLA as a single branch or as a common trunk with the ILA. The HLA perfuses the labiomental region of the chin anastomoses with the ILA to create a complex perioral vascular plexus.
The mental area (chin) derives its perfusion from a rich plexus of anastomoses between the mental artery, the submental artery and the rich plexus of connections between the inferior labial and labiomental arteries.
The current evidence base suggests facial vasculature has variable branching patterns, course (2-D) and depth (3-D). This anatomical knowledge is fundamental in the avoidance of complications and safest practice.
Soft tissue filler complications can be classified according to severity (mild, moderate, or severe); nature (ischemic complications and non-ischemic); or time of onset (early or late).
Intraarterial soft tissue filler embolus have been reported in all branches of the facial and ophthalmic artery which supports the evidence that no region of the face is risk free.
The Role of Anastomotic Vessels in Controlling Tissue Viability and Defining Tissue Necrosis with Special Reference to Complications following Injection of Hyaluronic Acid Fillers.
Vascular complications usually have cutaneous involvement but can extend to the subcutaneous fat, muscle, deep fat, tendons and even bone if unresolved, with potential for life altering consequences including tissue ischemia and loss, visual loss, pulmonary embolization, and stroke.
Vascular complications represent different risks associated with variation in arterial distribution patterns. Patients without an anastomosis between the FA and the DNA have lower risk of visual disturbance than patients with this anastomosis.
It is important to recognise the vast variation in facial vasculature that exists with less than 50% of patients possessing the standard description of FA distribution pattern and of those only 25% are bilaterally symmetrical.
Importantly statistical consistency exists within the literature as to the vessel depth. Cannula rather than a needle is generally considered to be the safest option, but practitioners still need to be vigilant with good anatomical knowledge as there are case reports of blindness following cannula injections.
The topographical areas of the face and the corresponding risk of vascular complications are summarised in Figure 11. The main risk of complications is found in layers two, three and four (Figure 12). The 2-D distribution has highly individual variation but 3-D anatomy is generally regarded as consistent. Regions of the face can be generally classified by risk and the risk is statistically related to the layers in which the vessels are located (Table 3). Understanding the 3-D depth of the vessel allows the injection to be in layers of lower risk. If the vessel has a good 3-D statistical probability to traverse deep in layer 4 then superficial injections in layer 2 reduce the risk and vice versa.
Figure 11Summary of the topographical areas of the face and corresponding risk of vascular complication.
*the superior temple compartment is the target zone. The danger in is the anterior deep temporal arteries in the inferior compartment. The tear trough is a unique area having only three layers, skin, muscle and bone. The layer of maximum risk is superficial layer two above the muscle but below the skin, the layer for injection is below the muscle supra-periosteal but still layer two since the technique creates a small channel between bone and muscle.
In a recent consensus the concept of graded training for nonsurgical cosmetic procedures were introduced highlight anatomical areas of increased risk require more specific training, greater supervision, and access to medical care.
The conclusion was that teaching required rethinking and a graded system from less risk to higher risk be employed. The high-risk indications should only be performed as experience and knowledge increases and conducted in correct clinical settings. Grade one procedures are those with a low risk of intravascular injection and embolic events. Excellent areas for beginner training and included jaw line, chin, marionettes, and lateral cheek. Grade two procedures are those with a moderate risk of intravascular injection and embolic events. These include the lips and perioral region which are considered a high risk for intravascular injection and embolisation but only a moderate risk of visual loss. Grade three procedures are those with a moderate risk with significant risk of serious intravascular injection and visual embolic event. High risk indications require strict technique good anatomical knowledge and product placement include temple nasolabial fold tear trough periorbital and medial cheek. Grade four procedures are those with a very high-risk of significant intravascular injection and blindness. These represent the regions perfused directly by the branches of the ICA. The practitioner requires to have progressed the graded framework, acquiring experience, knowledge, and training. These regions represent the highest risk including the nose glabella and forehead.
An in-depth understanding of applied surgical anatomy is essential for lower risk soft tissue filler injectable procedures. Regulated pathways of progression with core curriculum focused on education and clinical transferable skills are required. Further consideration for a mandatory qualification with specific intent to evaluate tangible competence skill judiciously and precisely without variation and subjectivity is paramount in this fast-moving discipline. In the present study we have focussed on the visual and descriptive basis for a safe approach to HA filler injections during cosmetic procedures. Through this illustrated grounding in surgical relevant anatomy, we hope that the new injector will be able to mitigate the risk of vascular complications in their own practise.
Financial Support
SRA is funded by the Welsh Clinical Academic Training (WCAT) Fellowship. ISW is funded via a EURAPS/AAPS Academic Scholarship.
Institutional ethical approval: None.
Reporting standards: Not applicable.
Conflicts of interest
None.
Acknowledgements
We would like to thank Dr Toni Burke who produced the artwork and illustrations for the article.
Evaluation of the facial artery on computed tomographic angiography using 64-slice multidetector computed tomography: implications for facial reconstruction in plastic surgery.
New anatomical insights on the course and branching patterns of the facial artery: clinical implications of injectable treatments to the nasolabial fold and nasojugal groove.
The Role of Anastomotic Vessels in Controlling Tissue Viability and Defining Tissue Necrosis with Special Reference to Complications following Injection of Hyaluronic Acid Fillers.
Authorship: All listed authors contributed to; 1) conception and design, acquisition of data, analysis and interpretation of data; 2) drafting the article or revising it critically for important intellectual content; 3) final approval of the version to be published; 4) agreement to be accountable for all aspects of the work.
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