Commentary on: Anatomical Variations in the Course of Labial Arteries: A Literature Review

This commentary refers to a review article regarding the anatomic variations in the course of the labial arteries by Samisadeh et al.1 The authors propose that careful, thorough knowledge of these labial vessels will protect against accidental vascular adverse events (VAE). The authors claim that in-depth understanding of the precise position and course of the labial arteries is “critical for safe injection and prevention of complications.” If only that were true. In my opinion, there are higher risk and lower risk areas, but unfortunately there are no “safe” areas to inject because anatomy at these small scales is not predictable. There exists some non-zero degree of risk of VAE regardless of the knowledge and experience of the injector. Some of the best and most knowledgeable among us have experienced VAEs not because we were lacking in anatomical knowledge or experience of technique, but rather because there always exists some risk that we cannot eliminate. This subtle but important distinction is not reflected in the language of this article, and I disagree with the premise that in-depth understanding of the anatomy will prevent vascular complications. Over the years, I have prepared many anatomic specimens in preparation for anatomy workshops or for publication. I have observed that vascular anatomy is variable not only between different specimens but also from side to side within the same specimen. In general, the degree of anatomical consistency between specimens varies with arterial size, with the smaller vessels demonstrating proportionally more variability than the larger named vessels. Most would agree that it is probably not possible to predict the precise origin and course of the smallest facial arteries. The main facial artery crosses the mandibular border within a thumb breadth of the anterior border of the masseter and then passes superiorly and anteriorly to pass within a thumb breadth of the oral commissure.2 This information tells us little about the branches to the chin, lips, and nose, which exhibit variable origins, courses, and branches.3-6 It is not possible to predict their location with any accuracy just by examination, although we can make some statistical probability statement regarding the vessel location (eg, we might state that a vessel will be found in a specific location 80% of the time). The authors offer a good discussion of the variations found in the normal face by analyzing the current peer-reviewed literature.1 They have listed facts and data points, but they fail to further distill or simplify the information into a form that is easier to remember and implement. There are also some reservations about the quality of the information reviewed. All the studies were cadaveric studies, not necessarily reflective of the anatomy of our patients. Furthermore, readers should be aware that some variation exists in the quality of the specimens utilized by the selected publications included in the review. For example, Cotofana et al’s excellent multicenter anatomical study7 used cadaveric data from both preserved anatomical specimens as well as from fresh cadavers. The average age of the fresh anatomical specimens was provided, but not for the preserved specimens. Anatomy laboratories often utilize specimens obtained from elderly donors that frequently feature muscular and fat atrophy (as well as preservation artefact), resulting in distorted surface landmarks on which measurements are based. The overall shape and size of the orbicularis oris muscle (and overlying fatty tissue) varies with age (in fact, it is the indication for treatment). Preservation with formalin and desiccation also cause some changes to the volume and delicate shape of the orbicularis oris muscle within the red lip. Employing data from elderly or preserved specimens to predict precise information regarding the vascular anatomy of young or middle-aged patients introduces some error into the analysis. In addition, some differences are probably also related to sex and race, so the most useful data for our purposes are qualitative and relative rather than absolute. To summarize, the reader should be skeptical about utilizing absolute measurements of vessel location from specific landmarks in living patients if the data were originally derived from preserved anatomic specimens from aged donors originating in genetically distinct populations. The data most applicable to the reader’s patient population would most likely be derived from anatomic specimens of a similar age, gender, and ethnicity (ie, genetic similarity to your patients). It might be helpful to use the inferior labial artery (ILA) location in the central third of the lower lip as an illustrative example. Most of the time the major inferior labial vessel will be found within a few millimeters of the surface of the lip posterior to the wet dry line (see Figure 1, cross-section of the central lower lip in this middle-aged cadaver). This statement was derived from dozens of dissections and is supported by several articles6-11 but disagrees with some very good multi-center studies that utilized preserved cadavers of older individuals.7 In middle-aged specimens (Figures 1 and 2), the vessel in the central one-third of the lip will typically be found in the submucosal plane (or immediately beneath a few superficial muscle fibers of the orbicularis oris), and the artery will typically lie immediately posterior to the wet-dry line of the red lip as clearly shown in the example in Figure 2. In formalin-preserved specimens, the process of preservation and desiccation distorts this relationship slightly such that the vessel appears in a slightly more inferior position. Rarely, the ILA may be found in an anterior position, near the vermillion border, but this is uncommon (reportedly 2%).1 In the lateral one-third of the lower lip, the ILA is typically found mainly inferior to the vermillion border within the orbicularis muscle, but it may sometimes lie on the upper surface of the muscle or rarely in the subcutaneous position, with the greatest variability near the oral commissure (modiolus). The ILA may enter the muscle near the modiolus or may pass anterior to the muscles medially a short distance before entering the orbicularis muscle. Injection of the oral commissure region, especially inferiorly, is very commonly performed, and these vessels should always be considered in these cases. The ILA most often arises from the facial artery (as shown in Figures 3 and 4) then travels superomedially towards the modiolus, but it may also arise from a common branch with the superior labial artery (Figure 5), the second most common pattern. It may also be found in other patterns. The ILA can arise from the facial artery inferiorally, laterally, or superiorly to the modiolus, so you cannot know where it is in this region just by examining your patient. Anatomical specimen showing the inferior labial artery in the central one-third of the lower lip. This is a specimen from a fresh (nonpreserved) female cadaver of 45 years of age. This specimen has not been injected with latex. Note the umbrella handle shape typical of the orbicularis oris muscle in adults (shape typically lost in atrophic, preserved, dehydrated specimens) and the location of the inferior labial artery (blue arrow). The inferior labial artery is deep to the oral mucosa and lying above the orbicularis oris muscle, immediately posterior to the wet-dry line of the lip, the most common location for this vessel in the central one-third of the lips. Reprinted with permission from Oxford University Press.12 Different anatomical specimen (female, aged 60 years, latex injected) showing position of inferior labial artery immediately posterior to the wet dry line. A small rectangular window has been cut in the oral mucosa immediately posterior to the wet dry line of the lower lip (larger blue dots) showing the inferior labial artery in its typical location. The vermillion border (white roll) of the lip is marked with small blue dots and the nasolabial fold has been left in situ for orientation (skin island with blue dots). Lateral view of the right facial artery (female, age 64 years, latex injected). The facial artery crosses the mandibular border, ascends superiorly, just lateral to the depressor anguli oris muscle and towards the inferior part of the nasolabial fold (nasolabial fold skin island left in place for orientation similar to specimen in Figure 5). Note the redundant loops of facial artery while the mouth is being held in the partially open position. (Not shown, the facial artery partially straightens out when jaw is held fully open.) The origin of the labial artery from the facial is shown (blue arrow). This is the most common pattern seen for the origin of the inferior labial artery. Compare with common origin shown in Figure 5. Another view of the same specimen as Figure 3. This photograph shows the redundant loops of the facial artery (yellow tie). The modiolus has a black suture tied across it. The superior labial artery (red arrow) is visible as well as a tiny submucosal vessel (yellow arrow) parallel to it. The origin of the inferior labial is again shown (blue arrow). Latex injected specimens show numerous small cutaneous and mucosal branches. Anatomical specimen (female, exact age unknown, latex injected) showing a common origin of the superior and inferior labial arteries from a common trunk (marked by a black suture) from the facial artery. (Incidental note: please ignore blue India ink staining of a fat compartment.) This is less common origin for the inferior labial artery. Most common origin is shown in previous images. The labial and facial arteries in the vicinity of the modiolus are typically tortuous because of the needed redundancy of length to allow us to open our mouths fully. Without this length redundancy, the arteries would be stretched out as the mouth opened, restricting blood flow. In fresh specimens, these vessels are loosely coiled in soft globular fatty tissues in the region lateral to the oral commissure (Figures 3-5). As the mouth opens, these loops of vessels straighten out. This illustrates another concept: the location of the vessels supplying the lips changes as the jaw is open or closed. Vessel location is not static in the mobile tissues around the lips and mouth. Similarly, when we stretch the overlying skin while conducting the treatment, I suspect we are also altering the underlying vascular anatomy (and this is relatively easy to demonstrate on nonpreserved cadavers). I am not sure if this is clinically significant or not. Finally, some patients will have labiomental arteries that traverse the chin horizontally, parallel to the ILA, and some will also have a vertical vessel near the midline arising from submental vessels. I mention these because they may become involved in injections to improve the projection of the chin or as a result of retrograde flow from the lips in the event of a VAE. The same points made about the variability of the inferior also apply to the superior labial artery. One or more vertical branches may exist from the superior labial that continue to the columella and the other nasal vessels (see an example in Figure 2). There may also be horizontal subalar vessels and/or lateral nasal vessels arising either as branches or terminal vessels of the facial near the nasolabial fold (the angular artery). The angular artery typically (but not always; hint: it is never “always”) anastomoses with the descending nasal branch of the supraorbital vessel (which in turn is one of the terminal vessels of the ophthalmic artery, the first intracranial branch of the internal carotid artery). It is through these collateral vessels (the watershed region between the internal and external carotid circulation) that filler may pass from the lip area all the way to the central retinal vessels. In summary, my concerns with this study involve these main points. First, the data used in the studies reviewed were obtained from cadavers rather than imaging studies of the living. Furthermore, the labial vessels likely change their anatomic relationships based on the position of the jaw as well as the amount of tissue stretch of the lips in the living patient. Second, the cadavers used in the studies utilized many elderly specimens, a skewed, nonrepresentative sample with various degrees of tissue atrophy. We are typically most interested in middle-aged individuals for fillers. Third, preserved specimens with desiccation artefacts probably introduced measurement error that skewed the measurements. Anatomic relations are probably not well maintained in the lips, which change volume dramatically with dehydration. Finally, the entire premise of the article is likely false, namely that knowledge of the normal arterial locations in the lips protects patients from VAEs. To repeat, there are higher risk and lower risk areas, but no zero-risk areas because blood vessels are ubiquitous in living tissues, including the vermillion and the dermis (as can be seen in the latex-filled cadaver photos; see Figure 4). If the tissue is alive, some blood vessels will be present, with very rare exceptions. You may now be wondering, “What’s the point of this?” To be blunt, these smaller vessels, although named, are small and quite variable in size, location, and branching on their way to the lips. No amount of preparation work in the anatomy laboratory will inform the practitioner in advance exactly where the arteries will be in a patient. The good news is that within the central one-third of the lips, the odds are in our favor that the artery will be just deep to that narrow submucosal strip just posterior to the wet dry line of the lips (Figures 1 and 2). Never say always, but if you always assume that the vessel will be located in this region, you will not be often wrong. The location uncertainty increases as we get closer to the corners of the mouth (more variation is typical there). The takea-way message is that we need to exercise caution regardless of location because there are vessels nearby everywhere. Someday soon we will probably have portable transcutaneous arterial viewers akin to the Christie Medical VeinViewer (Christie Medical Holdings, Inc., Memphis, TN) for cutaneous veins. We will (hopefully) someday be able to easily, noninvasively detect the presence of arteries in real time during a treatment session. Until then, we need to be cautious everywhere because we simply cannot eliminate all risk, no matter how much anatomy we know. The author is a paid Medical Director and Consultant for Allergan Canada and Merz Canada. The author received no financial support for the research, authorship, and publication of this article.