Understanding Lip and Perioral Anatomy

The lips and perioral region are a prominent facial feature, providing an essential role in how we present and communicate with each other. The lips, along with the eyes, are part of our central facial triangle representing the features that most often capture attention. Unsurprisingly, the lip and perioral region are highly requested areas for aesthetic rejuvenation, and yet can pose challenges to the aesthetic practitioner due to their dynamic nature and variable vascularity. Every lip is unique, with the ideal lip augmentation creating profile harmonisation, respecting ethnic variation, and fulfilling patient aims for treatment.

This article aims to review some of the latest knowledge with regards to lip and perioral anatomy, their successful treatment, and how to minimise complications.

Individual anatomy

Understanding the underlying anatomy in our injectable region is essential to treat patients safely and effectively. However, individual patient anatomy can vary considerably, and so it’s important to bear this in mind.

The lips can be considered in conjunction with the entire perioral region. The upper lip is bound by the infranasal region superiorly, the nasolabial grooves laterally, to the free edge of the vermilion border. The lower lip extends from the free edge of the lip and the oral commissures laterally, to the inverted U-shaped labiomental crease inferiorly. Above the lips are two vertical philtral columns and their midline depression, the philtrum. The upper and lower lip meet at the oral commissure.¹

The lips themselves are defined by the vermilion-cutaneous junction, with a thin, lighter-coloured line enhancing the characteristic colour from numerous capillaries against the surrounding skin. In the upper lip, two paramedian vermilion prominences form the Cupid’s bow.¹

The layers of the lip can be described from superficial to deep: the epidermis covered by skin, subcutaneous layer, the orbicularis oris muscle fibres and intra-oral mucous membrane. The intra-oral mucous membrane meets the exterior skin of the face at the wet/dry border. Lips can be described as ‘competent’ if lightly closed at rest, and ‘incompetent’ if at rest the lip seal is not maintained.¹

There are a number of muscles acting on the lips, the main group being the orbicularis oris muscle complex that encircles the mouth. The orbicularis oris is composed of long, vertical segments that curl outwards at both superior and inferior free margins to protrude the lips, with another 18 muscles attached (two pairs of nine).¹

The lips receive their blood supply from the labial arteries, running along the free border of the lip. The labial arteries can vary considerably in vessel size and distribution and are commonly torturous. The larger superficial labial artery supplies the upper lip; whilst the lower lip is supplied by the inferior labial artery. Both arise lateral to the oral commissure and pass behind the depressor anguli oris muscle to pierce the orbicularis oris and meet its contralateral partner in the midline.^2,3

The superior labial artery often lies at or above the level of the commissure, spanning on average 45mm and becoming superficial in the midline at 3mm deep.^1,2 It may even be unilateral in just under a third of patients.^2,3 Whilst the superficial labial artery often arises directly from the facial artery, the inferior labial artery by comparison can arise from four additional vessels: the superior labial artery, modiolar artery, ascending mental artery (AMA) and the labiomental artery.^4,5 Both the AMA and the labiomental artery lie superficially, with the former lying laterally to the midline in the submuscular plan, and the latter only 5mm under the skin.⁶

The labial arteries can vary in their depth as they span the lip, and their position can be divided into three regions:⁷

1. Submucosal: behind the orbicularis oris muscle (78.1%)
2. Intramuscular: within the orbicularis oris muscle (17.5%)
3. Subcutaneous: in the keratinised part of the lip (1.7%)

Hence, the lowest risk region is the subcutaneous plain and this is often the target region for aesthetic practitioners.⁷

Sensory nerve supply arrives from the mental and infra-orbital nerves, with movement supplied from the branches of the facial nerve including the buccal and marginal mandibular nerves. The bony support to the lip influences its projection: the maxilla for the upper jaw, the mandible supporting the lower, and the position or absence of the underlying teeth.¹

The danger zones

Aesthetic practitioners should have sufficient anatomical knowledge of the injecting area and have completed high-quality injectable training courses to ensure safe technique for product delivery, such as those registered with the Joint Council for Cosmetic Practitioners (JCCP). The medical practitioner will take a full medical history and undertake a thorough facial examination of the patient. Many complications can be minimised to the lowest possible risk, or certainly anticipated with these basic steps. One can consider there to be no completely safe area to inject in the face; all regions are interconnected and have the potential to reach the ophthalmic and cerebral circulation.⁶

The labial arteries travel in the region close to the vermilion border; in the majority of cases behind the wet/dry border. In the central third of the lip, it becomes more superficial and is more likely to be found within the orbicularis oris muscle itself. The highest risk zones of injection are whenever filler is placed deep (greater than 4mm), or posterior, to the wet/dry border, for instance in the submucosal plane, compared the less risky subcutaneous plane.^7,8,10

The philtral columns are a very infrequently, if ever, requested area for injection, as an enhanced philtrum can distract from the lip, and can be associated with ageing and masculinisation. More often than not, the practitioner decides if product placement may be beneficial in this region, especially as the midline area in both the lip and perioral region is incredibly vascular and potentially dangerous to inject.¹⁰ With regards to the philtral columns, there lie both superficial and deep tissue vascularity in the midline.¹⁰

How to avoid complications

The rise in lip and perioral fillers and their associated vascularity has led to a concern for the potential increase in serious adverse events and complications.¹¹ Their prompt identification and treatment ensure minimal harm to the patient both in the short and long term. Prior to commencing any aesthetic treatment, the patient should be well-informed as part of the consent process with regards to associated risks. These would include, but are not limited to, those frequently occurring and those with significant impact, including swelling, bruising, infection, nodules, palpable product, vascular occlusion, and tissue death.¹¹

Avoid filler in areas without a good blood supply and in areas of active infection or inflammation as these are already compromised areas with relatively poor vascular flow. Patients with a previous hypersensitivity reaction to any ingredients of the filler is an absolute contraindication to treatment. Injectable treatments can activate a dormant herpes simplex virus in those with a history, such that one should consider prophylactic antivirals. Avoid injecting in areas with previous permanent filler placement; a new filler can trigger acute inflammation or infection in these cases.¹²

I would recommend using general strategies to minimise the risk of complications and facilitation of patients’ treatment including:¹²

• Awareness of danger zones
• Product aspiration if applicable
• Slow injection speed with minimal pressure. Stop if resistance is encountered
• Small, superficial, and incremental product placement, for example 0.1-0.2ml
• Small syringe and needle to deliver the product precisely and with slow speed
• Blunt cannula where indicated can minimise bruising and swelling
• Continued patient assessment. Stop if there is any pain or discomfort, and routinely check the capillary refill in the immediately treated and surrounding area
• Massage the treated tissues firmly and consider a cool pack after the procedure

Vascular occlusion

Vascular occlusion is the most serious complication from lip augmentation, which can lead to irreversible tissue death (necrosis), scarring and potential blindness. This can be minimised by product aspiration, small volumes per bolus, and slow gentle product placement.¹² Superficial product placement (i.e. subcutaneously), further reduces the risk, and novel techniques take advantage of this anatomy by using a (shorter) 4mm needle.^13,14 Actively check for vascular occlusion in the treated area using capillary refill technique. You can do this by applying firm digital pressure for five seconds, with blanching resolving within one or two seconds on digit removal in unaffected tissues. In the event of vascular occlusion, current best practice is the treatment with high-dose pulsed hyaluronidase.¹⁵

Management

The use of hyaluronic acid products has a significant advantage in terms of reversing treatment in the event of a complication or dissatisfaction with treatment.¹⁵ The patient should be provided with verbal and written post-treatment instructions and contact details, with the injector easily reachable after treatment. Encourage the patient to get in contact if there are any problems post-treatment and offer a follow-up appointment for further patient support, for example a two-week complimentary review. Other complications can include undertreatment, overtreatment, and asymmetry, all resulting in degrees of patient dissatisfaction; which is why appropriate patient selection, proper consent prior to treatment and continued discussion are all essential to anticipate, manage and resolve these cases. Registering with the Complications in Medical Aesthetic Collaborative (CMAC) and the Aesthetic Complications Expert (ACE) Group World will provide invaluable information regarding aesthetic complications.¹⁵

Minimising the risk

The growing popularity of lip and perioral aesthetic treatments has re-highlighted the importance of understanding the surrounding anatomy and practicing sound techniques. Anatomical knowledge provides an invaluable roadmap to minimising treatment risk. Vascular occlusion is a small but significant complication, and those with an in-depth anatomical knowledge, significant practical training and the ability to recognise a complication, are the most able to treat patients safely.