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Understanding LesserKnown Vessel Anatomy Dr Emily Swift explores the infrequentlydiscussed vasculature associated with soft tissue for safer injectable treatments Anatomy underpins the safety and predictability of dermal filler procedures. A three-dimensional knowledge of head and neck anatomy is critical in order to carry out lower risk treatments. The face is highly vascular in nature and understanding the location, depth and typical branching patterns of blood vessels is crucially important to reduce the risk of necrosis, blindness, central nervous system complications and even fatality during a vascular occlusion.1 Vessel distribution is highly variable; however, depth is more consistent amongst individuals. The more educated injector understands and applies these core principals in order to visualise facial layers and structures in 3D. This enables the technique and product to be selected accordingly. The facial artery is often discussed in depth within publications and at conferences. It supplies a large proportion of facial skin and its path usually crosses many commonly injected areas. It arises from the external carotid artery and emerges on the face at the anteroinferior angle of the masseter muscle. It has a variable path, but usually runs upwards and forward, winding a tortuous course to the nasolabial line where it becomes the angular artery and passes up the side of the nose.2 Occlusion of arteries via soft tissue filler emboli causes infarction of skin, muscle, gland or organ, including the eye. Blindness can ensue if an embolus of filler occludes the ophthalmic artery (supplying the optic nerve).3,4 The central retinal artery (CRA) is part of ophthalmic artery and thus, the internal carotid system. Any arteries branching from this system have a higher risk of CRA occlusion due to the possibility of retrograde displacement of filler. This occurs if injection pressure exceeds arterial or venous blood pressure and the product moves backwards against the direction of blood flow. When the pressure of
the plunger is released, the filler moves forward again and creates an embolus blockage in a collateral artery branch.3,4 Therefore, any artery branching from the internal carotid artery has the potential to cause blindness if occluded, but also from the external carotid system due to several significant anastomoses between them (Figure 1 & 2).3,4 The equation for the volume for a cylinder (π2h) tells us that just 0.01ml of product would be enough to fill 5cm of a 0.05cm diameter vessel, which explains why very small amounts of filler can cause necrosis or loss of vision.5 Literature covering injectable vascular anatomy often focuses on arteries located in common treatment ‘danger zones’, however, all areas of the face should be classed as a danger zone, as no area is guaranteed to be ‘safe’.6 This article will focus on the lesser discussed vasculature associated with soft tissue in the areas of the most popular procedures.
Zygomatic and lateral orbital zone Cheekbone enhancement involves volume replacement below and lateral to the lateral canthus in the zygomatic zone to enhance the zygomaxillary point and create an attractive ogee curve. Tear trough rejuvenation is often requested due to soft tissue changes around the eye; the palpebromalar groove in the lateral zone creates a sunken, fatigued appearance. These two zones house significant arteries, knowledge of which is crucial to establishing safer procedures. Zygomaticofacial (cutaneous branch of the lacrimal artery) The internal carotid artery gives rise to the ophthalmic, then the lacrimal artery (Figures 1 & 2). This runs forward at the junction of the orbital roof and the lateral wall of the orbit. Here, it gives off the
Arteries and their branches in the face (purple originates from the external carotid artery and orange originates from the internal carotid artery):
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17.1
17.2
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21 22
24 17
27
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25 9
16
26
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4
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12 6 3
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4 2 1
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1. Common carotid a. 2. External carotid a. 3. Internal carotid a. 4. Facial a. 5. Submental a. 6. Inferior labial a. 7. Superior labial a. 8. Lateral nasal a. 9. Angular a. 10. Posterior auricular a. 11. Maxillary a. 12. Inferior alveolar a. 13. Mental a. 14. Buccal a. 15. Infraorbital a.
16. Transverse facial a. 17. Superficial temporal a. (17.1 frontal branch, 17.2 parietal branch) 18. Ophthalmic a. 19. Supraorbital a. 20. Supratrochlear a. 21. Dorsal nasal a. 22. Anterior ethmoidal a. 23. External nasal a. 24. Lacrimal a. 25. Zygomatic a. 26. Zygomaticofacial a. 27. Zygomaticotemporal a.
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Figure 1: The carotid systems: internal and external. Image adapted from von Arx T et al.23
Reproduced from Aesthetics | Volume 8/Issue 2 - August 2021