Unit 4 · Neck & danger zones
Where the anatomy stops being about appearance
The platysma closes the loop opened in Unit 1: it is the inferior continuation of the SMAS, which is why a neck treatment expresses itself in the lower face. The danger zones then set the boundary on everything covered so far — muscle anatomy gives you the surface landmarks, and vascular anatomy decides the consequence of getting them wrong.
Learn · Neck musculature
The platysma is a facial muscle that happens to sit in the neck
The platysma is the primary aesthetic muscle of the neck and the inferior continuation of the SMAS.
The sternocleidomastoid and the posterior cervical muscles are generally not aesthetic injection targets, but their relationship to neck anatomy and to key vascular structures is clinically important — the SCM's anterior border defines the posterior triangle, which is how the external jugular vein and cervical plexus branches are located.
Muscle explorer · Neck
Two muscles. Arrow keys move through the index.
Neck
Neck
Platysma
M. platysma
Tenses neck skin; pulls the mandible and lower lip inferiorly; assists in depressing the commissures.
Fascia of the pectoralis major and deltoid, in the infraclavicular region.
Inferior border of the mandible; blends with the muscles of the lower face and the SMAS superiorly; skin of the lower face and neck.
Cervical branch of CN VII.
Platysmal banding — visible vertical cords in the neck — is a primary indication for neuromodulator treatment (the "Nefertiti lift"). Bands are treated with multiple injections of 2–4 indicative BTX-A reference units along each visible band. The medial bands are the most prominent. Injection depth is subcutaneous to superficial platysma — care is taken to avoid the external jugular vein and carotid vessels, which lie deep to the platysma in the lateral neck.
Neck
Sternocleidomastoid
M. sternocleidomastoid (SCM)
Ipsilateral neck flexion; contralateral rotation; bilaterally, neck flexion and assistance with respiration.
Sternal head: manubrium sterni. Clavicular head: medial third of the clavicle.
Mastoid process and lateral superior nuchal line of the occipital bone.
Accessory nerve (CN XI) and C2–C3 cervical plexus.
Rarely a direct aesthetic target, except in specialist spasticity or torticollis practice. Its anterior border defines the posterior triangle of the neck — a key landmark for identifying the external jugular vein and cervical plexus branches.
Treating vertical bands in the neck can also change the definition of the jawline and the position of the oral commissures. Why should a neck injection have any effect on the lower face at all?
Hold your answer before you open this. The value is in having committed to a mechanism first.
The platysma is the inferior continuation of the SMAS. It inserts into the inferior border of the mandible and blends with the muscles of the lower face and the SMAS superiorly, so it is mechanically continuous with the layer that couples muscle contraction to skin movement across the whole face.
Its action follows from that. The platysma tenses neck skin, pulls the mandible and lower lip inferiorly, and assists in depressing the commissures. Weakening it removes an inferior vector that was acting on the jawline and the corners of the mouth — which is the anatomical basis of the Nefertiti lift.
Read the platysma alongside the depressor anguli oris from Unit 3. Both pull the commissure inferiorly and both are supplied by branches of CN VII, so a downturned commissure that persists after adequate DAO treatment is worth reassessing with the neck in view rather than escalating the dose at the mandible.
You are treating prominent medial platysmal bands. The injection depth described for this technique, and the reason for it, are:
Select an option to commit. The reasoning appears afterwards.
Platysmal bands are treated with multiple injections of 2–4 indicative BTX-A reference units along each visible band, at a depth that is subcutaneous to superficial platysma. The medial bands are the most prominent and are usually the first treated.
Depth here is a vascular decision. The external jugular vein and the carotid vessels lie deep to the platysma in the lateral neck, so the plane that reaches the band without passing beyond it is the plane that keeps those structures out of the field. Unit ranges are indicative BTX-A reference units and must be reconciled against current product-specific prescribing information.
Learn · Anatomical danger zones
Six regions where the consequence changes
Certain regions of the face carry elevated risk for vascular injury, nerve compromise or inadvertent muscle effects during injectable and energy-based treatments. What follows is not a comprehensive vascular anatomy reference — it is a muscle-anatomy-informed summary of clinically critical zones. A dedicated vascular anatomy module is recommended in conjunction with this content.
| Zone | Structures at risk | What this means for practice |
|---|---|---|
| Glabellar complex | Supratrochlear and supraorbital arteries, running in predictable pathways lateral to midline at the brow | Deep injections medial to the midpupillary line at brow level risk inadvertent intravascular injection, with documented cases of retinal artery embolism. |
| Nasal region | Dorsal nasal artery and angular artery, converging at the nasal tip | One of the highest-risk filler zones in the face. Muscle anatomy — nasalis, depressor septi — provides surface landmarks, but vascular awareness is paramount. |
| Infraorbital / tear trough | Infraorbital foramen and its emerging neurovascular bundle, at the midpupillary line approximately 8–10 mm below the infraorbital rim | Filler injection in this zone risks vascular occlusion with potential orbital sequelae. |
| Temporal region | Middle temporal vein (the "danger vein") and superficial temporal artery | The temporal fat pad is a high-risk filler zone; intravascular injection in the temporal artery has a retrograde pathway to the ophthalmic circulation. |
| Perioral | Superior and inferior labial arteries, running within the orbicularis oris muscle rather than at the vermilion border | Intramuscular injection with filler in the lip body carries a higher risk of intravascular injection than submucosal or subcutaneous placement. |
| Mandibular border (DAO region) | Facial artery, crossing the inferior mandibular border at approximately the anterior border of the masseter, then running superiorly toward the oral commissure in a variable but generally subdermal course | Awareness of this pathway is essential during commissure filler and DAO neuromodulator treatment. |
You are planning treatment in the tear trough. The infraorbital foramen and its emerging neurovascular bundle are located:
Select an option to commit. The reasoning appears afterwards.
The infraorbital foramen lies at the midpupillary line, approximately 8–10 mm below the infraorbital rim, and its neurovascular bundle emerges there. Filler injection in this zone risks vascular occlusion with potential orbital sequelae.
The landmark is only useful if it is located on the patient in front of you rather than recalled as a number. The midpupillary line is a moving reference, so it is established with the patient looking straight ahead and the head in neutral position before any product is drawn up.
Predict · Risk stratification
Not every danger zone is dangerous in the same way
The six zones above are not interchangeable. Before opening the reveal, commit to what separates the zones capable of causing visual loss from those where the consequence of an intravascular event is contained locally.
The lips are among the most vascular structures in the face, yet the glabella, nose and temple are the regions described as carrying the highest risk. What is the distinction being drawn?
Hold your answer before you open this. The value is in having committed to a mechanism first.
Not all facial regions carry equal vascular risk. Risk is highest in zones that supply the ophthalmic circulation via anastomoses: the glabella, nose and temporal region. Risk is lower, but not absent, in zones with terminal vessel supply without ophthalmic connection: the lips and chin.
All practitioners performing injectable treatments should have a current understanding of arterial anatomy, an emergency hyaluronidase protocol for HA fillers, and the ability to recognise the early signs of vascular compromise: blanching, pain disproportionate to the procedure, a livedo reticularis pattern, and vision changes.
The early signs of vascular compromise are blanching, pain disproportionate to the procedure, a livedo reticularis pattern, and vision changes. Recognition is time-critical, and an emergency hyaluronidase protocol for HA fillers must be in place before treatment begins, not sourced after an event.
A colleague describes avoiding the vermilion border during lip filler on the grounds that the labial arteries run along it. The correct anatomical position is:
Select an option to commit. The reasoning appears afterwards.
The superior and inferior labial arteries run within the orbicularis oris muscle, not at the vermilion border. Intramuscular injection with filler in the lip body therefore carries a higher risk of intravascular injection than submucosal or subcutaneous placement.
The plane, not the landmark, is what governs the risk. This is the same principle established with the SMAS in Unit 1: identical product, identical volume, identical region, and a different consequence depending on the layer it is deposited in.
Unit 4 summary
Clinical takeaways
- The platysma is continuous with the SMAS. It inserts at the inferior mandibular border, blends with the lower face muscles, and assists in depressing the commissures — which is why weakening it changes jawline and commissure position as well as neck contour.
- Band treatment is a superficial technique. Injection depth is subcutaneous to superficial platysma, because the external jugular vein and carotid vessels lie deep to the muscle in the lateral neck.
- Vascular risk is stratified by anastomosis, not by vascularity. The glabella, nose and temporal region supply the ophthalmic circulation via anastomoses and carry the highest risk. The lips and chin have terminal vessel supply without ophthalmic connection — lower risk, not absent.
- Recognition and protocol precede treatment. Blanching, pain disproportionate to the procedure, a livedo reticularis pattern and vision changes are the early signs of vascular compromise, and an emergency hyaluronidase protocol for HA fillers belongs in the room before the first injection.
Module 03.01 · Reference index
Sources
All anatomical and clinical statements in this module are drawn from or consistent with the following peer-reviewed and authoritative sources. This index is maintained as a living document and updated on each module review cycle.
- [1] Standring S, ed.
- Gray's Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. Elsevier; 2020. Chapters 29–31: Head and Neck Musculature. Primary anatomical reference for all muscle origin, insertion, action and innervation data in this module.
- [2] Mitz V, Peyronie M.
- The superficial musculo-aponeurotic system (SMAS) in the parotid and cheek area. Plast Reconstr Surg. 1974;58(1):80–88. Original description of the SMAS layer.
- [3] Rohrich RJ, Pessa JE.
- The fat compartments of the face: anatomy and clinical implications for cosmetic surgery. Plast Reconstr Surg. 2007;119(7):2219–2227. Facial fat compartments and their relationship to SMAS and muscle planes.
- [4] de Maio M, Rzany B.
- Botulinum Toxin in Aesthetic Medicine. 2nd ed. Springer; 2014. Comprehensive reference for neuromodulator injection anatomy and technique.
- [5] Braz AV, Humphrey S, Weinkle S, et al.
- Individual approach to the glabellar region. J Drugs Dermatol. 2013;12(12):1283–1294. Glabellar complex anatomy and injection pattern individualisation.
- [6] Pessa JE, Rohrich RJ.
- Facial Topography: Clinical Anatomy of the Face. Quality Medical Publishing; 2012. Regional facial anatomy with surgical and injectable clinical correlation.
- [7] Carruthers J, Carruthers A.
- Botulinum Toxin. 4th ed. Elsevier Saunders; 2013. Procedures in Cosmetic Dermatology Series. Standard clinical reference for neuromodulator anatomy and technique in aesthetic practice.
- [8] Cotofana S, Lachman N.
- Arteries of the face and their relevance for minimally invasive facial procedures: an anatomical review. Plast Reconstr Surg. 2019;143(2):416–426. Vascular anatomy in the context of aesthetic injectable treatments; danger zone reference.
- [9] Scheuer JF III, Sieber DA, Pezeshk RA, Campbell CF, Gassman AA, Rohrich RJ.
- Anatomy of the facial danger zones: maximising safety during soft-tissue filler injections. Plast Reconstr Surg. 2017;139(1):50e–58e. Systematic mapping of vascular danger zones by injection region.
- [10] Saban Y, Polselli R, Hamou H.
- Anatomy of the orbicularis oculi and its implications for blepharoplasty. Aesthetic Plast Surg. 2009;33(1):37–44. Periorbital muscle anatomy with surgical and injectable implications.
- [11] Botto-Mahan C, Hernando-Cañas V, Rosenfeldt H.
- Bifid zygomaticus major muscle: anatomy, incidence, and clinical implications. Dermatol Surg. 2020;46(10):1266–1272. Anatomical variant of zygomaticus major and its aesthetic relevance.
- [12] Flynn TC.
- Neuromodulator treatment in men. Dermatol Ther. 2007;20(6):407–413. Masseter anatomy and hypertrophy treatment; platysma banding protocols.
- [13] Fagien S.
- Botulinum toxin type A for periorbital and upper facial aesthetic procedures. Ophthalmol Clin North Am. 2001;14(2):275–295. Levator palpebrae ptosis mechanism and management with apraclonidine.
- [14] Netter FH.
- Atlas of Human Anatomy. 7th ed. Elsevier; 2019. Plates 119–130: Head and Neck. Visual anatomical reference for muscle location and relationship.
This module is in draft. If anything here reads as unclear, incomplete or clinically contestable, record it in the review form.