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  • The superficial musculoaponeurotic system (SMAS) is a fibromuscular layer connecting the facial muscles. Incisions and undermining within the subcutaneous fat above SMAS will not result in damage to motor nerves.

  • When planning reconstruction, the surgeon should consider cosmetic units, junctional lines, and resting skin tension lines to optimize the final aesthetic result.

  • The three branches of the trigeminal nerve (cranial nerve V) provide sensory innervation to the face.

  • The three main danger zones are areas where the temporal and marginal mandibular branches of the facial nerve and spinal accessory nerve lie superficial and can be easily injured. Damage to the temporal branch of the facial nerve may result in an ipsilateral eyebrow ptosis and obscuring of the superolateral visual field. The marginal mandibular branch of the facial nerve is vulnerable to damage along the inferior edge of the body of the mandible. Damage to the marginal mandibular branch of the facial nerve results in an asymmetrical smile. The spinal accessory nerve lies in the posterior triangle of the neck and may be identified by Erb’s point.

  • The rich vascular supply to the face from both the external and internal carotid ensures the reliable healing potential and viability of flaps and grafts in head and neck surgery.


Factors such as the increasing incidence of skin cancer, the desire to maintain a youthful appearance in an aging population that is living longer, and the financial pressure to perform procedures in less invasive and more cost-effective ways have made surgery a cornerstone of the practice of dermatology. Knowledge of anatomy is critical for a number of reasons, including communicating precisely with colleagues, performing safe and efficient procedures, achieving aesthetic and functional reconstruction, understanding the lymphatic drainage, and anticipating metastatic spread of cutaneous malignancies. Because the vast majority of these procedures are performed on the head and neck, this chapter focuses on the anatomy of this critical region.

This chapter focuses on five important concepts in head and neck anatomy, which are

  • The superficial musculoaponeurotic system (SMAS)

  • Topography and cosmetic units

  • Free margins

  • Relaxed skin tension lines (RSTL)

  • Facial motor nerves susceptible to damage during dermatologic surgery


An important concept in understanding head and neck anatomy is the SMAS, a layer of superficial fascia that envelopes and links the facial expression muscles with each other and with the overlying skin.

It stretches over the cheeks between the temporalis and frontalis muscles above and the platysma muscle below. The SMAS also attaches to the orbicularis oculi muscles anteriorly and the trapezius muscle posteriorly and includes the fascia of the forehead and galea of the scalp.

Most of the superficial muscles of the scalp and face insert into the skin either directly through fibrous bands running in the subcutaneous ...

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