skin tension lines

8/8/2019 Skin Tension Lines

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Skin Tension Lines

Skin tension lines (STLs) are the result of a complex interaction between internal

and external factors involving the skin. The intrinsic framework, which consists of

elastin and collagen, progressively loosens with age. Their interaction with themuscles of facial expression leads to the development of STLs. Generally, STLs

are perpendicular to the underlying muscles of the face. Aging, particularly

photoaging, tends to accentuate the appearance of STLs.

In the repair of STLs, the correct placement of the long axis of an excision parallel

to the STLs results in better scar cosmesis. Furthermore, flaps should be placed to

allow the suture lines to fall in STLs. Although STLs may vary between

individuals, some areas of the face have greater variability than others. Typically,

the forehead, which has 1 major muscle group that pulls it vertically, has littleindividual variability; nearly everyone has horizontal STLs. In comparison,

anatomic areas where multiple muscles act in different directions are likely to have

greater variability.

In elderly patients, the direction of the relaxed STLs is generally obvious. In areas

of ambiguity, excising the lesion as a circle and undermining it invariably pulls the

surgical defect into an oval with the long axis corresponding to the relaxed STL.

Skin tension lines. Illustrated by Charles Norman.


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Cosmetic Units and Subunits

Junction lines are fixed landmarks that separate the cosmetic units of the face.

Cosmetic subunits. Illustrated by Charles Norman.

Placing the suture lines on these boundaries (eg, eyebrow, nasolabial fold)

optimizes scar formation. When a surgical wound is closed, repairing the wound

in a cosmetic unit along a junction line is best. In larger defects that require a flap,

the best results are achieved by using tissue from the same or adjacent cosmetic

unit and by placing suture lines on the boundaries of those units. Subunits within

cosmetic units are often subtle and individually variable. Paying attention to

subtleties such as color, texture, sebaceous features, and hair characteristics help

in identifying the changes between the subunits.

The scalp and forehead are individual cosmetic units that are separated by the

hairline. In a bald individual, the top horizontal forehead crease serves as the

junction line. Subunits of the forehead include the glabella, temples, and eyebrows.


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Forehead subunits. Illustrated by Charles Norman.

The eyelids are a complex structure with multiple subunits that mimic the

underlying orbicularis oculi muscle. The largest component of the eyelid is the

orbital portion, which borders the eyebrow superiorly and the cheek inferiorly.

Just below the eyebrow is the preseptal area and then the pretarsal portion

where eyelashes insert. Additional components of the eyelid include the superior

palpebral fold, the palpebral fissure, the medial limbus, and the medial canthus.

Eyelid subunits. Illustrated by Charles Norman.


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The cheek region is subdivided by the anterior prominence of the clenched

masseter muscle. The masseter-parotid region lies posterior to this landmark and

is posteriorly bound by the ear. The mandibular region lies anterior to the

masseter and inferior to the lower lip. The malar subunit is around the zygoma

anterior to the masseter muscle. This subunit is referred to as the anterior region.

Subunits of the anterior region. Illustrated by Charles Norman.

The subdivisions of the external ear allow for good clinical descriptions of skin

lesions in this location.

Subunits of the ear. Illustrated by Charles Norman.


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The nose1

has the most subdivisions on the face.

Subunits of the nose. Illustrated by Charles Norman.

The horizontal root, which borders the glabella on the forehead, is positioned

superiorly. The mid nose contains the dorsum medially and is flanked by the 2

lateral sidewalls. The dorsum is inferiorly bordered by the tip, which ends in the

columella. The columella is the thin sliver of tissue that separates the nostrils on

the underside of the nose. The tip is bordered by the ala nasi, or alae, on both

sides, and the columella is flanked by the soft triangles, which also border the tip

andthealae.


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The lower part of the face is dominated by the subunits of the lip.

Subunits of the lower part of the face. Illustrated by Charles Norman.

Below the nose in the moustache area are the cutaneous regions of the upper lip,

which are separated from the cheek by the nasolabial fold. The middle depression

below the nose, known as the philtrum, is an important anatomic subunit because

even minimal displacement of this structure results in significant disfigurement.

The lips constitute the vermilion subunit. The cutaneous lower lip, which borders

the chin inferiorly and is bound by the nasolabial fold laterally, is below the

vermillion.


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Muscles of Facial Expression and the Superficial

Musculoaponeurotic System

Muscles of facial expression

The muscles of facial expression are unique in a number of ways. Rather than

inserting into bones or tendons, all of the muscles of facial expression originate

from or insert into the skin. They are all derived from the second embryonic

branchial arch and are innervated by the seventh cranial (facial) nerve. Different

anatomic areas of the face have synergistic and antagonist groups of muscles that

enable individuals to make varied facial expressions.

Muscles affecting the forehead and eyebrow include the frontalis muscle, which

creates the horizontal wrinkles on the forehead and assists with eyebrow elevation,

and the corrugators and procerus muscles, which are antagonistic muscles on theforehead. The orbicularis oculi muscles are a complex of muscles surrounding the

eyes; these assist with closing the eye tightly. This muscle lies superficially in the

eyelid skin and is encountered with even a shallow incision. The dominant muscle

of the nose is the nasalis muscle, which consists of nasal and alar components. Its

function is to compress and dilate the nares.

The mouth has the most extensive network of facial musculature and accounts for

much of an individual's capability of facial expression. The orbicularis oris

encircles the mouth and is the major component of the lips. The major functions of

the orbicularis oris muscle are to pull the lips against the teeth, to draw the lips

together, to pull the corners of the mouth together, and to pucker. This muscle is

also extremely important for the phonation of sounds that rely on the lips, such as

the pronunciation of the lettersM, V, F, and P.

A group of 6 muscles, collectively known as the quadratus labii superioris muscle,

controls the upper mouth. The 6 muscles are as follows:

The zygomaticus major muscle starts from the posterolateral zygomatic

bone and travels medially to insert on the upper portion of the orbicularisoris muscle. The zygomaticus major muscle helps in forming the lower

nasolabial fold and is primarily responsible in smiling.

The zygomaticus minor muscle arises just medially to the zygomaticus

major and assists with its functions.

The levator labii superioris muscle arises from the inferior portion of the

maxilla and inserts on the upper lip, more medially than the zygomaticus


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muscles. The levator labii superioris muscle helps elevate the medial part of

the upper lip and assists the zygomatic muscles with open smiling. The

levator and zygomaticus muscles form the nasolabial fold.

The levator anguli oris muscle is the most deeply positioned of the lip

elevators and inserts on the upper corner of the mouth to assist with lipelevation.

The risorius muscle arises over the parotid gland, inserts into the skin and

mucosa of the lateral corner of the mouth, and assists with smiling. The

risorius is not always present.

The buccinator muscle is neither an elevator nor a depressor of the lip. It

arises just posterior and medial to the last molar tooth and extends forward

to become continuous with the orbicularis oris muscle. The buccinator

muscle is the major component of the cheek musculature and prevents

overdistension of the cheek (eg, in playing a wind instrument). This muscleassists the orbicularis oris muscle in whistling.

The depressors of the lip include the depressor anguli oris, the depressor labii

inferioris, and the mentalis muscles. The marginal mandibular branch of the facial

nerve innervates the depressors of the lip.

The depressor anguli oris muscles arise from the lateral part of the

mandible and travel superomedially to insert, with the orbicularis oris

muscle, in the corners of the mouth. They function to depress and retract

the corners of the mouth.

The depressor labii inferioris muscles arise more medially on the mandible

and travel superiorly to insert, with the orbicularis oris muscle, in the lower

and medial part of the lip. Similar to the depressor anguli oris muscle, these

muscles assist with the depression and retraction of the lower lip.

The mentalis muscle, which is deep to both the depressor anguli oris and

labii inferioris muscles, arises from the mandible and lower lateral incisor

and courses inferiorly to insert on the skin covering the chin. The mentalis

muscle elevates and wrinkles the chin and assists in protruding the lower

lip.

Superficial musculoaponeurotic system

The facial musculature must work synergistically to allow for a wide range of

facial expressions. The superficial musculoaponeurotic system (SMAS) is a

discrete fibromuscular layer that envelops and interlinks the muscles to provide


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these synergies. The SMAS delineates the dissection planes for the extensive

undermining necessary in facial rejuvenation procedures.

In addition, the SMAS serves as a useful marker in assessing the location of vital

blood vessels and nerves. The superficial portion of the SMAS generally houses

the axial blood vessels and sensory nerves, whereas the deeper levels contain the

more vital motor nerves. The SMAS is generally located beneath the subcutaneous

fat and superficial to the muscles. Superior to the zygoma, the SMAS links the

temporalis, frontalis, occipitalis, and procerus muscles into a freely moveable

continuous plane that connects with the subgaleal space. Inferiorly, the fascial

anatomy is unclear; however, the SMAS interconnects the platysma, risorius, and

depressor anguli oris muscles inferior to the zygoma. The muscles of the medial

aspect of the face, including the orbicularis oculi, lip elevator, and nasal muscles,

are not ensheathed by an interconnected SMAS.


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Nerves

Sensory nerves

The trigeminal nerve, or cranial nerve (CN) V is primarily responsible for the

sensory innervation of the face. The cervical, facial, glossopharyngeal, and vagus

nerves have smaller contributions. The sensory nerves are typically located more

superficially than the motor nerves, along the junction of the fat and the SMAS.

Transection of the sensory nerves does not result in the serious morbidity that

motor nerve damage causes, and the recovery of sensory function after such injury

is typical.

The trigeminal nerve is divided into 3 branches: ophthalmic (CN V1), maxillary

(CN V2), and mandibular (CN V3).

Distribution of cranial nerve V. Illustrated by Charles Norman.

The V1 division provides sensation to the anterior part of the scalp, forehead,

upper eyelid, and nasal bridge. Branches that arise around the superior orbital rim

include the supraorbital, supratrochlear, infratrochlear, external nasal, and lacrimal

branches. The V2 division supplies sensation to the lower eyelid, nasal sidewalls

and columella, temple, and upper lip. Its major branch is the infraorbital nerve,

which emerges from the infraorbital foramen with the infraorbital artery and vein.

Other smaller branches include the zygomaticofacial and zygomaticotemporal

nerves. The V3 division is the largest and most complicated of the divisions of CN


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V. It is the only division that carries motor fibers. The mandibular nerves provide

sensation to the lower lip, chin, mandible, and preauricular areas.

The auriculotemporal, buccal, and mental nerves are the 3 major cutaneous

branches of the mandibular nerve. The auriculotemporal nerve sends sensory fibers

to the auricles, temples, and temporal parietal aspect of the scalp. In addition, it

provides sensation to the external auditory canals, eardrums, and

temporomandibular joints, and it carries some secretory fibers to the parotid

glands. The buccal nerve is inaccessible for nerve blocks because of its deep

location. It sends fibers to the cheek, mucosa, and gingiva. The mental nerve is the

continuance of the inferior alveolar nerve, and it emerges from the mental foramen

on the chin. It provides sensation to the chin, lower lip, mucosa, and gingiva of the

lower lip. The motor component of the trigeminal nerve primarily innervates the

muscles of mastication.

The cervical plexus lies deep to the sternocleidomastoid muscle. The plexus

provides sensation to several important structures and is derived from C2 through

C4. These nerves include the great auricular (C2, C3), lesser occipital (C2), greater

occipital (C2), third occipital (C3), transverse cervical (C2, C3), and

supraclavicular nerves. They send sensory fibers to the neck, posterior part of the

ear, and postauricular scalp. The spinal accessory and cervical nerves emerge near

the Erb point in the posterior triangle on the neck and are easily damaged during

cutaneous surgery.

Lastly, sensory branches of the vagus, glossopharyngeal, and facial nervesinnervate the skin of the external auditory canal, the concha, and the posterior

sulcus. Awareness of the sensory branches of the face allows the use of nerve

blocks, which provide effective anesthesia with minimal discomfort for the patient.

Mental, infraorbital, and supraorbital blocks are easily achieved after the

identification of their respective foramina, which lie in the midpupillary plane.


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Foramina for nerve blocks. Illustrated by Charles Norman.

Motor nerves

CN VII, also known as the facial nerve, provides motor innervation to all the

muscles of facial expression. CN VII also provides motor fibers to the digastric,

stylohyoid, and stapedius muscles. In addition, sensory innervation to the anterior

two thirds of the tongue, external auditory meatus, soft palate, and pharynx is

mediated via the facial nerve. The motor portion of the facial nerve is divided into

5 major branches, but individual variation is common, with numerous smaller

arborizations emanating from each major branch. The main facial nerve trunk

emerges from the stylomastoid foramen, which is covered by the mastoid process,

and along the posterior deep portion of the parotid gland. The main facial nerve

trunk then divides into the temporal, zygomatic, buccal, mandibular, and cervical

branches.

Branches of the facial nerve. Illustrated by Charles Norman.


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The temporal branch innervates the muscles of the upper part of the face

including the upper orbicularis oculi, frontalis, and corrugator muscles. This

branch is extremely susceptible to inadvertent injury because it travels

superficially when it crosses the middle portion of the zygoma.

Course of the temporal nerve and location of the Erb point. Illustrated by Charles Norman.

Transection of the temporal branch most prominently leads to unilateral frontalis

dysfunction, which leaves the patient with ptosis and the inability to raise his or her

eyebrows.

The zygomatic branch provides motor fibers to the lower orbicularis oculi,

procerus, some lip elevator, and some nasal muscles.

The buccal branch often has numerous anastomotic connections with the

zygomatic branch and sends fibers to similar muscles, in addition to the buccinator,

orbicularis oris, depressor anguli oris, and risorius muscles. The buccal and

zygomatic branches travel superficially over the buccal fat pad and just below the

SMAS. This orientation makes them susceptible to injury during face-lift

procedures. Transection of the nerves of the zygomatic and buccal branch leads tounpredictable defects, because muscular innervation in the mid face is variable.

In general, the marginal mandibular nerve does not have anastomotic connections.

It innervates the orbicularis oris and lip depressor muscles. The anatomic course of

the marginal mandibular nerve is unpredictable, but it should be considered in any

excision near the angle of the mandible and the inferior margin of the parotid


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gland. Transection of the marginal mandibular nerve leads to extreme cosmetic and

functional loss because the muscles of the mouth enable a significant amount of

facial expression. The marginal mandibular branch of the facial nerve has a

superficial course near the mandible and chin. This nerve usually lies anterior to

the facial artery, which is palpable anterior to a clenched masseter muscle.

Course of the marginal mandibular nerve. Illustrated by Charles Norman.

Transection of this nerve results in a droopy lip and subsequently drooling.

Excisions on the lips can also lead to drooling, but not because of the transection of

a motor nerve in this location.

The cervical branch is posterior and deep to the marginal mandibular nerve and

innervates the platysma muscle. The cervical branch is of little importance to the

cutaneous surgeon because its transection does not result in great functional or

cosmetic loss.

The cutaneous surgeon must be aware of the delayed effects of local anesthetic on

motor fibers. The unmyelinated sensory fibers lose conduction instantaneously,

whereas the deeper myelinated motor fibers may lose their function only after a

prolonged procedure with possibly greater anesthetic volume. Thus, the surgeon

should not be alarmed by the delayed onset of a facial muscle paralysis. This effecton the motor nerves can last as long as 12 hours, and the patient should be

appropriately counseled.


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Blood Vessels

The external carotid artery provides most of the arterial blood supply to the face;

the internal carotid artery makes a smaller contribution. The external carotid artery

is the origin of the facial artery deep to the mandible near the pharynx. The facialartery courses around the jaw anterior to the masseter, where it is palpable, and

continues superomedially to end as the angular artery near the medial canthus.

Along its path, the facial artery serves as the origin to the inferior and superior

labial arteries as well as smaller nasal branches. It provides the arterial blood

supply to the lips and the middle of the face. At its terminal point, the facial artery

connects with the ophthalmic artery, which provides important anastomoses with

the internal carotid system.

Prior to its terminal differentiation, the external carotid artery results in the

occipital and posterior auricular arteries, which supply the posterior part of thescalp and the postauricular areas. The terminal branches of the external carotid

artery are the superficial temporal and internal maxillary arteries.

The superficial temporal artery arises in the parotid gland superficial to the

branches of the facial nerve. The artery courses superiorly and results in the

horizontal transverse facial artery 2 cm inferior to the zygoma; the resultant artery

connects with the facial artery. As it continues superiorly, the superficial temporal

artery also becomes more superficial and is palpable posterior to the temporal

mandibular joint and anterior to the ear. The superficial temporal artery terminates

in the parietal and frontal branches, which deliver blood to the scalp. Along its

course, the superficial temporal artery provides blood to the lateral part of the face,

the temple, the forehead, and the scalp. It also serves as the origin for smaller

middle temporal and zygomatico-orbital arteries that supply some midfacial

structures.

The internal maxillary is a deep artery that forms where the superficial temporal

artery arises from the external carotid artery. Because of its deep location, the

cutaneous surgeon rarely encounters the internal maxillary artery. Important

branches of this artery include the infraorbital artery and the inferior alveolarartery, which continues through the mental foramen as the mental artery to provide

blood to the chin.

The internal carotid artery supplies arterial blood to the eyelids, the upper and

dorsal parts of the nose, the lower part of the forehead, and the scalp. The

important major branch of the internal carotid artery is the ophthalmic artery. The


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ophthalmic artery has supraorbital, supratrochlear, infratrochlear, dorsal nasal, and

external nasal branches that may form anastomoses with the external carotid

system through the angular artery.

The venous network of the face parallels the arterial system. Unlike the arteries,

the veins tend to be straighter and less tortuous. The facial vein parallels the facial

artery and drains blood from the middle of the face into the internal jugular vein.

The venous system of the medial aspect of the face (the dangerous triangle)

involves the drainage of the upper lip and paranasal areas. In this area, the facial

vein directly connects with the cavernous sinus, via the ophthalmic vein or

indirectly connects with it, via the pterygoid plexus. The lateral part of the face and

the scalp drain into the superficial temporal and retromandibular veins, which lead

into the external jugular vein.


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Lymphatics

The cutaneous surgeon often removes malignancies that can cause lymph node

metastases. Knowledge of lymph flow is essential for an adequate clinical

examination of the lymph nodes. Lymph flows from superficial areas to deep areasand then flows along 4 major tracts in an inferolateral direction to the collecting

nodes in the neck and jaw. Great individual variability exists in the lymph flow;

however, a general framework exists.

All the lymphatic fluid from the face eventually collects in a triangle of lymph

nodes in the neck. The transverse cervical chain forms the inferior horizontal leg of

the triangle, the spinal accessory chain forms the lateral leg, and the internal

jugular chain forms the medial leg. The superior point of the triangle includes the

superficial cervical and parotid nodes. The legs of the triangle are known as the

deep lateral cervical nodes.

At the junction of the internal jugular and transverse cervical chains, the

lymphatics enter the venous circulation at the jugulosubclavian junction. The

spinal accessory chain travels along the spinal accessory nerve, making its removal

more treacherous. This chain may be involved with early metastases from

malignancies in the nasopharyngeal and thyroid areas. The transverse cervical

chain is found along the transverse cervical vessels above the clavicle. The internal

jugular chain is the major collection point for the head and neck, and it is divided

into anterior and lateral divisions. By turning the patient's chin ipsilaterally and by

rolling the relaxed sternocleidomastoid muscles between his or her fingers, the

physician can clinically examine this group.

The postauricular node can be single or multiple, and it is located in the mastoid

area attached to the insertion of the sternocleidomastoid muscle. Drainage from the

ear can course anteriorly to the parotid nodes or inferiorly to the spinal accessory

and internal jugular chains. Superficial and deep occipital nodes drain the posterior

aspect of the scalp and the nuchal area. These nodes subsequently flow into the

spinal accessory chain.

The parotid nodes have extraglandular and intraglandular components. The

extraglandular nodes include the preauricular and infra-auricular subnodes and are

located in the parotid fascia. These nodes function as a unit with the intraglandular

nodes, which are deep in the gland. The parotid nodes drain into the submandibular

chain or transverse cervical chain.


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The facial nodes drain the mid face and are extremely variable between

individuals. From superior to inferior, they are the infraorbital, malar, buccinator,

and mandibular nodes. When present, these nodes are found in the subcutaneous

layer above the muscles of the face. The facial nodes drain into the submandibular

and submental chains.

The submandibular nodes are divided into 5 groups on the basis of their

relationship to the facial vein and the submandibular gland. The preglandular

nodes are below the platysma and anterior to the gland. The prevascular node is in

the precarious position on the facial artery and touches the marginal mandibular

nerve.

The postvascular nodes are also adjacent to the motor nerve. The existence of a

retroglandular group is disputed. The submandibular gland surrounds a large group

of intracapsular nodes. Many individuals have palpable nodes in the submandibulartriangle. For clinical examination, the submandibular nodes can be palpated when

the patient relaxes his or her neck muscles and moves his or her chin downward.

The submental nodes are above the mylohyoid and deep to the platysma in the

submental triangle. The nodes drain the middle two thirds of the lower lip, the

medial aspect of the cheek, and some facial nodes, and they can drain into the

ipsilateral and contralateral nodes in the neck. Examination of the submental nodes

is best accomplished by bimanually palpating the floor of the mouth and by

pushing up under the patient's chin.

The superficial lateral cervical nodes receive drainage from the parotid,

submandibular, and postauricular nodes. These cervical nodes are located on the

superior external jugular vein, and some believe that they are part of the parotid

infra-auricular nodes. The superficial lateral cervical nodes drain into the internal

jugular chain.


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Cutaneous Anatomy of the Neck

Muscles of the neck

The key cutaneous muscles of the neck are the platysma and sternocleidomastoid

muscles. The platysma is covered by the SMAS, which is continuous with the

lower muscles of the face, and it is also considered a muscle of facial expression.

The platysma is an extremely thin muscle that is superficial in the neck. The

sternocleidomastoid muscle extends from the medial clavicle to the postauricular

area and divides the neck into posterior and anterior triangles.

Key components of the anterior triangle include the internal and external carotid

arteries, the internal jugular vein, and the vagus and hypoglossal nerves. The

important structure to consider to the posterior triangle is the spinal accessory

nerve (CN XI), which innervates the sternocleidomastoid and trapezius muscles.Transection of the spinal accessory nerve results in a winged scapula and difficulty

with arm abduction. The superficial cervical plexus is also found in the posterior

triangle. The superficial cervical plexus has sensory, motor, and sympathetic

functions.

A crucial anatomic landmark in the posterior triangle is the Erb point. The spinal

accessory, great auricular, lesser occipital, and transverse cervical nerves all pass

within 2 cm above or below this location. The Erb point can be located by drawing

a line between the angle of the mandible and the mastoid process with the patient's

head slightly turned. The Erb point lies at the junction of the posterior border of thesternocleidomastoid muscle and the point 6 cm inferior to the midpoint of the line

drawn.


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Course of the temporal nerve and location of the Erb point. Illustrated by Charles Norman.

Blood vessels of the neck

The key blood vessels of the neck include the common and external carotid arteries

and the jugular veins. The common carotid, internal jugular, and vagus nerves are

found in the carotid sheath under the sternocleidomastoid and infrahyoid muscles

before the carotid arteries bifurcate into their external and internal branches.

The external jugular vein forms below the parotid gland and travels inferiorly

along the surface of the sternocleidomastoid muscle. The external jugular vein

empties into the subclavian or internal jugular veins after it pierces through the

superficial portion of the deep cervical fascia in the posterior triangle.

Skin tension lines

STLs typically lie in a transverse direction on the neck. The placement of excision

lines in this orientation is essential because hypertrophic or reddened scars often

result from misplaced excisions on the neck.


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Anatomic Surgical Pearls

Free margins are located on the eyelids, helices of the ears, lips, and alar rim and

columella. Unopposed tension caused by a surgical repair may distort these

structures. Wound closure in these locations often require flap and/or graftplacement to lessen the risk.

When designing flaps, borrow tissue from the same or adjacent cosmetic units to

minimize anatomic distortion and maximize tissue match.

A reservoir of skin for flaps or primary closure can be found on the lower and

posterior part of the cheek near the angle of the mandible. In older persons, this

area is the jowl. Other areas with redundant skin include the preauricular aspect of

the cheek, the temple, and the neck.

Subunits of the anterior region. Illustrated by Charles Norman.

Place the suture lines along STLs and on the boundaries of the cosmetic units

whenever possible.

Preoperatively identify the vital structures that might be damaged in the operative

field, and stay vigilant to avoid them. Examples of vital structures include the

temporal nerve in the upper part of the cheek and temple, the marginal mandibular

nerve on the jaw line, and CN XI at the Erb point.


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Identify sensory innervation to structures in the operative field, and perform a

nerve block wherever possible to minimize the patient's discomfort and distortion

of the operative field by using large amounts of lidocaine. Examples of sensory

innervations include the mental nerve on the chin and the supraorbital and

supratrochlear nerves in large lesions on the forehead.

When working in deeper planes, attempt to identify the SMAS, which can help in

locating and avoiding vital vessels and nerves.

skin tension lines

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