Skin & Fascia of neck

BY DR FAUZIA

WMC WAH CANTT

Neck

• OVERVIEW
• The neck is the transitional area between the base of the cranium superiorly and the clavicles inferiorly.
• The neck joins the head to the trunk and limbs, serving as a major conduit for structures passing between them.
• In addition, several important organs with unique functions are located here: the larynx and the thyroid and parathyroid glands, for example.

The neck is relatively slender to allow the flexibility necessary to position the head to maximize the efficiency of its sensory organs (mainly the eyeballs but also the ears, mouth, and nose).

Intro,,,,,

• Thus many important structures are crowded together in the neck, such as muscles, glands, arteries, veins, nerves, lymphatics, trachea, esophagus, and vertebrae.
• Consequently, the neck is a well-known region of vulnerability.
• Further, several vital structures, including the trachea, esophagus, and thyroid gland, lack the bony protection afforded other parts of the systems to which these structures belong.

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Region of vulnerability.

• The main arterial blood flow to the head and neck lie anterolaterally in the neck.
• Carotid/jugular blood vessels are the major structures commonly injured in penetrating wounds of the neck.
• The brachial plexuses of nerves originate in the neck and pass inferolaterally to enter the axillae and continue into and supply the upper limbs.
• In the middle of the anterior aspect of the neck is the thyroid cartilage, the largest of the cartilages of the larynx, and the trachea.
• Lymph from structures in the head and neck drain into cervical lymph nodes.

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Classification of neck

• Visceras NVB Muscles
• Glands/Endocrine gland L.N Soma(SCM, Trapezius)
• Thyroid Arteries(Carotids) Cavity(Ant. Group(Hyoid muscles
• Parathyroid Veins(IJV) (post. Group of paravertebral/

2. Air Pipe Scalene muscles)

1. Larynx
2. Trachea

3.Food pipe

1. Pharynx
2. esophagous

Fascia of neck

• Fascia is an internal connective tissue which forms bands or sheets that surround and support muscles, vessels and nerves in the body.
• In the neck, these layers of fascia not only act to support internal structures, but also help to compartmentalise structures of the neck.
• There are two fascias in the neck – the superficial cervical fascia and the deep cervical fascia.
• The fascial planes determine the direction in which an infection in the neck may spread.

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Cervical Subcutaneous Tissue and Platysma�

• The cervical subcutaneous tissue (superficial cervical fascia) is a layer of fatty connective tissue that lies between the dermis of the skin and the investing layer of deep cervical fascia
• . This tissue is usually thinner than in other regions, especially anteriorly.
• It contains;
• cutaneous nerves,
• blood vessels (EJV),
• superficial lymph nodes,
• and variable amounts of fat.
• Anterolaterally, it contains the platysma.

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Platysma(G. flat plate)

is a broad, thin sheet of muscle in the subcutaneous tissue of the neck.

Like other facial and scalp muscles, the platysma develops from a continuous sheet of musculature derived from mesenchyme in the 2nd pharyngeal arch of the embryo and is supplied by branches of the facial nerve, CN VII.

The external jugular vein (EJV), descending from the angle of the mandible to the middle of the clavicle, and the main cutaneous nerves of the neck are deep to the platysma.

Attachment

• It has two heads, which originate from the fascia of the pectoralis major and deltoid.
• The fibres from the two heads cross the clavicle, and meet in the midline, fusing with the muscles of the face. Superiorly, the platysma inserts into the inferior border of the mandible.
• The anterior borders of the two muscles decussate over the chin and blend with the facial muscles.
• Inferiorly, the fibers diverge, leaving a gap anterior to the larynx and trachea.
• Much variation exists in terms of the continuity (completeness) of this muscular sheet, which often occurs as isolated slips.
• Innervation to the platysma is via the cervical branch of the facial nerve.

Action/ Func.

• Acting from its superior attachment, the platysma tenses the skin, producing vertical skin ridges and releasing pressure on the superficial veins.
• Men commonly use this action of the platysma when shaving their necks and when easing tight collars.
• Acting from its inferior attachment, the platysma helps depress the mandible and draw the corners of the mouth inferiorly, as in a grimace(Pout).
• As a muscle of facial expression, the platysma serves to convey tension or stress.

Deep Cervical Fascia�

• The deep cervical fascia lies, as its name suggests, ‘deep’ to the superficial fascia and platysma muscle. 
• This fascia is organised into several layers; investing, pretracheal, and prevertebral
• These layers act like a shirt collar, supporting the structures and vessels of the neck.
• These layers support the viscera (e.g., the thyroid gland), muscles, vessels, and deep lymph nodes. The deep cervical fascia also condenses around the common carotid arteries, internal jugular veins (IJVs), and vagus nerves to form the carotid sheath.
• These three fascial layers form natural cleavage planes through which tissues may be separated during surgery, and they limit the spread of abscesses (collections of pus) resulting from infections.
• The deep cervical fascial layers also afford the slipperiness that allows structures in the neck to move and pass over one another without difficulty, such as when swallowing and turning the head and neck.
• We shall now look at the layers of the deep cervical fascia in more detail (superficial to deep):

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Investing Layer�

• The investing layer is the most superficial of the deep cervical fascia.
• It surrounds all the structures in the neck.
• At the “four corners” of the neck, it splits into superficial and deep layers to enclose (invest) the trapezius and sternocleidomastoid (SCM) muscles.
• These muscles are derived from the same embryonic sheet of muscle and are innervated by the same nerve (CN XI).
• They have essentially continuous attachments to the cranial base superiorly and to the scapular spine and acromion and clavicle inferiorly.
• The investing fascia can be thought of as a tube; with superior, inferior, anterior and posterior attachments:

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• Superior – attaches to the external occipital protuberance and the superior nuchal line of the skull.
• Anteriorly – attaches to the hyoid bone.
• Inferiorly – attaches to the spine and acromion of the scapula, the clavicle, and the manubrium of the sternum.
• Posterior – attaches along the nuchal ligament of the vertebral column i.e. Spinous processes of the cervical vertebrae

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Modifications

• Just inferior to its attachment to the mandible,
• the investing layer of deep fascia splits to enclose the submandibular gland;
• posterior to the mandible, it splits to form the fibrous capsule of the parotid gland.
• The stylomandibular ligament is a thickened modification of this fascial layer.
• .

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Supra sternal space

• Inferiorly between the sternal heads of the SCMs and just superior to the manubrium, the investing layer of deep cervical fascia remains divided into two layers to enclose the SCM; one layer attaches to the anterior and the other to the posterior surface of the manubrium
• A suprasternal space lies between these layers . It encloses the inferior ends of the anterior jugular veins, the jugular venous arch, fat, and a few deep lymph nodes.

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Pretracheal fascia

• The pretracheal layer of fascia is situated in the anterior neck.
• It spans between the hyoid bone superiorly and the thorax inferiorly (where it fuses with the pericardium).
• The trachea, oesophagus, thyroid gland and infrahyoid muscles are enclosed by the pretracheal fascia.
• Anatomically, it can be divided into two parts:
• Muscular part – encloses the infrahyoid muscles.
• Visceral part – encloses the thyroid gland, trachea and oesophagus.
• The posterior aspect of the visceral fascia is formed by contributions from the buccopharyngeal fascia (a fascial covering of the pharynx).

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The prevertebral fascia

•  surrounds the vertebral column and its associated muscles; scalene muscles, prevertebral muscles, and the deep muscles of the back.
• It has attachments along the antero-posterior and supero-inferior axes:
• Superior attachment – base of the skull.
• Anterior attachment – transverse processes and vertebral bodies of the vertebral column.
• Posterior attachment – along the nuchal ligament of the vertebral column
• Inferior attachment – fusion with the endothoracic fascia of the ribcage.
• The anterolateral portion of prevertebral fascia forms the floor of the posterior triangle of the neck. It also surrounds the brachial plexus as it leaves the neck and subclavian artery as it passes through the lower neck region – in doing so, it forms the axillary sheath.

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Carotid sheath

• is a tubular fascial investment that extends from the cranial base to the root of the neck.
• This sheath blends anteriorly with the investing and pretracheal layers of fascia and posteriorly with the prevertebral layer of fascia.
• The carotid sheath contains the:
• Common and internal carotid arteries.
• Internal jugular vein.
• Vagus nerve (CN X).
• Some deep cervical lymph nodes.
• Carotid sinus nerve.
• Sympathetic nerve fibers (carotid periarterial plexuses).
• The carotid sheath and pretracheal fascia communicate freely with the mediastinum of the thorax inferiorly and the cranial cavity superiorly. These communications represent potential pathways for the spread of infection and extravasated blood.

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Clinical Relevance: Fascial Spaces of the Neck�

• The neck fascia compartmentalises structures within the neck. These layers of tough fascia can limit the spread of infection (for example, a superficial skin abscess may be prevented from spreading deeper into the neck by the investing fascia).
• However, infections that reach the potential spaces between the neck fascia have a well-defined spread:
• Retropharyngeal space – located between the buccopharyngeal fascia (posterior aspect of the visceral pretracheal fascia) and the prevertebral fascia.
• Extends from the base of the skull to the posterior mediastinum.
• Visceral space – enclosed by the visceral pretracheal fascia.
• Extends from the hyoid bone to the superior mediastinum.

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Paralysis of the platysma

• ,resulting from injury to the cervical branch of the facial nerve, causes the skin to fall away from the neck in slack folds.
• Consequently, during surgical dissections of the neck, extra care is necessary to preserve the cervical branch of the facial nerve.
• When suturing wounds of the neck, surgeons carefully suture the skin and edges of the platysma. If this is not done, the skin wound will be distracted (pulled in different directions) by the contracting platysma muscle fibers, and an ugly scar may develop.