Skin, Fascia and Sternocleidomastoid

Introduction

Boundaries of Neck

• Superiorly: The neck extends to the external occipital protuberance, superior nuchal line, mastoid process, angle of mandible and inferior border of mandible.
• Inferiorly: It extends to the spine of C7 vertebra, superior border of scapula, acromion, clavicle and suprasternal notch.

SKIN OF THE NECK

• The skin of the neck is thin, and its cleavage lines (Langer’s lines) generally follow the natural skin creases.
• Surgical incisions made along these lines, particularly transverse incisions, usually heal with less prominent scarring.

Cutaneous Innervation

– The skin of the neck receives sensory fibres mainly from the anterior rami of C2, C3 and C4 spinal nerves through the following branches of the cervical plexus:

1. Transverse cervical nerve (anterior cutaneous nerve of neck).
2. Great auricular nerve.
3. Lesser occipital nerve.
4. Supraclavicular nerves.
5. The skin over the posterior midline of the neck is supplied by the posterior rami of C2, C3 and C4 spinal nerves.
6. The C1 spinal nerve usually has no cutaneous branch.
7. The C5–T1 spinal nerves mainly contribute to the brachial plexus supplying the upper limb.
8. The C4 dermatome may extend inferiorly towards the second rib, adjacent to the T2 dermatome.

SUPERFICIAL FASCIA OF NECK

– The superficial fascia of the neck is a thin layer of loose areolar tissue beneath the skin.

Contents

• Platysma muscle.
• Cutaneous nerves: Lesser occipital, great auricular, transverse cervical and supraclavicular nerves.
• Superficial veins: External and anterior jugular veins.
• Superficial lymph nodes.
• Fat: It is usually scanty but is relatively abundant in children and females.

– The cutaneous nerves and vessels initially lie deep to the platysma before reaching the skin.

Platysma

• It is a thin, broad sheet of muscle situated within the superficial fascia of the neck.
• Morphology: It represents a remnant of the panniculus carnosus found in lower animals.
• Development: It develops from the second pharyngeal arch.

Attachments

• Origin: It arises from the fascia covering the upper parts of the pectoralis major and deltoid muscles.
• Direction of fibres: Its fibres pass upward, forward and medially.
• Insertion:
  • Anterior fibres: They may cross the midline and attach to the lower border of the mandible.
  • Middle fibres: They insert into the lower border of the mandible.
  • Posterior fibres: They cross the mandible near the anterior border of the masseter and blend with muscles and skin around the angle of the mouth.

Innervation

– The platysma is supplied by the cervical branch of the facial nerve (CN VII).

Actions

• Anterior and middle fibres: They tense and wrinkle the skin of the neck and assist in depressing the mandible.
• Posterior fibres: They pull the angle of the mouth downward and laterally, contributing to expressions of fear and surprise.
• Venous return: Contraction of the platysma may help reduce compression of superficial veins in the neck.

Cutaneous Nerve of the Neck

·  The skin over the anterior and lateral aspects of the neck is supplied by branches of the cervical plexus (C2–C4).

·  These branches include:

1. Lesser occipital nerve (C2).
2. Great auricular nerve (C2, C3).
3. Transverse cervical nerve (C2, C3).
4. Supraclavicular nerves (C3, C4).

<H4>Superficial Veins of the Neck

The neck contains two main superficial veins:

1. External jugular vein.
2. Anterior jugular vein.

External jugular vein (EJV)

– The external jugular vein drains blood from the superficial regions of the scalp, face and neck.

Formation

– It begins just below the angle of the mandible by the union of:

1. Posterior division of the retromandibular vein.
2. Posterior auricular vein.

Course

• It descends obliquely downward and backward across the superficial surface of the sternocleidomastoid, deep to the platysma.
• It pierces the investing layer of deep cervical fascia approximately 2.5 cm above the clavicle.

Termination

– It terminates in the subclavian vein.

Tributaries

– The external jugular vein receives the following tributaries:

1. Posterior auricular vein (formative tributary).
2. Posterior division of retromandibular vein (formative tributary).
3. Posterior external jugular vein.
4. Oblique jugular vein, when present.
5. Transverse cervical vein.
6. Suprascapular vein.
7. Anterior jugular vein, occasionally.

Anterior jugular vein (AJV)

·  Formation: It begins below the chin by the union of small superficial veins draining the anterior neck.

·  Course: It descends close to the midline and pierces the investing layer of deep cervical fascia about 2.5 cm above the suprasternal notch. It then turns laterally, passing deep to the sternocleidomastoid.

·  Termination: It usually drains into the external jugular vein near its termination or directly into the subclavian vein.

·  Jugular venous arch: It connects both anterior jugular veins within the suprasternal space of Burns.

·  Median cervical vein: It occasionally forms when the right and left anterior jugular veins unite in the midline.

Superficial Lymph Node of the Neck

·  The superficial lymph nodes form a cervical collar around the junction of the head and neck.

·  They receive lymph from the superficial structures of the head and neck and drain into the deep cervical lymph nodes along the internal jugular vein.

Groups of Superficial Lymph Nodes

1. Submental nodes

• These are 3–4 nodes located beneath the chin, superficial to the mylohyoid muscle. They drain the central lower lip, chin, anterior floor of mouth, adjacent gums and tip of the tongue.

2. Submandibular nodes

• These are approximately six nodes situated around the submandibular gland, near the inferior border of the mandible. They drain the cheeks, nose, upper lip, gums and much of the anterior tongue.

3. Superficial parotid (preauricular) nodes

• These lie anterior to the tragus of the ear. They drain parts of the scalp, auricle, lateral eyelids and adjacent facial region.

4. Posterior auricular (mastoid) nodes

• These are 1–2 nodes situated over the mastoid process. They drain the posterior auricle and adjoining scalp.

5. Occipital nodes

• These are 1–2 nodes located near the attachment of trapezius to the occipital bone. They drain the posterior scalp.

DEEP CERVICAL FASCIA (FASCIA COLLI)

• The deep cervical fascia is a strong connective tissue layer that supports and separates the muscles, vessels, nerves and viscera of the neck.
• It forms protective sheaths and fascial compartments that influence the spread of infection.

The deep cervical fascia and its associated fascial structures include:

1. Investing layer of deep cervical fascia.
2. Pretracheal fascia.
3. Prevertebral fascia.
4. Carotid sheath.
5. Buccopharyngeal fascia.
6. Pharyngobasilar fascia.

Investing Layer of Deep Cervical Fascia

• It is the outermost layer of deep cervical fascia, surrounding the neck like a collar. It lies deep to the platysma and superficial fascia.

Attachments and tracings

Superiorly

– It attaches to the external occipital protuberance, superior nuchal line, mastoid process, styloid process, external acoustic meatus, lower border of zygomatic arch and mandible.

Inferiorly

– It attaches to the spine of scapula, acromion, clavicle and manubrium.

Posteriorly

– It is attached to the ligamentum nuchae and spine of C7 vertebra.

Anteriorly

– It attaches to the symphysis menti and hyoid bone and continues with the fascia of the opposite side.

Important Features

• The investing layer splits to enclose the sternocleidomastoid and trapezius muscles. It forms the roofs of the anterior and posterior triangles of the neck. It encloses the parotid and submandibular glands. It forms the suprasternal and supraclavicular spaces. It provides fascial pulleys for the intermediate tendon of digastric and inferior belly of omohyoid.

Features

Fascia Around Salivary Glands

Parotid gland

• The investing fascia splits into superficial and deep laminae around the gland. The thick superficial lamina forms the parotid fascia, which continues as the masseteric fascia. The deep lamina attaches to the styloid process and tympanic plate. Its thickened portion forms the stylomandibular ligament, extending from the styloid process to the angle of mandible. This ligament separates the parotid and submandibular glands.

Submandibular gland

• The investing fascia divides to enclose the gland. Its superficial lamina attaches to the lower border of mandible, while the deep lamina attaches to the mylohyoid line.

Suprasternal Space of Burns

– It is a narrow space between two laminae of investing fascia above the manubrium.

Contents

1. Sternal heads of sternocleidomastoid muscles.
2. Jugular venous arch.
3. Suprasternal lymph nodes.
4. Interclavicular ligament.

Supraclavicular Space

• It lies between two laminae of investing fascia above the middle third of the clavicle. The posterior lamina is related to the inferior belly of omohyoid.

Contents

1. Terminal part of external jugular vein.
2. Supraclavicular nerves.

Pretracheal Fascia

·  The pretracheal fascia is a layer of deep cervical fascia that covers the anterior and lateral aspects of the trachea. It encloses the thyroid gland and forms its false capsule.

Attachments

Superiorly

– It attaches to the hyoid bone, oblique line of thyroid cartilage and cricoid cartilage.

Inferiorly

• It extends into the superior mediastinum, passing anterior to the trachea and posterior to the brachiocephalic veins.
• It blends with the fibrous pericardium around the great vessels.
• Laterally, it contributes to the anterior wall of the carotid sheath.

Features

• False capsule: The pretracheal fascia surrounds the thyroid gland and supports it within the neck.
• Ligament of Berry: It is a thickening of the posterior part of the thyroid fascial capsule that attaches the gland to the cricoid cartilage and upper tracheal rings. This ligament firmly anchors the thyroid gland to the laryngotracheal framework.

Prevertebral Fascia

• The prevertebral fascia is a layer of deep cervical fascia covering the prevertebral muscles and cervical vertebral column.
• It forms the floor of the posterior triangle of the neck.

Attachments

• Superiorly: It attaches to the base of the skull, anterior to the atlas vertebra.
• Inferiorly: It extends into the superior mediastinum and blends with the anterior longitudinal ligament and endothoracic fascia.
• Anteriorly: It is separated from the buccopharyngeal fascia by the retropharyngeal and danger spaces.
• Laterally: It extends over the scalene muscles and contributes to the fascial floor of the posterior triangle.

Features

• It covers the prevertebral and scalene muscles.
• It lies deep to the cervical and brachial plexuses.
• The cutaneous branches of the cervical plexus emerge near the posterior border of sternocleidomastoid and pierce the investing fascia to reach the skin.
• Axillary sheath: It is a lateral extension of prevertebral fascia surrounding the axillary artery and brachial plexus.
• The axillary vein lies outside this sheath, allowing its expansion during increased venous return.

Spaces in relation to prevertebral fascia

1. Retropharyngeal space

• It lies between the buccopharyngeal fascia anteriorly and alar fascia posteriorly.
• It contains loose areolar tissue and lymph nodes and permits pharyngeal expansion during swallowing.
• A median fibrous raphe partially divides it into right and left compartments, called the spaces of Gillette.

2. Danger space

• It lies between the alar fascia anteriorly and prevertebral fascia posteriorly.
• It extends into the posterior mediastinum and provides a potential route for spreading infection.

3. Prevertebral space

– It lies behind the prevertebral fascia, around the vertebral column and associated muscles.

Carotid sheath

– The carotid sheath is a tubular condensation of deep cervical fascia surrounding the major neurovascular structures of the neck.

Formation

– It receives contributions from the investing, pretracheal and prevertebral layers of deep cervical fascia.

Extent

• Superiorly: It extends to the base of the skull around the carotid canal and jugular foramen.
• Inferiorly: It continues into the superior mediastinum and blends with the connective tissue surrounding the great vessels.

Contents

1. Common and internal carotid arteries lie medially.
2. Internal jugular vein lies laterally.
3. Vagus nerve (CN X) lies posteriorly between the artery and vein.
4. Cranial nerves IX, XI and XII are closely related to the upper part of the sheath.

Relations

• Anteriorly: The ansa cervicalis is embedded in its anterior wall, while sternocleidomastoid overlaps it.
• Posteriorly: The cervical sympathetic trunk lies behind the sheath, superficial to prevertebral fascia.

Clinical Integration

• Venous expansion: The relatively thin fascial covering around the internal jugular vein permits its distension.
• Neck dissection: The sheath may be opened during surgical removal of deep cervical lymph nodes in malignancy.

Buccopharyngeal Fascia

– The buccopharyngeal fascia is a thin layer of deep cervical fascia covering the outer surfaces of the pharyngeal constrictor and buccinator muscles.

Attachments and Extent

• Superiorly: It attaches to the pharyngeal tubercle at the base of the skull.
• Posteriorly: It forms the anterior boundary of the retropharyngeal space.
• Inferiorly: It continues with the connective tissue surrounding the oesophagus.

Pharyngobasilar Fascia

·  It is a strong fibrous layer forming the internal supporting framework of the pharyngeal wall.

·  It is particularly thick between the base of the skull and the upper border of the superior constrictor muscle.

·  Inferiorly, it becomes thinner and blends with the muscular layer of the pharynx.

PHARYNGEAL SPACES

– Three important spaces surround the pharynx: one retropharyngeal space and two parapharyngeal spaces.

1. Retropharyngeal Space

– It is a potential space situated behind the pharynx.

Boundaries

• Anteriorly: Buccopharyngeal fascia.
• Posteriorly: Alar fascia.
• Laterally: Carotid sheaths.
• Superiorly: Base of the skull.
• Inferiorly: It extends into the superior mediastinum.

Contents

1. Retropharyngeal lymph nodes.
2. Loose areolar tissue.

– A median fibrous partition partially separates the space into right and left compartments.

2. Parapharyngeal Space

– It is a wedge-shaped space situated on either side of the pharynx.

Boundaries

• Medially: Pharynx and buccopharyngeal fascia.
• Laterally: Medial pterygoid muscle and deep part of parotid gland.
• Posteriorly: It is related to the carotid sheath and prevertebral fascia.

STERNOCLEIDOMASTOID MUSCLE

·  The sternocleidomastoid is a long, flat muscle extending obliquely across the lateral aspect of the neck.

·  It is enclosed by the investing layer of deep cervical fascia.

Origin

• It has two heads: Sternal and clavicular.Identification feature

The sternocleidomastoid arises by two heads:

• Sternal head: It arises by a rounded tendon from the superolateral part of the anterior surface of the manubrium.
• Clavicular head: It arises by muscular and aponeurotic fibres from the superior surface of the medial one-third of the clavicle.

Direction of Fibres

• The sternal fibres pass upward, backward and laterally.
• The clavicular fibres ascend almost vertically, deep to the sternal fibres.
• Both heads unite in the lower neck, leaving a triangular depression between them called the lesser supraclavicular fossa.

Insertion

The muscle is inserted into:

1. The lateral surface of the mastoid process of the temporal bone.
2. The lateral half of the superior nuchal line of the occipital bone.

Innervation

·  Motor: Spinal accessory nerve (CN XI).

·  Proprioceptive: Anterior rami of C2 and C3 spinal nerves.

Actions

Unilateral contraction

• It turns the face towards the opposite side.
• It tilts the head towards the shoulder on the same side.

Bilateral contraction

• It flexes the cervical vertebral column.
• It extends the head at the atlanto-occipital joints.
• It draws the head forward, particularly when rising from a lying position.
• It assists in forced inspiration by elevating the sternum and clavicle when the head is fixed.

Clinical Integration