Anatomy of Superficial and Deep Cervical Fascia

Anatomy of the Cervical Fascia

The cervical fascia in the neck is a crucial anatomical concept, dividing the neck into various potential spaces. Understanding these fascial layers and their attachments is vital because infections in these deep neck spaces can be dangerous and lead to airway compromise.

The cervical fascia is generally divided into two main parts:

1. Superficial Cervical Fascia
2. Deep Cervical Fascia

The deep cervical fascia is particularly important due to its layered structure and implications for the spread of infection.

✨ Divisions of Cervical Fascia

Superficial Cervical Fascia

• A zone of loose connective tissue situated between the dermis and the deep fascia.
• Contains the superficial musculoaponeurotic system (SMAS) and envelops the platysma muscle.
• Often not clearly distinct as a separate layer.
• The potential space within the superficial fascia contains sensory nerves, superficial veins, and varying amounts of adipose tissue.

🧱 Deep Cervical Fascia

This is the more substantial and clinically significant fascia, divided into three main layers:

1. Superficial Layer (Investing Layer)
2. Middle Layer (Visceral Layer or Pretracheal Layer)
3. Deep Layer (Prevertebral Layer)

Let's explore the attachments and extensions of each layer in detail.

1. Investing Layer (Superficial Layer of Deep Cervical Fascia)

This is the outermost layer of the deep cervical fascia.

📍 Attachments:

• Posteriorly: Attached to the Ligamentum Nuchae and the spine of the 7th Cervical Vertebra.

• Anteriorly: Continuous with the same layer on the opposite side across the midline; attached to the Hyoid bone.

• Superiorly (from posterior to anterior):

  • External occipital protuberance and Superior Nuchal Line.
  • Mastoid Process.
  • Cartilaginous part of the External Auditory Canal (EAC).
  • Lower margin of the Zygomatic Arch.
  • Lower border of the Mandible (from angle to symphysis menti).

• Inferiorly (from posterior to anterior):

  • Acromial process and spine of the Scapula.
  • Upper surface of the Clavicle.
  • Suprasternal Notch (Manubrium Sterni).

↔️ Horizontal Extent:

• Wraps horizontally around the neck.

What are the 2 muscles enclosed in Investing Layer of Deep Cervical Fascia?

Which are the 2 triangle of neck whose roof is formed by Investing Layer of Deep Cervical Fascia?

↕️ Vertical Extent & Enclosures:

The investing layer splits to enclose several structures and spaces:

Splitting to enclose Glands (Superiorly):

What are the 2 glands enclosed by Investing Layer of Deep Cervical Fascia?

Splitting to enclose Spaces (Inferiorly):

• Splits inferiorly near the sternum/clavicle to form two spaces:

1- Suprasternal Space (of Burns)

• Triangular space above the manubrium sterni.

• Fascia splits into superficial and deep layers attaching to anterior/posterior borders of the suprasternal notch.

What are the contents of Suprasternal Space (of Burns)?

2- Supraclavicular Space

• Located above the middle third of the clavicle.

• Fascia splits to attach to anterior/posterior borders of the clavicle's upper surface. The posterior layer encloses the inferior belly of the Omohyoid muscle (forming the omohyoid fascia).

What are the contents of Supraclavicular Space?

✨ Investing Layer Summary (Everything "Two"):

An easy way to remember structures related to the Investing Layer:

• Encloses Two Muscles: Sternocleidomastoid, Trapezius.
• Forms Roof of Two Triangles: Anterior, Posterior.
• Encloses Two Glands: Parotid, Submandibular.
• Encloses Two Spaces: Suprasternal Space of Burns, Supraclavicular Space.
• Is Thickened Twice to form: Parotidomasseteric Fascia, Stylomandibular Ligament.
• Forms Two Fascial Slings for: Inferior belly of Omohyoid, Digastric tendon.
• Gives Origin to Two Fascial Processes: Pretracheal Layer, Prevertebral Layer (in a conceptual sense, though attachments are key).

2. Pretracheal Layer (Middle or Visceral Layer of Deep Cervical Fascia)

Located deep to the investing layer.

↔️ Horizontal Extent:

• Arises from the investing layer under the SCM cover.
• Passes medially to form the anterior wall of the Carotid Sheath.
• Splits to enclose the Thyroid Gland.
• Passes in front of the Trachea to meet the opposite side.
• Forms the Ligament of Berry, a fibrous band connecting the thyroid lobe to the cricoid cartilage.

↕️ Vertical Extent:

• Superiorly: Attached to the Hyoid bone (midline) and the oblique line of the Thyroid cartilage (each side), and the Cricoid cartilage.

• Inferiorly: Enters the thorax in front of the trachea and inferior thyroid veins, blending with the apex of the Fibrous Pericardium. At the thoracic inlet, it is continuous with the Suprapleural Membrane (Sibson's Fascia).

📦 Compartments Enclosed:

The pretracheal layer encloses two compartments:

• Muscular Compartment: Surrounds the Infrahyoid (Strap) Muscles (Sternothyroid, Sternohyoid, Thyrohyoid, Omohyoid).

• Visceral Compartment: Contains the Pharynx, Esophagus, Trachea, Thyroid Gland, Parathyroid Glands, and Buccinator muscle. The posterior part of this layer covering the pharynx/buccinator is sometimes called the Buccopharyngeal Fascia (extends from skull base to cricoid).

3. Prevertebral Layer (Deep Layer of Deep Cervical Fascia)

The deepest layer of the deep cervical fascia.

↔️ Horizontal Extent:

• Arises from the investing layer under the SCM cover.

• Passes medially to form the posterior wall of the Carotid Sheath.

• Covers the Cervical Vertebrae and the Prevertebral Muscles (Longus Colli, Longus Capitis, Rectus Capitis Anterior & Lateral).

• Covers the Scalene muscles and Levator Scapulae, forming the floor of the Posterior Triangle.

• The Cervical Plexus and Brachial Plexus lie beneath this fascia.

• Gives a tubular investment to form the Axillary Sheath around the cords of the Brachial Plexus and the Subclavian Artery (but the Subclavian Vein lies outside this sheath).

↕️ Vertical Extent & Splitting:

• Superiorly: Attached to the bones of the Skull Base.

• Inferiorly: Splits into two layers around the cervical vertebrae:

  • Anterior Layer (Alar Fascia): More anterior.
  • Posterior Layer (True Prevertebral Fascia): Closely adherent to the vertebral bodies and anterior longitudinal ligament.

Alar Fascia

• Extends inferiorly from the skull base to about the level of the 7th Cervical Vertebra, where it fuses with the visceral layer of the middle cervical fascia. This fusion limits the lowest extent of the Retropharyngeal and Danger spaces (above C7, the Danger Space continues into the posterior mediastinum).
• Covers the Cervical Sympathetic Trunk.

Carotid Sheath

Although not a separate layer, the carotid sheath is a tubular structure formed by contributions from the Investing, Pretracheal, and Prevertebral layers.

• Formation:
  • Anterior wall contributed by the Pretracheal fascia.
  • Posterior wall contributed by the Prevertebral fascia.
  • Investing layer contributes to the outer boundary.

What are the contents of Carotid sheath? What are it's relation to each other?

• The sheath is thicker around the arteries but looser around the internal jugular vein, allowing for its expansion during increased venous flow.

Conclusion

Understanding the complex layering and attachments of the deep cervical fascia is fundamental. These fascial planes define potential spaces like the Retropharyngeal Space and Danger Space, which are clinically significant pathways for the spread of infection from head and neck sites.