Anterior Neck - LO1

1. What is fascia? Which muscle is located in the superficial fascia of the neck? What are the 3 main deep cervical fascial layers? Why are these layers clinically important?

Fascia is the term for grossly visible connective tissue collections or sheaths deep to the skin (epidermis + dermis). From superficial to deep, the tissues are organized:

Epidermis → Dermis → Superficial fascia → Deep fascia

Superficial fascia is commonly referred to as subcutaneous (subQ) tissue or hypodermis, and is typically a layer of loose areolar connective tissue with varying amounts of adipose. Specifically, in the anterior neck, the hypodermis contains the platysma m(uscle). Platysma m. is a muscle of facial expression with a primary action of neck tension, and also plays a role in weak depression of the mandible and lower lip. The platysma m., like all muscles of facial expression, is innervated by the facial n. (CN VII), specifically the cervical br(anch). This muscle is a part of the Superficial Musculo-Aponeurotic System (SMAS), a superficial layer of muscles, aponeuroses, and fascia that are contiguous over the anterolateral neck and face.

Deep fascia is typically denser than superficial fascia, and is devoid of adipose tissue (fat). This fascia is important in surrounding and supporting muscle, organs (viscera), and neurovasculature.

Deep cervical fascia is located specifically in the neck with some extensions superiorly and inferiorly.

Three main deep cervical fascial layers:

• • Investing fascia

    • This is the most superficial layer of deep cervical fascia. As the name suggests, this layer invests the entirety of the neck deep to the skin and superficial cervical fascia (subcutaneous tissue).

  • Middle (pretracheal) fascia has 2 layers:

    • Muscular fascia: invests the infrahyoid mm. and is more anteriorly located

    • Visceral fascia: surrounds the majority of the viscera of the neck, including the thyroid gland, trachea, and esophagus

      • Buccopharyngeal fascia

        • Often described as a subdivision of the visceral layer of deep cervical fascia or described separately

        • Surrounds muscles of the cheek and pharynx

  • Deep fascia has 2 divisions:

    • Alar fascia: anteriorly located and attached to transverse processes of cervical vertebrae

    • Prevertebral fascia: posteriorly located, and closely associated with the anterior surfaces of vertebral bodies and intervertebral discs

Fascial spaces are either actual or potential spaces between these layers that form planes through which tissues can be separated, which is of particular importance in surgeries. The fascial spaces can limit or allow the spread of infections, etc.

The space between the buccopharyngeal fascia and the prevertebral fascia is the retropharyngeal space. The alar fascia subdivides the retropharyngeal space into two spaces: the 'true retropharyngeal space' (anteriorly), and the 'danger space' (posteriorly). The space (‘danger space’) between the prevertebral and alar fascia is of particular clinical importance as this is a potential area for infections to spread between the pharynx and mediastinum (a space within the thorax, medial to the lungs).