SN4 SHORT NOTE 5M ★ High-yield

Describe the layers of the deep cervical fascia and the fascial spaces of the neck.

Anatomy · 1st Professional — Pre-Clinical

Definition

The deep cervical fascia is the fibrous framework of the neck, arranged in layers that invest the muscles and viscera and define the fascial spaces along which infection spreads.

Layers

Layer	Extent	Encloses
Investing layer	Surrounds the whole neck like a collar	Splits to enclose trapezius and sternocleidomastoid, the parotid and submandibular glands
Pretracheal layer	From the hyoid to the pericardium	Thyroid gland (its false capsule), trachea, oesophagus; encloses the strap muscles
Prevertebral layer	From the base of the skull to T3	Prevertebral muscles and the vertebral column; forms the floor of the posterior triangle and the axillary sheath
Carotid sheath	Base of skull to the thorax	Common and internal carotid arteries, internal jugular vein, vagus nerve

The carotid sheath is thick around the artery and thin over the vein, so the vein can distend
The ansa cervicalis is embedded in its anterior wall
The sympathetic chain lies behind the sheath, on the prevertebral fascia — not within it

Special Features of the Investing Layer

Splits to form the parotid (parotidomasseteric) fascia, whose toughness accounts for the pain of mumps
Forms the stylomandibular ligament, separating the parotid from the submandibular gland
Suprasternal space (of Burns) — between its two laminae above the manubrium; contains the jugular venous arch, encountered in tracheostomy
Forms the pulley for the intermediate tendon of digastric and omohyoid

Fascial Spaces and the Spread of Infection

Space	Position	Danger
Retropharyngeal	Between the buccopharyngeal fascia and the prevertebral fascia	Infection can track down into the superior mediastinum
"danger" space	Between the alar and prevertebral layers	Extends to the diaphragm — hence the name
Pretracheal	In front of the trachea	Leads to the anterior mediastinum
Submandibular and sublingual	Floor of the mouth	LUDWIG angina — airway obstruction
Parapharyngeal	Lateral to the pharynx	Related to the carotid sheath; risk of carotid erosion and jugular thrombosis

Applied Aspects

Retropharyngeal abscess — in children from suppuration of the retropharyngeal nodes; causes dysphagia, stridor and a bulge in the posterior pharyngeal wall. Must be drained with the head low, to prevent aspiration
Ludwig angina — a true emergency; the airway must be secured early, and the floor of the mouth decompressed
Cervical lymph node tuberculosis may form a collar-stud abscess, burrowing through the investing layer to lie superficially
Fascial planes guide surgical incisions — skin creases are used for cosmetic reasons, and dissection then proceeds in bloodless fascial planes
Deep neck infections are commoner in diabetics and can progress to descending necrotising mediastinitis, which requires drainage of both neck and chest

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