Ch12: Neck I — Superficial Structures, Lateral Region & Root（颈部浅层与颈根部）

# Ch12: Neck I — Superficial Structures, Lateral Region & Root of Neck

Preparatory Mindset

The neck is organized by fascial layers (which create the potential spaces where infection spreads), triangles (which box the contents), and the root of the neck (where great vessels, the phrenic nerve, thoracic duct & brachial plexus pass). The fascia/spaces and the triangle contents are the two exam pillars.

Exam mindset: The lecture drills: the investing/prevertebral/pretracheal layers, the fascial spaces (suprasternal, pretracheal, retropharyngeal), triangle contents (occipital, omoclavicular, carotid, muscular, submandibular, submental), cervical plexus branches, and root-of-neck structures (subclavian branches, phrenic, thoracic duct).

Core Concepts

1. Fascia of the neck (3 layers)

2. Fascial spaces of the neck (clinical)

• Suprasternal space (of Burns): between the two layers of the investing fascia at the manubrium; contains areolar tissue, sternal head of SCM, lower part of anterior jugular vein. Clinical: trauma here → large bulging above the manubrium, may extend into the superior mediastinum
• Pretracheal space: around the trachea, bounded by investing fascia + infrahyoid muscles anteriorly, visceral fascia posteriorly; continues into the anterior superior mediastinum. Clinical: infection spreads into the thorax anterior to the pericardium; thyroid abscess here
• Retropharyngeal space (concept 97): between the buccopharyngeal fascia (pharynx) and the prevertebral fascia; loose CT. Clinical: infection may extend inferiorly into the superior mediastinum; air from ruptured trachea/bronchus/esophagus (pneumomediastinum) can pass superiorly

3. Triangles of the neck — contents (MUST KNOW)

Anterior triangle (bounded by mandible, midline, anterior border of SCM) — 4 triangles:

Posterior triangle (bounded by SCM, trapezius, middle third of clavicle) — 2 triangles:

4. Superficial veins of the neck

• External jugular vein (EJV): begins behind the angle of the mandible (posterior auricular + posterior division of retromandibular), descends superficial to SCM, deep to platysma, pierces the deep fascia above the clavicle → drains into subclavian vein
• Anterior jugular vein (AJV): starts below the chin, descends near the midline, connected across the midline by the jugular venous arch in the suprasternal space; opens into the EJV
• Clinical: EJV is visible when the jugular venous pressure rises; it can be injured in neck lacerations (air embolism risk)

5. Cervical plexus (C1-C4)

• Superficial (sensory) branches — "GLAST" or "GLASS": Great auricular, Lesser occipital, Anterior (transverse) cervical, Supraclavicular, (Sternocleidomastoid branch)
• Nerve point of the neck: the middle of the posterior border of the SCM — where the superficial branches emerge; used for cervical plexus block (anesthesia of the neck)
• Muscular (motor) branches: ansa cervicalis (C1-C3) → infrahyoid muscles (sternohyoid, omohyoid, sternothyroid, thyrohyoid — thyrohyoid from C1 via hypoglossal); phrenic nerve (C3-C5) → diaphragm

6. Root of the neck (MUST KNOW)

1. Vertebral artery 2. Internal thoracic (mammary) artery 3. Thyrocervical trunk → inferior thyroid, suprascapular, transverse cervical arteries 4. Costocervical trunk → supreme intercostal, deep cervical arteries

• Cupula of the pleura: rises 2-3 cm above the medial 1/3 of the clavicle (vulnerable to penetrating injury)
• Branches of the subclavian artery (mnemonic "VIT C"):
• Subclavian vein: anterior to the subclavian artery, separated by scalenus anterior; receives the EJV & thoracic duct
• Thoracic duct: on the LEFT — arches into the neck at the level of C7, drains into the junction of the left internal jugular & subclavian veins; right lymphatic duct on the RIGHT
• Vagus nerve (CN X): descends in the carotid sheath; left recurrent laryngeal loops under the aortic arch; right recurrent loops under the right subclavian artery
• Phrenic nerve (C3-C5): descends on the anterior surface of scalenus anterior (from lateral to medial), passes anterior to the subclavian vessels into the thorax — the key landmark on scalenus anterior
• Sympathetic trunk (cervical): behind the carotid sheath; stellate (cervicothoracic) ganglion → Horner's syndrome if injured (concept 92)

7. Scalenus anterior — the landmark of the root

• Structures in front: phrenic nerve (descending on it, lateral→medial), subclavian vein (in front of the artery? — actually the vein passes IN FRONT of scalenus anterior, the artery & plexus pass BEHIND)
• Structures behind: subclavian artery (2nd part) & brachial plexus (roots/trunks)
• Scalene fissure (interscalene): between scalenus anterior & medius → the subclavian artery & brachial plexus pass through
• Clinical: scalene syndrome / thoracic outlet: cervical rib may compress the lower trunk (C8-T1) & subclavian artery → Klumpke-type symptoms + vascular

High-Yield Points

• Fascia layers: investing (SCM/trapezius; suprasternal space), pretracheal (thyroid/trachea; pretracheal space → anterior mediastinum), prevertebral (vertebral column; axillary sheath laterally; retropharyngeal space → superior mediastinum)
• Carotid sheath contents: "CC IVV" — Common & Internal carotid arteries, Internal jugular vein, Vagus nerve (concept 98)
• Posterior triangle contents: "CN XI, cervical plexus, brachial plexus trunks, EJV, subclavian a. (3rd part)" — the accessory nerve crosses the posterior triangle obliquely (superficial → vulnerable)
• Cervical plexus block point: nerve point of the neck = mid-posterior border of SCM
• Subclavian artery branches: "VIT C" (Vertebral, Internal thoracic, Thyrocervical trunk, Costocervical trunk)
• Phrenic nerve: C3-C5, on the anterior surface of scalenus anterior — innervates the diaphragm
• Thoracic duct: left side, drains into left venous angle
• Scalene fissure: subclavian artery + brachial plexus pass behind scalenus anterior, subclavian vein in front
• Retropharyngeal space: between buccopharyngeal & prevertebral fascia → infection to superior mediastinum

Topic Summary

The neck is layered by the investing (SCM/trapezius, suprasternal space), pretracheal (thyroid/trachea, pretracheal space) and prevertebral (vertebral column, axillary sheath, retropharyngeal space) fasciae. The triangles box the contents: anterior triangle (submental, submandibular, carotid with the carotid sheath, muscular with the thyroid) and posterior triangle (occipital with CN XI & brachial plexus trunks; omoclavicular with the 3rd part of subclavian). Superficial veins (EJV, AJV with jugular arch), the cervical plexus (sensory GLAST at the nerve point; motor ansa cervicalis & phrenic), and the root of the neck (subclavian branches VIT C, phrenic on scalenus anterior, thoracic duct on the left, vagus/recurrent laryngeal, sympathetic trunk) complete the picture.