Cross-sectional Anatomy: Neck

Neck Overview & Levels - Axial Atlas

• Key Concept: Neck levels are crucial for staging & surgical planning, defined by consistent anatomical landmarks on axial imaging.
• Levels (Robbins/AJCC simplified for radiology):
  • Level I: Submental & Submandibular triangles.
    • IA: Submental (between anterior bellies of digastric).
    • IB: Submandibular (posterior to anterior belly, anterior to posterior belly of digastric).
  • Level II: Upper jugular (skull base to hyoid).
    • IIA: Anterior to spinal accessory nerve (CN XI).
    • IIB: Posterior to CN XI.
  • Level III: Middle jugular (hyoid to cricoid).
  • Level IV: Lower jugular (cricoid to clavicle).
  • Level V: Posterior triangle (posterior to SCM, anterior to trapezius).
    • VA: Superior (above cricoid arch inferior border).
    • VB: Inferior (below cricoid arch inferior border, supraclavicular).
  • Level VI: Anterior compartment (pretracheal, paratracheal, prelaryngeal/thyroid, recurrent laryngeal nerve nodes).
  • Level VII: Superior mediastinal nodes (between common carotid arteries, below top of manubrium to innominate artery).

⭐ Exam Favourite: The hyoid bone is a key landmark separating Level II (above) from Level III (below) in the jugular chain.

• Axial Views: Best for delineating fascial planes & lymph node groups.
  • Identify major vessels: Carotid arteries, Jugular veins.
  • Key muscles: Sternocleidomastoid (SCM), Digastric, Trapezius.
  • Bony landmarks: Hyoid, Cricoid, Clavicle, Mandible, Vertebral bodies.

📌 Mnemonic (Levels): "Superman Saves Many Little Puppies Always" (Submental/Submandibular, Superior jugular, Middle jugular, Lower jugular, Posterior triangle, Anterior compartment) - Note: Level VII not included in this common mnemonic.

Fascial Layers & Spaces - Infection Mazes

• Superficial Cervical Fascia (SCF): Encloses platysma.
• Deep Cervical Fascia (DCF):
  • Investing: Surrounds SCM, trapezius.
  • Pretracheal: Encloses thyroid, trachea, esophagus.
  • Prevertebral: Covers vertebral column, deep neck muscles.
  • Carotid Sheath: Common carotid a., IJV, CN X.

Key Neck Spaces & Infection Pathways:

• Retropharyngeal Space (RPS):
  • Buccopharyngeal fascia (ant) to alar fascia (post).
  • Infection → danger space.
• Danger Space (Space 4):
  • Alar fascia (ant) to prevertebral fascia (post).
  • 📌 Extends skull base to diaphragm; infection → rapid mediastinitis.
• Prevertebral Space:
  • Post. to prevertebral fascia; skull base to coccyx.
• Ludwig's Angina: Bilateral submandibular, sublingual, submental space infection.

⭐ Retropharyngeal abscess in children < 5 years often from URI; in adults, often from trauma/instrumentation.

Neck Viscera - Core Components

• Thyroid Gland: Butterfly-shape, anterior neck. Hyperdense on CT (iodine). Isthmus: 2nd-4th tracheal rings. Homogeneous enhancement.
  • Key signs: Nodules, goiter.
• Parathyroid Glands: Typically 4, posterior to thyroid. Small; visualized if abnormal (e.g., adenoma).
• Larynx: Cartilaginous framework (thyroid, cricoid, arytenoids).
  • Levels: Supraglottis, glottis, subglottis.
  • Assess: Cartilage invasion, cord mobility.
• Pharynx: Posterior to nasal/oral cavities, larynx.
  • Parts: Naso-, Oro-, Laryngopharynx.
• Trachea: Anterior to esophagus. C-shaped cartilages. Air-filled.
• Esophagus: Muscular tube, posterior to trachea. Usually collapsed.

⭐ The tracheoesophageal groove is a critical landmark housing the recurrent laryngeal nerve (RLN); injury leads to hoarseness.

Vessels, Nerves & Nodes - Vital Pathways

• Arteries:
  • CCA: Bifurcates C3-C4. ICA: no neck branches.
  • ECA: Supplies face/neck. Branches 📌 SALFOPMS (e.g., Sup. Thyroid, Facial).
  • Vertebral: From subclavian, in C6-C1 transverse foramina.
• Veins:
  • IJV: Main drainage, in carotid sheath.
  • EJV: Superficial.
• Nerves:
  • Vagus (X): In carotid sheath.
  • CN IX, XI, XII: Close to major vessels.
  • Phrenic (C3,4,5): To diaphragm. 📌 "C3,4,5 keeps diaphragm alive".
  • Sympathetic trunk: Posterior to sheath.
• Lymph Nodes (Levels I-VI):
  • I: Submental/mandibular. II: Upper Jugular. III: Mid Jugular.
  • IV: Lower Jugular. V: Posterior Triangle. VI: Central.

  ⭐ Virchow's node (left supraclavicular - Level IV) signals GI malignancy.

High‑Yield Points - ⚡ Biggest Takeaways

• Cervical fascial layers (investing, pretracheal, prevertebral, carotid sheath) determine spread of neck infections and tumors.
• Carotid sheath contents: CCA/ICA (medial), IJV (lateral), CN X (posterior).
• Retropharyngeal space infection is a red flag; can cause mediastinitis.
• Thyroid gland: note its lobes, isthmus, and relation to trachea/esophagus.
• Key landmarks: hyoid bone, thyroid cartilage, cricoid cartilage, epiglottis.
• Lymph node levels (I-VII) are vital for H&N cancer staging and treatment.
• Vertebral arteries run superiorly within transverse foramina (typically C1-C6).