Cross-sectional Anatomy: Neck

Cross-sectional Anatomy: Neck

Cross-sectional Anatomy: Neck

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Neck Overview & Levels - Axial Atlas

Axial neck anatomy: illustration vs. CT scan

  • 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.

Axial MRI neck showing fascial spaces

⭐ 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.

Axial CT neck with cystic lesion

⭐ 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).

Practice Questions: Cross-sectional Anatomy: Neck

Test your understanding with these related questions

A patient presented with 2 days history of fever. On examination there was a swelling in the neck and one side tonsil was pushed to midline. What is the most likely diagnosis:-

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Flashcards: Cross-sectional Anatomy: Neck

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Bulge in posterior pharyngeal wall on x-ray is seen _____laterally in acute retropharyngeal abscess

TAP TO REVEAL ANSWER

Bulge in posterior pharyngeal wall on x-ray is seen _____laterally in acute retropharyngeal abscess

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