🫀
AnatomyIQGet the App
🦒head neck

Neck Triangles Dissection Guide

Systematic guide to dissecting the anterior and posterior triangles of the neck, including the carotid sheath contents, cervical plexus, and clinical relationships. Essential for understanding neck surgery and central line placement.

Learning Objectives

  • ✓Define the boundaries of the anterior and posterior triangles
  • ✓Identify the carotid sheath and its contents
  • ✓Dissect the cervical plexus and its branches
  • ✓Examine the thyroid gland and its relations
  • ✓Understand the clinical significance of neck anatomy

Prerequisites

  • • Knowledge of neck surface anatomy
  • • Understanding of cranial nerve courses
  • • Review of laryngeal anatomy
  • • Familiarity with neck imaging

Equipment Needed

  • • Scalpel with #10 and #15 blades
  • • Dissecting scissors
  • • Forceps
  • • Probe
  • • Retractors
  • • Dissecting tray

Dissection Steps

Step 1:Skin Incision and Platysma

Make an incision from the mastoid process along the posterior border of SCM, then along the clavicle. Make a second incision from the mastoid along the inferior border of the mandible. Reflect skin flaps to expose the platysma muscle.

Key Structures

Platysma muscleExternal jugular veinGreat auricular nerveTransverse cervical nerve
Tip:The platysma is a thin sheet muscle of facial expression that spans from the mandible to the chest. It is innervated by the cervical branch of the facial nerve.

Step 2:Identify the Sternocleidomastoid

Cut through the platysma to fully expose the sternocleidomastoid muscle. Note its origin from the sternum and clavicle and insertion on the mastoid process. The SCM divides the neck into anterior and posterior triangles.

Key Structures

SternocleidomastoidSternal headClavicular headAccessory nerve (CN XI)
Tip:The accessory nerve (CN XI) enters the deep surface of SCM and can be found approximately 3-4 cm below the mastoid process.

Step 3:Dissect the Posterior Triangle

Define the boundaries of the posterior triangle: anterior (SCM), posterior (trapezius), inferior (middle third of clavicle). Identify the accessory nerve crossing the triangle, the cervical plexus branches, and the brachial plexus roots.

Key Structures

Accessory nerve (CN XI)Cervical plexus branchesBrachial plexus (superior trunk)Suprascapular arteryExternal jugular veinOmohyoid (inferior belly)
Tip:The accessory nerve is vulnerable in the posterior triangle during lymph node biopsies. Its damage causes shoulder droop and weakness raising the arm above horizontal.

Step 4:Identify Cervical Plexus Branches

Find the sensory branches of the cervical plexus emerging at the posterior border of SCM (Erb's point): lesser occipital, great auricular, transverse cervical, and supraclavicular nerves.

Key Structures

Lesser occipital nerve (C2)Great auricular nerve (C2-3)Transverse cervical nerve (C2-3)Supraclavicular nerves (C3-4)Erb's point
Tip:Erb's point is approximately at the junction of the upper and middle thirds of the posterior border of SCM. It's where the cervical plexus branches emerge.

Step 5:Dissect the Anterior Triangle

Define the boundaries: lateral (SCM), medial (midline), superior (inferior border of mandible). The anterior triangle contains several smaller triangles: submandibular, carotid, muscular, and submental.

Key Structures

Submandibular triangleCarotid triangleMuscular triangleSubmental triangleDigastric muscleOmohyoidSternohyoidSternothyroid
Tip:The anterior triangle is further divided by the digastric muscle (above) and omohyoid muscle (below) into its sub-triangles.

Step 6:Expose the Carotid Sheath

Retract the SCM laterally to expose the carotid sheath. Open the sheath to identify its contents: common carotid artery (medial), internal jugular vein (lateral), vagus nerve (posterior between them).

Key Structures

Carotid sheathCommon carotid arteryInternal jugular veinVagus nerveDeep cervical lymph nodesCarotid bifurcationCarotid sinusCarotid body
Tip:The carotid sinus (dilated region at the bifurcation) contains baroreceptors for blood pressure. The carotid body (at the bifurcation) contains chemoreceptors.

Step 7:Identify the Carotid Triangle Structures

In the carotid triangle, trace the common carotid artery to its bifurcation into internal and external carotid arteries. Identify the branches of the external carotid and the hypoglossal nerve crossing the arteries.

Key Structures

Common carotid arteryExternal carotid arteryInternal carotid arterySuperior thyroid arteryLingual arteryFacial arteryHypoglossal nerve (CN XII)Ansa cervicalis
Tip:The internal carotid has no branches in the neck. External carotid branches can be remembered: "Some Anatomists Like Freaking Out Poor Medical Students" (Superior thyroid, Ascending pharyngeal, Lingual, Facial, Occipital, Posterior auricular, Maxillary, Superficial temporal).

Step 8:Dissect the Thyroid Region

Identify the thyroid gland with its isthmus and lateral lobes. Note the superior and inferior thyroid arteries and their relationship to the recurrent laryngeal nerve. Identify the parathyroid glands on the posterior surface.

Key Structures

Thyroid gland (isthmus, lateral lobes)Superior thyroid arteryInferior thyroid arteryThyroid veinsRecurrent laryngeal nerveParathyroid glands (superior and inferior)
Tip:The recurrent laryngeal nerve runs between branches of the inferior thyroid artery (variable relationship). Damage during thyroid surgery causes hoarseness.

Clinical Correlations

  • •Carotid endarterectomy: surgical removal of atherosclerotic plaque from the carotid bifurcation to prevent stroke
  • •Internal jugular vein catheterization: central line placement using the carotid artery as a landmark
  • •Thyroidectomy: requires identification and preservation of recurrent laryngeal nerves and parathyroid glands
  • •Radical neck dissection: removes lymph nodes and may sacrifice accessory nerve, causing shoulder dysfunction

Common Mistakes to Avoid

  • ✗Damaging the external jugular vein when reflecting the platysma
  • ✗Confusing the internal and external carotid arteries (remember: internal has no branches)
  • ✗Not preserving the accessory nerve when dissecting the posterior triangle
  • ✗Missing the ansa cervicalis overlying the carotid sheath

Study Questions

  1. What are the boundaries of the carotid triangle?
  2. How would you locate the accessory nerve in the posterior triangle?
  3. What is the relationship between the recurrent laryngeal nerve and the inferior thyroid artery?
  4. Why is the internal jugular vein preferred for central line placement?
  5. What are the clinical consequences of damaging the accessory nerve?

Get AI Help in Lab

Instant anatomy answers while you study and dissect.

Download AnatomyIQ

FAQs

Common questions about this dissection

The internal carotid artery has no branches in the neck and is usually posterolateral at the bifurcation. The external carotid has multiple branches and is usually anteromedial. The carotid sinus is at the origin of the internal carotid.

The ansa cervicalis is a nerve loop formed by C1-3 fibers that innervates the infrahyoid (strap) muscles: sternohyoid, sternothyroid, and omohyoid. The superior root travels briefly with CN XII before descending.

More Lab Guides

💪 Anterior Forearm❤️ Heart Dissection🧠 Brain Dissection🏋️ Anterior Abdominal🦒 Neck Triangles🦵 Knee Joint