Triangles of neck
On this page 6 sections
Anterior triangle
Boundaries
| Boundary | Structure |
|---|---|
| Anterior | Midline of neck |
| Posterior | Anterior border of sternocleidomastoid (SCM) |
| Superior | Inferior border of mandible |
Subdivisions
| Triangle | Boundaries |
|---|---|
| Carotid | SCM Posterior belly of digastric Superior belly of omohyoid |
| Submental (Unpaired) | Right and left anterior bellies of digastric Hyoid forms the base |
| Submandibular (digastric) | Inferior border of mandible Anterior and posterior bellies of digastric |
| Muscular | Midline of neck Anterior border of SCM Superior belly of omohyoid |
Visual reference: the four subdivisions are separated by the digastric and omohyoid muscles.
Posterior triangle
Boundaries
| Boundary | Structure |
|---|---|
| Anterior | Posterior border of SCM |
| Posterior | Anterior border of trapezius |
| Inferior (base) | Middle third of clavicle |
| Roof | Investing layer of deep cervical fascia |
| Floor | Prevertebral fascia covering underlying muscles |
Contents
- Spinal accessory nerve (CN XI)
- Cutaneous branches of cervical plexus
- Roots and trunks of brachial plexus
- Third part of subclavian artery
- Subclavian vein (near the root of the neck, anterior to anterior scalene)
- External jugular vein, which pierces the investing fascia before draining into the subclavian vein
The inferior belly of the omohyoid divides the posterior triangle into:
| Subdivision | Alternative name |
|---|---|
| Superior | Occipital triangle |
| Inferior | Omoclavicular triangle (supraclavicular/subclavian triangle) |
High-yield clinical correlations
| Finding or scenario | Key answer | Explanation |
|---|---|---|
| Shoulder droop after posterior-triangle surgery | Spinal accessory nerve (CN XI) injury | Trapezius paralysis impairs shoulder shrug |
| Difficulty combing hair | Accessory nerve injury | Reduced ability to elevate and rotate the scapula |
| Spinal accessory nerve course | Traverses SCM, then crosses the posterior triangle | Vulnerable during lymph node biopsy |
| SCM contraction on one side | Head rotates to the opposite side | Also tilts the head toward the same side |
| Short neck during newborn intubation; absent right breath sounds | Possible right mainstem bronchial intubation | Tube insertion depth and head/neck position are more direct causes than a short neck itself |
| Shoulder weakness with ptosis and miosis | Consider combined accessory nerve and cervical sympathetic pathway injury | These findings suggest more than an isolated CN XI lesion |
Suboccipital triangle
| Feature | High-yield fact |
|---|---|
| Floor | Posterior atlanto-occipital membrane and posterior arch of atlas, with the suboccipital muscles forming the floor region |
| Important vessel | Vertebral artery (third part) |
| Important nerve | Suboccipital nerve (posterior ramus of C1) |
Clinical pearl: The vertebral artery passes through the suboccipital region and is vulnerable to trauma or procedures in this area.