M01.04.001 Anterior Triangle

The anterior triangle of the neck is an important anatomical region located at the front of the neck. It serves as a passage for many vital structures, including muscles, nerves, blood vessels, and lymph nodes. Understanding its borders, contents, and subdivisions is crucial for medical students, particularly when studying head and neck anatomy.

Borders of the Anterior Triangle

The anterior triangle of the neck is bounded by:

• The roof of the anterior triangle is covered by investing fascia.
• The floor of the triangle is covered by visceral fascia.

These boundaries form the anterior triangle, which can be subdivided into smaller triangles for further study.

Points to Remember:

• All triangles discussed here are paired, located on both the left and right sides of the neck.
• The anterior triangle contains both superficial and deep structures.

Contents of the Anterior Triangle

The anterior triangle contains a variety of important structures:

1. Muscles

• Suprahyoid muscles (above the hyoid bone):
  • Stylohyoid
  • Digastric
  • Mylohyoid
  • Geniohyoid
• Infrahyoid muscles (below the hyoid bone):
  • Omohyoid
  • Sternohyoid
  • Thyrohyoid
  • Sternothyroid

2. Vascular Structures

• Common Carotid Artery: Bifurcates into external and internal carotid arteries.
• Internal Jugular Vein: Drains venous blood from the head and neck.

3. Nerves

• Cranial Nerves:
  • Facial (VII)
  • Glossopharyngeal (IX)
  • Vagus (X)
  • Accessory (XI)
  • Hypoglossal (XII)

These nerves pass through or give off branches within the anterior triangle to innervate structures in the head, neck, and beyond.

Points to Remember:

• The anterior triangle is a key site for both vascular and neurological structures.
• The bifurcation of the common carotid artery within the triangle is clinically significant.

Subdivisions of the Anterior Triangle

The anterior triangle is divided into four smaller triangles by various muscles, most notably the suprahyoid and infrahyoid muscles. These subdivisions include the carotid, submental, submandibular, and muscular triangles.

1. Carotid Triangle

• Boundaries:
  • Superior: Posterior belly of the digastric muscle
  • Lateral: Medial border of the sternocleidomastoid
  • Inferior: Superior belly of the omohyoid muscle
• Contents: Common carotid artery (bifurcates into external and internal carotid arteries), internal jugular vein, Hypoglossal nerve, vagus nerve

Clinical Relevance:

• The carotid triangle contains structures that are easily accessible for surgery. The carotid sinus in this area is sensitive to pressure and regulates blood pressure through baroreceptors. Hypersensitivity in some individuals can cause syncope.

2. Submental Triangle

• Boundaries:
  • Inferior: Hyoid bone
  • Medially: Midline of the neck
  • Laterally: Anterior belly of the digastric muscle
• Contents: Submental lymph nodes (filter lymph from the floor of the mouth and parts of the tongue)

3. Submandibular Triangle

• Boundaries:
  • Superior: Body of the mandible
  • Anteriorly: Anterior belly of the digastric muscle
  • Posteriorly: Posterior belly of the digastric muscle
• Contents: Submandibular gland, facial artery, and vein, submandibular lymph nodes

4. Muscular Triangle

• Boundaries:
  • Superior: Hyoid bone
  • Medially: Midline of the neck
  • Supero-laterally: Superior belly of the omohyoid muscle
  • Infero-laterally: Inferior portion of the sternocleidomastoid muscle
• Contents: Infrahyoid muscles, thyroid gland, parathyroid glands, pharynx

Points to Remember:

• The anterior triangle is subdivided into functional areas for the examination of vessels, nerves, glands, and lymph nodes.
• Clinical access to structures like the carotid artery, internal jugular vein, and lymph nodes can often be achieved through these subdivisions.

Conclusion

The anterior triangle of the neck is a complex region containing essential structures for both diagnostic and surgical purposes. Its subdivisions allow for a detailed understanding of the anatomy and clinical relevance of the neck. Knowing the boundaries, contents, and functions of each triangle is critical for medical students, especially when considering procedures or assessing pathologies in the neck region.

Key Points:

• Borders: Inferior mandible, sternocleidomastoid, midline of the neck.
• Contents: Muscles (suprahyoid, infrahyoid), vascular structures (carotid arteries, jugular vein), cranial nerves (VII, IX, X, XI, XII).
• Subdivisions: Carotid, submental, submandibular, and muscular triangles.