What part of the pharynx corresponds to the C4-C7 vertebral level?

Vertebral Levels C4-C7 Correspond to the Hypopharynx

The vertebral levels C4-C7 correspond to the hypopharynx, which is the portion of the pharynx that extends from below the oropharynx to the level of the cricoid cartilage. 1, 2

Anatomical Relationships

• The hypopharynx lies behind the cricoid ring at the C4-C7 vertebral levels, not the esophagus as previously thought 2
• The phrenic nerve is typically found underneath the posterior border of the sternocleidomastoid muscle at the level of the cricoid cartilage, which corresponds to the C4-C6 vertebral levels 1
• The distal hypopharynx at the cricoid level is fixed with respect to the cricoid ring by a complex network of muscular and ligamentous structures, minimizing its mobility 1

Specific Vertebral Level Correlations

• The cricoid cartilage, which marks the inferior border of the hypopharynx, is located at:

  • C6 vertebral level in women (37% of cases)
  • C7 vertebral level in men (47% of cases) 3

• The superior limit of the thyroid cartilage is located at:

  • C4 vertebral level in women (60% of cases)
  • C5 vertebral level in men (52% of cases) 3

Clinical Significance

• During cervical magnetic stimulation (CMS) for respiratory muscle testing, a coil centered around C7 typically stimulates the third to fifth cervical roots, which innervate the diaphragm 1
• The hypopharynx at the cricoid level can be compressed by cricoid pressure, with the mean anteroposterior diameter reduced by approximately 35% (3.2 mm) 2
• This compression is maintained even when the cricoid ring is lateral to the vertebral body, as the hypopharynx and cricoid ring move together as an anatomical unit 2

Anatomical Variations

• The vertebral bodies of C3-C7 show significant variations based on sex and ethnicity:
  • Males have significantly wider, more elongated, and higher vertebral bodies compared to females 4
  • African American individuals manifest significantly greater vertebral bodies (width and length) in the upper and mid-cervical region (C3-C5) than European Americans 4
  • Cervical vertebral bodies become wider and more elongated with age, changing from a more round shape at C3 to a more oval shape at C7 4

Common Pitfalls in Identifying Cervical Levels

• The conventional method of identifying the most prominent cervical spinous process as C7 is unreliable in many cases (only 37.5% accuracy) 5
• The C6 spinous process is often misidentified as the most prominent cervical spinous process instead of C7 in nearly 48% of patients 5
• A more accurate method involves assisted flexion and extension of the patient's cervical spine and identifying the lowest freely moving spinous process as C6 and the following stationary cervical spinous process as C7 (77.1% accuracy) 5

Understanding these anatomical relationships is crucial for procedures involving the cervical spine, airway management, and nerve stimulation techniques targeting structures in this region.