Table 1 Anatomical structures defining the boundaries of the cervical levels and sublevels

IA

Symphysis of mandible

Body of hyoid

Anterior belly of contralateral digastric muscle

Anterior belly of ipsilateral digastric muscle

IB

Body of mandible

Posterior belly of diagastric muscle

Anterior belly of digastric muscle

Stylohyoid muscle

IIA

Skull base

Horizontal plane defined by the inferior border of the hyoid bone

The stylohyoid muscle

Vertical plane defined by the spinal accessory nerve

IIB

Skull base

Horizontal plane defined by the inferior body of the hyoid bone

Vertical plane defined by the spinal accessory nerve

Lateral border of the sternocleidomastoid muscle

III

Horizontal plane defined by the inferior body of hyoid

Horizontal plane defined by the inferior border of the cricoid cartilage

Lateral border of the sternohyoid muscle

Lateral border of the sternocleidomastoid or sensory branches of cervical plexus

IV

Horizontal plane defined by the inferior border of the cricoid cartilage

Clavicle

Lateral border of the sternohyoid muscle

Lateral border of the sternocleidomastoid or sensory branches of cervical plexus

VA

Apex of the convergence of the sternocleidomastoid and trapezius muscles

Horizontal plane defined by the lower border of the cricoid cartilage

Posterior border of the sternocleidomastoid muscle or sensory branches of cervical plexus

Anterior border of the trapezius muscle

VB

Horizontal plane defined by the lower border of the cricoids cartilage

Clavicle

Posterior border of the sternocleidomastoid muscle

Anterior border of the trapezius muscle

VI

Hyoid bone

Suprasternal notch

Common carotid artery

Common carotid artery

VII

Suprasternal notch

Innominate artery

Sternum

Trachea, esophagus, and prevertebral fascia