Ultrasound anatomy of the neck: The infrahyoid region.

The infrahyoid region of the neck includes the visceral, anterior cervical, posterior cervical, carotid, retropharyngeal, and perivertebral spaces. The visceral space contains the thyroid, parathyroid glands, larynx, hypopharynx, the cervical trachea, and esophagus, the recurrent laryngeal nerve. The carotid space contains two parts, which extend from the skull base to the aortic arch and are delimited by the three layers of the deep cervical fascia (superficial, middle, and deep). It contains the internal carotid artery, the internal jugular vein, cranial nerves (IX-XII), the sympathetic plexus (suprahyoid compartment), the common carotid artery, the internal jugular vein, vagus nerve (infrahyoid compartment). The retropharyngeal space is a midlinespace containing adipose tissue that extends from the skull base to the upper mediastinum. It is located posterior to the pharynx and cervical esophagus, anterior to the danger area and the perivertebral space.THE PERIVERTEBRAL SPACE EXTENDS FROM THE SKULL BASE TO THE CLAVICLES AND INCLUDES TWO PARTS: prevertebral and paraspinal. The prevertebral space includes the prevertebral muscles (long muscles of the neck and head), the scalene muscles (anterior, middle, and posterior), the roots of the brachial plexus, the phrenic nerve, the vertebral arteries and veins, and the vertebral bodies. The paraspinal space contains the paraspinal muscles and the posterior elements of the cervical spine.The posterior cervical space is a deep space located posterior to the sternocleidomastoid muscle. It contains the accessory nerve, the accessory chain lymph nodes, the pre-axillary component of the brachial plexus, and the dorsal scapular nerve. The anterior cervical space is located deep to the strap muscles and sternocleidomastoid muscle. It surrounds the front and sides of the visceral space and is related posteriorly to the carotid space. This article reviews the ultrasound features of the structures located in the infrahyoid region of the neck.