Anatomy

To understand the deep neck spaces, it is important to have an understanding of the fascial layers of the neck. There are two main fascial layers: the superficial cervical fascia and the deep cervical fascia. The superficial cervical fascia extends from the clavicle to the mandible and primarily encompasses the platysma muscle. It is not involved with the retropharyngeal space and will not be further discussed. The deep cervical fascia is divided into three components: the superficial, middle, and deep layers. The superficial layer of the deep cervical fascia encircles the neck and attaches to the spinous processes of the vertebrae posteriorly. Superiorly, the superficial layer invests the mandible and attaches to the zygomatic arch. Inferiorly it extends to the sternum and clavicle anteriorly and to the acromion process and scapula at the lateral and posterior aspects. ¹ The sternocleidomastoid and trapezius muscles are enclosed in the superficial layer, as are the parotid and submandibular glands. ¹ , ² The middle layer of the deep cervical fascia (also known as the pretracheal layer) can be divided into two components: the muscular layer and the visceral layer. The muscular layer is anterior and midline. Like the superficial layer, the muscular layer attaches to the sternum, clavicle, and scapula inferiorly. Superiorly, the muscular layer attaches to the hyoid bone and thyroid cartilage. The muscular layer contains the infrahyoid (strap) muscles. The visceral layer begins at the skull base at the posterior aspect and anteriorly attaches to the thyroid cartilage and hyoid. It envelops the larynx, pharynx, and thyroid gland and extends inferiorly to the pericardium, surrounding the trachea and esophagus. Superiorly, the visceral layer of the pretracheal fascia is known as the buccopharyngeal fascia, which is adherent to the posterior surface of the pharyngeal constrictors. The deep layer of the cervical fascia has a prevertebral layer and an alar layer. The prevertebral layer surrounds the prevertebral muscles and the spine and as such extends from the skull base to the coccyx. The alar fascia lies in between the visceral layer and the prevertebral fascial layers and is a looser fascia made of fibroareolar tissue. Laterally, it attaches to the transverse processes on either side and contains the superior laryngeal nerve and the sympathetic trunk. ³ , ⁴ The alar fascia fuses with the visceral layer anteriorly approximately at the level of the second thoracic vertebra. As the alar fascia extends anterior and laterally from the transverse process on either side, it contributes to the carotid sheath on all but the anterior surface. The carotid sheath is a distinct structure comprising all of the layers of the deep cervical fascia. It contains the carotid artery, internal jugular vein, and vagus nerve and extends from the skull base to the clavicle. At the clavicle the carotid sheath divides to encompass each of the contained structures separately. ³ Fig. 4.1 depicts an axial view with the different fascial layers.

The retropharyngeal space is bound superiorly by the skull base and extends inferiorly to the level of the second thoracic vertebra. The anterior border of the retropharyngeal space is the buccopharyngeal fascia, and the space is posteriorly bounded by the alar layer of the deep cervical fascia. ¹ , ³ The lateral borders are the carotid sheaths on each side ( Fig. 4.1 ). This space provides a direct conduit to the mediastinum. Additionally, processes can extend posteriorly to the “danger space,” which is immediately posterior to the retropharyngeal space and is bounded by the alar and prevertebral layers of the deep layer. The danger space extends laterally to the transverse processes and inferiorly to the posterior mediastinum. Finally, the prevertebral space is between the vertebral bodies and the prevertebral layer of the deep fascia. As such, it extends from the skull base to the coccyx ( Fig. 4.2 ).

Indications

The retropharyngeal space is a potential deep neck space that occasionally becomes clinically relevant. Most often this space is important in pediatric patients when lymph nodes in this space become necrotic and then the source of a deep neck infection. In adults the retropharyngeal space is most often clinically relevant when there is metastatic lymph node involvement in this space from various head and neck malignancies. Most commonly involved sites include the paranasal sinus, middle ear, auditory tube, nasopharynx, oropharynx, hypopharynx, and cervical esophagus. ⁵ Specifically, retropharyngeal node involvement has been well described in oropharyngeal, hypopharyngeal, and nasopharyngeal squamous cell carcinoma (SCC). Additionally, thyroid cancer metastatic to the retropharyngeal lymph nodes has been described. ⁵ Often the retropharyngeal lymph nodes are treated with radiation therapy because of the technical difficulty of reaching this space surgically.

Surgical treatment of retropharyngeal nodes, however, may be beneficial in certain circumstances. Generally, bimodal treatment for advanced head and neck cancers is recommended by the National Comprehensive Cancer Network (NCCN) whenever possible. In treatment of hypopharyngeal SCC involving the posterior pharyngeal wall, retropharyngeal lymph node dissection is thought to improve prognosis. ⁶ Additionally, if there is evidence of involvement on preoperative evaluation of oropharyngeal SCC, retropharyngeal node dissection is recommended for treatment of macroscopic disease. ⁷ With regards to metastatic papillary thyroid cancer, surgical treatment is especially important because it is essential to remove any gross disease prior to radioactive iodine treatment. ⁸ , ⁹

Generally, the retropharyngeal space is divided into medial and lateral spaces. The medial compartment is rarely if ever clinically relevant in adults. The lateral space becomes important when metastatic disease is present. ⁴ , ⁷ Access to this space from an external approach has traditionally required mandibulotomy or partial/total pharyngectomy. ⁵ With use of the da Vinci surgical robotic system (Intuitive Surgical), this space can be safely approached transorally.

In addition to resection of retropharyngeal lymph nodes, transoral dissection through the posterior pharyngeal wall also allows access to the upper cervical spine. This approach has been well described and can be used to access lesions at the inferior aspect of the clivus to the level of the third cervical vertebra. ¹⁰ While most descriptions of this approach are endoscopic or microscopic, recently the use of the da Vinci surgical robotic system has been described. ¹¹ , ¹² The robot-assisted approach has enabled better visualization in this narrow space and the opportunity for primary dural closure. ¹¹