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The retropharyngeal space (RPS) is the most important fascial space in the neck. The retropharyngeal space is an anatomical region that spans from the base of the skull to the mediastinum. This space is anterior to the prevertebral muscles and posterior to the pharynx and esophagus. The retropharyngeal space is bounded anteriorly by the buccopharyngeal fascia, laterally by the carotid sheath, and posteriorly by the prevertebral fascia. The RPS is divided by the alar fascia into two components–the “true” retropharyngeal space and the “danger space.” The true RPS is located anterior to the danger space and extends from the base of the skull to the alar fascia. The retropharyngeal space functions as one of the deep compartments in the head and neck; it divides into suprahyoid and infrahyoid components. The suprahyoid RPS is composed of adipose tissue and lymph nodes.[1] The infrahyoid RPS solely contains adipose tissue.[1] Within the true RPS, lymph nodes and fatty tissue are the predominant tissues. The suprahyoid RPS houses the retropharyngeal lymph nodes, which are responsible for most of the lymphatic drainage of the pharynx.[1] The retropharyngeal lymph nodes lie medial to the internal carotid artery and further divide into medial and lateral masses. The medial group atrophies throughout childhood, making children more likely to experience RPS infections than adults. The lateral group, named the nodes of Rouvière, persists throughout adulthood and can become a site of metastasis for head and neck cancers.[1][2] The alar fascia is subject to considerable anatomical variation.[3] The alar fascia is generally described as a layer of dense connective tissue lying within the coronal plane. This fascial layer separates the retropharyngeal space anteriorly from the danger space posteriorly.[4] The fascia is attached to the base of the skull superiorly and laterally to the right and left carotid sheaths. It has been described as extending to the second thoracic vertebra, where it fuses with the visceral fascia, although other levels are described as well, from C6 to T2.[3][5][6]

The alar fascia is subject to considerable anatomical variation.[3] The alar fascia is generally described as a layer of dense connective tissue lying within the coronal plane. This fascial layer separates the retropharyngeal space anteriorly from the danger space posteriorly.[4] The fascia is attached to the base of the skull superiorly and laterally to the right and left carotid sheaths. It has been described as extending to the second thoracic vertebra, where it fuses with the visceral fascia, although other levels are described as well, from C6 to T2.[3][5][6] The alar fascia separates the retropharyngeal space from the danger space located posterior to it. The danger space is so named because of the risk that an infection in this space can directly invade the mediastinum, causing serious and even fatal consequences such as mediastinitis, empyema, and necrotizing fasciitis.[4] The danger space courses more inferiorly than the true RPS, running into the posterior mediastinum until the level of the diaphragm. This anatomical connection between the pharynx and the mediastinum is where the danger space derives its name, as it serves as a potential channel for spreading infection between these two sites.[1][2] The danger space is composed of solely adipose tissue and, therefore, can be affected by diseases that do not affect the lymph nodes, such as lipoma and liposarcoma. An infection of the neck may spread through the prevertebral fascia and enter the retropharyngeal space.[7] An example of this is Pott disease of the spine. A retropharyngeal abscess has been reported after the extraction of wisdom teeth.[8] A peritonsillar abscess may also produce a retropharyngeal abscess.[9]