Retropharyngeal edema is the presence of nonpurulent fluid in the retropharyngeal space. The accumulation of fluid is thought to be due to altered lymphatic drainage or excess lymph production. There are multiple causes of retropharyngeal edema, including radiotherapy, internal jugular vein (IJV) thrombosis (Figs. 2A, 2B, 2C, and 2D), and retropharyngeal calcific tendinitis (Figs. 3A, 3B, and 3C). The latter is an inflammatory condition due to calcium hydroxyapatite deposition in the longus colli tendons [3]. Rupture of crystal deposits provokes an inflammatory response and results in acute neck pain and retropharyngeal space edema. Another common cause of retrophar yngeal edema is infection in spaces surrounding the retropharyngeal space. In an adult, the prevertebral space is the most common source of infection (Figs. 4A, 4B, and 4C), compared with the pharynx in children (Figs. 5A, 5B, 5C, 5D, 6A, 6B, and 6C).

Our four-step approach for evaluating retropharyngeal edema is as follows: first, with regard to fluid distribution, edema uniformly fills the retropharyngeal space from side to side. Second, edema has a smooth ovoid, rectangular, or “bow-tie” configuration on axial imaging and a diffuse craniocaudal distribution on sagittal images, with tapered inferior and superior margins; there is only mild mass effect. Third, there is no wall thickening or enhancement. Fourth, ancillary findings include IJV thrombosis, adjacent neck infection, and focal calcification anterior to C1–C2 in the longus colli tendons [4, 5].

Retropharyngeal edema does not require surgical drainage. Most cases resolve as the cause of edema is treated.

A suppurative retropharyngeal node is a reactive lymph node that has undergone liquefactive necrosis but is contained by the nodal capsule (also known as retropharyngeal adenitis or intranodal abscess) (Figs. 5A, 5B, 5C, 5D, 6A, 6B, and 6C). The process begins as a bacterial infection in the pharynx, paranasal sinuses, middle ear, or the prevertebral space. As infection drains to the retropharyngeal node, the node enlarges as the result of proliferation and invasion of inflammatory cells (i.e., reactive lymphadenopathy). Next, the node can become edematous and this is referred to as the presuppurative phase [6]. Finally, necrosis and pus formation occur to create a suppurative retropharyngeal node. Such infections are most commonly seen in early childhood before the retropharyngeal nodes atrophy.

Our four-step approach for evaluating suppurative retropharyngeal nodes is as follows: first, with regard to fluid distribution, such nodes are laterally located. Second, these nodes have a rounded or oval configuration, and the mass effect varies depending on the degree of nodal enlargement. Third, with regard to the wall, a thin hyperdense or enhancing rim may be found around this low-density node [7, 8]; an edematous node in the presuppurative phase can also be low density. Fourth, ancillary findings include evidence of the primary infectious source, such as otitis media or tonsillitis. Retropharyngeal edema is a common associated finding.

There is confusion in the literature about the terms “suppurative retropharyngeal node” and “retropharyngeal abscess.” Suppurative retropharyngeal node, or adenitis, is regarded as a more accurate description for infection contained by the nodal capsule. The distinction from abscess is important because many cases do not have purulent material at surgery and can be successfully managed medically. The sign of rim enhancement and a low-density center is less than 57% specificity for purulent material at surgery [6]. Shefelbine et al. [6] found that the volume of the hypodense focus is a better predictor of pus at surgery. In that study, patients with purulence present at surgery had a mean hypodense volume on CT of 4.4 cm³ [6]. Patients without purulence at surgery were grouped with those who responded to medical therapy. This group had CT scans with a smaller mean volume in the low-attenuation focus (2.2 cm³). The current treatment for suppurative retropharyngeal nodes is a trial of IV antibiotics if the patient's condition is stable [9, 10]. Surgical drainage is considered if there is progression after medical therapy or if the suppurative node is large at presentation.

Retropharyngeal abscess is most commonly due to rupture of a suppurative retropharyngeal node into the retropharyngeal space (Figs. 7A and 7B) and is contained only by the fascia surrounding the retropharyngeal space. Other less common causes of a retropharyngeal abscess are spread of infection from contiguous spaces across the fascial boundaries or direct inoculation from penetrating trauma (Figs. 8A and 8B). Before infection evolves into a walled abscess, it is known as retropharyngeal cellulitis or phlegmon. This condition can be difficult to differentiate from retropharyngeal edema. The typical clinical presentation of retropharyngeal abscess is acute to subacute onset of neck pain, dysphagia or odynophagia, and a low-grade fever.

Our four-step approach for evaluating retropharyngeal abscess is as follows: first, with regard to fluid distribution, a retropharyngeal abscess fills the retropharyngeal space from side to side [7, 8]. Second, retropharyngeal abscesses have an oval or rounded configuration; moderate-to-marked mass effect can produce anterior displacement of the pharynx and flattening of prevertebral muscles. Third, retropharyngeal abscess usually has a thick enhancing wall. Fourth, ancillary findings include evidence of primary infection or presence of a foreign body in traumatic causes. In addition, the radiologist should search carefully for complications [10, 11].

The mortality rate for retropharyngeal abscess is less than 1% [12] and has declined in the last 50 years because of the availability of antibiotics and early diagnosis with CT. The most urgent complication is airway compression from mass effect on the larynx and pharynx. Airway compromise is suggested in up to 3% of patients by the clinical symptom of stridor [12]. The other feared complications are rare and documented in the literature as case reports and case series. Infection can spread inferiorly via the danger space to the mediastinum, where it can result in mediastinitis, pericarditis, pleuritis, and empyema [13] (Figs. 9A and 9B). Infection can also break through the surrounding fascial planes and cause infection in the airway, spine, or carotid space. Vascular complications of carotid space infection include IJV thrombosis, carotid artery rupture, and pseudoaneurysm [14–16]. Finally, the infection itself can evolve into necrotizing fasciitis and sepsis [13]. Because these complications are associated with significant morbidity and mortality, a true retropharyngeal abscess usually requires prompt surgical drainage.