Pediatric Retropharyngeal Abscess Workup

Laboratory findings in retropharyngeal abscess are nonspecific. WBC counts can be elevated, with a mean level of 17,000/mcL. Ranges from 4,000-45,000/mcL have been recorded.

Send any aspirated or drained pus to the laboratory for culture and sensitivity. A Gram stain can help direct early empiric antibiotic therapy.

If an incision and drainage is performed, obtaining a piece of the abscess wall to assess pathology helps increase the yield of culture and sensitivity testing.

A lateral soft tissue neck radiography may be helpful in making the diagnosis of a retropharyngeal abscess. Perform the study during inspiration with the neck held in normal extension. Further, such a study, can also immediately help triage a potential airway emergency.

An abscess occupies the soft tissue space, which can be observed between the radiolucent airway (ie, pharynx, trachea) and the spine.

Widening of these soft tissues is pathologic until proven otherwise. Measuring at the level of C2, the distance from the anterior surface of the vertebrae to the posterior border of the airway should be 7 mm or less, regardless of the patient's age. At C6, this distance should be 14 mm or less in children younger than 15 years. A distance of 22 mm is considered normal in an adult. A simpler (but less precise) rule is that the soft tissue plain should be less than one half the width of the corresponding vertebral body.

A plain film may also demonstrate gas or a foreign body in the retropharyngeal space. The normal spinal lordosis may be reversed. With a child's head extended, the width of the soft tissue is no more than a vertebral body width in an average child. Obtaining the film with the head extended is important.

Unfortunately lateral plain radiography is not very sensitive or specific. One study demonstrated a 33% false-negative rate. False-positive rates are also high. Poor neck extension or an expiratory view which results in a falsely narrowed airway can produce a false-positive result. One recent study detailed 3 cases in which plain radiography missed 3 retropharyngeal abscesses due to nasopharyngeal location.^[7]

See image below.

Chest radiography should be performed if mediastinal or pulmonary involvement is suspected. Furthermore, patients who underwent transcervical or transoral drainage of a retropharyngeal space abscess and do not recover as expected should undergo chest imaging to rule out a developing mediastinitis or pneumonia.

CT scanning is currently the imaging modality of choice. Obtain a study with intravenous contrast to help demarcate the lesion and determine if vascular involvement is present. Inform the radiologist of the purpose of the study in advance, because a standard CT scan of the neck may not use thin enough slices (3-5 mm) and may not scan through the entire extent of the retropharyngeal space (the base of the skull to T2).

An abscess is found in the deep spaces of the neck. It is an area of low attenuation, surrounded by an enhanced ring. Gas is sometimes present within the abscess cavity. The nearby soft tissue is edematous, and fat planes may be obliterated. Neighboring structures, including the airway, can be compressed.

A CT scanning may be able to determine the presence of an abscess and help distinguish it from cellulitis (an abscess may have an area of central lucency). The study also can assist in determining the location of the abscess, extent of abscess spread, and presence of any complications.

CT scanning provides much more information than plain film. Depending on the study, CT scanning can be more than 90% sensitive^[5] . The positive predictive value has been estimated at 82%, and the negative predictive value has been estimated to be 100%.^[8]

The main disadvantage of CT scanning is that it is not located in a monitored setting. Ensure that patients with impending airway compromise are stabilized prior to leaving the acute care area. Portable plain film may have to suffice. Also, younger children may not tolerate a CT scan without sedation. Such medications can cause airway muscle relaxation with ensuing occlusion.

Shefelbine et al describe a case series of 30 pediatric patients with retropharyngeal abscesses.^[9] The authors concluded that a low attenuation focus with rim enhancement indicates a presuppurative or suppurative lymph node. The authors suggest that children with a hypodense focus diameter of 2 cm or less often respond to intravenous antibiotic therapy, whereas those children with a hypodense focus diameter of more than 2 cm likely require surgical intervention.

In contradistinction, Malloy et al reported a lack of correlation between CT findings and the presence of purulence at the time of surgical drainage. A statistically significant difference in size, rim enhancement, and prevertebral edema were not found between the purulent and nonpurulent groups.^[10]

Kirse and Roberson's series reported that scalloping is the most useful characteristic on CT scanning.^[11] Although rim enhancement was helpful, scalloping (irregularity of the abscess wall) had a stronger association with finding pus at the time of surgery. They also found that retropharyngeal edema was present in all their patients and was not helpful in distinguishing abscess from phlegmon.

Please see the CT scans in the images below.

MRI produces images superior to the other studies; however, it is usually unnecessary and rarely used, unless a concern is present that the abscess has spread to the CNS. Additionally, this study requires a protracted period of time in which the patient is in an unmonitored setting. Children usually require sedation for this test, which is also dangerous in any patient with a potentially unstable airway.

Ultrasonography is an imaging modality that has also been suggested for use in deep space neck infections. It is portable and does not use radiation. Ultrasonography can also be less traumatic to children, rarely requiring the use of sedation. In experienced hands, it can potentially determine the presence and location of an abscess and allow the clinician to distinguish an abscess from cellulitis. However, for surgical planning, ultrasonography provides limited assistance.

• See Surgical Care.

• Cultures of the wound cavity must be obtained.
• A Gram stain and culture of drained pus can be used to help determine the predominant organisms; this allows for targeted and selected antibiotic choice and assists in determination of a proper length of duration and route (intravenous, oral) of antibiotic treatment.