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Laboratory Studies

Children in whom intravenous therapy or hospitalization is considered should have a baseline urinalysis, and blood should be checked for a serum metabolic panel and a complete blood count with differential and may also be tested for serum markers of inflammation such as C-reactive protein and/or an erythrocyte sedimentation rate. Laboratory evaluation shows a leukocytosis with a propensity to immature cells. Monospot, as well as a throat culture or rapid strep test, should also be performed.

Radiologic Studies

Peritonsillar Abscess

Plain radiography has a limited role in the initial assessment of cases of peritonsillar cellulitis or abscess and may be reserved for cases in which fiberoptic nasopharyngolaryngoscopy is not available or possible. Contrast-enhanced computed tomography (CT) or gadolinium-enhanced magnetic resonance imaging (MRI) is useful in assessing young children with suspected PTA who are not cooperative with examination. It is also helpful for persistent symptoms (after 24–48 hours of therapy), especially if needle aspiration or surgical drainage had been performed initially. Imaging may reveal an unusual manifestation such as an inferior pole PTA.1 CT has a high sensitivity (approximately 90%) but modest specificity (60%) in detecting abscesses (as opposed to cellulitis) compared with operative findings.12

Retropharyngeal Abscess

In contrast to peritonsillar infections, radiologic studies are usually required for precise anatomic diagnosis of RPA. Lateral neck radiography provides only limited information and may show bulging of the retropharyngeal soft tissues, with resultant airway narrowing, loss of cervical lordosis, and a wide retropharyngeal space. The width of an abnormal retropharynx was defined by Wholey et al. in a 1958 paper as >7 mm in children 15 years of age or younger at the anteroinferior aspect of C2 and a wide retrotracheal space measured forward from the anteroinferior aspect of C6 of >14 mm (Figure 25–4).8

Figure 25–4.

Retropharyngeal abscess, lateral neck radiograph.

Contrast-enhanced CT and MRI are most useful, as these permit differentiation of abscess from phlegmon and anatomically localize the process to facilitate aspiration and surgical treatment. An abscess is identified by a rim-enhancing fluid collection, while a hypolucent area without ring enhancement is defined as phlegmon (Figures 25–5 and 25–6). Radiography may also localize a collection and indicate other sites of abscess formation as well as provide a means for objectively measuring abscess size and for following the progress of infection when clinical complaints are difficult to elicit, such as for a child with developmental delays.

Figure 25–5.

CT Scan, Retropharyngeal abscess.

Figure 25–6.

CT Scan, Retropharyngeal phlegmon.

Repeat imaging is generally not necessary for children who demonstrate unequivocal clinical improvement. Sequential radiography may be useful in monitoring the efficacy of therapy, particularly when surgery is not used initially or the patient is difficult to assess clinically because of age or cognitive development. Interventional radiologic techniques may have a role in some cases, for either therapeutic drainage or to provide diagnostic material for microbial culture. Consideration of the long-term effects of low-dose diagnostic irradiation should be weighed when selecting which type of study (e.g., CT that requires diagnostic irradiation vs. MRI that does not administer irradiation).13

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