Abstract
BackgroundThe diagnosis of a superficial abscess is usually obtained through history and physical exam but bedside ultrasound (US) and computerized tomography (CT) are sometimes used to assist in the diagnosis. It is unclear which imaging modality is superior for patients with superficial soft tissue infections. We compared the diagnostic accuracy of CT and US in patients with skin and soft tissue infections.MethodsPatients presenting with a suspected skin abscess that underwent both US and CT imaging were eligible for inclusion. Two physicians blinded to patient characteristics and other imaging results prospectively reviewed the CT and US images for pre-defined image elements, and in circumstances where there was disagreement between these interpretations, a third physician adjudicated the findings. The presence or absence of an abscess cavity was noted on imaging. Imaging detail was summarized using a pre-specified 4-point scale based on the degree of visible detail with higher numbers corresponding to greater detail. The clinical presence of an abscess was defined by surgical evacuation of purulence. Sensitivity and specificity for both CT and US were calculated using Chi square analysis. Comparison between imaging detail was performed using a Student's T-test. Data are presented with (95% confidence intervals) unless otherwise noted.ResultsOver an 18 month period 612 patients received a soft tissue bedside ultrasound with 65 of those patients receiving a CT for the same complaint. 30 of these 65 patients had an abscess located in the head and neck (37%), buttock (17%), lower extremity (17%), upper extremity (13%), torso (13%), or hand (3%). US demonstrated a sensitivity and specificity for the diagnosis of abscess of 96.7% (87.0% to 99.4%) and 85.7% (77.4% to 88.0%) respectively. The overall sensitivity and specificity of CT for the diagnosis of an abscess was 76.7% (65.5% to 82.8%) and 91.4% (81.8% to 96.7%) respectively Overall image detail ratings were superior for US compared to CT (3.5 vs 2.3, p = 0.0001).ConclusionUS is more sensitive then CT, but CT is more specific for superficial soft tissue abscesses. US demonstrated more visible detail within the abscess cavity compared to CT.
Highlights
The diagnosis of a superficial abscess is usually obtained through history and physical exam but bedside ultrasound (US) and computerized tomography (CT) are sometimes used to assist in the diagnosis
Differentiating a focal collection of purulence from diffuse infection of the skin is critical, as the former is treated with incision and drainage (I and D) and the latter is treated with antibiotics alone
This study was a retrospective review of patients with bedside US for a suspected skin abscess presenting to an urban academic emergency department over an 18month period
Summary
Interpretation of the presence or absence of an abscess on CT imaging was determined using the final interpretation in the patient record. Two physicians with experience in soft tissue US were blinded to patient characteristics, and the results of the CT reviewed the US images for the presence or absence of an abscess. Imaging was summarized using a four-point scale based on the degree of visible detail with higher numbers corresponding to greater detail (Figure 1) Both CT and US findings were determined using the same adjudication process described above. Final diagnoses The criterion standard for final diagnosis of an abscess was determined using documentation of evidence of abscess purulence using a structured electronic medical record review as described previously [6]. Sensitivity, specificity, and accuracy were calculated for each test
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