Chest CT in the emergency department for suspected COVID-19 pneumonia

Abstract

Purpose: In overwhelmed emergency departments (EDs) facing COVID-19 outbreak, a swift diagnosis is imperative. CT role was widely debated for its limited specificity. Here we report the diagnostic role of CT in two EDs in Lombardy, epicenter of Italian outbreak.

Material and methods: Admitting chest CT from 142 consecutive patients with suspected COVID-19 were retrospectively analyzed. CT scans were classified in "highly likely," "likely," and "unlikely" COVID-19 pneumonia according to the presence of typical, indeterminate, and atypical findings, or "negative" in the absence of findings, or "alternative diagnosis" when a different diagnosis was found. Nasopharyngeal swab results, turnaround time, and time to positive results were collected. CT diagnostic performances were assessed considering RT-PCR as reference standard.

Results: Most of cases (96/142, 68%) were classified as "highly likely" COVID-19 pneumonia. Ten (7%) and seven (5%) patients were classified as "likely" and "unlikely" COVID-19 pneumonia, respectively. In 21 (15%) patients a differential diagnosis was provided, including typical pneumonia, pulmonary edema, neoplasia, and pulmonary embolism. CT was negative in 8/142 (6%) patients. Mean turnaround time for the first COVID-19 RT-PCR was 30 ± 13 h. CT diagnostic accuracy in respect of the first test swab was 79% and increased to 91.5% after repeated swabs and/or BAL, for 18 false-negative first swab. CT performance was good with 76% specificity, 99% sensitivity, 90% positive predictive value and 97% negative predictive value.

Conclusion: Chest CT was useful to streamline patients' triage while waiting for RT-PCR in the ED, supporting the clinical suspicion of COVID-19 or providing alternative diagnosis.

Keywords: COVID-19; Computed tomography; Diagnosis; Emergency; Triage.

Fig. 1

Exemplifying CT findings for each class of COVID-19 pneumonia probability based on the presence of typical, indeterminate and atypical finding, or eventual absence of signs of viral pneumonia and alternative CT diagnosis. A is reported unenhanced thin-section axial CT image showing typical peripheral ground-glass opacity with superimposed interlobular septal thickening and intralobular lines visibility (“crazy-paving” pattern), involving both lungs. Unilateral involvement, considered one of the indeterminate features, is reported in B. Atypical findings (C) include bronchiolar wall thickening and tree-in-bud opacities with centrilobular nodules (arrows in C). Finally, alternative diagnosis (D) was reported in the case of chest CT findings not typical for interstitial pneumonia and with clear pulmonary or extra-pulmonary findings explaining symptoms and laboratory test alteration (e.g., pulmonary neoplasia, red arrow in D, associated with bilateral pleural and pericardial effusion)

Fig. 2

CT and swabs results in triaging patients with suspected COVID-19 pneumonia. Flowchart of CT findings and nasopharyngeal swab results in 142 febrile patients attending the EDs of two hospital in Lombardy with clinical suspicious of SARS-CoV2 infection. The agreement between CT and RT-PCR increased after first swab, for a total of 18 patients initially false negative at RT-PCR on nasopharyngeal swab. Interestingly, CT in addition to the high sensitivity had the advantage to provide differential diagnosis useful for patients’ clinical management

Fig. 3

Chest CT typical COVID-19 pneumonia in a patient with initially negative swab. A 61-year-old man suffering from fever (39 °C), cough, and dyspnea from 7 days, presented to the emergency department of San Raffaele Hospital in Milan. Clinical evaluation and laboratory tests resulted highly suspicious for SARS-CoV2-related pneumonia. Nasopharyngeal swab and chest CT were immediately performed. CT showed peripheral opacity with crazy-paving pattern and consolidation (red arrows) mainly involving the upper left lobe and the lower lobes, mainly with posterior distribution. CT findings resulted highly suggestive for SARS-CoV2 pneumonia, but results from the first swab (available only 24 h later) resulted negative. In consideration of high clinical and CT suspicion, another swab was collected after 3 days, and it finally resulted positive