SARS: radiological features

Abstract

Air-space disease is typical in severe acute respiratory syndrome (SARS) and may be indistinguishable from pneumonia of other causes. In the majority of patients, ground glass opacities on chest radiographs progress rapidly to focal, multifocal or diffuse consolidation. Unilateral involvement is common in the early acute phase, becoming bilateral at maximal lung involvement. Generally, radiographic opacities peak between 8 and 10 days after onset of illness, with radiographic scores reflecting temporal changes in clinical and laboratory parameters such as oxygen saturation (SaO2) and liver transaminases. Pleural effusions, cavitating consolidation and mediastinal lymphadenopathy are not typical radiographic features. Pneumomediastinum and pneumothoraces are complications that are associated with extensive disease, with or without assisted ventilation. The utility of high resolution computed tomography (HRCT) and CT scans lies in the confirmation of airspace opacities in cases with normal initial chest radiographs that have strong contact history and signs and symptoms highly suspicious of SARS during the outbreak, allowing early treatment and prompt isolation. The characteristic HRCT feature in the acute phase is ground-glass opacities with smooth interlobular septal thickening, sometimes with consolidation in a subpleural location, which progress rapidly to involve other areas of the lungs. Temporal lung changes documented on HRCT suggest that some residual opacities found may not be reversible.

Figure 1

Serial CXRs in a 38‐year‐old male with severe acute respiratory syndrome (SARS). (a) On admission only faint ground glass opacities are present in the right lower zone (arrow). (b) Within 36 h, the ground glass opacities have progressed to multifocal consolidation in both lower zones. (c) On day 4 of admission, diffuse consolidation is noted in the right lung with increase in left lower zone consolidation. (d) On day 8 of admission, pneumomediastinum (arrowheads) and surgical emphysema (arrows) are noted.

Figure 2

(a) CXR at presentation of a 52‐year‐old male with severe acute respiratory syndrome (SARS) showing focal consolidation in the right upper zone. (b) CXR of a 56‐years‐old male with SARS 1 week after admission showing bilateral diffuse consolidation. (c) CXR of the same patient illustrated in (b) after 3 weeks in the intensive care unit on high dose steroids showing bilateral upper lobe cavitating lesions (arrows). Superadded infection was suspected.

Figure 3

(a) HRCT scan of the thorax in a 28‐year‐old female patient with SARS on admission showing a patch of ground glass opacification in the left lung base with smooth interlobular septal thickening (arrows). (b) HRCT in a 39‐year‐old male with SARS 2 weeks after admission showing irregular reticular opacities superimposed on ground glass opacification (white arrows), pneumomediastinum (black arrowheads) and surgical emphysema (black arrows). (c) HRCT of the same patient illustrated in (b) obtained 5 weeks after admission shows persistent reticular opacities (white arrows) associated with bronchial dilatation (white arrowheads) in both upper lobes.