Introduction

At the onset of the severe acute respiratory syndrome (SARS) crisis, the majority of patients were presented with respiratory symptoms. As the epidemic progressed, either due to a different mode of transmission or a mutation of the virus, some SARS patients presented with minor or no respiratory symptoms but diarrhoea. Understandably, this created a problem with case definition and diagnosis, and the lack of a reliable and rapid biochemical test for SARS placed more emphasis on chest imaging findings for diagnosis of the disease.

The wide availability, speed and inexpensive nature of the chest radiograph (CXR) has made it the first-line imaging investigation when faced with a respiratory complaint. It is only fitting that the initial imaging investigation of SARS also starts here. This chapter presents the radiographic features of SARS and the differential diagnosis.

Pathological considerations

Viral infection of the respiratory tract may involve the upper system, from the common cold (rhinoviruses and coronaviruses), larynx (respiratory syncitial virus), trachea and bronchi (herpes simplex type 1) to the lung parenchyma (influenza). The initial phase in viral lung parenchymal involvement is called a pneumonitis. A local inflammatory response is directed towards the offending virus, an inflammatory cocktail of cells and fluid accumulate in the alveolar interstitium of the lung parenchyma. In bacterial infections this exudate spills over into the airspace and results in the classic consolidation.