Special Regional Edition Asia-Pacific
September 2004

Imaging News

SARS legacy lingers in Southeast Asia

The threat of severe acute respiratory syndrome has not disappeared. Imaging forms a key part of SARS diagnosis, along with clinical symptoms, patient history, and the laboratory polymerase chain reaction test, according a researcher from Hong Kong.

High-resolution CT can add weight to radiographic findings, but its use should be limited to certain patient groups to avoid unnecessary movement of patients and greater infection risk, said Dr. Clara Ooi, a radiologist at the University of Hong Kong's Queen Mary Hospital. Valid uses of HRCT include reexamination when chest x-ray signs of suspected SARS patients are normal, evaluation of questionable radiographic findings, and monitoring of complications or irreversible changes in the later stages of disease.

"Chest radiography is still the best method for initial evaluation. It is quick and can give a measure of disease severity," Ooi said during the opening lecture at the 10th Asian Oceanian Congress of Radiology, held in Singapore in April.

The AOCR was originally scheduled for July 2003 but was canceled due to fears about the spread of SARS. Congress organizers opted to begin the 2004 proceedings with a special session on imaging's role in diagnosing and managing SARS. Coincidentally, during the week of the AOCR, China reported a small cluster of confirmed and suspected SARS cases in Beijing and east Anhui Province. All cases were linked to a likely safety breach at a Beijing virology laboratory that was using the SARS coronavirus in research. About 1000 people were placed in isolation, the suspect lab was sealed off, and its 200 staff were placed under observation. The Chinese Ministry of Health ordered all major hospitals to recheck their records of unexplained deaths and pneumonia cases.

"These events show us that this could happen again. SARS has not gone away," Ooi said.

SARS may appear indistinguishable from other causes of pneumonia on chest x-ray, but evaluation of past patient data has revealed certain defining characteristics, she said. These include ground-glass opacities progressing quickly to focal, multifocal, or diffuse consolidation, occasional nodular opacities, purely upper lobe involvement, lobar consolidation, and partial resolution without treatment, as well as unilateral involvement during early acute phase, becoming bilateral at maximal lung involvement.

A retrospective review of confirmed SARS and non-SARS pneumonia patients presenting at Queen Mary from March to June 2003 has helped Ooi's radiology team define criteria for differential diagnosis. They have also examined differences in radiographic score between SARS survivors and patients who died.

"We hope that this information will help us in the event that SARS comes back," she said.

Many survivors of the 2003 SARS outbreak are now complaining of lingering effects. Radiologists at the Prince of Wales Hospital in Hong Kong observed that some young survivors developed severe avascular necrosis just a few months after hospital discharge, she said. Initiation of an imaging screening program revealed that most patients complaining of aching hips and knees had no real physical abnormalities. Yet MR scans showed that 12 out of 254 SARS survivors did have avascular necrosis, and 30% had nonspecific bone marrow abnormalities.

Reappraisal of drug therapies given to SARS patients revealed that survivors now suffering from osteonecrosis received a higher cumulative dose of steroids. Steroid treatment formed a major part of SARS therapy to combat inflammation, though the efficacy or safety of chosen drug protocols was not known.

"We were in uncharted territory when this epidemic started," Ooi said. "There were no controlled clinical

trials, treatment was largely controversial and anecdotal, and there are ongoing arguments and discussions about the best treatment approach."

In a separate study presented as a poster at the AOCR, radiologists from Tan Tock Seng Hospital in Singapore reviewed the efficacy of imaging in the initial assessment and subsequent follow-up of pediatric patients who contracted SARS last year.

Dr. Pua Uei and colleagues reassessed frontal chest radiographs taken between March and May 2003 of 34 SARS patients aged seven months to 12 years. They found 15 children with abnormal initial chest x-rays, which showed a higher incidence of ground-glass opacity over consolidation and a significant proportion of lower lobe infiltration.

Unilateral disease was more common than bilateral disease, while lesions appeared more often in the peripheral than in the central area. They found no hilar lymphadenopathy, lobar consolidation, pleural effusion, cavitation, or pneumothorax.

The authors stressed the dangers of considering chest x-ray evidence in isolation. They showed an image of a six-year-old girl who presented with a one-day history of fever. Serial x-ray imaging failed to show significant findings indicative of SARS. The child was later classified as a probable SARS victim, however, on the basis of a positive laboratory test, history of possible contact with another SARS patient, and history of fever.