AJR: CT has role in early detection of swine flu
Unenhanced chest CT lung window reveals that lingula, right middle lobe and both lower lobes show patchy, peripheral, rounded, peribronchial ground-glass opacities with air bronchograms. Image source: American Journal of Roentgenology
CT may help clinicians recognize incipient cases of severe influenza and improve the understanding of the pathogenesis of the disease, according to a study examining the role of imaging in a fatal case of the pandemic swine-origin influenza A (H1N1), which was published today by the American Journal of Roentgenology.

Although most cases of the H1N1 virus (S-OIV) have been self-limited, fatal cases raise questions about virulence and radiology’s role in early detection, according, Daniel J. Mollura, MD, from the department of radiology and imaging sciences at the National Institutes of Health Clinical Center in Bethesda, Md., and colleagues. They examined and reported the radiographic and CT findings in a fatal S-OIV infection.

The researchers said it is “essential that clinicians be able to recognize possible cases of pandemic H1N1 influenza in high-risk groups so that they order the appropriate diagnostic tests, begin specific antiviral therapy and prepare to provide intensive supportive measures as needed.”

In this case, a middle-aged man with no history of chronic pulmonary disease presented to the emergency department with a five-day history of fever, fatigue, nausea and diarrhea. He complained of an intermittent cough of approximately three days duration, as well as confusion the night before presenting to the hospital. He denied smoking and recreational drug use.

Hospital records indicated that his admission vital signs included a fever of 103.3°F, blood pressure of 92/53 mm Hg (systolic/diastolic), pulse of 84 beats per minute, respiration of 22 breaths per minute, and oxygen saturation of 95 percent on bilevel positive airway pressure ventilatory support. The physical exam was notable for a confused mental status, bibasilar pulmonary crackles on auscultation and obesity.

The hospital staff obtained a portable bedside chest radiograph at the initial evaluation, which showed peripheral patchy opacities. They noted hilar fullness, possibly accentuated by hypoinflation of the lungs. The patient was started on IV antibiotics, oseltamivir and corticosteroids.

The hospital staff also performed a chest CT the day of admission, which showed a peripheral distribution of patchy ground-glass opacities.

According to the authors, many of the opacities showed air bronchograms with normal-sized bronchial airways--each leading into each rounded ground-glass focus--and most large airways showed no significant wall thickening or plugging. The ground-glass opacities were located throughout the upper and lower regions of all lobes in a peribronchovascular distribution.

However, the CT study showed no evidence of a mosaic perfusion pattern, suggesting no localized air trapping or regional changes in blood flow, Mollura and colleagues wrote. There was an absence of centrolobular nodularity or tree-in-bud opacities, suggesting the absence of small-airway inflammation in the secondary lobules.

The chest CT in soft-tissue windows also displayed several notable negatives including the absence of mediastinal lymphadenopathy, as well as the absence of pleural or pericardial effusions.

An echocardiogram revealed moderate concentric left ventricular hypertrophy and an ejection fraction of 58 percent. A repeat CT was not performed and bedside portable radiography was limited due to the severity of the patient’s illness.

A recently published series of 18 cases of fatal S-OIV infection in Mexico demonstrated that patchy bilateral opacities were seen on radiography in all patients and one CT image showed ground-glass air-space density, the authors noted.

The researchers found that CT and radiography contributed to the early recognition of a noncardiogenic cause with severe progressive disease suggesting air-space infection and inflammation. In particular, “CT displayed a pattern of rounded peripheral ground-glass opacities that can be seen with severe peribronchial air-space disease, but were distinguished radiographically from cardiogenic edema.”

Mollura and colleagues concluded that CT for severe influenza cases is of benefit, particularly with the H1N1 strain, but noted that “[f]urther collection of radiographic data and pathologic–radiologic correlation are warranted.”

The study, which is currently available online, will be published in the December issue of the American Journal of Roentgenology.