AJR: CT bests x-ray for detecting H1N1 abnormals
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| Unenhanced chest CT lung window image of patient with swine flu. Image source: American Journal of Roentgenology |
The study group consisted of seven patients (six males, mean age 43) with the H1N1 virus—all of whom received chest x-rays and three patients had CT scans, according to the authors. All seven patients had initially presented with an influenza-like illness, thereby fulfilling the clinical criteria for diagnosing S-OIV infection.
"All patients with CT abnormalities showed abnormal findings on the corresponding chest x-rays," said lead author Amr M. Ajlan, MD, from the department of radiology at Vancouver General Hospital, University of British Columbia in Vancouver, B.C. "However, the extent of involvement was more diffuse and the distribution of disease was better characterized on CT.”
According to the researchers, five patients had posteroanterior- and lateral-projection initial x-rays, and the remaining two had bedside anteroposterior-projection initial x-rays. Six of the seven patients had follow-up radiographs. In five of those six patients, the follow-up x-rays were obtained one to two days after the presentation: in the posteroanterior and lateral projections in one patient and in a bedside anteroposterior projection in the other four patients. One patient had serial bedside anteroposterior-projection follow-up x-rays for the duration of a 17-day hospital stay.
Posteroanterior- and lateral-projection radiographs were obtained using a Multix unit from Siemens Healthcare. Bedside anteroposterior-projection radiographs were obtained on an AMX mobile unit from GE Healthcare, using 90 kV, 4 mAs and a 100 cm film–focus distance.
A thin-section multislice CT was performed in three of the seven patients. Two patients underwent a CT scan on admission, and the remaining patient underwent scanning within 24 hours after admission. The studies were performed on the 64-slice Definition CT from Siemens.
Ajlan and colleagues reported that the initial chest radiograph was normal in four of seven patients. Three patients had abnormal findings on the initial x-ray, with one patient having faint ground-glass opacities in the lower zone of the right lung.
In the three patients that had a CT scan, the authors reported that:
- One showed extensive ground-glass opacities and mild multifocal areas of consolidation in the left lung. The consolidation had peribronchovascular and subpleural predominance. Minimal basal predominance was noted as well.
- On another patient, bilateral multifocal asymmetric ground-glass opacities and small multifocal areas of consolidation were present in a predominant peribronchovascular and subpleural distribution.
- The third patient with an initial CT scan showed bilateral asymmetric ground-glass opacities and areas of consolidation with peribronchovascular predominance.
The researchers noted that none of the patients had nodular opacities, reticulation, or hilar or mediastinal lymph node enlargement evident on any of the radiographs or CT scans.
"The strength of our study is that all CT scans performed showed a similar distribution of abnormalities, which might help physicians prospectively diagnose H1N1 using medical imaging," Ajlan said.
"Most cases of H1N1 are mild and self-limited; however, high-risk patients are more likely to have severe complications. Our study suggests that CT is superior to standard chest x-rays and should be the imaging modality of choice in high-risk patients," he concluded.
The study will appear in the December issue of the American Journal of Roentgenology.