Pneumonia in novel swine-origin influenza A (H1N1) virus infection: high-resolution CT findings

Abstract

Objective: The purpose of our study was to review the initial high-resolution CT (HRCT) findings in pneumonia patients with presumed/laboratory-confirmed novel swine-origin influenza A (H1N1) virus (S-OIV) infection and detect pneumonia earlier.

Materials and methods: High-resolution CT (HRCT) findings of 106 patients with presumed/laboratory-confirmed novel S-OIV (H1N1) infection were reviewed. The 106 patients were divided into two groups according to the serious condition of the diseases. The pattern (consolidation, ground-glass, nodules, and reticulation), distribution, and extent of abnormality on the HRCT were evaluated in both groups. The dates of the onset of symptoms of the patients were recorded.

Results: The predominant CT findings in the patients at presentation were unilateral or bilateral multifocal asymmetric ground-glass opacities alone (n=29, 27.4%), with unilateral or bilateral consolidation (n=50, 47.2%). The consolidation had peribronchovascular and subpleural predominance. The areas of consolidation were found mainly in the posterior, middle and lower regions of the lungs. Reticular opacities were found in 6 cases of the initial MDCT scan. The extent of disease was greater in group 1 patients requiring advanced mechanical ventilation, with diffuse involvement in 19 patients (63.3%) of group 1 patients, and only 15/76 (19.7%) of group 2 patients (p<0.01, χ2 test). 20 cases (19%) of the 106 patients had small bilateral or unilateral pleural effusions. None had evidence of hilar or mediastinal lymph node enlargement on CT performed at admission or later.

Conclusions: The most common radiographic and CT findings in patients with S-OIV infection are unilateral or bilateral ground-glass opacities with or without associated focal or multifocal areas of consolidation. On HRCT, the ground-glass opacities had a predominant peribronchovascular and subpleural distribution. CT plays an important role in the early recognition of severe S-OIV (H1N1).

Fig. 1

A 36-year-old man with laboratory-confirmed S-OIV (H1N1). High-resolution CT (HRCT) scan obtained 10 days after the onset of symptoms. Axial CT image showed peripheral and lower lung predominant ground-glass opacities, and pneumomediastinum (arrows) (A and B).

Fig. 2

A 34-year-old pregnant woman with laboratory-confirmed S-OIV (H1N1). High-resolution CT (HRCT) scan obtained on the day of the onset of fever (A). Axial CT image showed ground-glass opacities peribronchovascular and subpleural predominance. 3 days later, the opacities became larger and thicker on the same level as A (B).

Fig. 3

A 36-year-old woman with laboratory-confirmed S-OIV (H1N1). Chest CT acquired at admission showed bilateral ground-glass opacities in all lung zones (A) and reticular opacities in right lower lobe. Follow-up CT performed 12 days after A showed follow-up CT reticular opacities forming a meshlike pattern (B).

Fig. 4

A 39-year-old woman with presumed H1N1. High-resolution CT scan obtained on 3 days after the onset of symptoms showed ground-glass opacities, thickening of interlobular septa (arrows) and intralobular lines in both sides.

Fig. 5

A-34-year-old man with laboratory-confirmed S-OIV (H1N1). Chest CT acquired at admission (3 days after symptom onset) showed a peripheral distribution of patchy ground-glass opacities (A). With progression of the symptoms, chest radiograph obtained 2 days after hospital admission (B) showed bilateral areas of consolidation in mid and lower lung zones. He was admitted to ICU on the same day for mechanical ventilation. The ground-glass opacities were located throughout the upper and lower regions of all lobes in a peribronchovascular distribution. CT scan obtained on the third days after A (C) showed diffuse bilateral ground-glass opacities, areas of consolidation predominately in subpleural and dependent lung regions.

Fig. 6

A 5-year-old girl with laboratory-confirmed S-OIV (H1N1). Chest CT scan obtained 6 h after the onset of fever showed focal ground-glass opacities in right lower lobe (A). Head CT acquired on the same day with A showed swelling and the decreases cerebral stem and bilateral thalamus (B). She was admitted to ICU for mechanical ventilation immediately. She died on third hospital day.