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Application & Imaging Features of SARS on HRCT

Application & Imaging Features of SARS on HRCT. KT Wong. Department of Diagnostic Radiology and Organ Imaging Chinese University of Hong Kong Prince of Wales Hospital Hong Kong. Background. Outbreak in medical ward in PWH in March

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Application & Imaging Features of SARS on HRCT

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  1. Application & Imaging Features of SARS on HRCT KT Wong Department of Diagnostic Radiology and Organ Imaging Chinese University of Hong Kong Prince of Wales Hospital Hong Kong

  2. Background • Outbreak in medical ward in PWH in March • To the end of May, over 300 SARS patients treated in our institution • Imaging play an important role - diagnosis - monitor progress and treatment response - assess long-term lung damage

  3. Indication • Not all patients with suspected SARS need HRCT scan • Initial cohort of 138 patients - 78% had abnormal CXR on presentation - 22% had normal initial CXR • Early diagnosis important for this group for prompt Tx and patient isolation Wong et al. Radiology Aug 2003

  4. Indication • Diagnostic yield depends on level of clinical suspicion • Initial cohort of 74 suspected patients - 34 / 74 with relative minor symptoms - all had negative HRCT - subsequent proven not SARS - 40 / 74 had positive HRCT - subsequent confirmed SARS Wong et al. Radiology Aug 2003

  5. Indication • High clinical index of suspicion and negative CXR • High clinical index with equivocal CXR findings (young female with dense breasts) • Not recommended - all patients with low clinical suspicion - high suspicion with definite CXR changes

  6. CXR Suspected SARS -ve +ve (if strong clinical suspicion) Treatment HRCT +ve -ve Follow-up Treatment

  7. Scanning Technique • Initial outbreak – both conventional and HRCT performed • Preliminary experience – lack of lymphadenopathy or pleural abnormality • Current protocol – perform only HRCT

  8. Scanning Technique • Supine position • Full inspiration (shallow breathing if SOB) • 1mm collimation, 6mm interslice gap • 120 kV, 140mA, scan time of 1 second • Whole scanning procedure of ~ 1 minute

  9. Scanning Technique • High-spatial frequency reconstruction algorithm • Image viewed at lung window setting - level: -700 HU - width: 1500 HU • Close patient monitoring • Strict infection control measures

  10. Imaging Features • Appearances: (initial cohort of 40 patients, 149 lesions) - Ground-glass opacification (68%) - Consolidation +/- GGO (32%) - Thickened intralobular interstitium (32%) - Thickened interlobular septa (24%) (‘Crazy-paving’ appearances) - Associated bronchiectasis (7%) Wong et al. Radiology Aug 2003

  11. Imaging Features • Location: - Peripheral / subpleural (72%) - Peripheral + central (20%) - Pure central unusual (8%) - Slight lower lobe predominance - half patients with bilateral involvement Wong et al. Radiology Aug 2003

  12. Imaging Features • Absence of following features - peribronchovascular interstitial thickening - mass / nodule - lymphadenopathy - pleural effusion - cavitation

  13. Reasons For Negative CXR • Lesions at radiographic blind-spots - Retrocardiac area - Paraspinal area - Posterior costophrenic sulcus - Peri-hilar area • Early disease with small areas of ground-glass opacification

  14. Role In Follow-up • Persistent CXR changes after discharge + functional impairment necessitate HRCT - assessment of nature of lung change (persistent alveolitis  steroid / immune Tx fibrosis  irreversible, steroid not useful) - extent of lung fibrosis - interval HRCT – serial change after Tx

  15. Follow-up • Initial cohort of 24 discharged patients • HRCT at ~ 37 days after admission • 23/24 (96%) – persistent GGO • 15/24 (62%) – HRCT evidence of fibrosis • 9 had HRCT at initial presentation - all had radiological improvement - residual GGO + interstitial changes Antonio et al. Radiology Sep 2003

  16. Follow-up • HRCT evidence of fibrosis - parenchymal band - subpleural lines - interlobular septal thickening - honey-combing - traction bronchiectasis - architectural distortion

  17. Follow-up • Patients with HRCT evidence of fibrosis - Older age group - Male > female - Longer hospital stay - Higher ICU admission rate - Higher peak LDH level - More requirement for pulse iv steroid Antonio et al. Radiology Sep 2003

  18. Limitations • Small number of patients • Relatively short follow-up - some HRCT changes may be reversible • No histology for confirmation of fibrosis • No correlation with lung function or objective assessment of exercise tolerance

  19. Take Home Messages • HRCT useful for early diagnosis of SARS • Not suitable as 1st line investigation • Indication of HRCT for suspected SARS - patients with high index of clinical suspicion and negative / equivocal CXR findings

  20. Take Home Messages • HRCT features includes - GGO +/- consolidation - interstitial thickening - peripheral / subpleural in location - slight lower lobe predominance - lack of cavitation, lymphadenopathy & pleural effusion

  21. Take Home Messages • HRCT useful in follow-up SARS patients with functional impairment and persistent CXR changes • Preliminary experiences – significant proportion of discharged patients with HRCT evidence of fibrosis • Need longer FU study with more patients for further assessment

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