CT appearance of parapneumonic effusions in children: findings are not specific for empyema.

OBJECTIVE: Although definitive differentiation of empyema from transudative parapneumonic effusion is based on the analysis of pleural fluid, certain CT findings have been described as highly suggestive of empyema. This study compares the CT findings of parapneumonic effusions with the results of thoracentesis, thoracoscopy, or both to determine whether these CT findings can reliably differentiate empyemas from transudative parapneumonic effusions in children.

MATERIALS AND METHODS: CT scans obtained to evaluate pleural or parenchymal complications of pneumonia were reviewed. Parapneumonic effusions were evaluated for the CT findings of pleural enhancement; parietal pleural thickening; thickening, increased attenuation, or both of the extrapleural subcostal fat: and edema of the extracostal chest wall. Each parapneumonic effusion was assigned a CT score on the basis of these CT findings. Individual CT findings and the CT score were correlated with the presence of empyema as determined by thoracentesis or thoracoscopy.

RESULTS: Thirty patients were identified as having a parapneumonic pleural effusion revealed on contrast-enhanced CT scans and by pleural fluid analysis. Twenty-one of these parapneumonic effusions met the clinical criteria for empyema, and nine were considered not to be empyemas. Neither any individual CT finding nor the CT score accurately differentiated empyema from transudative parapneumonic effusions (p > .1): pleural enhancement (empyema 100%, transudative effusion 89%), pleural thickening (empyema 57%, transudative effusion 56%), abnormal extrapleural space (empyema 66%, transudative effusion 67%), extracostal chest wall edema (empyema 33%, transudative effusion 56%), and average CT score (empyema 2.5. transudative effusion 2.3).

CONCLUSION: CT characteristics of parapneumonic effusions do not allow radiologists to accurately predict empyema. The presence or absence of such CT findings should not influence therapeutic decisions concerning the management of parapneumonic effusions.