Differentiation of lung abscess and empyema by ultrasonography.

To assess the value of chest ultrasonography in the differentiation between a lung abscess and empyema, 50 patients, including 24 cases of lung abscess and 26 cases of empyema, were studied. The ultrasonographic characteristics of a lung abscess included an irregular wall width, a blurred outer margin, an oval or round shape, an acute chest wall angle and a negative pleural separation. The ultrasonographic characteristics of empyema were an uniform wall width, a sharp outer margin, a lenticular shape, an obtuse chest wall angle and a positive pleural separation. A new ultrasonographic scoring system was proposed; a positive finding for each of the features: sharp outer margin, lenticular shape, obtuse chest wall angle and positive pleural separation was assigned a score of 1, while a negative finding was assigned a score of zero. The total scores for the four features were then assessed. Ninety-six percent of the empyema cases scored 2 or more, while 96% of the lung abscess cases scored 1 or zero. The efficacy of differential diagnosis was 96%. We conclude that chest ultrasonography is a useful tool in the differentiation between lung abscess and empyema and that ultrasonography alone is sufficient to make a correct diagnosis in most cases.