[Usefulness of chest CT in diagnosing pneumonia].

The usefulness of chest CT in diagnosing pneumonia was evaluated by a retrospective review of 110 pneumonia cases in which both plain chest radiograph and CT were obtained. Detection of abnormal opacities on chest radiograph was difficult or impossible in 9 cases (8.2%), requiring CT to detect them. The opacities which appeared consolidative, nodular, small nodular or cavitary on chest radiograph were shown as opacities of similar character on CT. On the other hand, many opacities of patchy, ground-glass or linear/reticular character on chest radiograph were shown as opacities of different character on CT. One case out of 3 of mycoplasma pneumonia, one case each of influenza viral pneumonia and pneumocystis carinii pneumonia and showed rather typical appearance on CT. Detection of pleural effusion on chest radiograph was difficult in 17 (58.6%) of 29 cases in which it was easily detected on CT. In conclusion, CT is useful in diagnosing pneumonia in limited cases, as follows: (1) indistinct abnormal opacity on chest radiograph despite positive clinical signs of pneumonia, (2) patchy, ground-glass or linear/reticular opacities on chest radiograph, (3) confirmation of pleural effusion, (4) close observation of sequential changes of opacity after starting treatment of pneumonia. In contrast, CT is not generally useful in evaluating consolidative opacities on chest radiograph.