CT differentiation of subphrenic abscess and pleural effusion

The computed tomographic scans of 38 patients with proven subphrenic abscesses and 28 patients with proven pleural effusions were reviewed without knowledge of the final diagnosis. In 26% of cases the hemidiaphragm could be identified directly as a stripe, while in 71% of cases only the hemidiaphragmatic contour could be seen. In 3% of cases the hemidiaphragm position was indeterminate because insufficient scans of the chest or abdomen were obtained. In the cases where the hemidiaphragm position could be established, the computed tomographic diagnosis was correct in 100% of subphrenic abscesses and in 96% of pleural effusions. Methods of identifying the hemidiaphragm on computed tomography and the possible pitfalls are discussed.