CT characteristics of expansions in the middle and posterior mediastinum.

Chest radiographs and computed tomographic (CT) findings in 42 patients with pathology of the middle or posterior mediastinum, confirmed by thoracotomy, were examined retrospectively. The possibility of using contrast-enhanced CT to distinguish between cysts and solid tumors on the one hand and benign and malignant tumors on the other was assessed. All the expansions were detectable on chest radiographs. It was only by using CT, however, that the extent of the tumors could be established. Simple cysts could be identified because of their water density even without administration of contrast medium. Bronchogenic cysts simulated solid tumors but showed no contrast enhancement. Other benign tumors showed both intense homogeneous and heterogeneous contrast enhancement, as did malignant tumors. Contrast enhancement was therefore not helpful in distinguishing these benign tumors from malignant ones. Thus only infiltration to adjacent organs was found indicative of malignancy; contrast medium administration was found helpful in this respect. The use of contrast medium is thus justified in studying expansions in the middle and/or posterior mediastinum.