[IMPORTANCE OF GAS MEDIASTINOGRAPHY (PNEUMOMEDIASTINUM) IN RADIOLOGICAL DIAGNOSIS OF THYMUS TUMORS].

Diagnostic pneumomediastinography in a series of 675 cases revealed that thymic tumours accounted for 13% of all mediastinal neoplasms. In more than 50% of instances, thymic enlargement associated with myasthenia gravis was not apparent on ordinary frontal or lateral tomograms prior to the injection of air. In this procedure 500 to 600 c.c. of air is injected into the anterior mediastinal space by the supra- and retro-sternal (or suband retro-xiphoid) route. One hour later, tomography is performed at appropriate angles and levels. Diagnostic pneumomediastinography is well tolerated, even by myasthenic patients. It is valuable in the positive and differential diagnosis of mediastinal disease and is especially useful in the detection of abnormal thymic shadows.Typically, benign enlargements of the thymus appear as comma- or banana-shaped retrosternal shadows of moderate density, separated from the breastbone and from the cardiovascular opacity. The significance of the presence of a notch visualized between the heart and the tumour is emphasized. An irregular shadow, a poor gaseous contrast, suggesting a locally invasive lesion, and adhesions usually are indicative of malignancy.