Imaging of mediastinal foregut cysts

This study was undertaken to determine the value of magnetic resonance imaging (MRI) in the diagnosis of mediastinal foregut cysts. The MRI scans of 56 patients (with a total of 57 mediastinal masses) were reviewed. The patients (26 women and 30 men) had been examined between March 1986 and April 1991 at a tertiary-care hospital. T1-weighted and T2-weighted spin-echo images were available in all cases. The signal intensity of the lesions was compared with that of normal fat and muscle; the size, shape and location of the mediastinal masses were also noted. The 57 lesions consisted of 15 lymphomas, 10 neurogenic tumours, 10 thyroid masses, 6 thymomas, 6 foregut cysts and 10 other masses. Forty-eight of the masses had a signal intensity similar to that of muscle in T1-weighted images and higher than, equal to or lower than that of fat in T2-weighted images. Nine of the masses appeared bright in T1-weighted images, and the signal intensity was less than or equal to that of fat. Of these, four were foregut cysts and five were lymphomas. Of the six foregut cysts, four had short T1 values (the signal intensity ratio for cyst to fat ranging from 0.78 to 0.98) and long T2 values; two had the characteristic appearance usually associated with cystic lesions containing serous fluid--long T1 and T2 values. All of the foregut cysts appeared to be of soft-tissue attenuation on computed tomography (CT), all were located in the middle or posterior mediastinum, and all were round or oval.(ABSTRACT TRUNCATED AT 250 WORDS)