Computed tomography of mediastinal masses

The ability of CT scanning of the mediastinum to distinguish specific tissue densities and to display in a transverse plane often provides unique diagnostic information unobtainable with conventional radiographic methods. We retrospectively analyzed the CT findings of 20 cases of proven mediastinal masses at the Department of Radiology, St. Mary Hospital , Catholic Medical College from February 1982 to June 1984. CT scans were performed with a Siemens Somatom 2 scanner. The technical factors involved were tube voltage 125 kVp, exposure time 5 seconds, 230 mAs, 256 X 256 matrices, and pixel size 1.3 mm. 8 mm slices were obtained at 1 cm interval from the apex of the lung to the diaphragm. If necessary, additional scans at 5 mm interval or magnify scans were obtained. After pre-contrast scan, contrast scans were routinely taken with rapid drip-infusion of contrast media (60% Convey, 150 cc). The results obtained were as follows; 1. Among 20 cases, 11 were tumors, 4 infectious masses and 5 aneurysms of great vessels, tortuous brachiocephalic artery and pericardial fat pad. In each case CT showed accurate location, extent, and nature of the masses. 2. Solid tumors were thymic hyperplasias, thymoma, thymus carcinoid, neurilemmoma and germ cell tumors (seminoma, embryonal cell carcinoma). Internal architecture was homogeneous in thymoma, thymus carcinoid, neurilemmoma, seminoma but inhomogeneous in thymic hyperplasias and embryonal cell carcinoma. CT numbers ranged from 16 to 49 HU and were variably enhanced. 3. Cystic tumors consisted of teratomas, cystic hygroma, and neurilemmoma. Teratomas contained calcium and fat, inhomogeneous mass with strongly enhancing wall. Cystic hygroma was nonenhancing mass with HU of 20. 4. All of germ cell tumors (2 teratomas and one each of seminoma and embryonal cell carcinoma) and one of 2 thymic hyperplasias had calcium deposit. 5. Tuberculous lymphadenopathies presented as a mass in the retrocaval pretracheal space and hilar region with HU ranging from 34 to 64 and enhancement was variable. Mediastinal abscess was almost not enhancing, presenting as an inhomogenous mass of 21 HU with mottled air densities. 6. Aneurysm of great vessels, tortuous brachiocephalic artery and pericardial fat pad which were often misinterpretted as mediastinal tumor on the conventional radiographic study could be easily distinguishable on CT scan.