Comparison of CT and chemical-shift MRI for differentiating thymoma from non-thymomatous conditions in myasthenia gravis: value of qualitative and quantitative assessment.

AIM: To evaluate the usefulness of computed tomography (CT) and chemical-shift magnetic resonance imaging (MRI) in patients with myasthenia gravis (MG) for differentiating thymoma (THY) from thymic lymphoid hyperplasia (TLH) and normal thymus (NT), and to determine which technique is more accurate. MATERIALS AND METHODS: Eighty-three patients with generalised MG who underwent surgery were divided into the TLH/NT group (A; 65 patients) and THY group (B; 24 patients). Differences in qualitative characteristics and quantitative data (CT: radiodensity in Hounsfield units; MRI: signal intensity index [SII]) between groups were tested using Fisher's exact test and Student's t-test. Logistic regression models were estimated for both qualitative and quantitative analyses. At quantitative analysis, discrimination abilities were determined according to the area under the receiver operating characteristic (ROC) curve (AUROC) with computation of optimal cut-off points. The diagnostic accuracies of CT and MRI were compared using McNemar's test. RESULTS: At qualitative assessment, MRI had higher accuracy than CT (96.4%, 80/83 and 86.7%, 72/83, respectively). At quantitative analysis, both the radiodensity and SII were significantly different between groups (p<0.0001). For CT, at quantitative assessment, the AUROC of the radiodensity in discriminating between groups was 0.904 (optimal cut-off point, 20 HU) with an accuracy of 77.1% (64/83). For MRI, the AUROC of the SII was 0.989 (optimal cut-off point, 7.766%) with an accuracy of 96.4% (80/83), which was significantly higher than CT (p<0.0001). By using optimal cut-off points for cases with an erroneous diagnosis at qualitative assessment, accuracy improved both for CT (89.2%, 74/83) and MRI (97.6%, 81/83). CONCLUSION: Quantitative analysis is useful in evaluating patients with MG and improves the diagnostic accuracy of CT and MRI based on qualitative assessment. Chemical-shift MRI is more reliable than CT in differentiating THYs from non-thymomatous conditions.

Bronchogenic cysts in the adult: diagnostic criteria derived from the correct use of standard radiography and computed tomography.

PURPOSE: This study was undertaken to identify the radiographic and computed tomography patterns allowing a diagnosis of bronchogenic cyst. MATERIALS AND METHODS: We retrospectively reviewed chest radiographs and CT scans of 21 adults (ten men and 11 women, age range 18-74 years) with a histologically confirmed diagnosis of bronchogenic cyst. RESULTS: Sixteen cysts were located in the mediastinum and five in the lungs. On chest radiography, mediastinal cysts appeared as sharply marginated rounded areas of increased opacity; intrapulmonary cysts also exhibited an air-fluid interface. CT confirmed these morphological features in all cases. In addition, analysis of attenuation values allowed the subdivision of mediastinal cysts into three groups: fluid density (four cases), air density (two cases) and soft-tissue density (ten cases). CONCLUSIONS: All bronchogenic cysts were visualised on chest radiography, but the findings were nonspecific and required further characterisation by CT. The CT findings proved to be diagnostic when cystic attenuation values were evident. When soft-tissue attenuation values were demonstrated, a confident diagnosis was not possible, and other solid lesions had to be considered. In such cases, magnetic resonance imaging may be helpful to ascertain the cystic nature of the lesions.