2. Imaging Diagnostic Center, Vietnam Military Medical University, Vietnаm.
Objectives: To evaluate the usefulness of chemical-shift magnetic resonance imaging (MRI) in patients with myasthenia gravis (MG) for differentiating thymoma from normal thymus and thymic hyperplasia.
Patients and Methods: 62 patients with MG were treated surgically in 103 Military Hospital and Cho Ray Hospitals from August 2014 to January 2017. All patients had undergone surgery to remove thymus, thymoma, and had pathology reports. All of them had not received any neoadjuvant chemo-radiotherapeutic treatment. MRI examination was obtained using a 1.5 T MRI unit (Intera, Philips Healthcare, the Netherlands) from the thoracic inlet to the cardiophrenic angle. Comparison of the chemical shift ratio(CSR) between two groups was processed by the T-Student test. Logistic multivariate regression was performed to estimate the probability that patients had thymoma by both predictive qualitative and quantitative variables. A p value of <0.05 was considered indicative a statistically significant differencefor all statistical analyses.
Results: 62 patients included 24 males (45.2%), 38 females (54.8%). Comparision with pathologic results, the sensitivity, the specificity and the accuracy of qualitative assessment were 97.3%, 88%, 93.5%, respectively. CSR value was very good criteria for distinguishing between thymoma and non-thymoma groups with the AUROC of 0.984 (95% CI: 0.914-1.000), and with an optimal cut-off point of 0.825. Applying this cut-off point, the specificity and the accuracy of quantitative assessment were 100%, 96%, 98.4%, respectively. An increase in 0.1 value of CSR for all shape, location and signal intensity leads to an increase of 10 times in the probability of finding thymoma.
Conclusion: Chemical shift magnetic resonance imaging is helpful in differentiating thymoma from normal or hyperplastic thymus based on quantifying fat tissue.
Keywords: Chemical-shift MRI, thymoma, myasthenia gravis