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

Abstract

Comparison of CT and chemical-shift MRI for differentiating thymoma from nonthymomatous 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 cutoff 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).

Chemical-shift MRI for diagnosis thymoma in myasthenia gravis: Value of qualitative and quantitative assessment

“…271 hyperplasia cases and 3% of the normal thymus cases [13]. Priola AM's study found that the mass form was found in 20/22 thymoma cases, and in 12/65 hyperplasia cases [6]. In our study, up to 34/37 (91.9%) thymoma were in mass form.…”

“…In the opposed-phase image (C), mass showed the absence of signal intensity loss relative to the in-phase image (D). CSR value were 0.68. logistic regression model for qualitative parameters and SII, Priola AM found that SII were significantly correlatedwith the probability of finding thymoma, because the probability of tumor presence decreased with increased SII (OR per 1% increase, 0.64; 95% CI: 0.71-0.58) [6]. Therefore, an increase 0.01 of value CSR or 1% of value SII for fixed age and gender leads to anincrease of 1.5 times and reduction of 36%, respectively, in the probability of finding thymoma.…”

“…Pirronti T showed the morphological criteria on CT to differentiate thymoma from hyperplasia [5]. On MRI, in addition to the same morphological criteria used for CT, Priola AM showed the specific MRI criteria for differentiation based on the absence of signal intensity loss on the opposed-phase relative to the in-phase image [6].…”

“…Thus, the normal or hyperplastic thymus showed the signal intensity loss but the thymoma did not. Studies of Inaoka T [15], Popa G [16], Priola AM [6] showed that signal intensity loss on the opposed-phase image is important for distinguishing between thymoma and non-thymoma. The results in Table 1 showed up to 36/37 thymoma cases did notexhibit the signal intensity loss, whereas only 3/25 non thymoma cases did not (p<0.0001) (Figures 3 and 4).…”

Multislice computed tomography performance in differential diagnosis of high‐density thymic cyst and thymoma in lesions less than 3 cm

“…The features displayed via MSCT had good spatial and density resolution. The shape, edge, and surrounding tissues of nodules can be clearly and completely displayed with precision and reliability through thin‐layer reconstruction, providing important information for diagnosis . This study shows that thymic cysts and low‐risk thymomas with a maximum diameter of the anterior mediastinum of ≤ 3 cm possess smooth borders, indicating that they are more likely benign lesions.…”