title: Comparison of CT and chemical-shift MRI for differentiating thymoma from non-thymomatous conditions in myasthenia gravis: value of qualitative and quantitative assessment.
abstract: OBJECTIVE
  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.
  
  
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Diagnostic Imaging, San Luigi Gonzaga University Hospital, Regione Gonzole 10, 10043, Orbassano, Torino, Italy. Electronic address: adriano.priola@inwind.it.
authors.forename: A M
authors.initials: AM
authors.lastname: Priola
authors.affiliation: Department of Diagnostic Imaging, San Luigi Gonzaga University Hospital, Regione Gonzole 10, 10043, Orbassano, Torino, Italy.
authors.forename: S M
authors.initials: SM
authors.lastname: Priola
authors.affiliation: Department of Diagnostic Imaging, San Luigi Gonzaga University Hospital, Regione Gonzole 10, 10043, Orbassano, Torino, Italy.
authors.forename: D
authors.initials: D
authors.lastname: Gned
authors.affiliation: Department of Mathematics "Giuseppe Peano", University of Torino, Via Carlo Alberto 10, 10123, Torino, Italy.
authors.forename: M T
authors.initials: MT
authors.lastname: Giraudo
authors.affiliation: Department of Pathology, San Luigi Gonzaga University Hospital, Regione Gonzole 10, 10043, Orbassano, Torino, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Fornari
authors.affiliation: Department of Diagnostic Imaging, San Luigi Gonzaga University Hospital, Regione Gonzole 10, 10043, Orbassano, Torino, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Veltri
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D003287:Contrast Media; D003937:Diagnosis, Differential; D006801:Humans; D007472:Iohexol / Q000031:analogs & derivatives; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000473:pathology*; D011446:Prospective Studies; D013945:Thymoma / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D013953:Thymus Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D003287:Contrast Media; D007472:Iohexol; C038192:iopromide