Korean J Radiol.  2019 May;20(5):854-861. 10.3348/kjr.2018.0699.

Quantitative Thoracic Magnetic Resonance Criteria for the Differentiation of Cysts from Solid Masses in the Anterior Mediastinum

• Hwang EJ
• Paek M
• Yoon SH
• Kim J
• Lee HY
• Goo JM
• Kim H
• Kim H
• Ackman JB

• KMID: 2442719
• DOI: http://doi.org/10.3348/kjr.2018.0699

Abstract

OBJECTIVE
To evaluate quantitative magnetic resonance imaging (MRI) parameters for differentiation of cysts from and solid masses in the anterior mediastinum.
MATERIALS AND METHODS
The development dataset included 18 patients from two institutions with pathologically-proven cysts (n = 6) and solid masses (n = 12) in the anterior mediastinum. We measured the maximum diameter, normalized T1 and T2 signal intensity (nT1 and nT2), normalized apparent diffusion coefficient (nADC), and relative enhancement ratio (RER) of each lesion. RERs were obtained by non-rigid registration and subtraction of precontrast and postcontrast T1-weighted images. Differentiation criteria between cysts and solid masses were identified based on receiver operating characteristics analysis. For validation, two separate datasets were utilized: 15 patients with 8 cysts and 7 solid masses from another institution (validation dataset 1); and 11 patients with clinically diagnosed cysts stable for more than two years (validation dataset 2). Sensitivity and specificity were calculated from the validation datasets.
RESULTS
nT2, nADC, and RER significantly differed between cysts and solid masses (p = 0.032, 0.013, and < 0.001, respectively). The following criteria differentiated cysts from solid masses: RER < 26.1%; nADC > 0.63; nT2 > 0.39. In validation dataset 1, the sensitivity of the RER, nADC, and nT2 criteria was 87.5%, 100%, and 75.0%, and the specificity was 100%, 40.0%, and 57.4%, respectively. In validation dataset 2, the sensitivity of the RER, nADC, and nT2 criteria was 90.9%, 90.9%, and 72.7%, respectively.
CONCLUSION
Quantitative MRI criteria using nT2, nADC, and particularly RER can assist differentiation of cysts from solid masses in the anterior mediastinum.

Keyword

Anterior mediastinum; Prevascular mass; MRI; Thymoma; Thymic cyst

MeSH Terms

Dataset
Diffusion
Humans
Magnetic Resonance Imaging
Mediastinal Cyst
Mediastinum*
ROC Curve
Sensitivity and Specificity
Thymoma

Figure

• 

  Fig. 1 Representative case from development dataset (cyst).Axial T2-weighted HASTE image (A), ADC map (B), pre- and post-contrast fat-suppressed T1-weighted images (C), and RER map (D) from 70-year-old male patient revealed 3.1 cm mass in anterior mediastinum (arrows). nT2, nADC, and RER values were 0.92, 1.50, and 5.3%, respectively. Pathologic diagnosis after surgical resection was thymic cyst. ADC = apparent diffusion coefficient, HASTE = half-Fourier-acquired single-shot turbo spin echo, nADC = normalized ADC, nT2 = normalized T2 signal intensity, RER = relative enhancement ratio

• 

  Fig. 2 Representative case from development dataset (solid mass).Axial T2-weighted HASTE image (A), ADC map (B), pre- and post-contrast fat-suppressed T1-weighted images (C), and RER map (D) from 65-year-old male patient revealed 1.6 cm mass in anterior mediastinum (arrows). nT2, nADC, and RER values were 0.32, 0.76, and 59.6%, respectively. Pathologic diagnosis after surgical resection was thymoma, type B2.

• 

  Fig. 3 Boxplots and ROC curves for differentiation between cysts and solid masses in development dataset.Boxplots in left column show results of comparison of image variables between cysts and solid masses. nT2, nADC, and RER differed significantly between cysts and solid masses. Horizontal dashed lines indicate cutoff values developed in ROC analyses. ROC curves in right column show results of ROC analyses for differentiation between cysts and solid masses. Although nT2, and nADC appeared to be significant variables, RER showed perfect separation between cysts and solid masses. nT2, nT1, and nADC are fraction values without units. AUROC = area under receiver operating characteristic curve, ROC = receiver operating characteristic

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