Korean J Radiol.  2019 Apr;20(4):671-682. 10.3348/kjr.2018.0400.

Distinguishing between Thymic Epithelial Tumors and Benign Cysts via Computed Tomography

Affiliations
  • 1Department of Radiology, Seoul National University College of Medicine, Seoul, Korea. yshoka@gmail.com
  • 2Department of Radiology, Seoul National University Hospital, Seoul, Korea.
  • 3Department of Radiology, Konkuk University School of Medicine, Seoul, Korea.
  • 4Department of Radiology, Konkuk University Medical Center, Konkuk University School of Medicine, Seoul, Korea.
  • 5Department of Nuclear Medicine, Seoul National University College of Medicine, Seoul National University Hospital, Seoul, Korea.
  • 6Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, Korea.

Abstract


OBJECTIVE
To investigate whether computed tomography (CT) and fluorine-18-labeled fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) may be applied to distinguish thymic epithelial tumors (TETs) from benign cysts in the anterior mediastinum.
MATERIALS AND METHODS
We included 262 consecutive patients with pathologically proven TETs and benign cysts 5 cm or smaller who underwent preoperative CT scans. In addition to conventional morphological and ancillary CT findings, the relationship between the lesion and the adjacent mediastinal pleura was evaluated qualitatively and quantitatively. Mean lesion attenuation was measured on CT images. The maximum standardized uptake value (SUVmax) was obtained with FDG-PET scans in 40 patients. CT predictors for TETs were identified with multivariate logistic regression analysis. For validation, we assessed the diagnostic accuracy and inter-observer agreement between four radiologists in a size-matched set of 24 cysts and 24 TETs using a receiver operating characteristic curve before and after being informed of the study findings.
RESULTS
The multivariate analysis showed that post-contrast attenuation of 60 Hounsfield unit or higher (odds ratio [OR], 12.734; 95% confidence interval [CI], 2.506-64.705; p = 0.002) and the presence of protrusion from the mediastinal pleura (OR, 9.855; 95% CI, 1.749-55.535; p = 0.009) were the strongest CT predictors for TETs. SUVmax was significantly higher in TETs than in cysts (5.3 ± 2.4 vs. 1.1 ± 0.3; p < 0.001). After being informed of the study findings, the readers' area under the curve improved from 0.872-0.955 to 0.949-0.999 (p = 0.066-0.149). Inter-observer kappa values for protrusion were 0.630-0.941.
CONCLUSION
Post-contrast CT attenuation, protrusion from the mediastinal pleura, and SUVmax were useful imaging features for distinguishing TETs from cysts in the anterior mediastinum.

Keyword

Mediastinum; Cystic mass; Thymic tumor; Computed tomography; FDG-PET/CT

MeSH Terms

Humans
Logistic Models
Mediastinum
Multivariate Analysis
Pleura
Positron-Emission Tomography
ROC Curve
Thymus Neoplasms
Tomography, X-Ray Computed
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