The aim of the study was to evaluate cystic thymic masses by using computed tomography (CT) and magnetic resonance (MR) scoring systems to differentiate nonneoplastic thymic cysts from cystic thymic neoplasms.

This retrospective multisite study included adult patients who underwent CT and MR imaging of the chest between 2007 and 2020 with any of the following impressions on cross-sectional imaging studies: “thymic mass with cystic component,” “unilocular or multilocular cystic thymic lesion,” “complex thymic cyst,” “thymic cyst with hemorrhage.” Two blinded radiologists reviewed and recorded specific imaging features as well as overall impressions on both CT and MR using a Likert scale scoring system. Data were analyzed, and diagnostic accuracy of CT and MR was compared using areas under the receiver operating characteristic curves (AUC).

Fifty-six patients were included, of which 45 (80%) had benign masses. Total of 21 patients (38%) had indeterminate scores on CT of which 3 (14%) were malignant, while only 6 (11%) had indeterminate scores on MR and 1 was malignant. Magnetic resonance scoring system (AUC, 0.95) performed better than CT scoring system (AUC, 0.86) in distinguishing benign versus malignant lesions (P = 0.06). Lack of enhancement within the mass was completely predictive of benign etiology (P < 0.001). Wall thickness of an enhancing cyst was predictive of malignancy, with AUC 0.93.

Magnetic resonance yielded higher specificity allowing a larger number of lesions to be confidently assigned a benign diagnosis. This could help in averting unnecessary follow-up, biopsies, or surgery. The authors recommend follow-up imaging with MR for prevascular masses, even those appearing “solid” on CT.