CT and MRI features in 22 cases of primary malignant thymic germ cell tumours

To analyse the computed tomography (CT) and magnetic resonance imaging (MRI) features of malignant thymic germ cell tumours (GCTs), in order to improve the accuracy of diagnosis of these tumours.

Twenty-two patients (20 men, two women; age, 28 ± 8.64 years) with malignant thymic GCTs confirmed at histopathology were enrolled retrospectively, and their CT and MRI findings were analysed.

According to the CT findings, malignant thymic GCTs usually manifest as a bulky mass that typically grows to both sides of the midline (20/22, 90.9%), with irregular shape (15/22, 68.2%), lobulation (12/22, 50%), ill-defined margin (9/22, 40.9%), and incomplete capsule (21/22, 95.5%). Twenty masses revealed heterogeneous density with multifocal necrosis or cystic change in 19 (86.4%). Most cases (16/18, 88.9%) showed mild to moderate enhancement, and the branch-like vessel was found in 14 (14/18, 77.8%) cases. The minimum apparent diffusion coefficient (ADC_min) and mean apparent diffusion coefficient (ADC_mean) values in 14 patients were (1.13 ± 0.45) and (1.37 ± 0.49) × 10^-3 mm²/s, respectively. Compared with CT findings, the incidences of an incomplete capsule, heterogeneous signal, and necrotic or cystic change on MRI images occurred in all patients with malignant thymic GCT. In addition, peritumoural oedema was found in all 14 (100%) cases.

MRI is superior to CT in showing incomplete capsule, peritumoural oedema, heterogeneous signal, and necrotic or cystic change of GCTs. Branch-like enhancement and multifocal necrosis may help the diagnosis of malignant thymic GCTs.