Oral 4.01: Comparison between computed tomography and magnetic resonance imaging in preoperative evaluation of thymic epithelial tumors

Background: Contrast enhanced computed tomography (CT) is currently the imaging modality of choice for distinguishing thymic epithelial tumors (TETs) from other anterior mediastinal masses, characterizing the primary tumor and staging disease. Currently the role of magnetic resonance imaging (MRI) in imaging TETs is limited to patients who cannot receive iodinated contrast material. The study’s main objective is to assess if chest MRI is as accurate as CT in staging TETs. The second objective is to see if newer shorter MRI sequences can replace conventional MRI sequences without loss of accuracy, leading to a short MRI study.

Methods: After IRB approval and patients’ informed consent, we prospectively reviewed CT and MRI studies obtained within 30 days prior to surgery in 20 patients with biopsy proven TET. CT was performed with intravenous contrast. Conventional MRI sequences included were SE T1 and FSET2 weighted as well as novel faster sequences [Fast Gradient-echo T1-weighted in-phase and opposed-phase, 3D LAVA, and fast spin echo triple echo Dixon (FTED) T2 weighted]. Each patient had an MRI cine sniff test as well as fluoroscopic sniff test for assessment of the phrenic nerve function. Conventional MRI sequences, Fast MRI sequences and CT scans were interpreted by three separate experiences chest radiologists who were blinded to each other’s studies and prior imaging studies. Both methods were compared and correlated with Masaoka-Koga staging. Local mediastinal involvement, invasion of phrenic nerve, pleura, lung and vessels was assessed. Sensitivity, specificity and accuracy of each imaging method were compared to surgical pathology.

Results: Among the study patients, 17 had thymoma and 3 thymic carcinoma, 12 patients had advanced disease (stage III/IV). Sensitivity (100%) was identical for all three imaging methods studies when assessing advanced stage disease but CT and new MRI sequences demonstrated a higher specificity (63%) and accuracy (85%) when compared with conventional MRI sequences (respectively, 50% and 80%). CT more accurately identified local mediastinal involvement (94%) compared with conventional and fast MRI sequences (76%). All imaging methods were similar in the assessment of phrenic nerve, vascular and lung involvement.

Conclusions: The performance of MRI is similar to that of CT in identifying patients with advanced stage TET. Since patients with advanced disease are usually treated with neoadjuvant therapy prior to surgery, MRI can replace CT in their initial evaluation as well as following neoadjuvant therapy prior to surgery thus decreasing cumulative radiation dose.

Keywords: Thymic epithelial tumors (TETs); computed tomography (CT); magnetic resonance imaging (MRI)