Magnetic Resonance Imaging for the Follow-up of Treated Thymic Epithelial Malignancies

Abstract

Purpose: The purpose of this article was to compare magnetic resonance imaging (MRI) depiction of thymic malignancy progression/recurrence with that of computed tomography (CT). Methods: We retrospectively reviewed all surgically treated thymic epithelial malignancy (TEM) patients between 2011 and 2018 who were followed-up with chest CT and MRI. We compared the detection of recurrence and metastatic disease between the CT and MRI scans in each of these patients. Results: Of 187 patients treated in our institution for TEM, 22 were followed-up with both CT and MRI. TNM stage at diagnosis was as follows: I (n=14), II (n=1), IIIa (n=4), IIIb (n=2), IVa (n=1), and IVb (n=0). Patients were followed-up for a mean of 6.2 years, range 0.7 to 17.7 years. The mean interval between CT and MRI was 5.4 (range, 1 to 15) months. Most patients had no recurrence (n=16), 4 had recurrence after R0 or R1 resection, 1 had stable disease, and 1 had progression of disease after R2 resection. CT and MRI performed equally in the identification of pleural spread (n=5), lymphadenopathy (n=4), and pulmonary metastases (n=1). Retrosternal recurrence (n=1) was identified by MRI despite sternotomy wire artifacts. MRI identified bone involvement and extension of disease into the thecal sac earlier and more readily. Three patients had an indeterminate mediastinal finding on CT that was correctly identified as a benign cyst or pericardial fluid collection by MRI. Conclusion: MRI is an alternative option to follow-up patients after treatment for TEM. However, for those with metallic sternotomy wires, we recommend alternating the follow-up with CT as well.

Imaging Evaluation of Thymoma and Thymic Carcinoma

“…Kerpel et al evaluated 22 of 187 patients who underwent resection for thymic epithelial tumors to assess the accuracy of MRI compared with CT for follow-up assessment. They concluded that MRI was an adequate alternative to CT for reassessment with the caveat that in patients with sternotomy wires alternating CT with MRI was recommended given associated artifact (24).…”

“…From years six to eleven alternating yearly CT and chest radiograph is performed, and then yearly chest radiographs thereafter. For resected stage III or IVa thymoma, thymic carcinoma, incomplete resection, or other high-risk tumors, additional CT of the thorax is recommended every six months for the first three years with consideration of CT one to three months after surgery to obtain a new baseline after post-surgical inflammation has resolved ( 12 , 24 ).…”

ACR Appropriateness Criteria® Imaging of Mediastinal Masses

“…CT currently cannot achieve this degree of tissue characterization. MRI has been shown to be slightly superior to CT for surveillance of treated TETs, although if there is insurmountable susceptibility artifact from sternotomy wires despite use of fast spinecho and other MRI techniques, alternating MRI and CT follow-up can be performed [100].…”

Thymic carcinoma vs. lung carcinoma—a radiologist perspective

“…MRI is performed in patients who wish to avoid radiation exposure, are allergic to CT contrast, or have renal dysfunction. MRI is most often utilized to answer specific questions, often involving a cystic component of tumors or extent of local invasion ( 2 ). Routine FDG PET/CT has an overall limited use specifically in the differentiation of thymic carcinoma from lung carcinoma since both tumors are aggressive and metabolically active.…”