A Case of Inflammatory Myofibroblastic Tumor (IMT) in Anteriror Mediastinum

Background. Inflammatory myofibroblastic tumors (IMTs) rarely occur in the anterior mediastinum. Case. The patient is a woman in her 60s. On a chest radiograph during a medical check-up, a protrusion was observed in the right first arch. Chest enhanced CT showed a well-defined mass with a long diameter of 74 mm on the right side of the anterior mediastinum. The mass was in close contact with the ascending aorta and was suspected to involve the epicardium. Fat-suppressed T2WI of MRI showed that the mass had heterogeneous high and low signal intensity. FDG-PET/CT showed FDG accumulation (SUVmax: 5.46) predominantly in the central part of the mass. An invasive thymoma (stage III) was suspected and resection of the mediastinal tumor was performed through midline sternotomy. The procedure was combined with pericardial resection and right transverse nerve resection. Histopathologically, spindle-shaped cells were sparsely distributed against a background of inflammatory cell infiltration and histiocytes. Immunostaining was positive for α-SMA. Based on the above, IMT was diagnosed. Conclusion. The possibility of a low-activity IMT should be considered when we find an anterior mediastinal mass with heterogeneous high and low signal intensity on fat-suppressed T2WI of MRI, with poor FDG accumulation.