Background: A wide spectrum of neoplastic and inflammatory lesions may present as mediastinal masses. The Inflammatory Myofibroblastic Tumor (IMT) is a rare lesion with uncertain etiology and variable biologic behavior. Case Report: A 58-year-old man presented to his primary care physician with right-sided neck swelling. A fine needle aspiration led to the diagnosis of stage I Non-Hodgkin’s lymphoma of the follicular large cell type. Staging work up also revealed a 3 cm triangular superior mediastinal mass located retrosternally, anterior to the aortic arch. The patient underwent three cycles of CHOP chemotherapy with considerable regression of the cervical lymph nodes. On follow-up evaluation, he was fatigued but had no significant physical findings or laboratory abnormalities. Repeat CT scans of the neck, chest, abdomen, and pelvis were done and showed that the superior mediastinal mass had remained unchanged. This mass was fluorodeoxyglucose (FDG) avid on positron emission tomography (PET) but was negative on gallium scan. It was considered non-lymphomatous, so a right thoracoscopic biopsy of the mass was done. Pathologic evaluation revealed spindle cell proliferation. The mass was subsequently resected via a partial median sternotomy and the final pathologic diagnosis was inflammatory myofibroblastic tumor. His lymphoma has remained in remission. Conclusions: The inflammatory myofibroblastic tumor is a rare, but important part of the differential diagnosis of a mediastinal mass. It has both inflammatory and neoplastic features. Complete surgical resection is both diagnostic and therapeutic.

Keywords: Myofibroblastic tumor, inflammatory pseudotumor, Mediastinum