Imaging and Mimics of Fibrosing Mediastinitis

Fibrosing mediastinitis (FM) is a condition characterized by excessive fibrotic reaction in the mediastinum, often leading to bronchial and/or vascular obstruction. FM is commonly due to granulomatous processes like prior histoplasmosis infection or sarcoidosis but may also be caused by other inflammatory processes like IgG4-related disease. Patients most often present with slowly progressive dyspnea, although patients can be asymptomatic or, rarely, acutely dyspneic. Chest CT is the imaging modality of choice; typical imaging findings of infiltrative soft tissue with vascular narrowing in the appropriate clinical setting are often diagnostic. However, the diagnosis of FM is sometimes challenging due to its rarity, and some malignancies masquerade as FM. Familiarity with the spectrum of imaging findings in FM allows radiologists to suggest the diagnosis. This Pictorial Essay describes the typical imaging features, atypical imaging appearances, and mimics of FM.