A pictorial review of F-18 FDG PET/CT imaging of fibrosing mediastinitis: An unusual benign mediastinal disease and mimickers

Objectives: Fibrosing mediastinitis (FM) is a rare benign clinical entity, and often difficult to distinguish from malignancy and other benign disease. FM should be kept in mind in the differential diagnosis of mediastinal mass lesions of unknown etiology. Therefore, recognizing the presentations of FM is important in daily clinical practice.

Background: FM is caused by proliferation of acellular collagen and fibrous tissue, which is characterized by excessive fibrotic reaction in the mediastinum and hilar/perihilar regions, and may compromise the airway, the great vessels and other mediastinal structures. There may be two types of fibrosing mediastinitis: focal and diffuse. Positron emission tomography with computed tomography (PET/CT) scan demonstrates increased fluorodeoxyglucose (FDG) uptake at the hilar lesions and mediastinal lymph nodes. Contents: This pictorial essay is to illustrate various representative examples with varieties of F-18 FDG PET/CT findings with different patterns of FM, including focal nodular, diffuse, symmetric patterns, as well as its mimics for differential diagnoses, including lung cancer, lymphoma, sarcoidosis, chronic pulmonary thromboembolism, and so on. FM also demonstrates a wide FDG uptake range which may mimic benign or malignant processes. Pulmonary vascular involvements by FM may result in pulmonary perfusion defects on V/Q scan and V/Q SPECT/CT as well. Presentation of contrast enhancing chest CT in FM is also discussed. Conclusion: It is imperative that the nuclear medicine physician/radiologist be aware of such mimics of malignancy and other benign disease in order to avoid miss diagnosis. Combination of clinical history, diagnostic CT, PET/CT and other nuclear medicine exam such as VQ scan can provide a better imaging interpretation. Selected References: 1.Garrana SH, Buckley JR, Rosado-de-Christenson ML, Martínez-Jiménez S, Muñoz P, Borsa JJ. Multimodality Imaging of Focal and Diffuse Fibrosing Mediastinitis. Radiographics. 2019 May-Jun;39(3):651-667.2.Takalkar, Amol M., MD*†; Bruno, Gabriel L., MD‡; Makanjoula, Akinloye J., MD§; El-Haddad, Ghassan, MD*; Lilien, David L., MD*; Payne, D Keith, MD§ A Potential Role for F-18 FDG PET/CT in Evaluation and Management of Fibrosing Mediastinitis, Clinical Nuclear Medicine: September 2007 - Volume 32 - Issue 9 - p 703-7063.Hu Y, Qiu JX, Liao JP, Zhang H, Jin Z, Wang GF. Clinical Manifestations of Fibrosing Mediastinitis in Chinese Patients. Chin Med J (Engl). 2016;129(22):2697-2702. 4.Onuki T, Ishikawa S, Matsuoka T, Iguchi K, Inagaki M. Dual-phase FDG-PET imaging shows suspected malignancy that histological examination later confirmed as sclerosing mediastinitis: report of a case. Ann Thorac Cardiovasc Surg. 2011;17(3):304-65.Chong, S., Kim, T.S., Kim, BT. et al. Fibrosing mediastinitis mimicking malignancy at CT: negative FDG uptake in integrated FDG PET/CT imaging. Eur Radiol 17, 1644-1646 (2007).