Fibrosing Mediastinitis Up-to-Date

Fibrosing mediastinitis, also known as sclerosing mediastinitis or mediastinal fibrosis, is a disorder characterized by an excessive fibrotic reaction in the mediastinum which can result in compromise of airways, great vessels, and other mediastinal structures [1]. The condition usually is a sequel of histoplasmosis, and its morbidity is directly related to the location and extent of fibrosis within the mediastinum. The IDSA practice guidelines for the management of patients with histoplasmosis, as well as other IDSA guidelines, can be accessed through the Infectious Diseases Society of America's website [2].

The clinical issues related to fibrosing mediastinitis will be reviewed here. General issues regarding the presentation and treatment of pulmonary histoplasmosis are discussed separately. (See "Pathogenesis and clinical features of pulmonary histoplasmosis" and "Diagnosis and treatment of pulmonary histoplasmosis".)

ETIOLOGY

Fibrosing mediastinitis results from an excessive host response to a prior infectious process which has involved the mediastinal lymph nodes. The most common precipitating factor is infection with Histoplasma capsulatum, a dimorphic fungus that is found commonly in the southeastern, mid-Atlantic, and central United States.

Infection with H. capsulatum is subclinical in the vast majority of patients. It begins as a pulmonary process and typically disseminates to mediastinal lymph nodes and other reticuloendothelial organs before specific cell-mediated immunity develops and contains the fungus. Depending upon the inoculum and the extent of host response, the involved mediastinal lymph nodes can enlarge and coalesce into an inflamed caseous mass referred to as a mediastinal granuloma, or less commonly can lead to a sclerosing process called fibrosing mediastinitis. (See "Pathogenesis and clinical features of pulmonary histoplasmosis".)

It is unclear why a minority of patients infected with H. capsulatum proceed to develop fibrosing mediastinitis, but genetic influences on the immune response may play a role. As an example, one case-control study involving 19 consecutive patients with fibrosing mediastinitis and 21,086 cadaveric kidney donors serving as controls found that the relative risk of fibrosing mediastinitis was 3.3 among persons with the HLA-A2 antigen [3]. (See "Human leukocyte antigens (HLA): A roadmap".)