Mediastinitis is defined as acute or chronic inflammation of the mediastinal structures.^{1,2,3,4,5,6,7} Two broad categories of acute mediastinitis are acute necrotizing mediastinitis and poststernotomy mediastinitis.⁸ Chronic mediastinitis has been arbitrarily subdivided into two categories: (1) granulomatous mediastinitis and (2) fibrosing or sclerosing mediastinitis.⁸

Poststernotomy mediastinitis has an incidence of 0.4% to 5% and a mortality of 16.5% to 47%.¹ The most frequent pathogen is Staphylococcus aureus.¹ Esophageal perforation, usually iatrogenic, is the second most frequent cause of acute mediastinitis, produced by common oropharyngeal flora, with a mortality rate of 20% to 60%, depending on the time of diagnosis.¹ The third most frequent cause is descending necrotizing mediastinitis, the origin being an oral caries in 60% and betahemolytic streptococcus the causative agent in 71.5% of cases.¹

Fibrosing (sclerosing) mediastinitis is a rare disorder characterized by the invasive proliferation of fibrous tissue within the mediastinum.^2,4,9,10 Many (and perhaps most) cases in the United States are thought to be caused by an abnormal immunologic response to Histoplasma capsulatum infection.^3,11,12 Additional infectious triggers implicated in the pathogenesis of fibrosing (sclerosing) mediastinitis include other fungal and mycobacterial organisms associated with granulomatous mediastinitis.^5,6

Fibrosing (sclerosing) mediastinitis may be associated sarcoidosis,¹³ rheumatoid arthritis,¹³ radiotherapy for Hodgkin disease,¹³ and mast cell activation disease.¹¹ Finally, there are rare immune-mediated (idiopathic) and drug-induced (e.g., methysergide) cases of fibrosing (sclerosing) mediastinitis.⁶ There is overlap between IgG4-related disease and fibrosing mediastinitis, both clinically and histologically.⁶ Interestingly, patients with idiopathic immune-mediated fibrosing (sclerosing) mediastinitis frequently have other disease manifestations such as retroperitoneal fibrosis or Riedel thyroiditis, all of which have been associated with the IgG4-related disease spectrum.⁶