Most cases are idiopathic

May be result of healed infection, such as tuberculosis or toxoplasmosis

May represent end stage of burned-out neoplasms, such as Hodgkin lymphoma or seminoma

May be secondary to autoimmune disorders, sarcoidosis, rheumatic fever, or drugs (e.g., methysergide)

Some cases thought to represent abnormal immune response due to delayed hypersensitivity reaction to infectious agents in susceptible individuals

Mediastinal mass or widening of mediastinum on chest x-ray and CT scan

Can show calcifications on imaging studies

Extensive subcarinal involvement most likely to lead to death due to encroachment of vital structures

Chronic course; may be self-limiting and regress spontaneously or progress to death due to respiratory compromise

Stage I: Edematous fibromyxoid tissue with fibroblastic spindle cells, eosinophils, mast cells, lymphocytes, plasma cells, and thin-walled blood vessels

Stage II: Thick bands of dense collagen haphazardly distributed and containing scattered fibroblastic spindle cells, lymphocytes, and plasma cells

Stage III: Dense acellular collagen with scattered lymphoid follicles and occasional dystrophic calcifications