Fibrosing mediastinitis (sclerosing mediastinitis) is a chronic inflammatory condition characterized by excessive fibrous tissue proliferation in the mediastinum. Most commonly develops as an exaggerated immune response to histoplasmosis infection (80%+ in USA), less commonly tuberculosis, sarcoidosis, or idiopathic. Fibrous tissue progressively encases and narrows mediastinal structures — airways, pulmonary arteries/veins, superior vena cava (SVC), esophagus. On CT, calcified or non-calcified infiltrative mediastinal soft tissue mass encasing vessels and airways is pathognomonic. Two forms are described: focal (granulomatous, calcified, usually unilateral) and diffuse (fibrous, less calcification, bilateral, more aggressive).
Age Range
25-55
Peak Age
40
Gender
Equal
Prevalence
Rare
Fibrosing mediastinitis most commonly results from an exaggerated immune response to Histoplasma capsulatum infection — granulomatous inflammation in mediastinal lymph nodes transforms into uncontrolled fibrous tissue proliferation. Histoplasma antigens trigger T-cell-mediated delayed-type hypersensitivity reaction; this reaction leads to excessive release of transforming growth factor-beta (TGF-beta) and other profibrotic cytokines. Fibroblasts become activated, collagen production increases, and dense fibrous tissue progressively encases mediastinal structures — pulmonary artery, pulmonary vein, SVC, trachea, main bronchi, and esophagus. Calcification reflects the healing process of prior granulomatous infection: dystrophic calcification develops in the necrotic granuloma center and appears as high-density foci on CT. In the focal form, unilateral calcified mass predominates; in the diffuse form, bilateral widespread fibrous proliferation surrounds vessels and airways. Vascular narrowing can lead to pulmonary hypertension, pulmonary venous obstruction, and SVC syndrome. Airway obstruction causes distal atelectasis and recurrent pneumonia.
On CT angiography, calcified or non-calcified infiltrative mediastinal mass encasing and narrowing pulmonary artery, pulmonary vein, and/or SVC — pathognomonic finding of fibrosing mediastinitis.
Infiltrative soft tissue mass in the mediastinum — ill-defined margins, invasive appearance to surrounding structures. In focal form, unilateral mass with dense calcification; in diffuse form, bilateral widespread fibrous tissue. Calcification is prominent in granulomatous form (80%+), may be absent or minimal in diffuse form.
Report Sentence
An infiltrative, calcified soft tissue mass is observed in the mediastinum, and fibrosing mediastinitis should be primarily considered.
On CT angiography, encasement and narrowing of pulmonary arteries, pulmonary veins, and/or SVC by fibrous tissue. Pulmonary artery narrowing leads to pulmonary hypertension, pulmonary vein narrowing to pulmonary venous obstruction, SVC narrowing to SVC syndrome. Narrowing may be focal or diffuse segmental.
Report Sentence
Encasement of pulmonary artery/vein and/or SVC by fibrous tissue with luminal narrowing is observed on CT angiography, consistent with vascular complication due to fibrosing mediastinitis.
External compression and narrowing of trachea and/or main bronchi by fibrous tissue. Bronchial narrowing may lead to distal atelectasis, air trapping, or obstructive pneumonia. Irregular bronchial wall thickening may be observed.
Report Sentence
Narrowing of the left/right main bronchus by fibrous tissue is noted with atelectasis/consolidation in the distal lung parenchyma.
On MRI, fibrous tissue shows low-to-intermediate T2 signal (mature collagen) — areas of active inflammation may be T2 hyperintense. Calcified areas show signal void on T1 and T2. MRI is complementary to CT in evaluating lumen and wall relationship of vascular structures.
Report Sentence
Mediastinal fibrous tissue shows low-to-intermediate T2 signal on MRI, consistent with chronic fibrotic process; areas of active inflammation were not/were identified.
Collateral vessel formation secondary to vascular obstruction — bronchial artery enlargement, azygos/hemiazygos vein dilation, anterior chest wall venous collaterals. In SVC obstruction, dilation of upper extremity and neck veins with chest wall collaterals is typical.
Report Sentence
Collateral vessel formation secondary to SVC/pulmonary vascular obstruction is observed, consistent with chronic vascular compromise.
FDG uptake is variable on PET-CT: low-to-moderate FDG uptake in areas of active inflammation (SUVmax 2-5), minimal or no uptake in mature fibrous areas. FDG uptake may be more prominent in diffuse form. PET-CT has limited value in differentiating from malignant processes (lymphoma, lung cancer).
Report Sentence
Low-to-moderate FDG uptake is observed in the mediastinal mass on PET-CT, consistent with active inflammatory component.
Criteria
Unilateral, localized, densely calcified mass. Strong association with histoplasmosis. Usually in right parahilar/subcarinal region. Better prognosis.
Distinct Features
Prominent calcification (80%+), unilateral involvement, surgical resection may be possible, vascular complications usually limited to single vessel.
Criteria
Bilateral, widespread, little or no calcification. Idiopathic or autoimmune etiology. More aggressive course, multiple vascular and airway involvement.
Distinct Features
Surgery usually not possible (bilateral widespread), may be associated with IgG4-related disease, may respond to immunosuppressive therapy, higher risk of pulmonary hypertension development.
Criteria
Elevated serum IgG4, IgG4+ plasma cell infiltration on histopathology, storiform fibrosis, obliterative phlebitis. Association with other IgG4-related diseases (autoimmune pancreatitis, retroperitoneal fibrosis).
Distinct Features
May show dramatic response to corticosteroid therapy. Multi-organ involvement should be investigated. Rituximab may be effective as second-line treatment.
Distinguishing Feature
Lymphoma usually presents as discrete lymphadenopathies, calcification is rare before treatment, enhancement is homogeneous. Fibrosing mediastinitis is infiltrative, calcified, shows vascular encasement. B symptoms are common in lymphoma.
Distinguishing Feature
Lung cancer mediastinal invasion is associated with primary pulmonary mass with spiculated margins, pleural retraction. No primary lung lesion in fibrosing mediastinitis. Calcification is rare in lung cancer, frequent in fibrosing mediastinitis.
Distinguishing Feature
Acute mediastinitis is associated with fluid collections, pneumomediastinum, pericardial/pleural effusion, and septic presentation. Fibrosing mediastinitis shows chronic fibrous mass and calcification. Acute mediastinitis is associated with surgical/perforation history.
Distinguishing Feature
Sarcoidosis shows bilateral hilar and mediastinal lymphadenopathy but vascular encasement is rare and mild. In fibrosing mediastinitis, vascular encasement and narrowing are dominant. Lung parenchymal involvement (nodules, ground glass) is more prominent in sarcoidosis.
Urgency
urgentManagement
medicalBiopsy
NeededFollow-up
3-monthTreatment of fibrosing mediastinitis is challenging and requires multidisciplinary approach. In focal form, surgical resection or stenting (vascular/airway) may be considered. In diffuse form, surgery is usually not possible. In IgG4-related cases, corticosteroid + rituximab may be effective. Pulmonary vasodilator therapy is needed for cases developing pulmonary hypertension. Emergency stenting or thrombectomy may be needed for SVC syndrome. Antifungal therapy is added if histoplasmosis infection is active. Biopsy is needed to exclude infectious/malignant processes. Serial CT angiography monitors progression of vascular complications.
Fibrosing mediastinitis has a chronic and progressive course. Treatment is difficult — surgery is generally not feasible. SVC syndrome, pulmonary hypertension, and airway obstruction may develop. Stenting is a palliative treatment option for vascular stenosis. Antifungal therapy is considered in histoplasmosis-endemic areas.