Fibrosing mediastinitis

Fibrosing mediastinitis (FM) is a rare non malignant acellular collagen and fibrous tissue proliferative condition occurring within the mediastinum. On imaging, the condition can sometimes mimic malignancy.

Epidemiology

Although it can potentially present at any age, it typically presents in young adults.

Clinical presentation

Affected patients usually present with signs and symptoms of obstruction or compression of the superior vena cava, pulmonary veins or arteries, central airways, or oesophagus.

Pathology

It is characterized by chronic inflammation and excessive fibrosis of mediastinal soft tissues. This  may lead to compression and sometimes occlusion of mediastinal structures. 

There are two main pathological types:

• focal: commoner ~80% ^5-6
• diffuse: ~20%

Causes

• idiopathic: most cases ¹²
• Histoplasma capsulatum infection (histoplasmosis): common in the United States and often gives a localised pattern ⁸
• Mycobacterium tuberculosis infection (pulmonary tuberculosis) ⁵
• concurrent intra-thoracic malignancy ⁵
• sarcoidosis
• radiation therapy
• drugs, e.g. methylsergide therapy ⁸

Associations

• Reidel thyroiditis
• retroperitoneal fibrosis
• Behcet disease (rare) ^10-11
• other autoimmune conditions:
  • rheumatoid arthritis (RA) ⁷
  • systemic lupus erythematosus (SLE) ⁷

Radiographic features

Plain film

Can be subtle and may be seen as non-specific widening of the mediastinum. There can be distortion and obliteration of normally recognizable mediastinal interfaces or lines. Other accompanying features include:

• calcification (mediastinal and/or hilar) ~85% (commoner in localised type) ³

CT/HRCT chest

Exact appearenceappearance can be variable and dependantdependent on the pattern of involvement. Typically affects the middle mediastinum and may show:

• mediastinal or hilar mass: especially in localised disease
• infiltrative region of soft-tissue attenuation which obliterates normal mediastinal fat planes and encases or invades adjacent structures: diffuse form

Other findings include:

• calcifications of the central mass or associated lymph nodes : especially if there has been preceding histoplasmosis
• tracheo-bronchialtracheobronchial narrowing ^2,4
• pulmonary infiltrates ²

MRI

Pattern of involvement is essentially similar to CT. Signal characteristics include:

• T1: typically heterogenousheterogeneous but overall iso signal to muscle 
• T2: variable with both high ³ and low ^2-3 signal within the same lesion
• T1 C+ (Gd): may show heterogenous enhancement

Complications

• superior vena caval (SVC) compression/obstruction/thrombosis
• pulmonary hypertension
• oesophageal compression

Treatment and prognosis

Fibrosing mediastinitis can have an unpredictable course, with both spontaneous remission or exacerbation of symptoms being reported.

It usually tends to be slowly progressive. There are three possible avenues for treatment: systemic antifungal or corticosteroid treatment, surgical resection, and local therapy for complications.

Surgical resection of affected region could be considered with localised disease. Some patients with the diffuse pattern show radiographic evidence of improvement with steroid therapy.

See also

• pulmonary hyalinising granuloma