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Chest Imaging

Chronic mediastinitis

chronic inflammation of the mediastinum which may progress to diffuse fibrosis. In patients with mediastinal inflammatory nodes, rupture of lymph nodes may induce an inflammatory response that results in mediastinal fibrosis. The causes of chronic mediastinitis are listed in Table 1.

Chronic mediastinitis, Table 1. Causes of chronic mediastinitis and associated diseases.

Granulomatosis processes
Tuberculosis
Histoplasmosis
Coccidioidomycosis
Sarcoidosis
Association with other sites of fibrosis
Retroperitoneal fibrosis
Riedel's thyroiditis
Orbital pseudotumour
Lineous perityphlitis (caecum)
Association with immunological disorders
Systemic lupus erythematosus
Rheumatoid lung disease
Raynaud's phenomenon
Drug-induced
Methysergide

Enlarged mediastinal nodes and adjacent fibrous tissue may compress adjacent mediastinal and hilar structures (chronic hilitis). Patients with chronic mediastinitis are often asymptomatic. The diagnosis is suggested by incidental detection of radiographic abnormalities. When present symptoms express compression of mediastinal vascular structures, trachea, bronchus or oesophagus. Chronic mediastinitis is the most common benign cause of superior vena cava obstruction. The radiographic features vary according to the bulk of the adenopathy and the obstructive phenomena. The chest film may be normal or demonstrate diffuse widening of the mediastinal contours or a localized mass. Calcifications of the mediastinal or hilar lymph nodes may be present, particularly in cases due to histoplasmosis or tuberculosis. Stenosis of the lower trachea or main bronchi may be detectable. Pulmonary oligaemia may be seen in cases of severe obstruction of the pulmonary artery, and pulmonary consolidation or atelectasis in cases of bronchial obstruction. CT is more sensitive in showing the enlarged mediastinal and hilar calcified lymph nodes. It may demonstrate any tracheal or bronchial stenosis, pulmonary or systemic vein compression, collateral venous pathways and any arterial compression (Fig.1). Pulmonary artery or vein compression may result in the presence of pulmonary infarct and bronchial obstruction may result in the presence of obstructive pneumonitis and atelectasis. Barium swallow may show narrowing of the oesophagus and occasionally downhill varices resulting from oesophageal venous collaterals in the case of superior vena cava obstruction. Although the CT findings of chronic mediastinitis are nonspecific the presence of multiple calcifications in the lymph nodes is suggestive of the diagnosis. When calcifications are absent MR imaging may play a major diagnostic role by demonstrating the low signal intensity of mediastinal fibrosis on both T1- and T2-weighted images.

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Fig.1

Post-tuberculous chronic mediastinitis incidentally discovered on a chest radiograph. Unenhanced CT shows the presence of a right hilar mass containing a large calcification (a). This mass obstructs the lumen of the right upper lobar bronchus by extrinsic compression and, as a result, induces an upper lobar atelectasis (b). A small lymph node calcification is also present in the precarinal area. Contrast-enhanced CT (c) shows a stenosis of the superior vena cava with abnormal intense opacification of the azygos vein (collateral venous circulation) and the absence of opacification of the anterior trunk of the right pulmonary artery (compressed by the mass). Bibrachial venography (d) confirms the existence of a stenosis of the distal part of the superior vena cava. (Courtesy of Stephane Lenoir, MD, Paris, France.)
Chronic mediastinitis, Fig.1 (a)
Chronic mediastinitis, Fig.1 (b)
Chronic mediastinitis, Fig.1 (c)
Chronic mediastinitis, Fig.1 (d)