Lymphadenopathy, mediastinal

Infections consist predominantly of tuberculosis and fungal infection pulmonary, particularly histoplasmosis and coccidioidomycosis. More rarely, lymphadenopathy may be seen in viral pneumonia and mycoplasma pneumonia infection. The neoplastic causes include lymphoma, leukaemia, metastatic carcinoma from lung cancer, cancer of the oesophagus and breast cancer. Among the extrathoracic primary tumours, kidney, testis, head and neck neoplasms are the most likely origins. Hilar and mediastinal lymphadenopathy may also be observed in Castlemans disease, amyloidosis thoracic, angioimmunoblastic lymphadenopathy, chronic berylliosis, Wegeners granulomatosis chest, cystic fibrosis and chronic mediastinitis. Sarcoidosis is a highly frequent cause of intrathoracic lymphadenopathy, particularly in young adults.

Chest radiographs and CT scanning have become the standard techniques for demonstration of intrathoracic lymphadenopathy.

Chest radiograph

On the chest radiograph, the ease with which lymph node enlargement can be recognized depends on the particular location (see lymph node classification chest). Enlargement of the right upper paratracheal nodes causes uniform or lobular widening of the right paratracheal stripe, and an increase in density of the superior vena cava of which the border may become convex to the lung. The enlarged right lower paratracheal nodes push the azygos vein laterally increasing the diameter of the combined opacities of both node and azygos arch (Fig.1). The aortopulmonary nodes may cause a bulge in the angle between the aortic arch and the main pulmonary artery. If they are substantially enlarged, the left upper paratracheal nodes induce mediastinal widening. The radiographic features of subcarinal node enlargement include the displacement of the azygo-oesophageal line that becomes convex to the lung, an increased opacity of the subcarinal space on the posteroanterior film and a lack of visibility of the external surface of the medial wall of the intermediate bronchus. Enlargement of the anterior mediastinal nodes may be substantial to be visible on the chest films. In such case, mediastinal widening is frequently bilateral and lobulated in outline. Increased opacity of the retrosternal area on the lateral view may be sometimes the early sign. Enlarged paraoesophageal and posterior mediastinal nodes produce displacement of the azygo-oesophageal and paraspinal lines. The radiographic signs of enlargement of hilar lymph nodes are hilar enlargement, lobulation of outline or rounded mass in a portion of the hilum (Fig.2).

CT

Lymph node enlargement is defined on the basis of a short-axis node diameter exceeding 1 cm. The assessment of lymph node size or node masses.

The first pattern may be seen in association with all causes of lymphadenopathy whereas coalescence of enlarged nodes suggests infections, granulomatous disease and neoplasm. Diffuse mediastinal involvement is more typical of lymphoma, large cell undifferentiated carcinoma and acute or chronic mediastinitis. CT can also be used to define the density of lymph nodes. Enlarged nodes may be calcified (see calcification mediastinal lymph node), or low in density and necrotic in appearance or can enhance following intravenous injection of contrast media. Low attenuation lymph nodes after administration of contrast media, with or without rim enhancement typically reflect the presence of necrosis (Fig.3). This finding is commonly seen in patients with tuberculosis (see tuberculous lymphadenopathy), fungal infection pulmonary, metastatic carcinoma and lymphoma. Postcontrast enhancement of enlarged hilar and mediastinal lymph nodes may suggest Castlemans disease, angioimmunoblastic lymphadenopathy, vascular metastases in particular from renal cell carcinoma, papillary thyroid carcinoma, and small cell carcinoma. The feature of enhancement has also been reported in Sarcoidosis, and tuberculous lymphadenopathy.

The CT appearance, as well as the associated features may help determine the cause of lymphadenopathy. In many circumstances, however, biopsy is required to establish the specific diagnosis.

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