Sarcoidosis is characterised by bilateral, symmetrical hilar and paratracheal lymphadenopathy. Some degree of lymphadenopathy is evident on a chest radiograph in about 70–80% of patients at some time during the course of the condition. Hilar lymph node enlargement ranges from the barely detectable to the massive and gives the hila a lobulated and usually well-demarcated outline. Occasionally hilar lymphadenopathy appears to be asymmetrical or, in 1–5% of cases, may even be strictly unilateral although this is distinctly unusual.
Paratracheal lymphadenopathy may be bilateral or unilateral and in the latter instance is usually right-sided. The most common manifestation of left-sided lymphadenopathy is enlargement of the aortopulmonary window nodes—a common and characteristic feature on the chest radiograph. Other mediastinal nodes (anterior prevascular, posterior and subcarinal) are often not identified as being enlarged on the chest radiograph but on CT are seen to be affected in about half of patients. In 90% of patients with lymphadenopathy, nodal enlargement is maximal on the first radiograph and usually disappears within 6–12 months. Recurrence of lymphadenopathy is exceedingly rare.
The affected lymph nodes may calcify, sometimes in a characteristic eggshell fashion. This latter feature is shared by only a few conditions such as silicosis and histoplasmosis. The calcification is of variable intensity but may be relatively light, and the affected lymph nodes are usually small in volume and evenly distributed throughout the mediastinum and hila (very different from calcified nodes due to tuberculous infection which usually follow a drainage path). About 40% of patients presenting with nodal enlargement will develop parenchymal opacities, usually within a year, and of these about one-third will go on to have persistent (fibrotic) shadowing.
Nodal enlargement does not develop after parenchymal opacities have appeared.
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