Pulmonary and mediastinal involvement of sarcoidosis is extremely common and is seen in over 90% of patients. Radiographic features are variable depending on the stage of the disease.
For a general discussion, please refer to the parent article: sarcoidosis.
Pulmonary manifestations are present in ~ 90% of patients. Pulmonary sarcoidosis most commonly affects patients between 20 and 40 years of age although it is seen essentially at any age 1. There is a slight female predominance, particularly among African-Americans and it is rare in Asians.
Clinical presentation is variable. Approximately 50% of patients are asymptomatic. The remainder present with either respiratory symptoms (e.g. cough and dyspnoea) or skin changes (e.g. erythema nodosum, lupus pernio, scars, plaques) 3.
Löfgren syndrome is an uncommon but specific acute presentation with a better prognosis.
Respiratory function tests tend to demonstrate a restrictive pattern with reduced lung volumes and reduced diffusion capacity. Obstructive components are usually seen in patients who also smoke, and are primarily attributable to the later 6.
Grossly multiple granulomas are seen in a characteristic lymphatic and perilymphatic distribution. Microscopically the granulomas are typically non-caseating and coalescent. Sarcoid granulomata are distributed mainly along the lymphatics in the bronchovascular sheath and, to a lesser extent, in the interlobular septa and subpleural lung regions. This distribution is one of the most helpful features in recognizing sarcoidosis pathologically and is responsible for the high rate of success in diagnosis by bronchial and transbronchial biopsies 10.
The granulomas may resolve spontaneously or progress to fibrosis.
Chest radiographic appearances are variable and depend on the stage (see: chest radiographic staging of sarcoidosis).
The most common manifestation is bilateral hilar and mediastinal nodal enlargement, which is seen at some stage during the illness in over three-quarters of patients 1,3. Classically the distribution is of bilateral hilar and right paratracheal nodal enlargement, which is known as the 1-2-3 sign or Garland triad. Involvement of right paratracheal nodes is not 'magical' but rather reflects the ease with which these nodes are identified on plain radiography. Left paratracheal and aortopulmonary nodes are also frequently enlarged, but harder to identify 3.
In patients with nodal enlargement, the hilar nodes are almost always involved. It is rare to have middle mediastinal nodal involvement without hilar involvement also. Unilateral hilar enlargement without mediastinal involvement is rare, seen only in 1-3% of cases 3. Anterior and posterior nodal enlargement is uncommon, and almost always seen in combination with mediastinal and hilar involvement 3. Nodes can be very large but typically do not abut the cardiac silhouette, in contrast to lymphoma in which the nodes are continuous with the pericardial outline 1.
In general, atypical patterns of nodal enlargement are more frequently seen in patients who are older than 50 years of age at presentation 3.
Eventual calcification of intrathoracic nodes is seen in 20% of cases after 10 years. The pattern of calcification is variable and includes: punctate; amorphous or eggshell (5%) 1,3.
Parenchymal features are varied depending on the individual patient and the stage of the disease. They include 1-3:
- reticulonodular opacities
- airspace-like opacities (alveolar sarcoidosis)
- usually ill-defined and peripheral
- may appear mass-like:
- more frequent in patients who are older than 50 years of age at presentation
- rarely solitary
- referred by some as sarcoid galaxy sign 4
- actually represent interstitial rather than an intra-alveolar process
- coalescence of multiple ill-defined nodules
- peripheral cavitation: cavitatory pulmonary sarcoidosis 3
- end-stage fibrosis
- occurs in approximately 20% of patients
- permanent coarse linear opacities
- typically radiating laterally from the hilum into the adjacent upper and middle zones
- upward and outward elevation of hila
- distortion of the normal distribution of vessels and fissures
- traction bronchiectasis
- usually small or moderate in size
- usually, resolve within 2-3 months 3
In 25-30% of cases, however, the radiologic findings are nonspecific or atypical, and in 5-10% of patients, the chest radiograph is normal despite the presence of pulmonary granulomas histologically.
Sarcoidosis is often termed the "great mimicker" as there is a vast range of HRCT presentations 7.
CT, and especially HRCT is better able to define parenchymal involvement as well as nodal enlargement and thus is especially useful in patients with normal chest x-rays (stage 0) or those with apparently nodal involvement only (stage I) 3. Features again protean. They vary from patient to patient and according to the stage of involvement.
Parenchymal findings include 1-5:
- irregular nodular thickening in a perilymphatic distribution
- small nodules may dominate and appear similar to miliary opacities 15
- nodules or large opacities measuring 1 to 4 cm in diameter
- confluence of many smaller nodules, thus irregular margins
- seen in 15 to 25% of patients
- may mimic consolidation
- frequently contain air bronchograms
- represent extensive interstitial sarcoid granulomas below the resolution of HRCT rather than alveolitis
- features of small airways disease (due to a granulomatous bronchiolitis) 8,9
- fibrosis (stage IV)
- linear bands of fibrosis
- typically radiate away from hila in all directions
- distortion of lung architecture
- posterior displacement of the upper lobe bronchi, indicating loss of volume in the posterior segments of the upper lobes
- upward and outward retraction of hila
- compensatory hyperinflation of the lower lobes
- traction bronchiectasis
- usually a minor feature and present only in patients with severe fibrosis
- mainly the middle and upper lung zones
- lower lobes predominance resembling UIP is rare
- adjacent to areas of dense fibrosis, likely to represent paracicatricial emphysema 5
- linear bands of fibrosis
Expiratory CT images in patients with sarcoidosis frequently show patchy air trapping at the level of the secondary lobules. The air trapping is presumably secondary to bronchiolar obstruction by submucosal granulomas, and is much more pronounced in patients who are also smokers 6.
Lymphadenopathy is, not surprisingly, better seen on CT, and is present in 80-90% of patients. Distribution tends to be symmetrical with hilar and middle mediastinal involvement. Calcification of hilar and mediastinal lymph nodes is relatively common.
Tracheal or bronchial involvement is only rarely seen, but may result in stenosis 3.
Can show PET avidity. PET-CT may be of value in identification of occult sites and sites suitable for biopsy and for the assessment of inflammatory active sarcoidosis in patients with prolonged symptoms 12.
Gallium-67 scintigraphy usually shows high uptake in active sarcoidosis and is useful for assessing disease activity and response to treatment, although as it is a non-specific marker of inflammation it is non-specific. It has a role also in detecting extra-thoracic involvement (see sarcoidosis) 3.
Treatment and prognosis
Treatment is predominantly with corticosteroids, which are usually administered only to patients with active disease. Unfortunately distinguishing active disease superimposed on chronic fibrotic changes is difficult and criteria are controversial 5.
Pulmonary involvement is responsible for the majority of morbidity and mortality in patients with sarcoidosis. The overall mortality rate is approximately 5%, with patients who present insidiously faring worse than those who present with an acute onset 1,3. Likelihood of resolution depends stage of disease at presentation 3:
- stage I: 60% resolution within 1-2 years
- stage II: 46%
- stage III: 12%
Recognised complications include 3:
- pulmonary fibrosis (stage IV)
- vascular compression
- aspergillomas complicated by haemoptysis
The differential often depends on the stage of disease and particular appearances:
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- systemic manifestations
- pulmonary and mediastinal manifestations (chest x-ray staging)
- cardiac manifestations
- musculoskeletal manifestations
- head and neck manifestations
- central nervous system manifestations
- abdominal manifestations
- cutaneous manifestations