For patients with thoracic sarcoidosis, when chest radiographic imaging results are correlated with the clinical findings, chest radiography may be the only imaging required. Approximately 60-70% of patients with sarcoidosis have characteristic radiologic findings. In 25-30% of patients, the radiologic changes are nonspecific or atypical, and in 5-10% of patients, the chest radiograph is normal. CT is more sensitive than chest radiography in the detection of mediastinal lymphadenopathy, and high-resolution CT (HRCT) shows subtle parenchymal lung disease with advantage. Left paratracheal, aortopulmonary window, and anterior mediastinal nodes are more readily demonstrated with CT.
Sarcoidosis is a multisystemic granulomatous disease of unknown etiology with variable presentation, prognosis, and progression (see the images below). Caesar Boeck first coined the term sarcoid in 1899 to describe one of the skin lesions of sarcoidosis because of its histologic resemblance to a sarcoma. In 1905, Boeck described a series of patients with sarcoid who presented with cough and nasal granulomas. These findings suggested the systemic nature of the disease. In 1915, Kusnitski and Bittorf described chest radiographic abnormalities in a patient with sarcoidosis.
Sarcoidosis, thoracic. Crops of numerous papules on the back of 33-year-old woman. Some papules have become confluent. Note that the skin in between the papules is of normal color. These lesions are usually associated with a good prognosis in sarcoidosis. Note also the scar sarcoid. Scars become infiltrated and purple, resembling keloids. These occur in active disease.
Sarcoidosis, thoracic. Close-up view of the previous image.
Sarcoidosis, thoracic. Lupus pernio affects poorly perfused areas, such as the nose, ear lobes, and fingers. These areas become swollen and indurated, with deep purplish red. The lesions are often associated bone cysts due to sarcoid granulomas, and the nasal bones may be eroded. In this 38-year-old woman, the lesions affect the periorbital areas and the nose. The fingers were also affected (not shown).
Sarcoidosis almost always affects the respiratory system. Most patients present with the classic combination of bilateral hilar lymphadenopathy, parenchymal disease of the lung, and eye or skin lesions; however, virtually any organ in the body may be involved. At diagnosis, about 50% of patients are asymptomatic, 25% complain of cough or dyspnea, and 25% have or develop eye symptoms or skin lesions (eg, such as erythema nodosum, lupus pernio, plaques or scars). When present, constitutional symptoms include weight loss, fatigue, weakness, and malaise. Symptoms of pulmonary involvement, such as dry cough and shortness of breath, develop in 20-30% of patients.
In general, sarcoidosis is a self-limiting subclinical process in 60-70% of cases. About 20-30% of patients are left with a variable degree of permanent lung damage. In 10-15% of the patients, sarcoidosis can become chronic. The incidence of ocular involvement is about 20-30%.
Bilateral hilar lymphadenopathy is the most common radiographic finding. Other radiographic findings include interstitial lung disease; occasional calcification of affected lymph nodes; and rarely, pleural effusions and thickening.
Because the disease so often involves thoracic structures, chest radiography plays a crucial role in the diagnosis, staging, and follow-up of sarcoidosis. The diagnosis is established when the clinical and radiographic findings are supported by histologic evidence of widespread noncaseating epithelioid cell granulomas in more than 1 organ or a positive Kveim-Stiltzbach skin test result (see the images below).
Sarcoidosis, thoracic. Series of histologic slides (see the next 2 images) from a patient with sarcoidosis show characteristic noncaseating granulomas with many giant cells. Courtesy of Sat Sharma, MD, FRCPC, FCCP, DABSM.
Sarcoidosis, thoracic. Series of histologic slides (see the previous image and the next image) from a patient with sarcoidosis show characteristic noncaseating granulomas with many giant cells. Courtesy of Sat Sharma, MD, FRCPC, FCCP, DABSM.
Sarcoidosis, thoracic. Series of histologic slides (see the previous 2 images) from a patient with sarcoidosis show characteristic noncaseating granulomas with many giant cells. Courtesy of Sat Sharma, MD, FRCPC, FCCP, DABSM.
Sarcoidosis, thoracic. Stage I disease. Standard posteroanterior chest radiograph in a 28-year-old man shows extensive bilateral hilar and mediastinal lymph node enlargement not associated with a pulmonary abnormality.
Sarcoidosis, thoracic. High-resolution CT scan in a young patient shows uniformly small, bilateral nodules in a miliary pattern. The patient also had mediastinal and hilar adenopathy. This is stage II disease.
Sarcoidosis, thoracic. Gallium-67 scans in a patient who had a normal chest radiograph. Study shows increased uptake in the lung fields, higher than the background activity. The appearances are compatible with pneumonitis secondary to sarcoidosis.
The clinical staging of sarcoidosis is based on the pattern of chest radiographic findings:
Stage 0 is a normal chest radiograph
Stage I is lymphadenopathy only
Stage II is lymphadenopathy and lung parenchymal disease
Stage III is parenchymal lung disease only
Stage IV is pulmonary fibrosis
At presentation, approximately 5-10% of patients have stage 0 disease; 50%, stage I; 25-30%, stage II; and 15%, stage III. Although most cases of sarcoidosis either regress or remain stable, 10-15% progress to pulmonary fibrosis. Generally, pulmonary function worsens with an increasing stage of disease, but radiologic staging does not correlate well with the severity of pulmonary function abnormalities. Often, the radiographic abnormalities appear worse than the degree of functional impairment actually present.
When chest radiographic results are correlated with the clinical findings, chest radiography may be the only imaging required.
Routine chest CT scanning is not usually indicated and adds little to patient care.
Approximately 60-70% of patients with sarcoidosis have characteristic radiologic findings. In 25-30% of patients, the radiologic changes are nonspecific or atypical, and in 5-10% of patients, the chest radiograph is normal. Thus, approximately 30-40% of patients can benefit from a CT scan. CT is more sensitive than radiography in the detection of lymphadenopathy and subtle parenchymal disease. High-resolution CT (HRCT) is useful in differentiating active disease from fibrosis. HRCT results are well correlated with the yield of biopsy.
The accumulation of gallium-67 (67Ga) is a sensitive but nonspecific indicator of active inflammation in patients with sarcoidosis. Gallium-67 avidity alone cannot be used to establish a diagnosis of sarcoidosis, and this finding has a limited correlation with the patient’s clinical status. However, 67Ga scintigraphy is useful in identifying extrathoracic sites of involvement, in detecting active alveolitis, and in assessing response to treatment.
Gallium-67 scans have low sensitivity and specificity as a diagnostic test; therefore, they are used infrequently. Gallium-67 scanning is useful in patients in whom the clinical picture remains confusing despite the presence of noncaseating granulomas in biopsy specimens, and it may be useful in differentiating chronic hypersensitivity pneumonitis from sarcoidosis.
No large imaging studies are available to assess sarcoid cardiac involvement. Some have suggested a combined use of67 Ga and thallium scans. However, the number of studies that have reported on this technique have been small and subject to significant bias. Moreover, because of patchy sarcoid cardiac involvement, endomyocardial biopsy, which is regarded as a standard technique in the diagnosis, is subject to sampling error.
Mycetomas may occur in more than 50% of patients with stage IV sarcoidosis and apical bullous disease. Although mycetomas may be clinically silent, hemoptysis is common. Life-threatening hemoptysis may be managed with the angiographic localization of bleeding and concurrent bronchial artery embolization in a minority of patients. Bronchial necrosis is more frequently encountered when absolute alcohol is used for embolization. The diagnosis is most confidently established when the clinicoradiologic findings are supported by histologic evidence of widespread noncaseating granulomas.
Limitations of techniques
The limitation of all techniques is the nonspecificity of most methods of diagnostic imaging. A chest radiograph can be normal in biopsy-proven sarcoidosis. A false-positive diagnosis may occur with a variety of granulomatous diseases. Problems may also arise with the biopsy material.
CT is expensive both in terms of money and the radiation burden. Gallium-67 scanning is also limited by nonspecificity, and the scans may show normal uptake in established disease. Gallium-67 scanning is also time-consuming and expensive.
Okada et al concluded that a chest radiograph and serum angiotensin-converting enzyme (ACE) levels sufficiently reflect disease activity and that, at present, routine evaluation with 67Ga scanning and bronchoalveolar lavage is not necessarily indicated in the long-term management of patients with pulmonary sarcoidosis. The authors performed a correlative analysis of longitudinal changes in bronchoalveolar lavage,67 Ga scanning, serum ACE activity, chest radiographic findings, and PFT results in pulmonary sarcoidosis.
The investigators found that, in terms of the usefulness for estimating disease activity, differences in the 4 indicators were negligible.