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Staging pulmonary sarcoidosis has been performed using the chest radiograph Scadding criteria for more than 50 years.
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High-resolution computed tomography (HRCT) is an essential diagnostic modality in diagnosing sarcoidosis.
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Pulmonary sarcoidosis is notorious for mimicking many other interstitial lung diseases.
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Fluorodeoxyglucose F 18 (FDG) PET/computed tomography (CT) is able to image active sarcoidosis in mediastinal and hilar lymph nodes, lung parenchyma, and myocardium.
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FDG PET/CT can be used to
Chest Imaging
Section snippets
Key points
Radiographic scoring systems: Scadding staging
Sarcoidosis is commonly staged according to its appearance on the chest radiograph following the Scadding criteria (Table 1).4 Stage 0 indicates no visible intrathoracic findings. Stage I represents bilateral hilar lymphadenopathy, which may be accompanied by paratracheal lymphadenopathy. Stage II represents bilateral hilar lymphadenopathy accompanied by parenchymal infiltration. Stage III represents parenchymal infiltration without hilar lymphadenopathy. Stage IV consists of advanced fibrosis
Large airway involvement
Sarcoidosis of the upper respiratory tract may involve the nose, sinuses, larynx, oral cavity, ear, trachea, and bronchi.12, 13 The incidence of sarcoidosis of the upper respiratory tract is approximately 5%.14 During bronchoscopy, common lesions in the trachea as well as in the bronchi are erythema, thickening of the mucosa, and a cobblestone appearance (Fig. 1), which yields a high number of granulomas on biopsy. A small study by Shorr and colleagues15 showed that 71% of sarcoidosis patients
Mediastinal and hilar lymphadenopathy
Lymphadenopathy is the most common intrathoracic manifestation of sarcoidosis, occurring in approximately 80% of patients during their illness, irrespective of radiographic staging.17, 18, 19, 20, 21, 22, 23 An overview of common and uncommon sites of thoracic lymphadenopathy in sarcoidosis is given in Box 1. In most cases, bilateral hilar lymphadenopathy is present (Fig. 2), with unilateral hilar adenopathy occurring in only 3% to 5% of patients.17, 24, 25 When present, unilateral hilar
Parenchymal involvement
The HRCT appearance of pulmonary sarcoidosis has a great variability and is notorious for mimicking many other interstitial lung diseases. The most important 2 radiological patterns in sarcoidosis with involvement of the lung parenchyma are the nodular pattern and the reticulonodular pattern. The distribution of nodules on HRCT can follow 3 different patterns: random distribution, centrilobular distribution, and perilymphatic distribution.
Mycetomas
The formation of mycetomas occurs in approximately 2% of sarcoidosis patients, especially in stage IV cystic disease.57 Fungal balls can develop in preexisting bullae or cysts that are colonized by fungi, usually Aspergillus species. The characteristic appearance of a pulmonary aspergilloma consists of a mobile opacity occupying part or most of the cavity. It is surrounded by a peripheral rim of air known as the air crescent sign or Monod sign (Fig. 10).58 A common symptom in patients with
Pleural Effusion
In sarcoidosis, granulomas can be found on both visceral and parietal pleura. This pleural localization as well as blockage of lymphatic channels by granulomas can result in pleural effusion. Pleural effusion, however, is an uncommon manifestation of sarcoidosis with an estimated incidence of 0.7% to 10% on chest radiograph.59, 60, 61, 62, 63, 64 In a more recent study, the occurrence of pleural effusion was studied with ultrasonography in 181 patients with sarcoidosis presenting at the
Necrotizing sarcoid granulomatosis
Necrotizing Sarcoid Granulomatosis (NSG) is a rare entity and seen as a variant of sarcoidosis with, however, some uncertainty.74 It is debated whether NSG is a manifestation of systemic sarcoidosis with necrotizing granulomata or a form of necrotizing angiitis with a sarcoid-like reaction.75 NSG is defined by a granulomatous vasculitis, confluent non-necrotizing granulomas, and foci of infarct-like necrosis with variable degrees of fibrosis.74, 76 Since the first article describing NSG in
Pulmonary hypertension
It is estimated that 1% to 6% of patients with sarcoidosis have pulmonary hypertension, most patients having advanced stages on chest radiography (Scadding stages III and IV).80, 81 Fibrosis or extensive parenchymal abnormalities are not always present, however, and the absence should not exclude further evaluation for pulmonary hypertension.82 Clinical characteristics are often atypical but some symptoms can suggest underlying pulmonary hypertension: dyspnea more severe compared with
Fluorodeoxyglucose F 18 Uptake in Sarcoidosis
FDG PET/CT is widely used in oncology. FDG is a glucose analogue that is transported through the cell membrane. Once in the cytosol, FDG is phosphorylated by hexokinase and metabolically trapped as FDG-6-phosphate. After annihilation, 2 gamma photons of 511 keV each are detected by the PET camera. The current resolution of PET cameras is up to 5 mm. FDG is a well-studied and practical tracer with various applications in medicine, without the need for an onsite cyclotron.
In sarcoidosis, the
Chest radiograph and fluorodeoxyglucose F 18 PET/computed tomography
Chest radiography is commonly performed at the initial presentation of sarcoidosis. It is cheap and widely available and in 85% to 95% of patients abnormal findings are present.95
Staging of pulmonary disease is based on the Scadding criteria for chest radiography. It describes the presence of bilateral hilar adenopathy, parenchymal involvement, and signs of fibrosis.4, 96, 97 Although the staging system provides prognostic information, differentiating between active inflammation, fibrosis, and
High-resolution computed tomography and fluorodeoxyglucose F 18 PET/computed tomography
HRCT is able to assess the lung parenchyma meticulously due to its high spatial resolution. It is, therefore, superior to conventional radiography in detecting parenchymal distortion, nodules, and early fibrosis. Volumetric scanning with multidetector CT scans has become routine in most institutions and enables imaging of the whole lung in 1 single breath-hold.98 It has become a powerful technique in the diagnosis of diffuse parenchymal lung disease. Compared with conventional chest
Summary
Pulmonary sarcoidosis has a great variability and is notorious for mimicking many other interstitial lung diseases. Knowledge of pulmonary manifestations is important in diagnosing sarcoidosis because more than 90% of patients present with thoracic involvement. Both HRCT and FDG PET/CT are essential modalities in diagnosing and evaluation of pulmonary sarcoidosis. In addition, FDG PET/CT demonstrates extra pulmonary disease most accurate and has an important role in cardiac sarcoidosis.
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Disclosures: None.