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Chest Radiographic Findings
Intrathoracic lymphadenopathy is the most common finding in sarcoidosis, occurring in over 85% of patients. The most common pattern is bilateral hilar and right paratracheal adenopathy. Left paratracheal and aorticopulmonary window nodes are also commonly enlarged, but they are less easily identified on PA chest radiographs. Bilateral hilar adenopathy, alone or in combination with mediastinal lymphadenopathy, occurs in 95% of patients with lymph node involvement (3,8,12) (Figure 7).
Unusual patterns of lymph node enlargement occasionally occur. Rarely, the middle mediastinal nodes (paratracheal, subcarinal, aorticopulmonary window, retroazygous) are involved in the absence of hilar adenopathy. Radiographic evidence of anterior mediastinal adenopathy is seen in less than 10% of cases. The posterior mediastinum is least commonly involved. The findings of isolated adenopathy in the anterior or posterior mediastinal compartments should call into question the diagnosis of sarcoidosis. Isolated unilateral hilar adenopathy is an unusual manifestation of sarcoidosis, occurring in only 1% 3% of patients (12,14) (Figure 8).
Patients older than 50 years of age at first presentation may have an atypical pattern of lymph node enlargement. Enlarged mediastinal lymph nodes without hilar adenopathy or unilateral hilar adenopathy occurs more frequently in this older age group (15).
Calcification of affected lymph nodes is related to duration of disease, occurring in 3% of cases after 5 years and in 20% after 10 years. Calcification can be amorphous, punctate, popcornlike, or eggshell (8,12,14) (Figure 9).
Parenchymal disease results from interstitial involvement by the granulomatous process. It may mimic air-space disease. The radiographic appearance of parenchymal disease can be fine nodular (Figure 10); reticulonodular (Figure 11); acinar (poorly marginated, small to large nodules or coalescent opacities) (Figure 12); and, very rarely, focal (solitary nodule or mass). Acinar opacities or interstitial granulomas in sarcoidosis may coalesce to give the appearance of the so-called alveolar form of sarcoidosis and may exhibit air bronchograms (16). The course of parenchymal disease is unpredictable. There are no radiographic criteria to distinguish reversible from irreversible parenchymal changes until irreversible fibrosis has been long-standing (8,12) (Figure 13).
Again, patients first presenting after the age of 50 years have a higher prevalence of solitary and multiple masslike opacities in the lung. They also have a higher prevalence of atelectasis (15).
Cavitation of parenchymal lesions is a rare finding in sarcoidosis, occurring in less than 1% of patients (14). When cavitation develops, secondary infection with mycobacteria or fungi must be ruled out. Cavitary pulmonary nodules, particularly in a peripheral, pleural-based distribution, occur more frequently in necrotizing sarcoid granulomatosis than in classic sarcoidosis. Necrotizing sarcoid granulomatosis is a variant of sarcoidosis that is predominantly an angiitis rather than an alveolitis (17,18,19) (Figure 14).
Involvement of the pleura by the granulomatous process may result in small to moderate effusions. These effusions usually clear radiographically in 2-3 months. Pleural thickening, usually in the lower chest, may result (8,12,14) (Figure 15).
Airway involvement can occur at virtually any location, from the epiglottis to the bronchioles. Tracheal stenosis is a rare finding. The bronchi can be extrinsically compressed by enlarged lymph nodes or obstructed by endobronchial granulomas. Scarring and fibrosis leads to bronchiectasis, stenosis, or frank occlusion (8,12).
CT Findings
Computed tomography (CT) is more sensitive than chest radiography in the detection of adenopathy and subtle parenchymal disease (12,20). Left paratracheal, aorticopulmonary window, and anterior mediastinal nodes are easily demonstrated by CT (8,12) (Figure 16). Early acinar patterns, parenchymal nodules (Figure 17), and nodular consolidation (Figure 18) are also better demonstrated.
High-resolution CT (performed with 1-1.5-mm section thickness and a high spatial frequency reconstruction algorithm) produces fine detail of the anatomic regions affected by the granulomatous process. High-resolution CT findings include areas of ground-glass attenuation (Figure 19), subpleural nodules, perivascular nodules ("beading" of vascular structures), irregular thickening of bronchovascular bundles, and thickening of interlobular septa (Figure 20) (21,22,23,24,25,26). The visualized nodules have irregular margins and correspond to coalescent interstitial granulomas. The foci of ground-glass attenuation may reflect areas of active alveolitis or diffuse microscopic interstitial granulomas that cannot be demonstrated by high-resolution CT. Unfortunately, good radiologic-pathologic correlation of these findings has not been established (27).
The CT findings of fibrosis in stage IV sarcoidosis often have an upper lung zone predominance. These findings include "honeycombing," bullae and cyst formation, and bronchiectasis (Figure 21) (12). High-resolution CT findings of fibrosis include lung distortion with posterior displacement of the main and upper lobe bronchi, abnormal central conglomeration of hilar and perihilar structures, upper lobe conglomerate masses, and traction bronchiectasis. The latter finding is typical of sarcoidosis but can also be seen in silicosis and tuberculosis (27).
As yet, magnetic resonance (MR) imaging has not supplanted CT in the evaluation of thoracic sarcoidosis. In patients with chronic infiltrative lung disease, MR imaging appears equal to CT in the demonstration of areas of air-space opacification but inferior to CT in the assessment of fine lung parenchymal anatomy or demonstration of fibrosis (26,27,28,29).
Gallium-67 Scintigraphic Findings
Accumulation of Ga-67 is a sensitive, but nonspecific, indicator of active inflammation in patients with sarcoidosis. Gallium avidity cannot be used alone to establish a diagnosis of sarcoidosis (30). However, Ga-67 scintigraphy is useful in identifying extrathoracic sites of involvement, detecting active alveolitis, and assessing response to treatment.
Gallium uptake in thoracic lymph nodes, the lungs, and salivary and lacrimal glands is particularly suggestive of sarcoidosis (Figure 22). How well the extent of gallium uptake in the lung correlates with the degree of alveolitis is controversial (31,32). However, Ga-67 scans may be useful as a baseline study at the time of diagnosis: If results of Ga-67 scintigraphy are initially positive, negative findings from a subsequent Ga-67 scan obtained during the course of treatment suggest that alveolitis has resolved. In such a patient, gallium may be a useful marker for disease in activity and response to therapy (3,5,30).
Radiologic Characteristics