British Journal of Radiology 74 (2001),859-861 © 2001 The British Institute of Radiology
Silicosis-induced pulmonary artery stenosis: demonstration by MR angiography and perfusion MRI
A H Mahnken, MD
1
C Breuer, MD
2 and
P Haage, MD
1
Departments of 1Diagnostic Radiology and 2Internal Medicine, University of Technology Aachen, Aachen, Germany
Correspondence: Andreas H Mahnken, MD, Department of Diagnostic Radiology, University Hospital, University of Technology Aachen, Pauwelsstraße 30, 52074 Aachen, Germany
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Abstract
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Silicosis is a common occupational disease. We present a 64-year-old male patient suffering from symptomatic silicosis due to compression of the pulmonary arteries by enlarged hilar lymph nodes. Clinical symptoms and diagnostic imaging modalities are described, with emphasis on cross-sectional imaging. MR angiography and perfusion MRI of the lung in silicosis are described, and their diagnostic value in pneumoconiosis is discussed.
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Introduction
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Pneumoconiosis typically causes chronic lung disease, with silicosis being the most common type. Characteristic lung changes in silicosis are interstitial nodules ranging from a few millimeters to large confluent masses. Enlargement of the hilar lymph nodes and emphysema are frequently seen. Exclusive hilar silicosis is rare. A complicated form of silicosis is progressive massive fibrosis. Silicosis is usually first diagnosed by chest radiography. CT, especially high resolution CT (HRCT), and scintigraphy are well established imaging modalities in the diagnosis and follow-up of silicosis. The imaging characteristics and the value of MRI in silicosis [1, 2] have been reported. Ventilation and perfusion MRI are the most recent as yet established developments in pulmonary imaging. We present a patient suffering from hilar accentuated silicosis. Utilization of MRangiography (MRA) and perfusion MRI are described.
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Case report
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A 64-year-old male patient was admitted with progressive exercise-induced dyspnoea. The patient had a 31-year history of silicosis due to his prior occupation as a coal miner. Pulmonary artery hypertension was known for 14 years. An exploratory thoracotomy 10 years previously included a lung biopsy and had been performed to confirm the diagnosis of silicosis. Surgery showed multiple indurated hilar lymph nodes surrounding the pulmonary arteries. Macroscopically, the lung showed only minor anthracotic changes. The biopsy specimen verified the diagnosis of silicosis.
Physical examination and blood tests on admission were unremarkable. The electrocardiogram showed an incomplete right bundle branch block. Ergometry had to be discontinued due to dyspnoea and excessive increase of systolic arterial blood pressure. Cardiac failure was ruled out by echocardiography. On catheter examination, the mean pulmonary artery pressure was 43 mmHg with a markedly elevated arterial resistance of 381.1 dyn.s.cm-5. A pressure gradient of 8 mmHg was measured in the right pulmonary artery. Emphysematous lungs with a disseminated nodular pattern and apical pleural fibrosis were depicted on chest radiography (Figure 1
). The hila were enlarged. CT, performed to exclude a hilar tumour, demonstrated multiple, partly calcified hilar lymph nodes on both sides (Figure 2). These lymph nodes led to compression of the central pulmonary arteries, especially the lower left and the upper right pulmonary artery. MRA demonstrated severe obstruction of the lower left pulmonary artery and less severe obstruction of the right pulmonary artery without signs of pre- or post-stenotic dilatation (Figure 3a). Perfusion MRI showed delayed perfusion of the left inferior and right superior lobe of the lung, correlating with obstruction of the corresponding pulmonary arteries, but no persistent perfusion deficits were depicted (Figure 3b). Comparable findings were seen on perfusion scintigraphy obtained 14 years earlier. The patient received therapy with acetylcysteine (single 600 mg dose in the morning). On discharge he was in good condition and the initial symptoms had slightly regressed.
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Figure 1. Chest radiograph shows small irregular opacities with a reticulonodular pattern as well as bilateral hilar lymphandenopathy. Post-operative changes from diagnostic thoracotomy 10 years previously are visible in the lower zone of the left lung.
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Figure 2. (a) Contrast enhanced CT demonstrates partly calcified lymph nodes at the right hilum (arrows), close to the upper right pulmonary artery. (b) CT also shows enlarged calcified left hilar lymph nodes (arrows).
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Figure 3. Maximum intensity projection reconstructions of 3D MR angiography (TR 3.7, TE 1.1, flip angle 40°) clearly depict stenosis of the lower left (arrow) and upper right (curved arrow) pulmonary artery, as well as a minor stenosis of the proximal lower right pulmonary artery (arrowhead). The locations of the stenoses correlate with the calcified hilar lymph nodes shown on CT. (b) Dynamic perfusion MR images (TR 2.5, TE 0.7) of the lung show a perfusion deficit of the upper zones of the right lung and the lower zones of the left lung (left-hand image). After 8 s the perfusion deficit is evened out (right-hand image). This finding results from the pulmonary artery stenoses.
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Discussion
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The main problem in silicosis is impaired lung function owing to structural changes of the lung parenchyma, which may lead to dyspnoea. These changes usually lead to pulmonary arterial hypertension and consequent right heart insufficiency. The long-term prognosis of silicosis is therefore determined by two important risk factors: forced expiratory volume and pulmonary artery pressure [3]. Pulmonary hypertension in this patient was not due to his minor structural lung changes but to pulmonary artery obstruction caused by hilar lymphadenopathy. To the best of our knowledge, symptomatic silicosis due to enlarged hilar lymph nodes has not previously been described. Hilar lymphadenopathy as a single finding in silicosis has been described previously, but these changes had not caused clinical symptoms [4].
Silicosis is typically diagnosed by chest radiography, patient history and functional parameters including spirometry. Further useful imaging tools are CT, ventilation and perfusion scintigraphy, single photon emission computed tomography and most recently MRI. It is a well known fact that the radiographic degree of silicosis according to the International Labour Office classification does not necessarily correlate with the impairment of lung function. Further information is provided by HRCT of the lung, which detects changes of the lung parenchyma more sensitively than plain chest radiography [5]. HRCT also offers a better correlation between imaging and histological findings than plain chest radiographs [6]. Lung scintigraphy is another diagnostic approach. This technique allows assessment of lung ventilation and perfusion. Nevertheless, discrepancies between scintigraphy, chest radiography and functional parameters are a known problem [7].
MRI is the most recent diagnostic approach to the imaging of the lung. Its suitability in silicosis has been shown in previous studies [1, 2]. MRI is capable of depicting alveolitis as well as fibrotic tissue [8]. Compared with CT, MRI has some disadvantages at present. Its anatomical resolution is lower [9] and MRI is not yet capable ofadequately demonstrating emphysematous changes, which are common in silicosis. Conversely, MRI offers some very important advantages compared with other imaging modalities. The patient is not exposed to irradiation. MRI allows differentiation between silicotic and neoplastic changes because the signal intensities of neoplastic and fibrotic tissue differ [10].
The newly developed ventilation imaging tools are still to be evaluated on a broader clinical scale, but they have a similar potential as ventilation scintigraphy. Perfusion MRI allows evaluation of peripheral lung perfusion in a similar way as perfusion scintigraphy [11]. Combined with MRA of the pulmonary arteries, a detailed assessment of the degree of disease is possible. In the patient presented here, good correlation between perfusion MRI and scintigraphy was seen. MRA not only depicted stenosis of the right pulmonary artery with the known pressure gradient but also showed a significant stenosis of the left lower lobe artery that was not assessed by catheterization. Further development of pulmonary MRI holds the promise of obtaining and illustrating the same information as CT, scintigraphy and conventional angiography but in a single examination without radiation exposure.
Received for publication March 16, 2001.
Accepted for publication May 14, 2001.
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Abstract
Introduction
