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Original Report |
1
Department of Radiology, Box 3808, Duke University Medical Center, Rm. 2523
Blue Zone South, Durham, NC 27710.
2
Present address: Department of Radiology, Queen's University at Kingston, c/o
Kingston General Hospital, Kingston, Ontario, K7L 2V7 Canada.
3
Division of Cardiology, Department of Medicine, Duke University Medical
Center, Durham, NC 27710.
Received December 6, 2000;
accepted after revision February 28, 2001.
Address correspondence to L. E. Heyneman.
Abstract
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CONCLUSION. Chest radiography in affected patients typically reveals a small hemithorax and ipsilateral pulmonary artery as well as ipsilateral septal thickening. CT shows, in addition, ground-glass attenuation, the absence of a pulmonary vein connection to the left atrium, and abundant mediastinal venous collateral vessels. MR imaging is helpful in further characterizing the vascular abnormalities. Angiography may help to confirm the diagnosis.
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All patients underwent conventional chest radiography and CT examinations. The CT scans were obtained on different scanners using a variety of scan techniques (collimation, 1.5, 5, and 10 mm). Two studies were performed both before and after the administration of IV contrast material. The patient with hematemesis underwent axial T1-weighted, gradient-echo, and phase-contrast MR imaging performed on a 1.5-T scanner (General Electric Medical Systems, Milwaukee, WI) to evaluate patency of the portal vein and the intrathoracic vasculature.
The diagnosis of unilateral pulmonary vein atresia was defined by cardiac catheterization and pulmonary angiography in all patients. The diagnosis was confirmed at pneumonectomy in two patients. The third patient was treated conservatively with bronchial artery embolization and to date has required no further therapy.
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In all patients, CT scans confirmed a small hemithorax and a small ipsilateral pulmonary artery. No soft tissue was seen adjacent to the pulmonary artery to suggest an obstructing mass, and no evidence of bronchial obstruction was seen to explain the mediastinal shift (Fig. 1B).
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The pulmonary veins on the affected side were not identified. The margin of the left atrium in the expected location of the pulmonary veins was completely smooth, without evidence of rudimentary pulmonary veins (Figs. 2A). Confluent low-attenuation soft tissue was present in the mediastinum adjacent to the left atrium and extended from the region of the left atrium into a subcarinal and paraesophageal location (Figs. 1B, 2A, and 3A). In one patient, the region of confluent low-attenuation soft tissue extended superiorly in a paratracheal location to the level of the great vessels. After the administration of IV contrast material, the abnormal perihilar, mediastinal, and fissural soft tissue showed heterogeneous enhancement. A persistent left superior vena cava was present in one patient. In all three patients, the small affected lung exhibited diffuse ground-glass attenuation and smooth thickening of the interlobular septa and bronchovascular bundles (Fig. 1C).
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MR imaging, performed in one patient, confirmed unilateral absence of the pulmonary veins and revealed abnormal retrocrural collateral vessels that corresponded to the paraesophageal soft tissue identified on CT (Fig. 3B). Furthermore, phase-contrast images revealed retrograde flow in the ipsilateral pulmonary artery. High signal on gradient-echo sequences in the affected lung corresponded to regions of interlobular septal thickening on CT. Because of the patient's hematemesis, the portal vein was evaluated and was found to be patent, with normal hepatopetal flow.
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The diagnosis of congenital unilateral pulmonary vein atresia was confirmed by cardiac catheterization and pulmonary angiography in all patients. Several findings suggested the diagnosis. In all three patients, markedly increased pulmonary capillary wedge pressures were noted in the affected lungs, consistent with pulmonary vein obstruction. The ipsilateral pulmonary arteries were hypoplastic. Oxygen saturation in the affected pulmonary arteries was higher than in the contralateral pulmonary arteries, suggesting the presence of systemic artery flow into the hypoplastic pulmonary arteries. The presence of systemic collaterals was confirmed by the visualization of reversed pulmonary artery blood flow on the affected side, a finding that was also noted on MR imaging. In two cases, absence of the ipsilateral pulmonary veins was identified on venous phase imaging of the left atrium (Fig. 2B). In the third case, the patient with hematemesis, a definitive diagnosis was made by pulmonary capillary wedge angiography in which contrast material was force-fully injected into the distal pulmonary vascular bed. Peripheral pulmonary veins were identified, but no connection to the left atrium was seen; instead the veins drained into a paraesophageal venous plexus (Fig. 3C).
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One patient with hemoptysis underwent percutaneous coil embolization of the systemic arterial collateral vessels with a therapeutic result. Two patients, one with recurrent pneumonia and one with both hemoptysis and hematemesis, underwent ventilation—perfusion scanning as part of a workup before pneumonectomy. The ventilation scans showed normal findings, but virtually no perfusion to the affected lung was seen (Fig. 2C). These two patients subsequently underwent pneumonectomy of the nonfunctioning lung. At surgery, the affected lungs had multiple macroscopic transpleural and mediastinal collateral vessels. The macroscopic pulmonary veins were hypoplastic. Pathologic examination of the pneumonectomy specimens confirmed the hypoplasia of the macroscopic veins and revealed other areas of microscopic venous atresia. The pulmonary veins were markedly thickened, with sclerotic walls often resulting in obliteration of the lumina. Severe hypertensive changes were present in peripheral veins and venules.
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To our knowledge, the CT and MR imaging findings of unilateral congenital pulmonary vein atresia have not been described. The CT scans of all three of patients showed a small hemithorax with ipsilateral mediastinal shift, a diminutive ipsilateral pulmonary artery, and absence of ipsilateral pulmonary vein drainage into the left atrium. The left atrial wall at the expected site of insertion of the ipsilateral pulmonary vein was completely smooth, without evidence of even a rudimentary pulmonary vein. No bronchial obstruction was seen as the cause of the mediastinal shift. All three CT studies also revealed abnormal confluent mediastinal soft tissue, likely representing collateral pulmonary-to-systemic venous channels. Venous collaterals were confirmed angiographically in one patient and surgically in two.
The presence of mediastinal collateral vessels likely relates to the embryologic development of the pulmonary veins. The primitive pulmonary veins initially drain into the systemic system via the vitelline and cardinal veins. The pulmonary veins later coalesce to form a pulmonary vein confluence that fuses with the left atrium [6]. It is postulated that failure of normal incorporation of the pulmonary veins into the left atrium results in persistence of the connections between the pulmonary circulation and the vitelline and cardinal venous systems, and thus drainage into the portal vein and vena cava [2].
Pulmonary artery and parenchymal abnormalities were also present. The ipsilateral pulmonary artery was diminutive, likely because of preferential pulmonary artery perfusion to the contralateral side, with resultant impaired growth of the affected pulmonary artery [5]. This pulmonary artery hypoplasia likely accounts for the arterial systemic-to-pulmonary collateral vessels. The interlobular septal thickening, bronchial wall thickening, and ground-glass opacities likely reflected both pulmonary vein hypertension and engorged lymphatics.
Gradient-echo and phase-contrast MR imaging further characterized the vascular abnormalities. Reversal of flow in a small pulmonary artery implied the presence of systemic-to-pulmonary arterial collaterals. Blood in the systemic collateral vessels flowed retrogradely into the ipsilateral, then contralateral, pulmonary arteries, then coursed through the contralateral lung into the left atrium. The ipsilateral pulmonary veins were absent. Most abnormal mediastinal soft tissue on CT was confirmed to represent vasculature on MR imaging. MR imaging was specifically helpful in excluding the presence of a central obstructing mass.
Despite the ability of MR imaging to characterize vascular abnormalities, the diagnosis of unilateral pulmonary vein atresia is usually made angiographically. The presence of systemic-to-pulmonary arterial collaterals is suggested both by reversal of blood flow in the pulmonary artery and by an increase in oxygenation in the ipsilateral pulmonary artery. The absence of venous opacification on venous phase imaging is virtually diagnostic, and the visualization of atretic pulmonary veins via capillary wedge angiography is definitive [2].
Adult patients with this entity may present a diagnostic dilemma. The confluent mediastinal and hilar soft tissue may suggest lung cancer or fibrosing mediastinitis that involves the hilar vessels, resulting in a small ipsilateral pulmonary artery and pulmonary vein obstruction. However, the presence of a small hemithorax without evidence of bronchial obstruction should suggest a congenital abnormality.
In summary, congenital unilateral pulmonary vein atresia is a rare abnormality that may present in adults with signs and symptoms of hemoptysis or respiratory infections. CT findings include a small hemithorax with ipsilateral mediastinal shift, small ipsilateral pulmonary artery, absence of the pulmonary vein connection to the left atrium, and parenchymal abnormalities such as interlobular septal thickening, peribronchovascular thickening, and ground-glass opacities. The presence of a small hemithorax without evidence of bronchial obstruction suggests a possible congenital abnormality. Abnormal mediastinal and hilar soft tissue is commonly caused by pulmonary-to-systemic venous collaterals. MR imaging may confirm the presence of vascular collaterals and may show retrograde flow in a small pulmonary artery on the affected side. Although the diagnosis may be suggested by a clinical history of recurrent infection, the definitive diagnosis of hemoptysis, or coexistent congenital heart disease, usually requires cardiac catheterization, including pulmonary angiography.
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