(Radiology. 2000;217:437-440.)
© RSNA, 2000
Case 28: Proximal Interruption of the Right Pulmonary Artery1
Sheila D. Davis, MD
1 From the Department of Radiology, New York Presbyterian Hospital, 525 E 68th St, New York, NY 10021. Received February 22, 1999; revision requested April 8; revision received July 7; accepted July 26. Address correspondence to the author. (e-mail: sdd2001@mail.med.cornell.edu).
Index terms: Diagnosis Please • Lung, congenital malformation, 60.1413, 60.1494 • Lung, CT, 60.12112 • Pulmonary arteries, abnormalities, 564.155 • Pulmonary arteries, CT, 564.12112
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HISTORY
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A 67-year-old man, a retired farmer, presented with increasing dyspnea at exertion for more than 1 week prior to admission. His medical history was remarkable for dilated cardiomyopathy that was believed to be secondary to heavy ethanol intake, as well as mitral regurgitation and ventricular ectopy. About 30 years prior to admission, he had experienced episodes of hemoptysis.
At physical examination at admission, the patient was tachypneic, with a respiratory rate of 24 breaths per minute. There were rales halfway up both hemithoraces, diminished breath sounds in the right upper lung field, and a third heart sound at cardiac auscultation. Laboratory data were unremarkable. An electrocardiogram revealed first degree atrioventricular block and left bundle branch block. The patient’s symptoms improved with treatment with digoxin, furosemide, and captopril for left-sided congestive heart failure. Posteroanterior and lateral chest radiographs obtained 3 days after admission are shown (Fig 1).
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Figure 1a. (a) Posteroanterior chest radiograph. Volume loss within the right hemithorax is indicated by elevation of the hemidiaphragm and shift of the heart, mediastinum, and tracheal air column to the right. A vertically oriented curvilinear shadow (black arrows) represents the anterior junction line that is displaced into the right hemithorax. Within the small right lung, there is a fine reticular pattern peripherally. There also appears to be pleural thickening (arrowheads) superolaterally. Rib notching (white arrows) is suggested within at least the fifth and sixth ribs. The right hilum is not well seen, but the left pulmonary artery (open arrow) appears enlarged. (b) Lateral chest radiograph. An enlarged left pulmonary artery (arrow) is visible. The retrosternal region is also more radiolucent because of hyperinflation of the left lung. (c) Close-up collimated view of the right lung from a. Reticulation within the peripheral aspect of the right lung is seen more clearly. The black arrows point to the anterior junction line, the arrowheads point to apparent pleural thickening, and the white arrows point to rib notching.
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Figure 1b. (a) Posteroanterior chest radiograph. Volume loss within the right hemithorax is indicated by elevation of the hemidiaphragm and shift of the heart, mediastinum, and tracheal air column to the right. A vertically oriented curvilinear shadow (black arrows) represents the anterior junction line that is displaced into the right hemithorax. Within the small right lung, there is a fine reticular pattern peripherally. There also appears to be pleural thickening (arrowheads) superolaterally. Rib notching (white arrows) is suggested within at least the fifth and sixth ribs. The right hilum is not well seen, but the left pulmonary artery (open arrow) appears enlarged. (b) Lateral chest radiograph. An enlarged left pulmonary artery (arrow) is visible. The retrosternal region is also more radiolucent because of hyperinflation of the left lung. (c) Close-up collimated view of the right lung from a. Reticulation within the peripheral aspect of the right lung is seen more clearly. The black arrows point to the anterior junction line, the arrowheads point to apparent pleural thickening, and the white arrows point to rib notching.
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Figure 1c. (a) Posteroanterior chest radiograph. Volume loss within the right hemithorax is indicated by elevation of the hemidiaphragm and shift of the heart, mediastinum, and tracheal air column to the right. A vertically oriented curvilinear shadow (black arrows) represents the anterior junction line that is displaced into the right hemithorax. Within the small right lung, there is a fine reticular pattern peripherally. There also appears to be pleural thickening (arrowheads) superolaterally. Rib notching (white arrows) is suggested within at least the fifth and sixth ribs. The right hilum is not well seen, but the left pulmonary artery (open arrow) appears enlarged. (b) Lateral chest radiograph. An enlarged left pulmonary artery (arrow) is visible. The retrosternal region is also more radiolucent because of hyperinflation of the left lung. (c) Close-up collimated view of the right lung from a. Reticulation within the peripheral aspect of the right lung is seen more clearly. The black arrows point to the anterior junction line, the arrowheads point to apparent pleural thickening, and the white arrows point to rib notching.
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IMAGING FINDINGS
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Posteroanterior and lateral chest radiographs (Fig 1) revealed substantial volume loss within the right hemithorax, with elevation of the hemidiaphragm and shift of the heart and mediastinum toward the right. The left lung was hyperinflated and herniated over to the right, as indicated by a displaced anterior junction line on the frontal projection image and a more radiolucent retrosternal area on the lateral image (Fig 1). The right hilum was not well seen, whereas the left hilum appeared enlarged on both images. Because of rightward rotation of the mediastinum, the left pulmonary artery was more anterior than usual and in the expected position of the right pulmonary artery. On the right, there appeared to be pleural thickening superolaterally, a pattern of fine reticular markings in the lung peripherally, and a suggestion of rib notching (Fig la, 1c).
Contrast material–enhanced computed tomographic (CT) scans (Figs 2, 3) were obtained during the patient’s stay in the hospital. Sequential scans obtained at mediastinal window settings revealed prominence of the left main pulmonary artery and its divisions (Fig 2). There was, however, complete absence of the mediastinal portion of the right main pulmonary artery. At the right hilum, the interlobar portion of the right pulmonary artery was seen, but this appeared small. Contrast-enhanced intercostal arteries, coursing within prominent areas of extrapleural fat at several levels, supplied collateral circulation to the right lung; this finding of extrapleural fat accounts for the appearance of pleural thickening on the chest radiograph. Reticular areas of increased attenuation peripherally within the small right lung represented transpleural collateral vessels (Fig 3). Although the right lung was small, the bronchial branching pattern was normal. There was no evidence of bronchiectasis. Marked hyperinflation of the left lung, which herniated over to the right anterior to the mediastinum, was demonstrated.
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Figure 2a. (a-d) Transverse contrast-enhanced cephalocaudal contiguous CT scans obtained at mediastinal window settings (width, 400 HU; level, 26 HU; 10-mm collimation) reveal an enlarged left main pulmonary artery (small arrow in b and c), but the mediastinal portion of the right pulmonary artery is completely absent. The interlobar portions (large arrow in c and d) of the right and left pulmonary arteries are depicted, but the right is diminutive compared with the left. Prominent regions of extrapleural fat (white arrowheads in a and b) contain enlarged, contrast-enhanced intercostal collateral vessels (black arrowheads in a and b); this finding of extrapleural fat accounts for the appearance of pleural thickening on the chest radiograph.
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Figure 2b. (a-d) Transverse contrast-enhanced cephalocaudal contiguous CT scans obtained at mediastinal window settings (width, 400 HU; level, 26 HU; 10-mm collimation) reveal an enlarged left main pulmonary artery (small arrow in b and c), but the mediastinal portion of the right pulmonary artery is completely absent. The interlobar portions (large arrow in c and d) of the right and left pulmonary arteries are depicted, but the right is diminutive compared with the left. Prominent regions of extrapleural fat (white arrowheads in a and b) contain enlarged, contrast-enhanced intercostal collateral vessels (black arrowheads in a and b); this finding of extrapleural fat accounts for the appearance of pleural thickening on the chest radiograph.
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Figure 2c. (a-d) Transverse contrast-enhanced cephalocaudal contiguous CT scans obtained at mediastinal window settings (width, 400 HU; level, 26 HU; 10-mm collimation) reveal an enlarged left main pulmonary artery (small arrow in b and c), but the mediastinal portion of the right pulmonary artery is completely absent. The interlobar portions (large arrow in c and d) of the right and left pulmonary arteries are depicted, but the right is diminutive compared with the left. Prominent regions of extrapleural fat (white arrowheads in a and b) contain enlarged, contrast-enhanced intercostal collateral vessels (black arrowheads in a and b); this finding of extrapleural fat accounts for the appearance of pleural thickening on the chest radiograph.
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Figure 2d. (a-d) Transverse contrast-enhanced cephalocaudal contiguous CT scans obtained at mediastinal window settings (width, 400 HU; level, 26 HU; 10-mm collimation) reveal an enlarged left main pulmonary artery (small arrow in b and c), but the mediastinal portion of the right pulmonary artery is completely absent. The interlobar portions (large arrow in c and d) of the right and left pulmonary arteries are depicted, but the right is diminutive compared with the left. Prominent regions of extrapleural fat (white arrowheads in a and b) contain enlarged, contrast-enhanced intercostal collateral vessels (black arrowheads in a and b); this finding of extrapleural fat accounts for the appearance of pleural thickening on the chest radiograph.
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Figure 3. Transverse CT scan obtained at lung window settings (width, 2,000 HU; level, -700 HU; 3-mm collimation). Fine reticular increased attenuation (arrowheads) within the small right lung represents transpleural collateral vessels. Herniation of the hyperinflated left lung into the right hemithorax, associated with displacement of the anterior junction line (arrow), is visible.
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DISCUSSION
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The main pulmonary arteries are derived from the proximal aspects of the sixth aortic arches during the first 16 weeks of intrauterine development (1,2). Proximal interruption of the right or left pulmonary artery is an uncommon anomaly. It has been suggested that the term "interruption" be used in preference to "absence" of a pulmonary artery, in view of the fact that the intrapulmonary vascular network remains intact (2). With a blind end at the hilum, these pulmonary vessels continue to develop independently and receive oxygenated blood through systemic collateral vessels, such as the bronchial, intercostal, internal mammary, subclavian, or innominate arteries (2–4). With interruption on the right, there may even be an anomalous artery arising from the ascending aorta (3,4). In most cases, the interrupted pulmonary artery lies on the side opposite the aortic arch (2). Interruption of the left pulmonary artery is usually associated with other cardiovascular congenital anomalies, most commonly tetralogy of Fallot (4,5).
Patients with interruption of the right pulmonary artery have been grouped into three categories: group 1, those having an associated left-to-right shunt, usually a patent ductus arteriosus; group 2, those having associated pulmonary hypertension; and group 3, those having an isolated anomaly without pulmonary hypertension (5). Whereas individuals in groups 1 and 2 are unlikely to survive beyond infancy, those in group 3 often present as adults, either with incidental recognition of an abnormal chest radiograph or with hemoptysis.
Chest radiographic findings that are characteristic of proximal interruption of a pulmonary artery have been well described (2–7). There typically is volume loss within the hemithorax, as evidenced by elevation of the hemidiaphragm and shift of the heart and mediastinum to the affected side. The contralateral lung is hyperinflated and herniates over into the smaller hemithorax. The hilum on the affected side is inapparent, whereas the hilum of the contralateral lung appears enlarged because the uninterrupted pulmonary artery is receiving the entire output of the right ventricle. In cases of enlarged intercostal and transpleural vessels, there may also be a fine reticular pattern at the periphery of the small lung, in association with pleural thickening and evidence of rib notching (2,4,8).
The findings of a small right hemithorax and diminutive hilum in the example case may suggest other diagnoses as well. Simple pulmonary hypoplasia is often radiographically indistinguishable from proximal interruption of a pulmonary artery, particularly when the pulmonary artery is markedly hypoplastic (9). Pulmonary hypoplasia may also occur in the context of the hypogenetic lung syndrome. A characteristic scimitar-shaped shadow, representing the anomalous draining vein, is frequently present in cases of hypogenetic lung syndrome and should help differentiate this entity from proximal interruption of a pulmonary artery.
In Swyer-James syndrome, a small or normal-size hemithorax is typically hyperlucent compared with the normal side, with evidence of air trapping on expiratory radiographs. In proximal interruption of a pulmonary artery, the small lung may also appear hyperlucent, creating potential confusion with Swyer-James syndrome (3). It has been observed, however, that the lung on the side of the interrupted pulmonary artery is often equally or even slightly more radiopaque compared with the contralateral lung (1). This is attributed to the fact that it contains fewer and smaller alveoli, possibly because exposure to desaturated (low oxygen tension) blood is an important stimulus for development of alveoli in the first 8 years of life (1). Expiratory radiographs were not obtained in the example case, but in proximal interruption of the pulmonary artery, regardless of how radiopaque the affected lung is, the bronchial tree is normal and there is no air trapping.
In view of the additional findings of apparent pleural thickening and a reticular pattern, one might also consider postinflammatory changes and fibrosis. It is unlikely, however, that there would be marked discrepancy in the size of the hila. Furthermore, the finding of rib notching would not be expected.
In the example case, the patient’s symptom of increasing dyspnea was most likely related to his acquired cardiac disorders, but the remote history of hemoptysis is compatible with the radiographic diagnosis of proximal interruption of the right pulmonary artery. Attributed to rupture of thin-walled, hypertrophied collateral vessels, hemoptysis occurs in about 10% of cases of interruption of a pulmonary artery (10,11). Such episodes of hemoptysis are usually minor and self-limited, but massive hemoptysis may rarely occur, requiring emergency treatment by means of pneumonectomy or embolization of systemic collateral vessels (10,11).
Definitive diagnosis, by means of contrast-enhanced CT, of proximal interruption of the pulmonary artery has been described (12,13). Invasive angiography may thus be obviated, unless embolization is required for control of hemoptysis. Absence of the mediastinal portion of the pulmonary artery and presence of a small hilar segment of the affected pulmonary artery are both well demonstrated at CT. As in the example case, prominence of contrast-enhanced intercostal collateral vessels may also be revealed (12).
An advantage of CT over angiography is that CT allows concurrent evaluation of the bronchial tree and lung parenchyma, in addition to the major vascular structures. In proximal interruption of a pulmonary artery, the bronchial branching pattern is normal, excluding the possibility of hypogenetic lung syndrome, and there is generally no evidence of bronchiectasis, which is a CT finding in the Swyer-James syndrome (14). Fine reticulation due to collateral vessels within the lung on the side of the interrupted pulmonary artery is readily apparent at CT. Magnetic resonance (MR) imaging has also been used for noninvasive evaluation of unilateral pulmonary arterial anomalies, including proximal interruption of a pulmonary artery (12,13,15). With MR imaging, the intravenous administration of iodinated contrast material is avoided.
Our congratulations to the 36 individuals who submitted the most likely diagnosis (proximal interruption of the right pulmonary artery) for Diagnosis Please, Case 28. The names and locations of the individuals, as submitted, are as follows:
- Marco Aurelio A. Amaro, São Paulo, Brazil
- Cicero Amorim, São Paulo, Brazil
- Angus Baird, Birmingham, Ala
- Michael P. Buetow, MD, Okemos, Mich
- Aguinaldo Cunha Zuppani, São Paulo, Brazil
- Julio Dabdab, São Paulo, Brazil
- J. F. K. de Villiers, Gisborne, New Zealand
- Ravi V. Desai, Chandigarh, India
- Jack T. English, LaCrosse, Wis
- Jamil Jacob Filho, São Paulo, Brazil
- Manoj Jain, MD, Chandigarh, India
- Stefanos Lachanis, MD, Athens, Greece
- Guilherme F. Lemos, São Paulo, Brazil
- Ana Karina M. R. Lima, São Paulo, Brazil
- Nelson Lobelo, Bogota, Cundinamarca, Colombia
- Margarete Massignan, São Paulo, Brazil
- Robert E. Mindelzun, MD, Palo Alto, Calif
- Sergio J. Moguillansky, MD, Cipolletti, Rio Negro, Argentina
- Cristiane Moskorz, São Paulo, Brazil
- L. Alain Nchimi, Liège, Belgium
- Julio Neves Junior, São Paulo, Brazil
- Mizuki Nishino, MD, Kyoto, Japan
- David M. Panicek, MD, New York, NY
- Luiz J. Sales Campos, São Paulo, Brazil
- Raymond Selouan, MD, Beirut, Lebanon
- Carla Andrea M. Silva, São Paulo, Brazil
- Mauricio Soares Rizzuto, São Paulo, Brazil
- Paul Stark, MD, La Jolla, Calif
- Denis Tack, MD, Charleroi, Belgium
- J. Takasugi, Mercer Island, Wash
- Carlos E. Triana Rodriguez, Bogotá, Colombia
- Gustavo A. Triana, Santa Fe De Bogota, Colombia
- Christopher Vittore, MD, Rockford, Ill
- Edward Williams, Grand Cayman, Cayman Islands, British West Indies
- Tatsuya Yamamoto, Fukui, Japan
- Joe Yut, Olathe, Kan
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FOOTNOTES
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Part 1 of this case appears 4 months previously and may contain larger images.
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TOP
HISTORY
IMAGING FINDINGS
