Congenital Pulmonary Venolobar Syndrome: Spectrum of Helical CT Findings with Emphasis on Computerized Reformatting 1

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1 EDUCATION EXHIBIT 1175 Congenital Pulmonary Venolobar Syndrome: Spectrum of Helical CT Findings with Emphasis on Computerized Reformatting 1 ONLINE-ONLY CME See /rg_cme.html. LEARNING OBJECTIVES After reading this article and taking the test, the reader will be able to: Describe the main components of congenital pulmonary venolobar syndrome. Recognize the most common vascular, airway, and pulmonary parenchymal CT findings in affected patients. Select a scanning protocol that will allow optimal anatomic evaluation with minimal radiation exposure. Eli Konen, MD Lisa Raviv-Zilka, MD Ronald A. Cohen, MD Monica Epelman, MD Inbal Boger-Megiddo, MD Jacob Bar-Ziv, MD Julius Hegesh, MD Amos Ofer, MD Osnat Konen, MD Miriam Katz, MD Gabi Gayer, MD Judith Rozenman, MD The term congenital pulmonary venolobar syndrome refers to a wide spectrum of pulmonary developmental anomalies that may appear singly or in combination. The main components of congenital pulmonary venolobar syndrome are hypogenetic lung (including lobar agenesis, aplasia, or hypoplasia), partial anomalous pulmonary venous return, absence of pulmonary artery, pulmonary sequestration, systemic arterialization of lung, absence of inferior vena cava, and accessory diaphragm. The recent introduction of multisection helical computed tomography (CT), combined with use of advanced postprocessing graphic workstations, allows improved noninvasive delineation of complex congenital anomalies. A single fast (5 15-second) CT scan now enables the radiologist to (a) generate angiogram-like images of the anomalous pulmonary arteries and veins; (b) demonstrate tracheobronchial abnormalities by generating simulated bronchographic or bronchoscopic images; and (c) depict associated parenchymal abnormalities on axial, coronal, or sagittal images, which once represented an important advantage of magnetic resonance imaging over CT. Multisection helical CT is a helpful diagnostic tool in the preoperative evaluation of patients with suspected congenital pulmonary venolobar syndrome. RSNA, 2003 Abbreviations: IVC inferior vena cava, SSD shaded surface display Index terms: Bronchopulmonary sequestration, Lung, abnormalities, , Lung, CT, Venolobar syndrome, ; 23: Published online /rg From the Department of Diagnostic Imaging (E.K., L.R.Z., M.K., G.G., J.R.) and the Pediatric Cardiology Unit (J.H.), Chaim Sheba Medical Center, Tel-Aviv University, Tel Hashomer 52662, Israel; the Department of Diagnostic Imaging, Children s Hospital, Oakland, Calif (R.A.C.); the Department of Diagnostic Imaging, Rambam Medical Center, Technion-Israel Institute of Technology, Haifa, Israel (M.E., A.O.); the Department of Diagnostic Imaging, Hadassah University Hospital, Jerusalem, Israel (I.B.M., J.B.Z.); and the Department of Diagnostic Imaging, Sapir Medical Center, Tel-Aviv University, Kfar Sava, Israel (O.K.). Recipient of a Cum Laude award for an education exhibit at the 2002 RSNA scientific assembly. Received January 8, 2003; revision requested March 6 and received April 17; accepted April 21. Address correspondence to E.K. ( konen_e@yahoo.ca). RSNA, 2003

2 1176 September-October 2003 RG f Volume 23 Number 5 Introduction The term congenital pulmonary venolobar syndrome was coined by Felson (1) and comprises a heterogeneous group of uncommon abnormalities that may occur singly or in combination and that involve anomalous connections of the pulmonary parenchyma, the pulmonary and systemic vasculature, and, rarely, the gastrointestinal tract (1 3). Although most patients are asymptomatic, some with concurrent cardiac anomalies or severe forms of pulmonary atresia or hypoplasia may have clinical symptoms at an early age. Surgical intervention may be required in selected cases involving intractable infection, hemoptysis, and congestive heart failure or pulmonary hypertension due to excessive shunting (4,5). Identification of abnormal pulmonary and systemic vessels as well as tracheobronchial anomalies is essential for accurate diagnosis in the preoperative evaluation of affected patients. Traditionally, angiography has been the technique of choice for imaging of vascular anomalies, especially when pulmonary sequestration or hypogenetic lung syndrome (scimitar syndrome) is suspected (5,6). Previous studies performed with earlier generations of computed tomography (CT) scanners have shown CT to be helpful in the evaluation of congenital pulmonary venolobar syndrome but incapable of demonstrating the anomalous vessels in many cases (7 10). More recently, several studies have suggested the use of CT angiography as a noninvasive alternative in cases of pulmonary sequestration or hypogenetic lung syndrome (11 17). The recent introduction of multisection helical CT, combined with use of advanced postprocessing graphic workstations, allows improved delineation of the complex and variable anatomic abnormalities seen in patients with congenital pulmonary venolobar syndrome. In this article, we discuss the methods and technique used in a study of 31 patients with various manifestations of congenital pulmonary venolobar syndrome (pulmonary sequestrations and variants, partial anomalous pulmonary venous return, horseshoe lung, proximal pulmonary arterial interruption) that was performed with multisection helical CT and computerized reformatting. We also discuss and illustrate the spectrum of common and uncommon imaging findings in these patients. In addition, we discuss the possible drawbacks of CT in the evaluation of patients with congenital pulmonary venolobar syndrome. Methods and Technique We retrospectively reviewed CT angiographic studies performed at four medical centers between January 1995 and July 2000 in 31 patients with congenital pulmonary venolobar syndrome. Nineteen patients were male and 12 were female. Patient age ranged from 2 days to 42 years (mean age, 10.9 years). Twenty-three patients were under 18 years old, and 11 were neonates. Clinical manifestations prior to CT angiography included recurrent bouts of pneumonia (n 9), prenatally diagnosed pulmonary sequestration (n 8), congestive heart failure (n 9), incidental radiographic findings in asymptomatic adult patients (n 5), a low Apgar score at birth (n 2), and mild-effort dyspnea and wheezing (n 1). Six of the eight patients in whom pulmonary sequestration was prenatally diagnosed were asymptomatic. Nonionic iodinated contrast material (iohexol [Omnipaque 300; Nycomed, New York, NY or Schering, Berlin, Germany] or ioversol [Optiray 320; Mallinckrodt Medical, St Louis, Mo]) was used. The contrast material (mean dose, 2 ml/ kg) was injected into a peripheral vein of the arm with a power injector at a rate of 1 4 ml/sec. The examinations were performed with either a double-detector helical CT scanner (Twin; Marconi, Cleveland, Ohio) or a quad-section CT scanner (MX-8000, Marconi) with a pitch of 1.5 or 2. Scanning time varied from 12 to 30 seconds. Collimation was 1 mm in 10 patients, 2 mm in 13 patients, 2.5 mm in seven patients, and 4 mm in one patient, with 30% 50% reconstruction overlap between sections. Scanning was performed during a single breath hold in cooperative patients or during quiet respiration in infants and young children. Computerized reformatting was performed with an image processing workstation running on a Silicon Graphics O2 platform (Omniview MX, Marconi). The following computerized reformatting techniques were used prospectively at the original institutions: multiplanar reformatting (n 23), shaded surface display (SSD) (n 7), maximum intensity projection (n 6), minimum intensity projection (n 6), volume rendering (n 4), and virtual bronchoscopy (n 2). Virtual bronchoscopic images were generated to correspond to fiberoptic bronchoscopic images (ie, appearing as if the patient were in a prone position). CT revealed 22 sequestrations in 21 patients (one patient had a bilateral sequestration, and three patients had associated partial anomalous

3 RG f Volume 23 Number 5 Konen et al 1177 Figure 1. Pulmonary sequestration in a 6-year-old boy with recurrent episodes of right lower lobe pneumonia. (a) Axial CT angiogram obtained at the level of the lung bases shows a consolidation with large vessels centrally (arrows) in the right lower lobe. (b) Axial CT angiogram obtained inferior to a shows that the vessels originate from a large artery (arrow) that crosses inferior to the diaphragm. (c, d) SSD (c) and magnified volume-rendered (d) reformatted images clearly demonstrate a systemic aberrant artery (arrow) that originates from the celiac trunk (arrowhead in d) and supplies the right lower lung. In c, the trachea and lungs are highlighted in blue and the ribs and lungs are partially transparent. AO aorta. Surgery revealed an intralobar sequestration. pulmonary venous return), hypogenetic lung in seven, absence of the left main pulmonary artery in four, systemic arterialization of lung in one, and horseshoe lung in one. In 21 patients, CT findings could be correlated with findings at other procedures, including angiography (n 9; indications for angiography included shunt quantification and embolization of aberrant arteries in patients with congestive heart failure), surgery (n 8), Doppler ultrasonography (US) (n 2), and bronchoscopy (n 2). Clinical follow-up is ongoing but thus far uneventful in three additional asymptomatic infants with a prenatal diagnosis of sequestration. Pulmonary Sequestrations and Variants Pulmonary sequestration is defined as a segment of lung parenchyma that is separated from the tracheobronchial tree and is supplied with blood from a systemic rather than a pulmonary artery (1,18). The blood supply usually comes from the descending thoracic aorta, but in about 20% of cases it comes from the upper abdominal aorta, celiac artery (Fig 1), or splenic artery (18). Sequestrations may be either intralobar or extralobar.

4 1178 September-October 2003 RG f Volume 23 Number 5 Figure 2. Pulmonary sequestration with an associated suspected gastric duplication in an asymptomatic male neonate. (a) Coronal multiplanar reformatted image shows an aberrant artery (arrowhead) that arises from the descending thoracic aorta and supplies a mass in the left lung base. An adjacent infradiaphragmatic cystic mass is also noted (C). (b) On an axial image obtained at the level of the gastric fundus, the cystic mass (C) is seen to project into the stomach, a finding that is compatible with gastric duplication. Intralobar sequestrations are contained within the visceral pleura of the normal adjacent lung. They are more common than extralobar sequestrations by a 3:1 ratio, and over 50% of intralobar sequestrations may be asymptomatic by the time the patient reaches 20 years of age. In 95% of cases, venous drainage is to the pulmonary veins, resulting in a unique left-to-left shunt. Intralobar sequestrations are associated with other anomalies (usually diaphragmatic hernia) in about 15% of cases. In contrast, extralobar sequestrations are contained within a distinct visceral pleural coat. Only 10% of extralobar sequestrations remain asymptomatic, and most occur in the first 6 months of life. More than 80% drain into the right side of the heart via the azygos vein, hemiazygos vein, and inferior vena cava (IVC), resulting in a left-to-right shunt. In 65% of cases, there are associated anomalies (Fig 2), the most common being diaphragmatic hernia. Rare variants of sequestration such as bilateral sequestration (Fig 3) and gastric or esophageal lung (Fig 3e) (3) have been reported in both extra- and intralobar sequestrations. Our series included a higher number of patients with sequestration (n 21) than with hypogenetic lung syndrome (n 7). In contrast, the series by Woodring et al (2) included a higher number of patients with hypogenetic lung syndrome. This difference might be explained by the advances in imaging techniques over the past 20 years. Our series was based on patients who were referred for helical CT, whereas some patients in the series by Woodring et al were seen before CT was available. Indications for imaging procedures in use at that time (eg, radiography, angiography) and, thus, patient selection, were most likely different. In addition, our series included a relatively large number of asymptomatic patients (eight of 21) in whom sequestrations were identified at routine prenatal US; these sequestrations would not have been identified and included in a study performed 25 years ago. A previous report of spontaneous involution of pulmonary sequestration in two asymptomatic children raised the question of whether such patients should be treated surgically (19). CT is a useful method for measuring the volume of pulmonary sequestrations: In our series, repeat CT showed volume reduction of a bilateral sequestration after embolization therapy in one case (Fig 3f) and spontaneous regression of vascularity in two others. Larger, sequential series will be needed to confirm whether pulmonary sequestration is a more common abnormality than was previously thought and to determine the natural history of this anomaly. Partial Anomalous Pulmonary Venous Return Partial anomalous pulmonary venous return is present when one or more, but not all, of the pulmonary veins drain into a systemic vein, resulting in a left-to-right shunt. Partial anomalous pulmonary venous return is usually an isolated finding

5 RG f Volume 23 Number 5 Konen et al 1179 Figure 3. Bilateral pulmonary sequestration that caused congestive heart failure in a male neonate. The patient s condition was diagnosed prenatally at US. (a) Combined SSD and multiplanar reformatted image shows an anomalous artery that arises from the descending thoracic aorta and bifurcates to supply two enhancing soft-tissue masses in the lung bases. (b, c) Curvilinear multiplanar reformatted images clearly delineate the anomalous arteries in the right (b) and left (c) lung bases. (d) Findings on an aortogram obtained before successful embolization of the aberrant arteries are virtually identical to and thereby help confirm the CT angiographic findings (cf a). (e) Axial minimum-intensity-projection reformatted image reveals an accessory aerated aberrant bronchial tree (arrow) that connects the two masses. The aberrant bronchial tree is separated from the normal tracheobronchial tree, a finding that suggests a rare connection to the esophagus or stomach. AO aorta. (f) On a follow-up CT angiogram obtained 1 year after embolization, the volume of the left sequestration is significantly reduced and the right sequestration has almost totally disappeared. Note the steel coils (arrows) used for embolization of the right aberrant artery.

6 1180 September-October 2003 RG f Volume 23 Number 5 Figure 4. Hypogenetic lung syndrome in a 22-year-old asymptomatic woman. (a) Axial CT angiogram obtained at the level of the lung bases shows a large anomalous vein (*) that drains into a dilated inferior vena cava (IVC). (b) Volume-rendered reformatted image demonstrates that the anomalous vein (*) drains into the IVC below the level of the right hemidiaphragm. L liver. (c) Anteroposterior venous phase pulmonary angiogram obtained for shunt quantification helps confirm the presence of an anomalous pulmonary vein. (d) On a minimum-intensity-projection reformatted image, the right upper lobe bronchus is not seen, allowing visualization of the associated hypogenetic lung and central bronchi. and is more frequently seen on the right side. Most patients are either mildly symptomatic or asymptomatic. Hypogenetic lung syndrome (scimitar syndrome) is a rare type of partial anomalous pulmonary venous return in which an anomalous pulmonary vein is the draining vein for part or all of the right lung, emptying into the IVC (Fig 4a 4c) either above or below the diaphragm. The anomalous vein may on occasion drain into the hepatic veins, portal veins, azygous vein, coronary sinus, or right atrium. The anomalous vein is usually associated with various degrees of hypoplasia of the right lung and with a hypoplastic or aplastic pulmonary artery. The right lung may have abnormal lobation (frequently only two lobes), and the bronchographic pattern may mimic that of the left lung (Fig 4d) (8). About one-fourth of affected patients have associated congenital heart disease, most often a sinus venosus atrial septal defect. Reported associated anomalies include bronchogenic cyst, horseshoe lung, accessory diaphragm, and hernia. Horseshoe Lung Horseshoe lung is a rare congenital malformation in which an isthmus of pulmonary parenchyma extends from the right lung base across the midline behind the pericardium and joins the posterobasal segments of the lungs (Fig 5) (4). In most

7 RG f Volume 23 Number 5 Konen et al 1181 Figure 5. Horseshoe lung in a male neonate. (a) Axial CT scan obtained at the level of the lung bases shows an isthmus of pulmonary parenchyma (arrow) that extends behind the heart and joins the posterobasal segments of both lungs. An anomalous right pulmonary vein (*) drains into the IVC. (b) Volume-rendered reformatted image of the airways and lung parenchyma reveals partial fusion of the lungs posterior to the heart and an abnormal bronchus that arises from the left main bronchus and crosses the thoracic midline. (c) Coronal multiplanar reformatted image shows an anomalous right pulmonary vein (*) that drains into the IVC below the level of the right hemidiaphragm. (d) SSD reformatted image of the pulmonary artery demonstrates an inferior branch (*) that arises from the right pulmonary artery ( ) and crosses the midline to the base of the left lung. (e) Anteroposterior arterial phase pulmonary angiogram helps confirm the CT angiographic findings. * anomalous branch, right pulmonary artery.

8 1182 September-October 2003 RG f Volume 23 Number 5 Figure 6. Interruption of the left pulmonary artery in a 36-year-old man who was born with a persistent truncus arteriosus (surgically repaired in childhood). (a) Axial CT angiogram obtained at the level of the carina shows interruption of the left main pulmonary artery. The left lung is mildly hypoplastic with decreased vascularity. Note the calcified conduit (*) that connects the right ventricle to the main pulmonary artery and an aneurysmal ascending aorta (AO). (b) Coronal multiplanar reformatted image shows peripheral linear areas of increased attenuation in the left lung (arrows). This finding, which was confirmed at angiography, represents collateral vessels that invade the lung through the pleura. Inset demonstrates the plane of reformation. cases, horseshoe lung is associated with hypogenetic lung syndrome (Fig 5b). Other associated findings include a hypoplastic right pulmonary artery, an abnormal systemic arterial supply from the aorta to the right lung, and bronchial sequestration. Pulmonary Arterial Interruption Interruption of the proximal portion of a pulmonary artery is more common on the right side. The peripheral pulmonary arteries in both lungs are usually intact because they are supplied by systemic collateral arteries. Interruption of the proximal left pulmonary artery is less common and is usually associated with congenital heart disease (Fig 6), particularly tetralogy of Fallot and a ventricular septal defect. In the absence of other congenital anomalies, there is almost always a right aortic arch (Fig 7) (5). The affected lung and hilum are usually decreased in size, and pulmonary vessels are absent or markedly decreased in size (Figs 6a, 7a), rendering the lung radiolucent. Systemic arteries usually replace the absent pulmonary arterial supply through mediastinal and transpleural collateral vessels, which cause serrated thickening of the pleura and the appearance of subpleural parenchymal bands (Fig 6b) (20). Other associated findings may include an asymmetric thoracic cage, mosaic attenuation, and bronchiectasis (20). Helical CT can also delineate the spatial relationship between the abnormal vascular anatomy and associated tracheobronchial tree abnormalities (Fig 7b 7d). Drawbacks of CT The main disadvantage of using CT versus US or magnetic resonance imaging is exposure of the patient to ionizing radiation. Pediatric patients may have increased sensitivity to ionizing radiation (21). The increased number of detectors on multisection helical CT scanners allows thinner collimation and a similar or even shorter scanning time compared with earlier CT scanners. However, the use of thinner collimation increases patient exposure to ionizing radiation and is not always clinically justified. For example, a decrease in collimation from 2.5 to 1.25 mm will result in a 35% increase in radiation dose (22). Radiation exposure can be reduced by increasing pitch and decreasing beam energy (kilovolt peak) and photon fluence (milliampere-seconds value). It is the radiologist s responsibility to choose the protocol that will provide the maximum amount of clinically important information with minimal radiation exposure.

9 RG f Volume 23 Number 5 Konen et al 1183 Figure 7. Interruption of the left main pulmonary artery in a 16-year-old boy. (a, b) Axial CT scans obtained at the level of the right main bronchus (a) and bronchus intermedius (b) (arrows) show interruption of the left main pulmonary artery. Note the compressed right main bronchus between the right-sided descending aorta (Ao) and a prominent right main pulmonary artery (RPA). The mediastinum is shifted to the left due to an associated hypoplastic left lung. (c) SSD reformatted image (superior view) delineates the spatial relationship between the prominent single pulmonary artery (blue), the right-sided descending aorta (AO [red]), and the compressed right main bronchus. (d) Virtual bronchoscopic reformatted image obtained at the level of the carina ( supine position) shows the right main bronchus (R) with a compressed fishmouth shape. L left main bronchus. Conclusions Multisection helical CT is a helpful diagnostic tool in the preoperative evaluation of patients with suspected congenital pulmonary venolobar syndrome. It allows detailed evaluation of vascular, tracheobronchial, and pulmonary parenchymal abnormalities with a single short, noninvasive procedure. References 1. Felson B. Chest roentgenology. Philadelphia, Pa: Saunders, 1973; Woodring JH, Howard TA, Kanga JF. Congenital pulmonary venolobar syndrome revisited. Radio- Graphics 1994; 14: Gerle RD, Jaretzki A III, Ashley CA, Berne AS. Congenital bronchopulmonary-foregut malformation: pulmonary sequestration communicating with the gastrointestinal tract. N Engl J Med 1968; 278: Frank JL, Poole CA, Rosas G. Horseshoe lung: clinical, pathologic and radiologic features and a new plain film finding. AJR Am J Roentgenol 1986; 146: Ellis K. Developmental abnormalities in the systemic blood supply to the lungs. AJR Am J Roentgenol 1991; 156: Kravitz RM. Congenital malformations of the lung. Pediatr Clin North Am 1994; 41:

10 1184 September-October 2003 RG f Volume 23 Number 5 7. Yamanaka A, Hirai T, Fujimoto T, Hase M, Noguchi M, Konishi F. Anomalous systemic arterial supply to normal basal segments of the left lower lobe. Ann Thorac Surg 1999; 68: Godwin JD, Tarver RD. Scimitar syndrome: four new cases examined with CT. Radiology 1986; 159: Rappaport DC, Herman SJ, Weisbrod GL. Congenital bronchopulmonary diseases in adults: CT findings. AJR Am J Roentgenol 1994; 162: Ikezoe J, Murayama S, Godwin JD, Done SL, Verschakelen JA. Bronchopulmonary sequestration: CT assessment. Radiology 1990; 176: Hopkins KL, Patrick LE, Simoneaux SF, Bank ER, Parks WJ, Smith SS. Pediatric great vessel anomalies: initial clinical experience with spiral CT angiography. Radiology 1996; 200: Amitai M, Konen E, Rozenman J, Gerniak A. Preoperative evaluation of pulmonary sequestration by helical CT angiography. AJR Am J Roentgenol 1996; 167: Chung JW, Park JH, Im JG, Chung MJ, Han MC, Ahn H. Spiral CT angiography of the thoracic aorta. 1996; 16: Cho SY, Kim HC, Bae SH, et al. Demonstration of blood supply to pulmonary sequestration by MR and CT angiography. J Comput Assist Tomogr 1996; 20: Frush DP, Donnelly LF. Pulmonary sequestration spectrum: a new spin with helical CT. AJR Am J Roentgenol 1997; 169: Franco J, Aliaga R, Domingo ML, Plaza P. Diagnosis of pulmonary sequestration by spiral CT angiography. Thorax 1998; 53: Zylak CJ, Eyler WR, Spizarny DL, Stone CH. Developmental lung anomalies in the adult: radiologic-pathologic correlation. 2002; 22:S25 S Felker RE, Tonkin IL. Imaging of pulmonary sequestration. AJR Am J Roentgenol 1990; 154: Garcia-Peña P, Lucaya J, Hendry GMA, McAndrew PT, Duran C. Spontaneous involution of pulmonary sequestration in children: a report of two cases and review of the literature. Pediatr Radiol 1998; 28: Sakai S, Murayama S, Soeda H, et al. Unilateral proximal interruption of the pulmonary artery in adults: CT findings in eight patients. J Comput Assist Tomogr 2002; 26: Brenner DJ, Elliston CD, Hall EJ, Berdon WE. Estimated risks of radiation-induced fatal cancer from pediatric CT. AJR Am J Roentgenol 2001; 176: McNitt-Gray MF. AAPM/RSNA Physics Tutorial for Residents: topics in CT radiation dose in CT. 2002; 22: This article meets the criteria for 1.0 credit hour in category 1 of the AMA Physician s Recognition Award. To obtain credit, see