The "Broken Ring" Sign in Magnetic Resonance Imaging of Partial Anomalous Pulmonary Venous Connection to the Superior Vena Cava

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1 Case Report The "Broken Ring" Sign in Magnetic Resonance Imaging of Partial Anomalous Pulmonary Venous Connection to the Superior Vena Cava PAUL R. JULSRUD, M.D., RICHARD L. EHMAN, M.D., Department of Diagnostic Radiology In two patients with partial anomalous pulmonary venous connection to the superior vena cava, we attempted to demonstrate the pertinent anatomic abnormalities by using magnetic resonance imaging. The results show that magnetic resonance imaging is an ideal cardiovascular imaging modality. The observation of a "broken ring" structure in the magnetic resonance image of the superior vena cava is proposed as a diagnostic sign of partial anomalous pulmonary venous connection to the superior vena cava. The utility of magnetic resonance imaging (MRI) in medical diagnosis is well substantiated, and investigators continue to discover new applications for this procedure. 1 " 3 Currently, cardiac MRI is of considerable interest because of its ability to demonstrate clearly the intracardiac anatomy noninvasively. The size and position of the cardiac chambers, the location of the atrioventricular and semilunar valves, the spatial relationships of the great vessels, and the presence of intracavitary or intramural masses have been documented by use of this technique. 4 " 7 Although the relevance of this information to cardiac diagnoses is obvious, two-dimensional echocardiography is also currently used to demonstrate these components of cardiac anatomy. In addition to being noninvasive, however, two-dimensional echocardiography has the advantage of acquiring data in real time, and thereby it provides functional information as well. Although closed-loop playback of electrocardiographic-gated MRI images seeks to remedy this apparent shortcoming, the main advantage of MRI is its ability to demonstrate clearly both intracardiac and extracardiac vascular structures in transverse, sagittal, and coronal planes, with all planes having comparable spatial resolution. In addition, the Address reprint requests to Dr. P. R. Julsrud, Department of Diagnostic Radiology, Mayo Clinic, Rochester, MN "flow void phenomenon" is a fortuitous property of MRI in cardiovascular imaging. 8,9 While producing striking contrast of signal intensity between the vessel lumen and wall, it also portends future absolute flow measurements in MRI because the signal intensity of a moving tissue sample (flowing blood) is related to the velocity of that sample and the timing and location of the excitation pulse relative to image acquisition.' 0 The ability to obtain electrocardiographic-gated magnetic resonance images routinely and the capability to monitor patients closely throughout the study have expanded the clinical use of MRI in our cardiac patients. In this report, we illustrate the use of MRI to confirm the structural abnormality present in a well-recognized cardiovascular anomaly, partial anomalous pulmonary venous connection. SUBJECTS AND METHODS Our Institutional Review Board approved this study, and informed consent was obtained from both patients. Case reports of these two patients with partial anomalous pulmonary venous connection illustrate the potential use of MRI in diagnosing congenital heart anomalies. Both patients had the most common type of partial anomalous pulmonary venous connection, in which the right upper pulmonary vein is connected to the superior vena cava.' Ί Neither patient had a cardiac pacemaker or a recently Mayo Clin Proc 60: ,

2 Mayo Clin Proc, December 1985, Vol 60 MAGNETIC RESONANCE IMAGING "BROKEN RING" SIGN 875 placed aneurysm clip, which would have precluded our use of MRI. The magnetic resonance unit used in this study had a 0.15-tesla resistive magnet for proton imaging at 6.4 MHz. Cardiac gating was accomplished by triggering the pulse sequence on the R wave of the electrocardiographs signal, which was transmitted by means of a fiberoptic link. Spin echo pulse sequences with an echo delay time of 40 ms, a repetition time dependent on the R-R interval (approximately 900 to 1,100 ms), and two excitations per phase encoding view provided images of diagnostic quality. A multislice technique, with acquisition of four or six sections depending on the R-R interval, was used. The first section was obtained immediately after the R wave. Successive sections had incremental delays of approximately 125 ms. The scanning time averaged 8 to 10 minutes for multislice acquisition. The patients were closely monitored visually and electrocardiographically. We also used a battery-powered Doppler device to display the patient's peripheral pulse when the electrocardiographic signal was obscured by artifact during the period of actual imaging. 12 The total time of each patient's examination was approximately 45 minutes. Both patients tolerated the examination well, and no adverse effects were noted. RESULTS 3-75"7-63i Case 1. A 17-year-old girl had clinical evidence of right-sided heart failure and chest roentgenographic evidence of cardiomegaly. A two-dimensional echocardiographic examination disclosed right atrial, right ventricular, and left atrial enlargement. The left ventricle was of normal size and had an ejection fraction of 48%. The echocardiographer was convinced that ali the pulmonary veins had been identified and that they were connected to the left atrium. The final echocardiographic impression was that this patient most likely had a restrictive cardiomyopathy. During cardiac catheterization, a 20% increase in hemoglobin oxygen saturation was discovered in the midportion of the superior vena cava. Angiography demonstrated a right upper pulmonary vein that received the right upper and middle lobe pulmonary veins and entered the superior vena cava approximately 3 cm proximal to the junction of the superior vena cava and the right atrium (Fig. 1). Selective injection of the left pulmonary artery demonstrated an intact interatrial septum. MRI was performed to evaluate its ability to demonstrate the cardiovascular anatomy of this congenital anomaly. In a patient with normal anatomy, a distinct ringlike structure is evident on a transverse magnetic & ** ε-3ο-βγ Fig. 1 (case U.Angiogram in 30 right anterior oblique projection. Note transvenous catheter in superior vena cava, with its tip in the anomalously connected right upper pulmonary vein. resonance image because of the high-intensity signal from the mediastinal fat surrounding the superior vena cava (Fig. 2). This ring represents the wall of the superior vena cava, which is made highly visible because of the surrounding low-intensity signal from the air-containing lung and the flow void in the lumen of the superior vena cava. The ringlike appearance of the superior vena cava on a transverse MRI view in a patient without anomalous pulmonary venous connection to the superior vena cava is normally broken only at the point of entrance of the azygos vein (Fig. 3). The coronal magnetic resonance image displays the lateral wall of a normal superior vena cava as an uninterrupted structure that extends from the entrance of the left subclavian vein to the right atrium (Fig. 4). The corresponding transverse and coronal images in this patient illustrated a ring that was "broken" in its lateral aspect and a discontinuous lateral wall of the superior vena cava, respectively (Fig. 5). These findings corresponded to the point of entrance of the anomalously connecting right upper pulmonary vein into the superior vena cava, as revealed previously by angiography. Figure 6 illustrates two transverse images that proceed caudally from the transverse scan in Figure 5. They demonstrate an enlarged superior vena cava entering a dilated right atrium and an intact superior portion of the interatrial septum. Two additional coronal sections reveal the interruption in the lateral wall of the superior vena cava due to the partial anomalous pulmonary venous connection (Fig. 7 A) and dilatation of both atria, an enlarged coro-

3 876 MAGNETIC RESONANCE IMAGING "BROKEN RING" SIGN Mayo Clin Proc, December 1985, Vol 60 (L-3oc3>-W os.,.?-7-av* Fig. 2. A, Transverse spin echo magnetic resonance image of normal anatomy at level of right pulmonary artery. Arrow points to lateral wall of superior vena caval "ring." B, Diagram of structures demonstrated in A. A = ascending aorta; D = descending aorta; MPA = main pulmonary artery; RPA = right pulmonary artery; 5 = superior vena cava. nary sinus, and an intact interatrial septum (Fig. 7 ß). The patient underwent surgical correction, at which time the aforementioned anatomy was confirmed. Pathologic examination of the biopsy specimens obtained at the time of operation revealed no evidence of acute myocarditis but did identify moderate endocardial fibrosis, mild interstitial fibrosis, and moderate myocardial cellular hypertrophy consistent with either a restrictive or a hypertrophic cardiomyopathy. Case 2. A 72-year-old man had Parkinson's disease and chronic atrial fibrillation accompanied by congestive heart failure. During evaluation of his condition, an echocardiogram demonstrated an enlarged right ventricular cavity and flattening of the interventricular septum, findings that suggested the presence of pulmonary arteri- al hypertension. The interatrial septum appeared intact echocardiographically. Cardiac catheterization was performed to investigate further the possibility of pulmonary arterial hypertension. A 10% increase in hemoglobin oxygen saturation was detected in the superior vena cava. Angiography established the diagnosis of a partial anomalous pulmonary venous connection that involved the right upper pulmonary vein, which entered the superior vena cava just above the junction of the superior vena - <H>0- J2I c bz Fig. 3. Transverse spin echo magnetic resonance image, demonstrating normal posterior break in superior vena caval "ring" due to entrance of azygos vein. Longer arrow indicates the arch of azygos vein, and shorter arrow indicates ascending azygos vein. Note intimal flap in descending aorta in this image of a patient with aortic dissection. Fig. 4. Coronal spin echo magnetic resonance image in plane of the junction of the superior vena cava and the right atrium, demonstrating uninterrupted lateral wall of superior vena cava (arrow). Note absence of tricuspid valve in this image of patient with tricuspid atresia. RA = right atrium; RV = right ventricle.

4 Mayo Clin Proc, December 1985, Vol 60 MAGNETIC RESONANCE IMAGING "BROKEN RING" SIGN *-5i-tf JA Z-3I- 8f Fig. 5 (case 1). A, Transverse spin echo magnetic resonance image at level of carina, demonstrating break in lateral aspect of superior vena caval "ring" (arrow) and pronounced dilatation of superior vena cava. B, Coronal spin echo magnetic resonance image in plane of superior vena cava (S). Note "break" in lateral wall of superior vena cava at point of anomalous pulmonary venous connection (arrow). PA = pulmonary artery. cava and the right atrium, and an associated sinus venosus atrial septal defect (Fig. 8). The magnetic resonance images were not optimal because of motion artifacts induced by an involuntary body tremor, which was thought to be a component of the patient's parkinsonism. Nevertheless, the transverse images revealed the "broken ring" sign and also demonstrated the defect in the superoposterior aspect of the interatrial septum, diagnostic of a sinus venosus atrial septal defect (Fig. 9). DISCUSSION Current techniques used in MRI produce sufficient contrast and spatial resolution to display both intracardiac a os 2-3/-S: and extracardiac thoracic vascular anatomy adequately. Although the specificity and sensitivity of this diagnostic method remain to be established, the display of the pertinent anatomic features of partial anomalous pulmonary venous connection to the superior vena cava, as illustrated in our two cases, suggests that MRI may be the imaging modality of choice for detection of this cardiovascular malformation. Moreover, MRI seems to be a valuable alternative for further investigation of other congenital heart diseases, inasmuch as accurate diagnosis of these conditions often depends on defining the structural abnormality present. In addition, pediatric patients should be excellent candidates for MRI because smaller coils could be used, and the quality of the images could thereby be improved. 75*7-6 äi o2 Fig. 6 (case 1). Transverse spin echo magnetic resonance images, which proceed caudally from transverse slice shown in Figure 5 A. A, Transverse section below entrance of anomalously connecting pulmonary vein, demonstrating dilated superior vena cava (5) with intact "ring." B, Transverse section at level of aortic valve (A), demonstrating dilated right and left atria in conjunction with an intact superior portion of interatrial septum (arrow). LA = left atrium; RA = right atrium.

5 878 MAGNETIC RESONANCE IMAGING "BROKEN RING" SIGN Mayo Clin Proc, December 1985, Vol ^ Χ-3Ι-ΖΪ ^34 /y f Fig. 7 (case 1). Coronal spin echo magnetic resonance images. A, In plane of anomalously connected pulmonary vein (arrow). B, In plane 1 cm posterior to image in A, demonstrating intact interatrial septum. Note dilatation of both atria and enlarged coronary sinus immediately inferior to interatrial septum. MRI is noninvasive and unencumbered by some of the limitations of two-dimensional echocardiography, such as the difficulty in obtaining an adequate acoustic window in postoperative patients. The failure of echocardiography to disclose the partial anomalous pulmonary venous connection in the two patients described herein is attributable to the lack of a global view of the intrathoracic anatomy. Therefore, MRI should be used with increasing frequency as a method of further evaluation in suspected cases of congenital or acquired cardiovascular disorders. 3-77^-^33 *3 <?-//-gy REFERENCES 1. Axel L, Kressel HY, Thickman D, Epstein DM, Edelstein W, Bottomley P, Redington R, Baum S: NMR imaging of the chest at 0.12 T: initial clinical experience with a resistive magnet. AJR 141: , Fletcher BD, Jacobstein MD, Nelson AD, Riemenschneider TA, Alfidi RJ: Gated magnetic resonance imaging of congenital cardiac malformations. Radiology 150: , O'Donovan PB, Ross JS, Sivak ED, O'Donnell JK, Meaney TF: Magnetic resonance imaging of the thorax: the advantages of coronal and sagittal planes. AJR 143: , Higgins CB, Stark D, McNamara M, Lanzer P, Crooks LE, Kaufman L: Multiplane magnetic resonance imaging of the heart and major vessels: studies in normal volunteers. AJR 142: , Crooks LE, Barker B, Chang H, Feinberg D, Hoenninger JC, Watts JC, ArakawaM, Kaufman L, Sheldon PE, BotvinickE, Higgins CB: Magnetic resonance imaging strategies for heart studies. Radiology 153: , 1984 Fig. 8 (case 2). Angiogram obtained by means of a transvenous catheter in superior vena cava with its tip positioned in anomalously connecting right upper pulmonary vein (RPV), with use of a compound angulated view (70 left anterior oblique and 20 caudocranial). Note right-to-left shunting of contrast material, which substantiates sinus venosus atrial septal defect (arrow). LA = left atrium; RA = right atrium; S = superior vena cava.

6 Mayo Clin Proc, December 1985, Vol 60 MAGNETIC RESONANCE IMAGING "BROKEN RING" SIGN if IA-S\ i3 3-TH-JL33 ol 7-/2-?Ϋ Fig. 9 (case 2). Transverse spin echo magnetic resonance images with motion artifact caused by tremor in patient with Parkinson's disease. A, Plane of image above level of entrance of anomalous pulmonary venous connection, demonstrating normal complete superior vena caval "ring." (See Figures 2 A and B for comparison.) B, Plane of image at level of entrance of anomalous pulmonary venous connection. Note break in lateral aspect of superior vena caval "ring" (arrow). C, Plane of image immediately inferior to the junction ofthe superior vena cava and right atrium, demonstrating interruption in interatrial septum due to sinus venosus atrial septal defect in superoposterior aspect of interatrial septum. Arrow indicates edge of interatrial septum adjacent to sinus venosus atrial septal defect. (See Figure 6 B for comparison.) Dinsmore RE, Wismer GL, Levine RA, Okada RD, Brady T): 9. Magnetic resonance imaging of the heart: positioning and gradient angle selection for optimal imaging planes. AJR 143: , Herfkens RJ, HigginsCB, Hricak H, Lipton MJ, Crooks LE, Lanzer P, Botvinick E, Brundage B, Sheldon PE, Kaufman L: Nuclear magnetic resonance imaging of the cardiovascular system: nor- 11. mal and pathologic findings. Radiology 147: , 1983 Axel L: Blood flow effects in magnetic resonance imaging. AJR : , 1984 Mills CM, Brant-Zawadzki M, Crooks LE, Kaufman L, Sheldon P, Norman D, Bank W, Newton TH: Nuclear magnetic resonance: principles of blood flow imaging. AJR 142: , 1984 Singer JR: Blood flow measurements by NMR. In Nuclear Magnetic Resonance Imaging in Medicine. Edited by L Kaufman, LE Crooks, AR Margulis. New York, Igaku-Shoin, 1981, pp Brody H: Drainage ofthe pulmonary veins into the right side ofthe heart. Arch Pathol 33: , 1942 Roth JL, Nugent M, Gray JE, Julsrud PR, Berquist TH, Sill JC, Kispert DB, Hayes DL: Patient monitoring during magnetic resonance imaging. J Anesthesiol (in press)