Two adult patients with cor triatriatum, which was shown by echocardiography and magnetic resonance imaging (MRI) using both spin-echo and cine-MR techniques, are presented. Spin-echo MRI clearly demonstrated an anatomical relationship between the membrane and pulmonary veins or left atrial appendage, which was not clear on transthoracic echocardiography. In addition, cine-MRI depicted abnormal flow through the fenestration of the anomalous membrane (case 1 and 2) and shunted flow through the associated atrial septal defect (case 2).
(Chest 1994; 106:1586-89)
ASD=atrial septal defect;
US=ultrasonography;
MRI=magnetic resonance imaging
Cor triatriatum is an uncommon congenital cardiac malformation in which the left atrium is subdivided into two chambers by an anomalous membrane. The common pulmonary vein persists as an accessory chamber that communicates with the true chamber connected to the left atrial appendage and the mitral valve. Communication between the two chambers is accomplished by one or more fenestrations in the membrane, which produces ventricular inflow obstruction similar to that in mitral stenosis.
Although spin-echo magnetic resonance imaging (MRI) provides excellent preoperative delineation of the anomalous membrane,(1)(2) the usefulness of cine-MRI in depicting the hemodynamics of the blood flow through the fenestration in the membrane has not been reported to our knowledge. We present two cases of cor triatriatum in which surgery was performed, and emphasize the usefulness of cine-MRI in the evaluation of the anatomy and hemodynamics of cor triatriatum.
CASE REPORTS
CASE 1
A 25-year-old man was admitted to the hospital because of exertional dyspnea. At the time of physical examination, heart sounds were normal and no cardiac murmur was heard. A chest radiograph showed pulmonary venous congestion. Transthoracic ultrasonography (US) demonstrated an anomalous membrane in the left atrium. However, the anatomical relationship between the membrane and pulmonary veins or left atrial appendage was not clear. On transthoracic color Doppler US, abnormal flow was observed in the chamber anterior to the membrane (true chamber), but the fenestration of the membrane was not detected. The patient was examined with MRI on a 1.5-T superconducting system (Signa; GE Medical Systems, Milwaukee). On spin-echo imaging, the membrane in the left atrium and flow-related hyperintensity area in the chamber posterior to the membrane (accessory chamber) were observed. Pulmonary veins were connected to the accessory chamber and the left atrial appendage was connected to the true chamber. On cine-MRI, signal void was observed in the left atrium through the fenestration of the membrane, which could not be detected by transthoracic color Doppler flow imaging or spin-echo MRI (Fig 1). The blood flow was noted as a jet stream along the left atrial and ventricular septa in the early diastolic phase and changed direction in the late diastolic phase, turning back to the closed mitral leaflet. No other cardiac abnormalities were found. At surgery, the presence of an anomalous membrane with a 1-cm fenestration was confirmed in the left atrium.
CASE 2
A 26-year-old man was admitted to the hospital because of exertional dyspnea and fatigue. Physical examination revealed no significant findings. No cardiac murmur was heard. Transthoracic US demonstrated an anomalous membrane in the left atrium and an atrial septal defect (ASD). On transthoracic color Doppler US, abnormal flow in the true chamber and shunted flow through the ASD were observed. However, the anatomical relationship between the membrane and the pulmonary veins or the left atrial appendage was not clear, and the fenestration of the membrane could not be detected with US alone. The MRI of the heart was obtained using spin-echo and cine-MR techniques. Spin-echo MRI clearly depicted the membrane in the left atrium and revealed that the pulmonary veins were connected to the accessory chamber and that the left atrial appendage was connected to the true chamber. In addition, cine-MRI depicted not only the signal void through the fenestration of the anomalous membrane, but also shunted flow through the associated ASD (Fig 2). At surgery, an anomalous membrane with a 1.5-cm fenestration and 2-cm ASD were confirmed.
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DISCUSSION
Clinical manifestation of cor triatriatum depends on the size of the fenestration in the anomalous membrane, the existence of anomalous pulmonary venous drainage and other associated anomalies. Depending on the degree of disturbance of the pulmonary venous return, the lesion might go undetected until adulthood.(3)
With the use of transthoracic US, the anomalous membrane was not always detected, and even if visualized, the whole structure could not be delineated because of limited acoustic windows and ultrasonic artifacts. This was partly overcome by the newly developed transesophageal US.(4)(5)(6)(7) On transesophageal US, however, the posterior portion of the left atrium close to the transducer can be missed because of the lack of spatial resolution in the near field of the transducer.(7) Differential diagnoses on the basis of US results include mitral stenosis, dilatation of the coronary sinus associated with the anomalous pulmonary venous return or persistent left superior vena cava, especially supravalvular mitral ring.(4)(5)(6) Supravulvular mitral ring can be anatomically distinguished from cor triatriatum by its location below the left atrial appendage.
The MRI with spin-echo technique is effective for visualization of anatomic abnormalities in congenital heart disease. There have been two reports concerning the usefulness of spin-echo images in the evaluation of cor tratriatum.(1)(2) In these reports, although the abnormal membrane was clearly visualized on spin-echo MRI, the fenestration of the anomalous membrane could not be detected with spin-echo technique. Cine-MRI, with a new pulse sequence, has been recently used to evaluate dynamic cardiac function and hemodynamics in congenital and acquired heart diseases.(8) High velocity flow and turbulent flow can be observed as low-signal intensity contrasted against a background of high-signal intensity representing normal blood flow. In our two cases, while neither transthoracic US nor MRI with spin-echo technique could show the fenestration, cine-MRI clearly depicted the fenestration and abnormal flow through the fenestration as low-signal intensity.
The inherent limitations of this new technique include limited in-plane spatial resolution, partial volume artifacts, and poor data acquisition due to cardiac arrythmias. Also, the images are not available in real time. Despite these limitations, cine-MRI, like standard spin-echo MRI, is able to scan all of the left atrium without hindrance from anatotomic obstacles, and it is suited for assessing the hemodynamics of this disease.
Whenever left ventricular inflow obstruction is suspected from clinical findings and transthoracic echocardiographic studies are not diagnostic, MRIs should be obtained. We believe that a combination of spin-echo and cine-MRI obviate the need for cardiac catheterization.
REFERENCES
(1)Rumancik WM, Schulman MH, Rutkowski MM. Magnetic resonance imaging of cor triatriatum. Pediatr Cardiol 1988; 9:149-51
(2)Bisset GS, Kirks DR, Strife JL, Schwartz DC. Cor triatriatum: diagnosis by MR Imaging. Am J Radiol 1987; 149:567-568
(3)Marin-Garcia J, Tandon R, Lucas RV, Edwards JE. Cor triatriatum: study of 20 cases. Am J Cardiol 1975; 35:59-66
(4)Ostman-Smith I, Silverman NH, Oldershaw P, Lincoln C. Cor triatriatum sinistrum: diagnostic features on cross-sectional echocardiography. Br Heart J 1984; 51:211-19
(5)Jacobstein MD, Hilschfeld SS. Concealed left atrial membrane: pitfalls in the diagnosis of cor triatriatum and supravalve mitral ring. Am J Cardiol 1982; 49:780-786
(6)Glaser J, Goren A, Ilan M, Vidne B. Cor triatriatum sinistrum: diagnosis by Doppler echocardiography. Cardiology 1990; 77:472-76
(7)Schluter M, Langenstein BA, Thier W. Transesophageal two-dimensional echocardiography in the diagnosis of cor triatriatum in the adult. J Am Coll Cardiol 1983; 2:1011-1015
(8)Sechtem U, Pflugfelder PW, Gould RG, Holt W, Lipton MJ, Higgins CB. Cine MR imaging: potential for the evaluation of cardiovascular function. Am J Radiol 1987; 148:239-246
COPYRIGHT 1994 American College of Chest Physicians
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