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J Thorac Cardiovasc Surg 1997;114:134-138
© 1997 Mosby, Inc.
BRIEF COMMUNICATIONS |
San Francisco, Calif.
Received for publication Nov. 27, 1996 accepted for publication Dec. 11, 1996. Address for reprints: V. Mohan Reddy, MD, Division of Cardiothoracic Surgery, University of California, San Francisco, 505 Parnassus Ave., M593, San Francisco, CA 94143-0118.
Since Collett and Edwards
1 and the Van Praaghs 2 described their respective classifications of truncus arteriosus in 1949 and 1965, there has been extensive debate regarding the morphology and morphogenesis of lesions involving a common arterial trunk. 3-5 Among the points of disagreement is the issue of whether truncus arteriosus can occur with an intact ventricular septum. Recently, we encountered a patient whose lesion was diagnosed before operation as truncus type A1/A2 but was found intraoperatively to have an intact ventricular septum and an abnormal truncal valve complex with separate orifices guarding the left and right ventricular outflow tracts.
Clinical summary.
The patient was born after an uncomplicated term pregnancy and weighed 3145 grams at birth. Soon after birth, the patient began to have mild respiratory distress and received inpatient oxygen therapy for 3 days. A loud systolic murmur was detected at that time, and the patient underwent an initial cardiologic workup 6 days after birth. Echocardiography suggested a large single vessel arising from the heart, mainly committed to the right ventricle, a distorted single semilunar valve that was mildly stenotic and regurgitant, large pulmonary arteries arising from the trunk, and a secundum atrial septal defect. A diagnosis of truncus arteriosus type A1/A2 was made, and the patient was started on a regimen of digoxin and furosemide. The patient was referred to our institution for further evaluation and surgical treatment. At 28 days of age, an ascending aortogram was performed to better characterize the degree of truncal insufficiency. Results were consistent with the typical angiographic appearance of truncus type A2 and confirmed mild regurgitation, apparently entirely into the right ventricle (Fig. 1). At 30 days of age, the patient underwent operation.
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On retrospective evaluation of the preoperative echocardiogram, the semilunar valve structure observed at surgery could be appreciated from the parasternal short-axis view. Doppler color-flow mapping allowed distinction of two separate early systolic jets at the level of the semilunar valve (Fig. 3).
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1-5 Among the contested issues in this debate is the question of whether truncus arteriosus can exist in the presence of an intact ventricular septum. In 1965, the Van Praaghs 2 proposed a novel classification for truncus arteriosus that included two types of truncus with intact ventricular septum: types B2 and B4, which are analogous to types A2 and A4 except with an intact ventricular septum and separate semilunar valve orifices. In addition to the few cases they characterized in their 1965 report and subsequent reports, 6,7 other investigators have since described truncus with restrictive or functionally nonexistent ventricular septal defects, as well as truncus arising exclusively from the right 8 or left 9 ventricle with an intact ventricular septum. Excepting such rare cases, many morphologists argue that types B2 and B4 do not represent subtypes of truncus arteriosus at all, 3,4 but are simply the absence of the aortopulmonary septum, a severe form of aortopulmonary septal defect (aortopulmonary window) along the lines of the type IV defect proposed by Meisner and coworkers 10 or the complex lesion described by Berry and colleagues. 11 Neither hypothesis has been proven definitively, and both have their merits. Although several cases of complete repair in patients with truncus type B4 (or absent aortopulmonary septum with interruption of the aortic arch) have been reported, 11 to our knowledge no cases of neonatal repair of truncus type B2 have been described. Along the lines of this debate, some may believe that the situation described in the present report would be more aptly characterized as an aortopulmonary septal defect. Although we agree that some similar lesions may be aortopulmonary septal defects, rather than forms of truncus arteriosus, the lesion described here is better characterized as truncus with intact ventricular septum. Several morphologic features of this lesion appeared to be highly consistent with truncus arteriosus and to argue against simple aortopulmonary septal defect. Most notably, the semilunar valve apparatus was grossly abnormal, with a single anulus enclosing two valve orifices. The left-sided valve tissue was not normally seated between the atrioventricular valves, resulting in narrowing of the left ventricular outflow tract, and the left-sided component of the semilunar valve was bicuspid. The valve component guarding the right ventricular outflow tract was regurgitant and extremely dysplastic, with essentially a single large leaflet attached opposite the septal ridge. The tissue separating the two orifices was septal muscle. The free edge of this muscle extended to the plane created by the anulus of the valve, and the arterial tissue at the base of the common trunk did not extend onto the freestanding ridge of the conal septum. Attached to this ridge on both left and right sides was extremely dysplastic valve tissue. On external inspection, the base of the common trunk was seen to be cylindric, with no aortopulmonary septal invagination, even at the level of the valve, and the pulmonary arteries were seen to arise separately from the posterolateral aspect of the trunk, as in truncus type A2. Also, there was a single coronary artery coming off of the trunk, which is much more often the case with truncus than with aortopulmonary septal defect.
From a surgical perspective, how one chooses to classify this lesion is of little consequence. Standard techniques of repair for both truncus arteriosus and aortopulmonary septal defect were not applicable. Just as the lesion was highly unusual, the approach employed was individually tailored to the situation, with closure of the regurgitant right-sided semilunar valve orifice and reestablishment of continuity of the right ventricle to the pulmonary artery with an allograft conduit.
One of the most intriguing issues raised by this case is that although truncus arteriosus and aortopulmonary septal defects share the feature of deficient aortopulmonary septation, most investigators believe that they nonetheless derive from distinct anomalous developmental processes. 2-5 The strongest evidence supporting the etiologic disparity of these defects is the difference in the spectrum of associated lesions. For example, although both can occur in conjunction with interrupted aortic arch, truncus is almost always associated with type B interruption, whereas aortopulmonary septal defects are typically found with type A interruption. Similarly, truncus is frequently associated with DiGeorge syndrome, whereas such an association is almost never present in patients with aortopulmonary septal defects. Despite these widely acknowledged differences, there is a zone of ambiguity that continues to obfuscate our understanding of the pathogenetic relationship between truncus arteriosus and aortopulmonary septal defect, as the lesion described here certainly illustrates.
Footnotes
From the Divisions of Cardiothoracic Surgerya and Pediatric Cardiology,b University of California, San Francisco, Calif. 
References
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