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AJR Integrative Imaging LIFELONG LEARNING FOR RADIOLOGY |
1 Department of Radiology, University Hospital, UMDNJ-NJ Medical School, 150 Bergen St., UH C-320, Newark, NJ 07103-2406.
Received February 15, 2007; accepted after revision February 15, 2007.
Address correspondence to P. D. Maldjian
(maldjipd{at}umdnj.edu).
The educational objectives for this self-assessment module are for the participant to exercise, self-assess, and improve his or her understanding of the diagnostic imaging approach to dextrocardia.
Keywords: cardiac imaging • dextrocardia • heart
INTRODUCTION
This self-assessment module on the diagnostic imaging approach to dextrocardia has an educational component and a self-assessment component. The educational component consists of one required article that the participant should read. The self-assessment component consists of six multiple-choice questions with solutions. All of these materials are available on the ARRS Website (www.arrs.org). To claim CME and SAM credit, each participant must enter his or her responses to the questions online.
EDUCATIONAL OBJECTIVES
By completing this educational activity, the participant will:
REQUIRED READING
(available at www.arrs.org)
RECOMMENDED READING
INSTRUCTIONS
| QUESTION 1 In the setting of congenital heart disease, which of the following descriptions is most reliable for identification of the morphologic right atrium?
QUESTION 2 In the setting of congenital heart disease, which of the following features is most reliable for identification of the morphologic right ventricle?
QUESTION 3 Which of the following statements describes the relationship of the pulmonic valve to the aortic valve in a patient with situs inversus totalis who is otherwise normal?
QUESTION 4 Which of the following abnormalities is most common in polysplenia syndrome?
QUESTION 5 Which of the following statements concerning congenitally corrected transposition of the great arteries (TGA) is FALSE?
QUESTION 6 Which of the following is LEAST likely to be encountered as a cause of dextrocardia?
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Solution to Question 1
In the setting of congenital heart disease, the most reliable feature for identification of the morphologic right atrium (or venous atrium) is the connection to the inferior vena cava [1, 2]. Option B is the best response. The superior vena cava, especially a persistent left superior vena cava, can enter the morphologic left atrium (systemic atrium) [3]. Option A is not the best response. The morphologic right atrium has a triangular appendage with a wide ostium. It is the morphologic left atrium that has a tubular appendage with a narrow orifice [1]. Option C is not the best response. Although one would usually expect the atrium connected to the morphologic right ventricle to be the morphologic right atrium, this is not always so as with congenitally corrected TGA. Discordant atrioventricular and ventriculoarterial connections are characteristic of this disorder; hence the morphologic right atrium connects to the morphologic left ventricle, and the morphologic left atrium connects to the morphologic right ventricle. Option D is not the best response. It is usually the morphologic left atrium, not the right, that receives the pulmonary veins [4]. Option E is not the best response.
Solution to Question 2
The morphologic right ventricle is best characterized by the presence of an infundibulum, a muscular region that separates the inflow region from the outflow region. Option C is the best response. The absence of an infundibulum in a morphologic left ventricle results in proximity of the inflow bicuspid and the outflow semilunar valves. Hence, the valves share a fibrous annulus, termed "fibrous continuity of the valves." Option A describes a characteristic of the morphologic left ventricle and is not the best response. Well-formed papillary muscles and a smooth surface devoid of trabeculations along its side of the interventricular septum are properties of a morphologic left ventricle. Options B and D are not the best responses. The morphologic right ventricle has a tricuspid inflow valve, whereas the morphologic left ventricle has a bicuspid inflow valve [5]. Option E is not the best response.
Solution to Question 3
In normal individuals (situs solitus with no congenital heart disease), the pulmonic valve is anterior, superior, and slightly to the left of the aortic valve. Hence, option A describes the configuration seen in normal individuals and is not the best response. With situs inversus, in the absence of any other abnormalities, the configuration is the mirror image of normal, which is termed "inversion of the great vessels." Hence, the pulmonic valve is anterior, superior, and slightly to the right of the aortic valve. Option B is the best response. In TGA, the pulmonic valve is usually posterior to the aortic valve. TGA can be further classified on the basis of the left-to-right relationship between the aorta and the pulmonary artery. D-TGA (dextro-TGA) is the configuration in which the transposed aortic valve is to the right of the transposed pulmonic valve. L-TGA (levo-TGA) is when the transposed aortic valve lies to the left of the transposed pulmonic valve [6]. Hence, options C and D describe D-TGA and L-TGA, respectively. Option E is not the best response because it describes the configuration of the valves associated with partial transposition complexes such as double-outlet right ventricle.
Solution to Question 4
Of the choices given, azygos or hemiazygos continuation is most commonly associated with polysplenia syndrome, which is reported to occur in 58-100% of cases. Option C is the best response. Bilateral superior vena cava occurs in 33-50% of polysplenic patients but is more strongly associated with asplenia syndrome, reported to occur in up to 71% of asplenia cases. Option A is not the best response. Bilateral hyparterial bronchi are characteristic of polysplenia syndrome. Bilateral eparterial bronchi (option B) and bilateral trilobed lungs (option E) are associated with asplenia syndrome. Options B and E are not the best responses. Total anomalous pulmonary venous return is also more strongly associated with asplenia syndrome, occurring in about 70% of cases [7]. Option D is not the best response.
Solution to Question 5
Congenitally corrected TGA is characterized by the presence of both discordant atrioventricular and discordant ventriculoarterial connections. The transposition is said to be "corrected" because the morphologic left atrium empties into a morphologic right ventricle that connects to the aorta, while the morphologic right atrium empties into a morphologic left ventricle that connects with the pulmonary artery. The discordant atrioventricular connections combine with the discordant ventriculoarterial connections (the definition of TGA) to maintain separation of the systemic and pulmonary circulations. Options A and B, which are true, are not the best responses. Associated cardiac anomalies such as ventricular septal defect, pulmonary outflow obstruction, and systemic atrioventricular valve dysfunction are commonly associated with congenitally corrected TGA. Option E is true and is not the best response. The tricuspid valve (the inflow valve of the morphologic right ventricle) is dysplastic in approximately 25% of cases, resulting in tricuspid insufficiency, which presents clinically in these patients as mitral regurgitation presents in patients without congenital heart disease. The outflow valve of the morphologic right ventricle (the systemic ventricle) in congenitally corrected TGA is usually normal. Option C is false and is the best response. Arrhythmias are also commonly associated with congenitally corrected TGA, with complete atrioventricular block occurring in up to 30% of patients [8]. Option D is true and is not the best response.
Solution to Question 6
Dextrocardia with situs inversus, also called mirror image dextrocardia, is the most common type of dextrocardia in the general population (present in 1-2/20,000). The incidence of congenital heart disease is low, about 2-5% [9]. Option A is not the best response. Dextroversion is the second most common type of dextrocardia representing extreme right-sided cardiac rotation relative to normal. Option B is not the best response. The term "dextroversion" is usually applied to all cases of dextrocardia with situs solitus [4]. In the most common form of dextroversion, a D-ventricular loop is formed during embryogenesis with the apex pointing to the right, but the apex of the primitive heart fails to migrate from the right to the left hemithorax. Although the right atrium and right ventricle remain to the right, they are located posterior to the corresponding left-sided chambers. In the less common variant of dextroversion, an L-ventricular loop forms (with the apex pointing to the left) and the primitive heart migrates into the right thoracic cavity. These patients have situs solitus with congenitally corrected TGA [10, 11]. Option E is not the best response. Dextrocardia can also occur in polysplenia syndrome in up to 50% of cases [12]. Option C is not the best response. Dextrocardia also occurs in association with all forms of congenitally corrected TGA in up to 30% of cases. Of the choices given, option D is the least likely to be encountered because situs inversus and congenitally corrected TGA (two rare abnormalities) must occur simultaneously in the same patient [9, 13]. Option D is the best response.
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