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Clinical Letters

Hypoplasia of the Posterior Mitral Leaflet Concurrent With a Supravalvular Mitral Ring: A Rare Cause of Congenital Mitral Stenosis Videos online at www.jultrasoundmed.org

A 13-month-old infant with a preexisting diagnosis of bronchopneumonia presented with symptoms of dyspnea. Transthoracic echocardiography showed a dilated left atrium and dysplastic mitral valve. The mitral valve was characterized by a short anterior leaflet, but the posterior leaflet was virtually absent; instead, there was an anomalous bulky muscular structure replacing the posterior leaflet (Figure 1A and Videos 1 and 2). Transthoracic echocardiography also revealed an annular membranelike structure that was attached to the atrial wall and the anterior mitral leaflet and in close proximity to the posterior muscular structure (Figure 1A and Videos 1 and 2). The findings were consistent with a supravalvular mitral ring. During diastole, color Doppler imaging displayed a mitral inflow turbulent jet (Figure 1B), and continuous wave Doppler imaging revealed severe mitral stenosis (mean diastolic pressure gradient, 20 mm Hg).

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Three-dimensional echocardiography additionally allowed distinct visualization of the posterior muscular structure (viewed from the left ventricle) and the supravalvular mitral ring (Figure 1, C and D, and Videos 3 and 4). Viewed from the left atrium, the supravalvular mitral ring appeared as a circumferential diaphragm with a small offcenter orifice (Figure 1D).

Other anomalies potentially coexisting with the dysplastic mitral valve, including a ventricular septal defect, patent ductus arteriosus, and hypoplastic aortic arch, were also present in this infant. The patient underwent surgical repair, by which the diagnosis was confirmed.

Figure 1. A, Two-dimensional apical 4-chamber echocardiogram showing hypoplasia of the mitral valve and the supravalvular mitral ring (arrows). B, Transthoracic apical 4-chamber Doppler echocardiogram showing convergent flow during diastole. C, Three-dimensional echocardiographic view from the left ventricle. The dysplastic mitral valve appears as a short anterior mitral leaflet and posterior anomalous bulky muscular structure (arrows). D, Three-dimensional echocardiographic view from the left atrium. The supravalvular mitral ring appears as a circumferential diaphragm with a small off-central orifice (arrow). AMVL indicates anterior mitral valve leaflet; LA, left atrium; LV, left ventricle; PMS, posterior muscular structure; SO, small orifice; and SVMR, supravalvular mitral ring. A

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We postulate that the anomalous posterior muscular structure may have occurred because of developmental arrest during conversion of the muscular chordae and leaflets to thin connective tissue structures.1,2 To the best of our knowledge, a case of congenital mitral stenosis characterized by a developmental arrest–induced posterior mitral leaflet concurrent with a supravalvular mitral ring in vivo has not been reported previously. Jing Zhang, MB, Feifei Sun, MB, Weidong Ren, MD, PHD, Yangjie Xiao, MB, Ying Zhan, MB Department of Ultrasound Shengjing Hospital of China Medical University Shenyang, China doi:10.7863/ultra.33.4.736

References 1.

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Schoenwolf GC, Bleyl SB, Brauer PR, Francis-West PH. Development of the Heart. In: Larsen’s Human Embryology. 4th ed. Philadelphia, PA: Churchill Livingstone; 2009:369–370. Kalangos A, Oberhansli I, Baldovinos A, Beghetti M, Friedli B, Faidutti B. Hypoplasia of the posterior leaflet as a rare cause of congenital mitral insufficiency. J Card Surg 1997; 12:339–342.

J Ultrasound Med 2014; 33:735–740

Hypoplasia of the posterior mitral leaflet concurrent with a supravalvular mitral ring: a rare cause of congenital mitral stenosis.

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