Shone’s complex is a rare congenital heart defect consisting of multiple, left-sided obstructive heart lesions including: supra-valvar mitral ring or membrane, parachute mitral valve, sub-aortic membrane and coarctation of the aorta. Shone’s variant, or incomplete Shone’s syndrome, is more common and typically diagnosed when only two or three left-sided obstructions are present in the setting of left heart hypoplasia (mitral valve, aortic valve, left ventricle aortic arch). A supra-valvar mitral ring is characterized by a membrane of connective tissue superior to the mitral valve orifice, which causes restriction of blood flow through the valve. A parachute mitral valve is typically characterized by a chordal attachments to a single papillary muscle, most commonly, the posteromedial papillary muscle. This results in a narrowed mitral valve annulus. The mitral valve leaflets are often thickened and dysplastic with limited mobility and restriction of flow. The sub-aortic stenosis may be membranous or muscular with restriction of blood flow below the aortic valve and across the left ventricular outflow tract. A bicommissural aortic valve is a common finding in patients with Shone’s syndrome, and typically results in valvar aortic stenosis. Coarctation of the aorta is described as narrowing of the aortic arch, typically at the level of the aortic isthmus. The transverse arch may be elongated and hypoplastic. This narrowing makes it difficult for blood to pass through resulting in less blood being sent to the lower body. True Shone’s complex, when all four defects are present, is rare and the term Shone's like complex is often used to refer to multiple sites of left sided obstruction and hypoplasia.
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