Aortic Coarctation (CoA) Imaging

Updated: Sep 18, 2020
  • Author: Vibhuti N Singh, MD, MPH, FACC, FSCAI; Chief Editor: Eugene C Lin, MD  more...
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Practice Essentials

Coarctation of the aorta (CoA) is a common congenital cardiovascular defect characterized by upper-body hypertension resulting from constriction of the aorta. Constrictions vary in degree; they may occur at any point from the transverse arch to the iliac bifurcation. [1]  Aortic coarctation is most commonly found just distal to the origin of the left subclavian artery. The vascular malformation responsible for coarctation is a defect in the vessel media, giving rise to a prominent posterior infolding (the “posterior shelf”), which may extend around the entire circumference of the aorta. [2, 3, 4]

Coarctation is caused by an abnormality in development of the embryologic left fourth and sixth aortic arches. It occurs in 40 to 50 of 100,000 live births and in twice as many males as females. Aortic coarctation is commonly treated after birth or during childhood. [1, 2]

According to guidelines for suspected aortic coarctation by the American College of Cardiology/American Heart Association (ACC/AHA), useful initial imaging and hemodynamic evaluation is by transthoracic echocardiogram, including suprasternal notch acoustic windows. [5]

The European Society of Cardiology guidelines largely agree with the ACC/AHA recommendations. They recommend that intervention be considered in hypertensive patients with more than 50% aortic narrowing relative to the aortic diameter at the level of the diaphragm as seen on MRI, CT scan, or invasive angiography, regardless of the pressure gradient. [6]

Radiography

The findings on radiographic examination depend on the age of the patient and on the effects of hypertension and collateral circulation. Infants with severe coarctation have cardiac enlargement and pulmonary congestion. During childhood, the findings are not striking until after the first decade, when the heart tends to be mildly or moderately enlarged because of the prominence of the left ventricle.

The enlarged left subclavian artery commonly produces a prominent shadow in the left superior mediastinum. Notching of the inferior border of the ribs from pressure erosion by enlarged collateral vessels is common by late childhood. In most instances, an area of poststenotic dilatation of the descending aorta is present. [7]

Echocardiography

The segment of coarctation may usually be visualized by 2-dimensional echocardiography; associated anomalies of the mitral and aortic valve may also be demonstrated. The descending aorta is hypopulsatile. [8, 9]

Color Doppler imaging is useful for demonstrating the specific site of the obstruction. Pulsed and continuous-wave Doppler study may be used to determine the pressure gradient directly at the area of coarctation. However, in the presence of a patent ductus arteriosus, the severity of the narrowing may be underestimated. [10]

Prenatal detection of coarctation may improve neonatal survival and reduce morbidity. Findings of ventricular asymmetry, arterial disproportion, and hypoplasia of the aortic arch/isthmus on fetal echocardiogram should raise suspicion of aortic coarctation. However, despite advances in imaging, diagnostic confirmation is often achieved only after postnatal echocardiography is performed. [11, 12, 13]

Cardiac magnetic resonance

Transthoracic echocardiography is the primary imaging modality for suspected CoA, but cardiac magnetic resonance imaging (CMR) is the preferred advanced imaging modality for noninvasive diagnosis and follow-up of CoA. [14, 15]

Cardiac catheterization

Cardiac catheterization with selective left ventriculography and aortography is useful in evaluating selected patients who have additional anomalies; it is also useful as a means of visualizing collateral blood flow. In cases that are well defined by echocardiography, diagnostic catheterization is usually not required before surgery.

CT angiography

In a study of 239 infant patients with aortic coarctation (CoA) who underwent CT angiography (CTA) and echocardiography, 4 anatomic features showed significant differences between mild and severe CoA: smallest aortic cross-sectional area indexed to body surface area (P< 0.001), narrowest aortic diameter (CoA diameter) indexed to height (P< 0.001), diameter of the descending aorta at the diaphragmatic level (P< 0.001), and weight (P=0.005). CoA diameter indexed to weight was associated with the risk of recoarctation. [16]

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Radiography

The diagnosis of coarctation of the aorta may be established from the posteroanterior (PA) chest image alone in up to 92% of patients. Widening of the left subclavian artery border is the most common finding, but the most useful radiographic sign is an abnormal contour of the aortic arch, which may appear as a double bulge above and below the usual site of the aortic knob.

This pattern has been described as a figure-3 sign. The upper arc of the 3 is the dilated arch proximal to the coarctation and/or a dilated left subclavian artery. The lower arc or bulge represents poststenotic dilatation of the aorta immediately below the coarctation. The indentation between the 2 bulges is the coarctation itself. When the esophagus is filled with barium, a reverse 3 or E sign is often seen; it is a mirror image of the areas of prestenotic and poststenotic dilatation.

The 3 sign is variable in that the upper arc may be small and the lower arc large, or vice versa. Superior mediastinal widening or sternal scalloping, caused by large internal mammary collateral arteries, is visible in some patients. A prominent left ventricular border often occurs with coarctation, particularly when a bicuspid aortic valve is associated with aortic stenosis.

Bilateral symmetrical rib notching, readily appreciated on the chest image, is diagnostic of aortic coarctation. It is the result of obstruction of blood flow at the narrowed aortic segment, in conjunction with collateral blood flow through the intercostal arteries. Rib notching is unusual in infancy but becomes more frequent with increased age; it is present in 75% of adults with coarctation. Rib notching occurs along the inferior margin of the third to the eighth ribs; it is caused by pulsation of dilated intercostal arteries.

The major pathways of collateral flow include the following:

  • Subclavian artery to the internal mammary artery to the intercostal arteries

  • Subclavian artery to the costovertebral trunk to the intercostal arteries

  • Transverse cervical and suprascapular arteries to the intercostal arteries

Radiographic findings depend on the age of the patient and on the effects of hypertension and collateral circulation. In infants with severe coarctation, cardiac enlargement and pulmonary congestion are present.

During childhood, the findings are not striking until after the first decade, when the heart tends to be mildly or moderately enlarged because of the prominence of the left ventricle. The enlarged left subclavian artery commonly produces a prominent shadow in the left superior mediastinum. Notching of the inferior border of the ribs from pressure erosion by enlarged collateral vessels is common by late childhood. In most instances, an area of poststenotic dilatation of the descending aorta is present. [17, 18]

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Magnetic Resonance Imaging

MRI vividly portrays the anatomy of the coarctation. It also demonstrates the bicuspid valve and the state of left ventricular function, as well as restenosis following angioplasty or surgical repair (see the image below). [19, 20, 21, 22, 23, 24, 25] The degree of confidence is very high. Transthoracic echocardiography is the primary imaging modality for suspected CoA, but cardiac magnetic resonance imaging (CMR) is the preferred advanced imaging modality for noninvasive diagnosis and follow-up of CoA. [14, 15]  Four-dimensional cardiac magnetic resonance (CMR) has been shown to provide additional guidance before initiation of invasive procedures. [24, 26]

Aortic coarctation visualized by MR imaging. Aortic coarctation visualized by MR imaging.
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Ultrasonography

The segment of coarctation may usually be visualized by means of 2-dimensional echocardiography. Associated anomalies of the mitral and aortic valve may also be demonstrated. The descending aorta is hypopulsatile. Color Doppler imaging is useful for demonstrating the specific site of the obstruction. Pulsed and continuous-wave Doppler imaging may be used to determine the pressure gradient directly at the area of coarctation. In the presence of a patent ductus arteriosus, the severity of the narrowing may be underestimated. [8, 13, 10]

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Angiography

Cardiac catheterization with selective left ventriculography and aortography is useful in selected patients who have additional anomalies. It is also useful in visualizing collateral blood flow. In cases that are well defined by echocardiography, diagnostic catheterization is usually not required before surgery (see the image below). [27]

Aortic coarctation visualized by aortic angiograph Aortic coarctation visualized by aortic angiography.
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