Aortic Coarctation Imaging 

Coarctation of the aorta 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]

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.^[2]

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.

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.

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.

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.^{[3, 4]}

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).^{[5, 6]} The degree of confidence is very high.

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.

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).^[7]