12 year-old female presenting with claudication. On physical exam patient was found to have blood pressure discrepancies between upper and lower extremities.

Figure 1: High grade stenosis (minimal diameter < 2 mm) of the aorta just distal to the origin of the left subclavian artery. Extensive collateral vessels are formed via the internal mammary artery and intercostals arteries. Note the differences in enhancement proximal and distal to the area of stenosis. Differences in signal intensity suggest that the descending aorta is predominantly supplied by collateral circulation.

Figure 2: Left subclavian artery is enlarged in caliber, probably reflecting collateral flow. . Collateral vessels are visualized (intercostals, internal mammary artery). Incidentally noted direct origin of the left vertebral artery off the aorta.

Movie 1: Short axis image of the heart demonstrates a “fish-mouth” appearance of the aortic valve. This is consistent with a bicuspid aortic valve. There is diffuse left ventricular hypertrophy .

Aortic coarctation.

Aortic coarctation is a congenital anomaly of unknown etiology. The underlying abnormality of the aortic media causes eccentric narrowing of the aortic lumen. This narrowing results in an in-folding of the aortic wall adjacent to the orifice of the left subclavian artery and, thus, creates a tight stenosis of the left ventricular outflow tract. A pressure gradient is created across the coarctation site, with pressure gradients of more than 20-25 mm Hg defining moderate to severe coarctation.

There are 2 types of coarctation: localized (adult or postductal) and diffuse (infantile or preductal). The postductal type is more common and results from a short segment of narrowing near the ligamentum arteriosum, and occurs distal to the left subclavian artery. These patients are asymptomatic until later in childhood and commonly present with hypertension, differential arm/leg blood pressures, claudication, and/or a heart murmur. The preductal type has a long segment of hypoplastic narrowing just distal to the origin of the brachiocephalic artery. These patients present early in infancy and childhood with congestive heart failure. There is a higher association of other cardiac anomalies (85% of cases have bicuspid aortic valve) and the prognosis for these patients tends to be worse than those with the postductal type of coarctation.

A characteristic appearance of the aorta on chest radiographs is a “reverse 3” configuration of the aortic knob and proximal descending aorta. The “figure 3” is formed by pre-stenotic dilation of the ascending aorta, the indentation of the coarctation site, and the post-stenotic dilatation of the descending aorta. In addition, there may also be inferior rib notching, commonly ribs 3-9. Rib notching is due to the pressure erosion by the enlarged and tortuous intercostals arteries and usually indicates long-standing obstruction. These intercostals arteries provide collateral blood flow to circumvent the stenotic aortic segment.

MRI is currently the initial imaging modality of choice for aortic coarctation. Parasagittal imaging in the 30o to 40o left anterior oblique plane with cardiac gating can demonstrate both the ascending and descending aorta. The site and extent of stenosis as well as collateral vascularization can be accurately defined. Cine MR images and phase-contrast flow quantification can provide additional hemodynamic information

References:

1. K Amplatz and JH Moller. Radiology of Congenital Heart Disease. Baltimore: Williams & Wilkins, 1993.
2. WE Brandt and CA Helms. Fundamentals of Diagnostic Radiology. Baltimore: Williams & Wilkins, 1999.
3. J Bogaert, AJ Duerinckx, and FE Rademakers (eds). Magnetic Resonance of the Heart and Great Vessels: Clinical Applications. Berlin: Springer, 1999.