2006-01-04T12:21:00.000-06:00

Answer
Thoracic aortic coarctation: The plain chest radiograph (see Image 2a) shows clinically significant abnormalities, including an enlarged left ventricle with irregularity of the descending aortic contour, and a characteristic figure-3 sign with notching of the inferior aspect of the lower rib. These findings suggest aortic coarctation in the thoracic aorta. The CT scan confirms the diagnosis, demonstrating absence of the descending aorta on an axial section in the midthorax. This absence is due to coarctation of the aorta distal to the left subclavian artery. Note the enlarged internal mammary arteries that provide collateral flow (see Image 2b). Aortic coarctation has a male predominance, with a male-to-female ratio of 2-4:1. Although coarctation can occur at any place in the aorta, one categorization method describes it in relation to the ductus arteriosus, a remnant of the sixth left aortic arch that connects the pulmonary trunk to the aorta in utero at the lower concave surface of the aortic arch directly opposite the left common carotid and the left subclavian arteries. Two major categories are described: preductal and postductal (usually distal to the left subclavian artery). Unlike postductal coarctation, preductal coarctation is usually discovered early in life. Because of a coexisting patent foramen ovale and patent ductus arteriosus, the fetus in utero does not experience changes in normal fetal blood-flow patterns. If the aorta is completely interrupted or if coarctation is nearly complete at birth with closure of the ductus arteriosus, the neonate may have rapid decompensation due to congestive heart failure, metabolic acidemia, and oliguria. In these cases, prostaglandin E1 (PGE1) (0.05-0.15 mcg/kg/min) is infused to open the ductus arteriosus. In nonsevere preductal coarctations, the mortality rate can be as high as 11% if the condition is not corrected before 6 months of age. With preductal coarctations, coexistent cardiac anomalies are relatively common. Bicuspid aortic valve is associated with 85% of preductal aortic coarctations, and Turner syndrome is associated with 13-15%. Preductal coarctation is also referred to as tubular hypoplasia if long-segment hypoplastic narrowing, usually distal to the origin of the innominate artery, is present. Postductal coarctations are usually discovered incidentally late in life. These anomalies are usually isolated defects with a low incidence of associated anomalies. Patients may present with symptoms such as headache, epistaxis, visual disturbances, or possibly exertional dyspnea or stroke. Relative hypertension or a gradient in systolic blood pressure between the arms and legs may be present. Checking the patient's blood pressure in both arms is important because the origin of the right subclavian distal to the coarcted segment may be anomalous. A systolic murmur may be heard over the left precordium or between the scapulae, and the femoral pulses may be absent or diminished, with a delayed upstroke. Children younger than 5 years and young adults may have signs of collateral circulation, such as enlarged palpable collateral vessels and audible bruits. In postductal coarctations, collateral flow involves the subclavian arteries and their branches, including the third through ninth bilateral intercostals (leading to notching of the inferior ribs) and the anterior spinal, lateral thoracic, internal mammary, scapular, and transverse cervical arteries. Other patterns of collateralization also can occur. If the coarctation is just proximal to the left subclavian artery, unilateral notching of the right rib results because of relatively increased right collateral flow. Unilateral left-rib notching can also result when an aberrant right subclavian artery arises distal to the coarctation. With this vascular anomaly, the collateral flow is predominantly through the branches of the left subclavian artery, and, as noted before, the blood pressure in the right upper extremity is relatively lower than that of the left upper extremity. The radiographic figure-3 sign refers to an indentation of the lateral margin of the aorta, with poststenotic dilatation. A reverse-3 sign can be seen on barium esophagograms as a result of the same anomaly. Other radiographic findings associated with long-standing aortic coarctation are elevation of the left ventricular apex and linear, wavy opacities behind the sternum as a result of dilated internal mammary arteries. Treatment of aortic coarctation is ideally performed at 3-5 years of age because this is early enough to prevent irreversible hypertension but late enough to avoid restenosis. Treatment is surgical, and the perioperative mortality rate is 3-11%. Procedures include patch angioplasty, creation of a left subclavian arterial flap (Waldhausen procedure), and resection with end-to-end anastomosis. Postsurgical complications include restenosis, residual coarctation, mesenteric arteritis, and chronic persistent hypertension. For more information on aortic coarctation, see the eMedicine article Aortic Coarctation (within the Internal Medicine specialty). References
Brant WE, Helms CA. Fundamentals of Diagnostic Radiology. Baltimore, MD: Lippincott Williams & Wilkins. 2nd ed. 1999: 575-6.
Dahnert W. Radiology Review Manual. Baltimore, MD: Lippincott Williams & Wilkins. 2nd ed. 1996: 459-60.
Maziarz DM, Koutlas TC. Coarctation of the Aorta and Interrupted Aortic Arch: Surgical Perspective. eMedicine Journal [serial online]. 2005. Available at: http://www.emedicine.com/ped/topic2824.htm.
Shah S, Calderon DM. Aortic Coarctation. eMedicine Journal [serial online]. 2005. Available at: http://www.emedicine.com/med/topic154.htm.
BACKGROUNDDA 28-year-old man presents to his primary care physician with complaints of persistent headaches. He reports that the headaches occur frequently and has had episodes of "blacking out" after feeling "lightheaded," which he describes as blurring of his vision and feeling as if he were going to pass out. He also reports dyspnea on exertion and bilateral lower-extremity claudication with moderate exertion, such as jogging or walking briskly. His history is negative for chest pain or tightness, palpitations, or neurologic symptoms. He denies smoking and taking any illegal substances. He denies any previous health problems and a family history of medical conditions.Physical examination reveals a blood pressure of 180/85 mm Hg in his right upper extremity and 175/85 mm Hg in his left upper extremity. His heart rate is 75 beats per minute, and this respiratory rate is normal at 12 breaths per minute. His temperature is 37°C. Auscultation of the chest reveals clear lungs on both sides, without wheezing, rales, or rhonchi. The patient has a normal heart rate and rhythm, without extra heart sounds or rubs. Of interest, a left infraclavicular systolic murmur is noted. His femoral pulses seem to be diminished, as are his posterior tibial and dorsalis pedis pulses. The rest of the physical examination and complete neurologic examination yield unremarkable findings. A frontal chest radiograph shows abnormalities (see Image 1a); therefore, a chest CT scan with intravenous contrast enhancement is also obtained (see Image 1b). What is the diagnosis?
Hint Assessment of the patient's blood pressure in the lower extremities would have been helpful during physical examination.
Authors:
Jeremy Logan, MD, University of New Mexico Hospital Residency, Department of Radiology, Albuquerque, New MexicoGautam Dehadrai, MD, Staff Physician, Department of Radiology, Veterans Administration Hospital, Albuquerque, New Mexico

eMedicine Editor:
Rick Kulkarni, MD, Attending Physician, Director of Informatics, Department of Emergency Medicine, Olive View - UCLA Medical Center, Assistant Professor of Medicine, David Geffen School of Medicine at UCLA

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