Classifications

The DeBakey classification is based on the extent of the dissection. Type I dissections involve the ascending aorta and extend around the arch distally. Type II dissections are limited to the ascending aorta. Type III begins beyond the arch vessels.

The Stanford classification divides dissections by their proximal extent. Stanford type A are those involving the ascending aorta, regardless of whether the primary entry tear exists distally and extends in a retrograde direction into the ascending aorta. Stanford type B dissections begin after the arch vessels and are the same as DeBakey type III. With this schema, proximal dissections are seen more frequently in necropsy series and distal dissections are reported in greater number in clinical series, probably because these patients survive longer. The distinction of proximal from distal dissection is important because patients with distal dissection have a better outcome with medical treatment, whereas those with proximal dissection live longer after surgical treatment.

Complications

Aortic rupture into the pericardium, pleural space, or mediastinum can be suggested on the plain chest film by a large heart diameter, pleural fluid, and a wide mediastinum. This heralds the need for immediate pericardiocentesis and other cardiopulmonary supportive measures. A dissection can partially or completely occlude a branch of the aorta by compression of the true channel by the false channel or by adjacent compression from an intimal flap. Any artery arising from the aorta can be occluded, but the right coronary artery and the three arch vessels are commonly affected. Surgical treatment aims at preventing retrograde tear into the heart and pericardium by resecting the segment that contains the entry tear. An interposition graft is then inserted, collapsing the false channel distally. Dissections in the aortic root are treated with a composite graft with the prosthetic aortic valve sewn to the graft and the coronary arteries replanted into the sides of the graft.

When there is dissection of the ascending aorta, over half the patients have aortic regurgitation, which contributes to hemodynamic instability. Aortic regurgitation can be caused by an asymmetric tear that misaligns one leaflet below the other, by a tear that results in a flail leaflet, or by disruption of the annulus with subsequent lack of coaptation of the leaflets. Subsequent proximal dissection may extend into the walls of the heart, producing a fistula between the aorta and the atria or the right ventricle.

Pathologic Causes and Contributing Factors

The cause of aortic dissection is frequently ascribed to cystic medial necrosis, although a more accurate histologic description is a degeneration of the media with loss of elastic tissue and muscle cells. Cystic medial degeneration may occur as an isolated disease, or it may be part of a generalized connective tissue disease as in Marfan syndrome or Ehlers-Danlos syndrome. Cystic medial lesions are associated with Marfan syndrome, the leading cause of dissection in persons under age 40 years. The major abnormality associated with aortic dissection is systemic hypertension, which is present in about 70% of patients. Other associated abnormalities include congenital bicuspid aortic valves, coarctation of the aorta, Turner syndrome, pregnancy, and aortic surgery.

Plain Film Findings

The plain film findings of dissection are indirect but can suggest the need for further evaluation (Fig. 11-5). An abnormally wide mediastinum, separation of calcium from the wall of the aortic arch, a left apical pleural cap, pleural fluid, and displacement of the trachea and esophagus from the midline are important characteristics of a thoracic aortic abnormality. However, the chest film findings are insensitive for the detection of aortic dissection: Nearly one fifth of patients with dissection have normal chest films.

FIGURE 11-5 Aortic dissection and aneurysm. A, The chest film shows an aortic aneurysm beginning at the aortic arch and extending distally in a tortuous aorta that crosses to the right side of the thorax (large arrows) before returning to the midline to enter the aortic hiatus of the diaphragm. A mass in the right paratracheal region (small arrows) suggests an aneurysm in the brachiocephalic artery. B, The lateral chest film shows a scalloped appearance to the distal aortic arch (black arrows). The mass in the posterior thorax (white arrows) is the aorta passing in front of the spine behind the left atrium to make a bend in the right side of the chest before returning to the midline. C, An angiographic subtraction image shows the small brachiocephalic aneurysm. The dissection begins after the left subclavian artery with an intimal flap (arrow). The superior extent of the saccular aneurysm adjacent to the left subclavian artery is also visible on the chest film in the supraclavicular region.

Tomographic Imaging

Computed tomography with intravenous contrast, magnetic resonance imaging (MRI), and echocardiography all have excellent sensitivity and specificity for detecting aortic dissection but each has limitations specific to its technology. Optimal computed tomography (CT) imaging is with intravenous contrast on a spiral scanner (Figures 11-6, 11-7). Spiral CT requires a correctly timed bolus of contrast media and has streak artifacts from the pulsating aortic wall that can mimic the intimal flap. Multidetector CT scanners with three-dimensional postprocessing reconstructions can rival the accuracy of catheter angiography.

FIGURE 11-6 Aortic dissection. Optimum timing of computed tomography imaging following contrast bolus clearly defines both the true and false channels level of (A) the ascending aorta and (B) the aortic arch in the axial plane and of the ascending aorta in the (C) coronal and (D) sagittal planes. Note the more dense true lumen (black *) and a less dense false lumen (white *).

FIGURE 11-7 Computed tomography signs of aortic dissection. A, At the aortic arch level, intravenous contrast outlines calcium (arrow) in the intimal flap between the two channels. B, A nonopacified hematoma is posterior to two components of the false channel in the ascending aorta. C, At the level of the main pulmonary artery, a separate dissection has a displaced, calcified intima (arrow). D, An angiogram confirmed a type A dissection beginning in the aortic root and causing severe aortic regurgitation. Both coronary arteries fill from the true channel. A separate entry (arrow) after the left subclavian artery partly occludes it.

(Courtesy John A. Kaufman, MD.)

Magnetic Resonance Imaging

MRI does not require intravenous contrast and has more options to characterize the extent of the dissection. The imaging plane can be placed parallel to that of the aorta in addition to the coronal and axial slices. “White blood” gradient echo sequences and phase reconstruction techniques can help identify slowly flowing blood in the false channel. The major limitation of MRI is the resolution of the arch vessels, so that the distal extent of the dissection into small arteries is frequently not shown.

Because of slow blood flow, clotted false channels, and occasionally the twisted shape of the intimal flap, aortic dissection can be difficult to distinguish from other types of aneurysm and aortitis (Fig. 11-8). MRI is particularly useful in these situations because different pulse sequences and reconstruction techniques can be exploited to produce a distinction between flowing blood and static tissue. Spin echo sequences producing “black blood” images easily show the intimal flap when there is moderate flow in both channels. But in regions of slowly flowing blood, the signal in that region may be similar to tissue in the aortic wall and adjacent mediastinum. A number of techniques exist that can image slow velocity differences and separate nonmoving and clotted blood in the false channel from slow-moving blood. Even echocardiographic rephasing, the fortuitous occurrence of velocity compensation in the second echocardiogram, is recognized as a higher signal intensity in the second echocardiogram in regions of slowly flowing blood (Fig. 11-9). A caveat is that failure of the signal intensity on the second echocardiogram to be greater than the first echocardiographic image is often observed in regions of complex velocity changes such as those that occur in vortices and eddies around bends in the aorta.

FIGURE 11-8 Double-channeled aortic dissection. A, Spin echo images show the intimal flap in the aortic arch, which is delineated by a “black blood” signal void from flowing blood in both the true and false channel. B, An axial view shows the dissection limited to the descending aorta, a Stanford type B. The false channel is larger than the true channel and has some signal intensity because of slower blood velocities.

FIGURE 11-9 Even echocardiographic rephasing. Signal intensity in the false channel of an aortic dissection increases from the first echocardiographic image (A) to the second echocardiographic image (B), indicating slowly flowing blood. This effect is also seen in the left atrium (LA) and right atrium (RA).

(From Miller SW, Holmvang G: Differentiation of slow flow from thrombus in thoracic magnetic resonance imaging, emphasizing phase images, J Thorac Imaging 8:98-107, 1993.)

One of the most sensitive ways to make the distinction between thrombus and slowly flowing blood is to reconstruct the original data as a phase image. All MRIs are generated as complex numbers, which are typically reconstructed as magnitude images. However, the same data can be displayed as a phase image, which then becomes a picture of the velocity of the tissue within each pixel. The phase image needs to be interpreted with the magnitude image to identify the area of concern where a thrombosed channel may be present. Changes in signal intensity, including alternating white to black phase breaks in the phase image, indicate flowing blood (Fig. 11-10).

FIGURE 11-10 Magnitude and phase images. A, Increased signal intensity from the blood is seen in a spin echo image of a tortuous aorta with an aortic dissection. The intimal flap (arrow) begins at the acute bend in the aorta near the diaphragm. Note the signal void in the eddy flow at the inner wall of this bend. B, Concentric circular phase breaks at the bend in the aorta are generated by nonuniform blood velocity. The false channel of the dissection after the bend in the aorta (arrow) has the same signal intensity as the adjacent mediastinum, indicating thrombosis of this channel.

(From Miller SW, Holmvang G: Differentiation of slow flow from thrombus in thoracic magnetic resonance imaging, emphasizing phase images, J Thorac Imaging 8:98-107, 1993.)

Another strategy that can be quite helpful is to obtain a gradient echo cine study through the area that has questionable flow in the standard spin echo image. With velocity compensation, the gradient echo pulse sequence should be obtained at only one slice to avoid the inflow of partly saturated spins from a neighboring slice (Fig. 11-11).

FIGURE 11-11 Gradient echo cine study of aortic dissection. A, In midsystole there is a “white blood” signal indicating flow in the descending aorta in both the small anterior true channel and the larger posterior false channel. B, In diastole, the signal intensity in the false channel is almost absent, indicating much slower flow than in the anterior true channel. The variation in signal intensity in the false channel through the cardiac cycle establishes that it is not thrombosed.

(From Miller SW, Holmvang G: Differentiation of slow flow from thrombus in thoracic magnetic resonance imaging, emphasizing phase images, J Thorac Imaging 8:98-107, 1993.)

Unlike the other techniques, transesophageal echocardiography (TEE) can be carried out at the bedside. The major advantage over the other techniques is the quantitation of aortic regurgitation with color-flow Doppler. Its disadvantage is that the aortic arch cannot be completely imaged with either the transthoracic or transesophageal technique.

Angiography

When dissection is suspected, the purpose of angiography is to establish a diagnosis, visualize the proximal and distal extent, and identify serious complications. The decision whether to treat dissection medically or surgically depends on many factors. Typically, the dissection involving the proximal aorta is treated surgically, and the dissection in the descending aorta is treated medically. Therefore, the thoracic image must delineate the extent of the dissection, and in particular, determine if it involves the ascending aorta.

Catheter Approach

The site of catheterization will depend on which pulses are present. If no extremity pulses are felt, a pulmonary angiogram with delayed follow-through may show the dissection. However, a general principle is that angiography should be performed with an injection as close to the abnormality as possible, and therefore a femoral, axillary, or brachial arterial approach is preferred. Because the left iliac artery is most frequently involved with a dissection, the preferred route is a percutaneous transfemoral approach from the right side.

The ultimate goal is to place the catheter in the true lumen of the aorta about 2 cm above the sinotubular ridge of the aortic root. The identification of the true channel cannot always be ascertained from catheter location, the size of the channel, or the speed of blood flow alone because the false channel may compress the true channel in unusual ways. Separation of a catheter from the greater curvature of the aortic arch by a centimeter or more confirms the presence of an abnormality. The false channel generally has less flow velocity than the true channel and therefore fills later. Another sign that the false channel is opacified is that there are no arteries originating from it.

Although there has been much concern about the potential consequences of injecting into the false channel (such as possible extension of the dissection or aortic rupture), a more important criterion for a safe angiographic injection is the rapid washout of contrast material during the test injection. This assures a large-capacity reservoir for the contrast agent, allowing a safe injection. At times, even on the final angiogram, it is not possible to determine which is the true or which is the false channel; however, you can still perform an adequate and safe angiogram as long as a high-pressure injection is not made into a cul-de-sac. Either the true channel or false channel may be the main conduit, and therefore filming should extend about 20 seconds to see late filling. If only one channel appears to fill, either the false channel is clotted or it is a retrograde dissection with a distal entry point. Another injection, distal to the first, in the descending aorta with filming over the thorax should opacify the false channel if it is patent. Based on clinical presentation, an abdominal aortogram may be appropriate to search for complications involving the arteries to the gut, kidneys, and legs.

Signs of Dissection

The intimal flap, a lucency several millimeters thick outlined by contrast on both sides, is the hallmark of dissection. You can often identify the actual entry from one channel into another or into multiple channels and the subsequent flow of blood in either an antegrade or retrograde direction. This intimal tear may extend only a few centimeters (Fig. 11-12) or may extend the entire length of the aorta, even into peripheral vessels (Fig. 11-13). The leaflets of the aortic valve, particularly with annuloaortic ectasia or Marfan syndrome, may be effaced and appear as a lucency; the large aortic leaflets can be difficult to distinguish from a true intimal tear in the aortic root, particularly if large-film technique is used. Cine angiography usually resolves this problem. True tears may be further differentiated by their origin above the sinotubular ridge and extension backward into the valve.

FIGURE 11-12 Aortic dissection. The lucency representing the intimal flap (arrows) extends from the aortic root around the arch. The false channel is less dense than the true lumen and occupies the greater curvature of the aortic arch. Aortic regurgitation has opacified the left ventricle.

(Courtesy Christos A. Athanasoulis, MD.)

FIGURE 11-13 Aortic dissection. Early (A) and late (B) films show the intimal flap (arrows) extending from the aortic root distally into the abdomen. The curved arrow points to one of several communications between the false channel on the greater curvature and the true channel medially. Note the multiple intimal tears (arrowheads) in the descending aorta.

An ulcerlike projection from the aorta may represent an early sign of dissection, although other types of aneurysms, including those caused by infection and penetrating atherosclerotic ulcer, may be associated with this finding. The base of the ulcer represents the defect in the intima leading to a thrombosed false channel (see Figure 11-13). In the descending aorta where side branches originate, the ulcer may be an occlusion or detachment of the intima from an intercostal artery.

The false channel may not opacify during angiography and, therefore, may present as a thick wall (usually >1 cm) along the greater curvature of the aorta (Fig. 11-14). An eccentric wall thickness greater than 1 cm is unusual in a clotted atherosclerotic or syphilitic aneurysm or aortitis. An unopacified channel may occasionally be seen if the injection was made proximal to the entry tear and the distal dissection has extended in a retrograde direction. Before the diagnosis of a thrombosed false channel is made, an injection should be made with the catheter at the level of the diaphragm to search for retrograde flow from a distant entry site. The thrombosed false channel has been called a “healed” dissection and is less liable to rupture late. Initially, the true channel is frequently smaller than the false channel, although either may enlarge to greater than the normal aortic width, then justifying the term dissecting aneurysm.

FIGURE 11-14 Thrombosis of the false channel. The mass (arrows) on the greater curvature never opacified on delayed films. The diameter of the false channel is greater than that of the aorta. The small, saccular aneurysm in the aortic arch may represent a site of rupture into the false channel.

Aortic regurgitation may result from three mechanisms (Fig. 11-15):

FIGURE 11-15 Mechanisms of aortic regurgitation in aortic dissection. A, Circumferential tear with widening of the aortic root and separation of the aortic cusps. B, Displacement of one aortic cusp substantially below the level of the others by the pressure of the dissecting hematoma. C, Actual disruption of the aortic annulus leading to a flail cusp.

(From Slater EE, DeSanctis RW: The clinical recognition of dissecting aortic aneurysm, Am J Med 60:625-633, 1976.)

FIGURE 11-16 Annuloaortic ectasia. An intimal flap (arrow) of a dissection in association with annuloaortic ectasia has resulted in severe regurgitation into the left ventricle (LV).

FIGURE 11-17 Annuloaortic ectasia. Annuloaortic ectasia and aortic dissection, with the intimal flap seen on other films, caused prolapse of one of the aortic cusps (arrows). The left ventricle (LV) is opacified by mild aortic regurgitation.

FIGURE 11-18 Aortic dissection. Aortic dissection (arrow) occurred along with a false aneurysm from an aortotomy for an aortocoronary bypass graft. The distortion of the annulus resulted in severe aortic regurgitation.

In addition to occluding or transecting any vessels from the aorta, a dissection may compromise other mediastinal vessels. The expanding hematoma of the false channel may compress the right pulmonary artery. Similarly, it may both displace and compress the superior vena cava. On the left side of the mediastinum, because the false channel extends posterolaterally, the pulmonary veins are occasionally compressed. If this abnormality leads to reduced flow through the left lung, then a dissection may be confused with pulmonary embolism on a ventilationperfusion lung scan.

Surgical Treatment

The primary goals of surgical treatment of dissection are to prevent extension back to the heart and pericardium and prevent aortic rupture. The usual surgical procedure in the ascending aorta is to replace it with a prosthetic graft. If there is also aortic regurgitation, a composite graft is used, consisting of an aortic valve prosthesis sewn into the proximal end of the graft; the proximal coronary arteries are then transected and replanted into the graft (Bentall procedure). Angiography after surgery may show the distal intimal flap with normal or reduced flow in the false channel, or a thrombosed false channel. Also, extension of the dissection, enlargement of the aneurysm, or reduction in blood flow from an aortic branch may occur despite the proximal graft replacement. After surgery, over 80% of dissections will retain the opacification of both the true and false lumina, suggesting the presence of additional distal fenestrations.

Root Enlargement

In Marfan syndrome, the sentinel vascular abnormalities in the aorta are aortic regurgitation, fusiform dilatation of the aorta, and dissection. These are represented pathologically by cystic medial necrosis. Degeneration of the aortic media leads to dilatation of the annulus. The aortic leaflets are spread apart and aortic regurgitation ensues. However, patients who do not have other features of Marfan syndrome may have annuloaortic ectasia. The term annuloaortic ectasia describes pear-shaped dilatation of the sinuses of Valsalva and the proximal aorta. Persons without the Marfan syndrome but with annuloaortic ectasia are usually male (by a 2:1 ratio) and are typically first seen after age 40 (Fig. 11-19). Those with Marfan syndrome have clinical symptoms at a much younger age. The aorta in homocystinuria may have an identical appearance.

FIGURE 11-19 Annuloaortic ectasia without Marfan syndrome in a 43-year-old male. A, Axial computed tomography scan demonstrating a grossly enlarged ascending thoracic aorta (black *). B, Aortic arch transition point from dilated (white *) to normal caliber (black *). C, Three-dimensional reconstruction demonstrating the enlarged ascending (*) and normal caliber descending (**) thoracic aorta. Bovine anatomy (arrow) of the great vessels.

Marfan Syndrome Presentation

In contrast to isolated annuloaortic ectasia, Marfan syndrome is a generalized disorder of connective tissue demonstrating autosomal dominant inheritance and manifested by cardiovascular, ocular, and skeletal abnormalities. Involvement of the cardiovascular system occurs in more than half of affected adults. Dilatation of the aortic annulus and ascending aorta are usually the first abnormal signs. Later, aortic regurgitation appears, which may ultimately cause left ventricular failure. Aortic dissection is a common complication and is frequently the cause of death (Fig. 11-20). Mitral regurgitation is the most common cardiac abnormality in children and is the result of redundant, elongated chordae tendineae and overlarge leaflets that produce prolapse of the leaflets into the left atrium. Calcification of the mitral annulus in children may occasionally be seen.

FIGURE 11-20 Marfan syndrome. Aortic dissection. Computed tomography scan, sagittal plane reformatting. Note the more dense true lumen (black arrow) and a less dense false lumen (black *).

Radiologic Techniques

Many of the clues to the diagnosis of Marfan syndrome are frequently visible on the chest film (Fig. 11-21). On the frontal film, the thoracic cage appears large and elongated with large-volume lungs. The heart may be shifted to the left from a narrow anteroposterior thoracic diameter. In normal young adults less than 20 years of age, the aorta should be inapparent. In contrast, aortic elongation and ectasia in this age group are common signs of Marfan syndrome. Cardiomegaly is usually nonspecific and may reflect only the pectus excavatum, but aortic regurgitation from annuloaortic ectasia and mitral regurgitation from prolapsing mitral leaflets are common conditions that pathologically enlarge the heart. On the lateral film, a pectus excavatum is frequently identified as well as a narrow thoracic diameter.

FIGURE 11-21 Marfan syndrome. A, The elongated thorax and the apparently large lungs are nonspecific and somewhat insensitive skeletal signs. The heart has slight levocardia. The aortic arch is slightly dilated. B, The pectus excavatum and narrow anteroposterior diameter of the thorax have displaced the heart into the left side of the thorax. The posterior rounding of the left ventricle does not necessarily indicate enlargement but may be caused by the posterior displacement of the heart. Note the dilated aorta (arrows) from the arch to the diaphragm.

Marfan patients without symptoms are easily observed with serial MRI every 6 to 12 months. Surgical referral is usually undertaken if a previously stable aortic aneurysm begins to enlarge or if the aortic arch and descending aorta exceed a diameter of 5 cm. MRI allows detection of the onset of annuloaortic ectasia (Fig. 11-22) with dilatation of the aortic root and ascending aorta, and visualization of a dissection. Aortic regurgitation can be observed and quantified with velocity-encoded pulse sequences. Observations on the aortic root and quantification of aortic regurgitation can also be made by echocardiography.

FIGURE 11-22 Magnetic resonance images in annuloaortic ectasia. A, The thorax has a narrow anteroposterior diameter with a mild pectus excavatum. The aortic root (AO) is huge and occupies a major portion of the left hemithorax in front of the left atrium (LA). B, A sagittal plane image shows the loss of the sinotubular ridge as the aneurysm extends from the sinuses of Valsalva to half of the ascending aorta. The LA is quite dilated.

Aortography is usually reserved for urgent clinical situations in which noninvasive imaging was inconclusive. Some surgeons request coronary angiography to evaluate whether a dissection extends near or into the coronary arteries. Occasionally, aortography can identify an entry site of a dissection that is not apparent on other methods (Fig. 11-23).

FIGURE 11-23 Annuloaortic ectasia. The aneurysm involves both the sinuses of Valsalva and the proximal half of the ascending aorta. The dilatation of the annulus has secondarily caused aortic regurgitation. The left ventricle is enlarged and is densely opacified, indicating a severe degree of insufficiency.

Etiology

Dilatation of one or all of the sinuses of Valsalva may be associated with abnormalities in the aortic valve or the aorta. These aneurysms may be classified radiologically as discrete (localized to the sinuses) or annuloaortic (involving both the aortic root and the ascending aorta). The classic type is annuloaortic ectasia with a pear-shaped configuration of the aortic root and equal dilatation of all sinuses.

An outline of sinus of Valsalva aneurysms is presented in Box 11-4. Discrete aneurysms that involve a single sinus are usually congenital (Fig. 11-24), although rarely dilatation of two or all three sinuses may also be congenital. These are generally less than 4 cm in diameter and involve mainly the right sinus. The tissue in the aortic annulus adjacent to the leaflet histologically has sparse fibroelastic elements and grossly may have fenestrations through the cusp. A sinus of Valsalva aneurysm can develop as a consequence of a ventricular septal defect. One of the ways a ventricular septal defect can close spontaneously is to form fibrous tissue around its edges. As the membranous ventricular septal defect becomes smaller, the adjacent leaflet of the aortic valve is pulled inferiorly into the defect. The clinical consequence of the developing leaflet prolapse is that the left-to-right shunt through the ventricular septal defect is transformed to that of aortic regurgitation.

FIGURE 11-24 Two examples of rupture of a congenital sinus of Valsalva aneurysm into the right ventricle (RV). A, A supravalvular aortogram in the left oblique projection opacifies the right ventricle. The right sinus (r) of Valsalva is large, indicating a congenital origin. A jet (arrow) of contrast densely opacifies the right ventricle. No aortic regurgitation occurred. B, Large right sinus (arrows) has a “windsock” shape and extends into the right ventricle. A ventricular septal defect was present in infancy but closed spontaneously. The size of the fistulous connection is small, as judged by the degree of right ventricular opacification.

Acquired discrete aneurysms usually involve all three sinuses if they are a consequence of a generalized inflammatory process, for example, syphilis or an immune complex aortitis. Aortic root abscesses are actually false aneurysms since they erode through the aorta into cardiac or mediastinal tissue.

Because the sinuses of Valsalva lie completely within the cardiac silhouette (Fig. 11-25), the discrete type of aneurysm is not visible on the plain chest film. If the ascending aorta is also dilated, the right side of the mediastinum will have the characteristic convexity of the aorta as it extends into the adjacent lung.

FIGURE 11-25 Aortic aneurysm. The arrow indicates a large sinus of Valsalva aneurysm in a patient with a repaired coarctation and bicommissural aortic valve. DAo, descending aorta; LA, left atrium; RA, right atrium.

Calcification

Calcification of the sinuses of Valsalva above the aortic leaflets is rare. If there is also extensive aortic calcification, this indicates syphilitic aortitis. Mild calcification of the nondilated sinuses and flecks in the ascending aorta suggest the presence of type II hyperlipoproteinemia. Rarely, congenital or nonsyphilitic aneurysms in the aortic root may calcify.

Complications

Aortic regurgitation is the main complication of progressive dilatation of the aortic annulus and the resultant lack of coaptation of the leaflets. Any type of sinus of Valsalva aneurysm can rupture into an adjacent structure. The onset is abrupt with severe aortic regurgitation or a torrential left-to-right shunt. Most sinus aneurysms rupture into the right sinus; they perforate anteriorly into the right ventricular outflow tract, dissect into the ventricular septum, or perforate posteriorly in the right atrium. Aneurysms of the noncoronary sinus rupture into the right atrium. Rupture of the left sinus into the left atrial appendage is extremely rare. When an aneurysm ruptures, aortography shows contrast medium entering the cardiac chamber and opacifying downstream structures on subsequent films (Fig. 11-26). Both a left ventriculogram and an aortogram may be necessary to distinguish a ventricular septal defect with aortic regurgitation from a ruptured sinus of Valsalva aneurysm. The contrast in the right ventricle from an aortogram could have passed into the left ventricle from aortic regurgitation and then across a ventricular septal defect, or it could have flowed directly from the aorta through the rupture into the right ventricle.

FIGURE 11-26 False aneurysm of the sinus of Valsalva from aortic root infection. A, An unruptured abscess cavity (arrows) fills from the aorta and compresses the right atrium and ventricle. B, In a different patient, the aortic root abscess has ruptured into the right ventricle (RV). Aortic regurgitation is moderate. In both examples, all three sinuses of Valsalva have similar size, making a congenital etiology unlikely. The point of rupture was through the aortic annulus above the leaflet. LV, left ventricle.

Because an aneurysm of the right sinus of Valsalva can compress and distort adjacent structures, significant hemodynamic complications can occur as the aneurysm dilates. Right coronary artery compression, superior vena cava obstruction, right ventricular outflow obstruction, and endocarditis can produce dramatic clinical events.

Takayasu Aortitis

Takayasu was a Japanese ophthalmologist who in 1908 described a woman with an unusual arteriovenous network in the retina. Similar findings and absence of peripheral pulses have given this disease the names pulseless disease, aortic arch syndrome, middle aortic syndrome, occlusive thromboaortopathy, and atypical coarctation.

Classifications

There are four types of Takayasu aortitis (Fig. 11-27). The Shimizu-Sano or type 1 is characterized by stenoses throughout the aortic arch and the innominate, carotid, and subclavian arteries. Type 2, or Kimoto type, shows segmental stenoses in the descending thoracic and abdominal aortas, including in the renal arteries. The Inada, or type 3, includes stenoses of both the aortic arch and the distal thoracic and abdominal aorta. Pulmonary artery stenoses with any aortic involvement define the disease as type 4. The most prevalent type of Takayasu disease is type 3 (55%), followed by type 2 (11%) and type 1 (8%). About half of these patients have pulmonary stenoses. Aortic regurgitation is usually mild, although it may occasionally be severe.

FIGURE 11-27 Takayasu disease. A, Type I has stenoses in the aortic arch and its vessels. B, A variant form may have only local aneurysms. C, Type II has stenoses in the descending thoracic and abdominal aorta. D, Type III has features of both types I and II. E, Type IV has pulmonary artery involvement along with aortic disease.

Imaging Assessment

Because of its diffuse and widespread nature, you may need both MRI and angiography to assess the extent and severity of Takayasu aortitis. Biplane thoracic aortograms or gradient echo MRI will detect aortic regurgitation and aortic arch stenosis (Figures 11-28, 11-29, 11-30). Abdominal aortography or magnetic resonance angiography will outline renal artery involvement and evaluate the arteries to the legs and gastrointestinal tract (Fig. 11-31). Occasionally, you will need angiography and ventilation-perfusion scans to assess pulmonary involvement. Conventional CT and CT angiography are useful in disease diagnosis (Fig. 11-32).

FIGURE 11-28 Takayasu aortitis. The lumen of the descending aorta is irregular and narrow from the isthmus to near the diaphragmatic hiatus.

FIGURE 11-29 Takayasu arteritis. Photographic subtraction of multiple irregular and fusiform stenoses present in the subclavian, carotid, and vertebral arteries. The left subclavian artery (LS) is occluded and fills from collaterals. Note the several small mediastinal collateral vessels above the aortic arch. LC, left carotid artery; LV, left vertebral artery; RC, right carotid artery; RS, right subclavian artery; RV, right vertebral artery.

FIGURE 11-30 Takayasu aortitis. Digital subtraction angiography (DSA) demonstrating irregular and diffuse narrowing of the descending thoracic aorta (arrows).

FIGURE 11-31 Thoracoabdominal aortitis. Thoracic (A) and abdominal (B) aortograms show a stenosis in a long segment of the aorta extending across the aortic hiatus of the diaphragm. C, Another patient had complete occlusion of the aorta below the renal arteries. Abundant mesenteric and retroperitoneal collateral channels opacified the iliac arteries on later films.

FIGURE 11-32 Takayasu aortitis. Contrast chest computed tomography demonstrating aneurysmal enlargement of the distal aortic arch (*). A, Axial imaging shows the aneurysm to be saccular with thick aortic wall (white arrow). B, Same patient, sagittal reformatted view.

The earliest change seen on the angiogram is an irregularity or narrowing of the aortic lumen even though there is no pressure gradient. MRI frequently shows a thickened aortic wall (Fig. 11-33). More severe stenoses have collateral circulation with reconstitution of distal vessels. Associated aneurysms may be either saccular or fusiform and show an irregular dilatation of a long segment of the aorta. A distal stenosis in the aorta may secondarily produce proximal aortic dilatation, so it may be difficult to distinguish a concomitant aortitis of the proximal aorta from secondary dilatation of a normal aortic wall as a result of a more distal stenosis.

FIGURE 11-33 Takayasu aortitis. A, T1-weighted noncontrast axial image demonstrate a small aortic lumen (white arrow) and thick aortic wall (white *). B, T1-weighted sagittal reformatted image demonstrating a long segment stenosis of the distal thoracic aorta (white arrow). C, Magnetic resonance angiography with contrast. Saggital reformatted image showing a long segment stenosis (white arrow) of the distal thoracic aorta at the level of the diaphragm.

Other Types of Aortitis

Inflammation of the media and adventitia is common in the acute phase in all types of aortitis. As healing progresses, the damaged tissue is replaced by collagen. The collagen forms part of the scar, retracts, crinkling the intima, and creates the “tree bark” appearance of the luminal surface of the aorta seen in all types of aortitis. Much later, superimposed atherosclerosis and degenerative calcification represent the end stage of the inflammatory process.

From an imaging perspective, the aorta dilates in response to the weakened structural support of its wall (Fig. 11-34). As a rule, the ascending aorta dilates more than the arch, and the abdominal aorta is little involved (the opposite of atherosclerosis). As healing progresses, the aortic wall may become quite thick (Fig. 11-35). Aortic rupture can occur as a consequence of any type of aortic dilatation from aortitis. Aortic regurgitation mainly is from dilatation of the aortic annulus, but there may be inflammatory valvulitis and bacterial endocarditis. As listed in Box 11-5, giant cell arteritis, ankylosing spondylitis, rheumatoid arthritis, the aortitis associated with rheumatic fever, relapsing polychondritis, Reiter syndrome, and syphilis all may produce aortic regurgitation and dilatation of the ascending aorta and arch. The aorta may be involved in the collagen diseases of systemic lupus erythematosus, scleroderma, and rarely in ulcerative colitis or psoriasis. Although these entities pathologically and clinically are rather specific, the major angiographic finding is fusiform and symmetric dilatation of the aorta.

FIGURE 11-34 Reiter syndrome. A, The aneurysmal ascending aorta projects anteriorly and obscures the right hilum. B, Magnetic resonance imaging with spin echo sequence in an oblique plane parallel to the aorta shows the aneurysmal ascending aorta with its thin anterior wall. The stenotic bicuspid aortic valve (arrows) is domed in this systolic frame. C, An adjacent image shows mild ectasia in the aortic arch and a normal descending aorta.

FIGURE 11-35 Giant cell aortitis. A, A magnitude image of a spin echo image shows a high signal intensity in the thick wall of the ascending aorta. To distinguish slowly flowing blood from solid tissue, a phase image (B) was constructed that has the same gray intensity in the aortic wall as in the nonmoving chest wall, indicating no flow. The salt-and-pepper appearance of the lungs and blood in the aorta reflect a statistical noise from tissue with low signal. A thrombosed false channel of a dissection could have a similar appearance.

Ankylosing Spondylitis

Ankylosing spondylitis affects that portion of the aorta behind the sinuses of Valsalva (Fig. 11-36). The process extends downward to the aortic cusps, which becomes thickened, and upward a few centimeters in the ascending aorta. Ankylosing spondylitis is one kind of severe aortitis that crosses the distinct junction of the sinotubular ridge as it dilates the aortic root and ascending aorta. In contrast to syphilis, the scarring process in ankylosing spondylitis involves the sinuses of Valsalva, both the free edge and the base of the aortic leaflets, and extends below the aortic valve to the mitral annulus. In syphilis, the scarring begins above the sinuses of Valsalva and only the free edge of the aortic valve is thickened and curled.

FIGURE 11-36 Aortitis mainly involving the ascending aorta. A, Dilatation of the aortic annulus by ankylosing spondylitis has resulted in severe aortic regurgitation. B, Giant cell aortitis has produced an aneurysm 10 cm in diameter extending from the aortic root to the innominate artery. Moderate aortic regurgitation was present on other films.

Behçet’s Disease

Behçet’s disease is a rare vasculitis with oral, skin, and genital ulcers, eye lesions, aneurysms of the aorta and pulmonary arteries, and occlusion of the vena cava. Although any of the medium-sized and large arteries may be involved by this disease, the aorta and pulmonary arteries are the most common site (Fig. 11-37). The ostium of arteries originating from the aorta may be stenosed or occluded. The Hughes-Stovin syndrome with pulmonary aneurysms and venous thrombosis may be the same disease as Behçet’s disease without the oral and genital ulcers. Other similar entities are the aortic aneurysms and brachiocephalic stenoses in Takayasu disease.

FIGURE 11-37 Behçet’s disease. A, Magnetic resonance image shows a large aneurysm in the aortic arch (A) which partially compresses the left pulmonary artery (P) inferiorly. B, A photographic subtraction of the thoracic aortogram identifies the neck of the aneurysm beginning after the left subclavian artery and extending 10 cm into the descending aorta.

Cardiovascular Syphilis

The hallmark of cardiovascular syphilis is aortitis, which is the consequence of spirochete infection of the aortic media with subsequent inflammation and scarring. Later, focal medial necrosis ensues, along with intimal fibrous proliferation. In this late phase, there are no spirochetes but scarring of the aortic wall and loss of elastic tissue produce a weakness in the wall, which is (paradoxically) quite thick. Superimposed on the intima is severe atherosclerosis with plaques and calcification. Both the incidence and severity of aortitis are greatest in the ascending aorta, followed by the arch, the descending aorta, and rarely, the upper abdominal aorta. This distribution differs from pure atherosclerosis, in which the lower abdominal aorta is most likely to be severely affected.

The aortitis of syphilis characteristically involves the ascending aorta and begins above the sinotubular ridge. The sinotubular ridge is preserved and does not dilate. The diagnosis of aortitis rests on two signs: calcification and dilatation. Calcification, which occurs in about 25% of those with luetic aortitis, is initially thin with sharp margins. Later, when severe atherosclerosis has developed, there are larger, irregular chunks of calcium. The calcification tends to occur along the anterolateral wall of the aorta, but in later stages involves the entire circumference (Fig. 11-38). Calcification of the ascending aorta is also seen in pure atherosclerosis, and rarely, in Takayasu arteritis so that neither its presence nor absence is diagnostic. However, a densely calcified ascending aorta from the sinuses of Valsalva to the arch vessels is typical of the severe, superimposed atherosclerosis of cardiovascular syphilis.

FIGURE 11-38 Luetic aortitis. Extensive “eggshell” calcification extends from the aortic annulus through the entire thoracic aorta.

Aortic aneurysm occurs in about half of patients with cardiovascular syphilis and is mainly found in the thoracic aorta (Fig. 11-39). Counting multiple aneurysms, approximately 50% occur in the ascending aorta, 30% in the arch, 15% in the descending aorta, and less than 5% in the abdominal aorta. These aneurysms may rupture into or compress the adjacent superior vena cava, bronchi, esophagus, pulmonary artery, and pleural and pericardial cavities. The sinuses of Valsalva may be the site of syphilitic aneurysms either with primary involvement or with extension of the dilated ascending aorta. In contrast to sinus dilatation from cystic medial necrosis, luetic involvement of the sinuses may be eccentric. Although the shape of the aneurysms is unpredictable, they tend to be eccentric and saccular. In the series of Steinberg and colleagues, of 60 luetic aneurysms, 43 (72%) were saccular, and 17 (28%) had fusiform dilatation.

FIGURE 11-39 Luetic aneurysm. The fusiform aneurysm in the ascending aorta does not involve the aortic root. The thoracic aorta was densely calcified on preliminary films. The descending aorta is unusually jagged and rough from severe superimposed atherosclerosis. The aortic leaflets are thick and have a slight jet through them. On later films, mild regurgitation opacified the left ventricle.

(Courtesy Arthur C. Waltman, MD.)

Aortic regurgitation is the most frequent complication of syphilitic aortitis, occurring in 60% of those with cardiovascular syphilis. The edges of the leaflets are also thickened and do not coapt, but calcification of the leaflets usually does not occur unless there is concomitant rheumatic or atherosclerotic disease. Regurgitation can also result from dilatation of the aortic annulus with separation of the valve commissures. Although the aortic regurgitation may be mild to severe, aortic stenosis is not a feature of aortic valve disease.

Coronary artery ostial stenosis from syphilis does not extend into the coronary artery itself, but rather results from abundant intimal thickening in the sinuses of Valsalva. In Heggtveit’s series 26% of the patients had luetic coronary ostial stenosis. These stenoses may produce myocardial ischemia but necropsy study shows little evidence that this occurs. Occasionally, the coronary arteries may be aneurysmal, a finding that may reflect the primary disease or the secondary aortic regurgitation.

Penetrating Wounds

Since ancient times, physicians have recognized penetrating wounds of the heart and great vessels. With early diagnosis and treatment, modern medical and surgical techniques have enabled some victims to survive injuries to the heart and aorta. The sequelae of penetrating wounds to the heart include cardiac tamponade, left-to-right shunts, usually between the ventricles, valve injuries, true and false ventricular aneurysms, coronary artery lacerations and occlusions, and retained foreign bodies. When there is emergency surgery for stab wounds to the heart, postoperative angiography may be necessary to check for unsuspected communications between chambers or to the great vessels. When the injury penetrates the anterior chest wall, it commonly punctures the right ventricle or left anterior descending coronary artery; the left ventricle, right atrium, and left atrium are less frequently harmed.

Penetrating trauma as a result of medical procedures or devices is becoming increasingly common with widespread use of indwelling intravenous and interarterial catheters, including the intraaortic balloon pump. Cardiac tamponade from perforation of the right ventricle by a pacing electrode is a recognized complication of cardiac pacing. Catheter fragments may migrate to a distal vascular bed and perforate the vessel wall to form a false aneurysm or cause an arterial dissection.

The purpose of imaging in evaluating penetrating cardiovascular trauma is severalfold:

The type of imaging performed in a trauma situation obviously depends on the clinical setting. In certain kinds of trauma, multiple vascular injuries are likely to be present, for example, with gunshot wounds and severe automobile accidents. In these situations, it is wise to consider the possibility of multiple cardiac and arterial injuries and to perform adequate imaging to delineate their extent.

Blunt Trauma

Blunt trauma to the heart and great vessels is frequent in severe automobile accidents in which there is high-speed deceleration on impact, in falls from a great height, and in blast and percussive injuries. If cardiac injury is absent, about 20% of these victims will survive a traumatic aortic rupture for a variable amount of time. Of those who survive, the rupture is usually at the site of the aortic isthmus, whereas in those who die it is more often in the ascending aorta.

Aortic Tears

Although the aorta may be torn in any location, in over 90% of nonpenetrating trauma patients who survive the point of the laceration is the isthmus. It is here that the relatively mobile ascending aorta and arch join the rigid descending aorta, which is fixed by the pleura, resulting in a plane of shear. The tears at the isthmus are usually transverse but are occasionally ragged or spiral. When the aorta is completely ruptured, the distal end may retract several centimeters so that the intervening vascular channel is composed entirely of periadventitial and pleural tissue (Fig. 11-44). Lesser injuries that may be imaged include intimal hemorrhage with laceration, and occasionally, intravascular thrombus attached to the isthmus.

FIGURE 11-44 Traumatic aortic laceration. A, An incomplete tear in the aortic isthmus involves only the inferior curve of the aorta. B, An incomplete tear may occur in the greater curve of the aorta opposite the ligamentum arteriosum. C, A complete transection of the aorta has a circumferential false aneurysm in the aortic isthmus.

A partial rupture will produce a false aneurysm that is eccentric and saccular. When the laceration is complete, a traumatic aortic rupture will appear as a fusiform aneurysm, in which case the bulge represents not the vessel wall but the retropleural and mediastinal containment of the false aneurysm. As with all false aneurysms, there is the potential to expand and rupture, a process that can happen quickly or extend over many years.

In the 10% of patients with traumatic rupture of the aorta from blunt trauma, the origins of the innominate, left carotid, or left subclavian arteries are injured, occasionally with other injury to the ascending aorta. The innominate artery injury may be a pseudoaneurysm at its origin or in its proximal segment. This artery may also be occluded, in which case collateral circulation comes from the circle of Willis and flows retrograde into the ipsilateral vertebral artery.

The imaging evaluation in the diagnosis of suspected aortic transection remains controversial even after hundreds of articles analyzing the role of the chest film, CT, transesophageal ultrasound, and angiography (Figures 11-45, 11-46, 11-47, 11-48). The imaging of each patient needs to be individualized according to the amount of trauma, the cardiovascular stability of the patient, and the medical resources available. Several guidelines appear to have reasonable reliability in the triage of patients with blunt chest injury. The chest film is a useful first step in mild trauma, in addition to identifying lung and musculoskeletal injuries, because if it is normal with no signs of mediastinal hemorrhage, then it is quite unlikely that an aortic tear is present. If, however, despite the negative chest film, the amount of trauma or its mechanism was potentially sufficient to tear the aorta, then CT or angiography is required for definitive diagnosis (Fig. 11-49). In like manner, normal findings on chest CT with intravenous contrast virtually exclude aortic injury. If the CT shows mediastinal widening or hemorrhage, the diagnostic possibilities are arterial injury, which requires surgery, or rupture of small mediastinal veins, which does not. In these instances, aortography, although not foolproof, is the accepted practice (Fig. 11-50).

FIGURE 11-45 Aortic arch injury. A, Pseudoaneurysm at site of vessel wall injury (black *) at the aortic isthmus, the transition point between the distal arch and the descending aorta. B, Pseudoaneurysm (black *) at the aortic isthmus in the coronal plane. C, Contrast angiography with a pigtail catheter in the distal aortic arch demonstrating the incomplete tear (white arrow). D, Transesophageal echocardiogram demonstrating the traumatic pseudoaneurysm (white *).

FIGURE 11-46 Aortic arch injury. A, Magnetic resonance imaging demonstrating a large traumatic pseudoaneurysm (black *) at the distal aortic arch. B, Magnetic resonance angiography maximum image projection showing the pseudoaneurysm (black *) at the aortic isthmus in the coronal plane.

FIGURE 11-47 Aortic arch injury. Pseudoaneurysm at site of vessel wall injury (white arrow) and thickening of the periaortic soft tissue (black arrow).

FIGURE 11-48 Traumatic pseudoaneurysm. A pseudoaneurysm often extends in a longitudinal direction along the aorta (arrows) as demonstrated on this sagittal computed tomography image.

FIGURE 11-49 Arch angiography. The position of a diagnostic catheter should be close to the area of interest. A, A catheter in the proximal aortic arch results in poor evaluation of the aortic root. The catheter should have been positioned more proximally in the ascending aorta (black arrow). B, With the diagnostic catheter closer to the aortic root (black arrow), the injury is clearly defined (white arrow).

FIGURE 11-50 Aortic transection from a motor vehicle accident. A, The complete transection is in the aortic isthmus after the left subclavian artery. The large false aneurysm represents the parietal pleura, which is the only constraining tissue preventing rupture into the pleural space. B, The transection occurred obliquely and produced retropleural elevation by the extending hematoma, manifested by mediastinal and apical capping (straight arrows). A jet of contrast media (curved arrow) is coming through the tear. C, An incomplete traumatic laceration (arrow) can look similar to an aortic diverticulum. Clinical history and cross-sectional imaging are needed to make this distinction.

Cardiac Injury

Blunt trauma to the heart and pericardium is seen indirectly on chest films with signs of cardiac tamponade and ventricular dysfunction (Box 11-7). An enlarging cardiac silhouette or pulmonary edema implies cardiac injury. In general, echocardiography and angiography are needed to analyze the site and physiologic extent of the trauma.

Damage to the cardiac valves occurs much less frequently with nonpenetrating chest trauma. The aortic valve may be disrupted along the base of the leaflets or by laceration of the middle or edge of a cusp (Fig. 11-51). Damage to the mitral and tricuspid valves is rare and is associated with varying degrees of leaflet stability, culminating in a flail leaflet when a papillary muscle is ruptured.

FIGURE 11-51 Traumatic laceration of the aortic root. A, Two false aneurysms (white and black arrows) are separated by a thin membrane. The distortion of the cuspal attachments has created mild aortic regurgitation. B, In the left anterior oblique projection, the disrupted aortic root is expanded in both anterior and posterior directions.

Myocardial ischemia after blunt trauma is a sign of coronary artery injury. The task of cardiac imaging is to distinguish among cardiac contusion, myocardial infarction from preexisting coronary artery disease, and direct traumatic injury to the coronary artery. Coronary arteriography may demonstrate normal coronary arteries, indicating that there is a contusion of the heart. There may be coronary tears, dissections, or extrinsic stenoses from an adjacent hematoma. When an artery is transected, the distal ends constrict in a natural attempt to reduce blood flow so that arteriographic visualization may be subtle. After injury to the coronary arteries, ventriculography may show abnormalities such as ventricular aneurysm, pseudoaneurysm, or papillary muscle dysfunction. After a penetrating injury, there may be arteriovenous fistulas, either to the adjacent coronary vein or into the coronary sinus, right atrium, or right ventricle.

Appearance

Atherosclerotic thoracic aneurysms can be either saccular or fusiform. The saccular variety involves expansion of only a portion of the wall and looks like an eccentric blister when viewed in tangent (Fig. 11-52). The most common type is the fusiform aneurysm in which the entire aortic segment is cylindrically dilated (Fig. 11-53). The thin wall of the aortic aneurysm may appear thick because of a laminated thrombus within the sac. The aortic lumen may not be dilated if the aneurysm contains an intraaneurysmal thrombus. In such cases, the correct diagnosis of thrombus in an aneurysm may hinge on locating intimal calcifications in the wall of the aorta, which is widely separated by thrombus from the apparent lumen or on finding an adjacent soft tissue mass that is concentric to the aneurysm.

FIGURE 11-52 Saccular atherosclerotic aneurysm. A photographic subtraction of an aortogram shows a saccular aneurysm 7 cm in diameter on the lesser curvature of the aortic arch. The aneurysm originates opposite the left subclavian artery and compresses and distorts adjacent mediastinal structures.

FIGURE 11-53 Fusiform atherosclerotic aneurysm. The ascending aorta is mildly dilated and slight aortic regurgitation fills the left ventricle. The fusiform aneurysm extends from the left subclavian artery distally and was followed below the diaphragm on other injections. The irregular lucency in the arch is caused by poor mixing of blood and contrast media around a large plaque. Note the thick wall (arrows) representing intraluminal thrombus.

Location

Atherosclerosis of the thoracic aorta is usually confined to the transverse arch and descending aorta. If the entire aorta is evaluated, the greatest amount of atherosclerosis, aneurysms, and occlusions is in the infrarenal section with decreasing frequency of atherosclerotic disease in the suprarenal segment, the descending aorta, and the arch. Atherosclerotic plaques, seen angiographically as intimal irregularity and luminal narrowing, are regularly seen in persons from all countries where malnourishment is not a major problem. Fine linear calcifications in both the ascending and descending aorta are more commonly seen with uncomplicated atherosclerosis.

The diseases that are associated with the greatest extent of atherosclerotic change in the ascending aorta are type II hyperlipoproteinemia, syphilis, and diabetes mellitus. In type II hyperlipoproteinemia, the calcific deposits involve the sinuses of Valsalva and aortic cusps, but they rarely produce aortic stenosis. Diabetes mellitus and syphilis may also result in extensive plaques in the ascending aorta. Severe calcification confined to the ascending aorta as seen on a chest radiograph represents dystrophic calcification from any inflammatory process, including atherosclerosis. An aortitis such as Takayasu disease may calcify after many years.

Imaging

Imaging in the diagnosis of atherosclerotic thoracic aortic aneurysms is performed with spiral CT, MRI (Fig. 11-54), or biplane angiography. With MRI, the oblique image plane can be rotated to show the entire aorta. The images should show:

FIGURE 11-54 Thoracic aortic aneurysm with thrombus. A, Spin echo pulse sequence poorly differentiates the lumen of the aorta from thrombus because of slowly flowing blood. B, With flow-related enhancement, the moving blood appears bright and is clearly distinguishable from adjacent thrombus.

(From Miller SW, Holmvang G: Differentiation of slow flow from thrombus in thoracic magnetic resonance imaging, emphasizing phase images, J Thorac Imaging 8:98-107, 1993.)

Roughly half of those patients with thoracic aneurysms also have abdominal aneurysms. Therefore, when there is possible thoracic surgery, abdominal imaging should be performed to screen for multiple aneurysms.

Penetrating Aortic Ulcer

One of the complications of atherosclerosis is development of a penetrating atherosclerotic ulcer. Penetrating atherosclerotic ulceration of the thoracic aorta was first described in 1934. A cholesterol plaque in the lumen of the aorta ruptures, disrupting the internal elastic lamina, and subsequently dissects into the aortic media. The media layer is then exposed to pulsatile blood flow, resulting in an intramural hematoma and a variable degree of aortic dissection. The hematoma may penetrate the aortic wall and become contained by the adventitia. At this stage, the ulcer is considered a contained rupture or a pseudoaneurysm. Uncommonly, the aortic ulcer may perforate through the adventitia and rupture into the pleural space, resulting in a fistula into adjacent organs such as the esophagus or bronchus.

The presence of dissection in this process is not the same type of dissection seen in classical aortic dissection. In penetrating aortic ulcers, the flap is irregular and thick and does not significantly encroach on the true lumen of the aorta. The dissection also is limited in the extent of its course. The dissection is usually focal, whereas, in classic aortic dissection, the dissection plane often extends the entire length of the aorta. This focal and limited dissection may be secondary to scarring within the media as a result of atherosclerotic disease. Most penetrating aortic ulcers occur in the descending thoracic aorta in an area of severe atherosclerosis, although rarely they are present in the ascending aorta and in the abdominal aorta. Roughly 42% of patients with penetrating aortic ulcer also show evidence of abdominal aortic aneurysmal disease. Ulcers can occur in the ascending thoracic aorta, which may weaken the aortic wall resulting in disruption of the aortic valve and subsequent aortic regurgitation.

The clinical presentation is frequently that of a sudden onset of severe chest pain similar to that seen in myocardial infarction or aortic dissection. Characteristically, these patients are elderly and have diffuse arteriosclerosis and hypertension. Anterior chest pain tends to correlate with ascending aortic lesions, whereas descending aortic lesions usually cause back pain. Coronary artery disease, cerebral vascular disease, and peripheral vascular occlusions are common features. The differential diagnosis in this situation includes acute coronary syndromes, aortic dissection, intramural hematoma, true aortic aneurysm, pulmonary embolism, and penetrating ulcer of the aorta. With penetrating ulcer, there are few specific clinical signs; in particular, there is no pulse deficit, aortic regurgitation, stroke, or visceral vessel compromise. The presence of any of these suggests a classical dissection. A less common presentation is embolism of atheromatous debris or an overlying thrombus, resulting in ischemia and even infarction of downstream tissue. Examples of embolic disease are cerebrovascular accident and distal lower limb ischemia.

The chest film frequently shows diffuse or focal enlargement of the descending thoracic aorta with a widened mediastinum. If the aortic ulcer is leaking, there may be pleural effusions. To obtain a precise diagnosis, further imaging is required such as angiography, CT, MRI, or TEE. Contrast-enhanced, cardiac-gated multidetector CT is nearly 100% sensitive and specific for evaluating acute aortic syndrome. TEE is about 95% sensitive and specific for diagnosing acute aortic dissection, and intramural hematoma, and associated valvular regurgitation; however, this modality is operator dependent, and therefore accuracy in test performance and interpretation can vary. Penetrating ulceration may be more difficult to identify by TEE than by CT or MRI. Angiography has become less popular as a first-line investigation because of its invasive nature and because it may give rise to false-negative results if the ulcer is not profiled on the projections obtained. On CT, penetrating ulcers appear as focal excavation or crater within an area of mural thickening (Fig. 11-55). The aortic wall is frequently thickened, and there is inward and upward displacement of the calcified intima by the hematoma. Extensive adjacent calcification and ragged edges help to distinguish this entity from aortic dissection. Intravenous contrast may flow into a crescentic intramural hematoma, which can extend into the mediastinum.

FIGURE 11-55 Penetrating atherosclerotic ulcer. A, Noncontrast computed tomography (CT) showing a hematoma (white *) beyond the calcified wall of the descending aorta. A noncontrast scan easily defines atherosclerotic calcium. B, Contrast-enhanced CT showing a broad neck ulcer filling with contrast (white *). C, Contrast CT, sagittal plane showing two separate ulcers (white *) and less dense contrast dissecting from the more distal ulcer into surrounding hematoma (white arrow).

Because multiple ulcers may be present, the entire aorta should be imaged. Imaging may also reveal pleural and pericardial fluid, mediastinal hematoma, or a pseudoaneurysm. The presence of a pleural effusion has been shown to be a risk factor for progression of the ulceration.

MRI may be the best modality for differentiating intramural hematoma from atherosclerotic plaque and chronic intramural thrombus. By MRI a subacute hematoma in the wall of the aorta demonstrates high signal intensity on both T1- and T2-weighted images. As the methemoglobin is further degraded and absorbed, the signal intensities will return to those of adjacent tissues (Fig. 11-56).

FIGURE 11-56 Penetrating atherosclerotic ulcer. A, A lateral thoracic aortogram shows an ulcerated plaque with a broad neck (black arrows) near the diaphragm. A thick anterior wall (white arrows) displaces the para-aortic pleura anterior to the ulcer. B, The thick wall in the descending aorta on the computed tomography scan has a focal region of high signal (arrow) and a crescentic band of lesser intensity in the dissecting hematoma. C, The alternating bands of signal intensity indicate hemorrhage into the aortic media. D, A band of high signal intensity (arrow) in the aortic arch on spin echo magnetic resonance image is part of the extension of the penetrating ulcer. The high signal intensity reflects the subacute hemorrhage.

(Courtesy S. Mitchell Rivitz, MD.)

The natural history of penetrating aortic ulcers continues to emerge in the literature. Most penetrating ulcers are probably asymptomatic, with a small number causing a clinical problem. If the patient presents with pain, he or she is at significant risk of having or developing complications such as pseudoaneurysm or contained rupture, fistula or even free rupture. Over the next few days, the pain may resolve as the ulcer stabilizes. If the pain continues or recurs, this corresponds to progression of the pathologic process and the probable development of complications. If the pain subsides or complications have not occurred, the ulcer may remain unchanged for many years, although there is a possibility of aortic dilatation and aneurysm formation.

Management strategies may be divided into those for symptomatic and those for asymptomatic ulcer. Most diagnoses are made in the patient presenting acutely with chest or back pain. The patient should receive immediate intravenous analgesia to control pain and an antihypertensive agent to reduce blood pressure and so decrease the chance of rupture. Patients with penetrating ulcer of the descending aorta or arch should be considered a high-risk group and early operative repair has been recommended to prevent rupture.

If pain resolves with medical therapy alone and there is no radiographic evidence of deterioration, conservative management may be recommended. If this is adopted, oral antihypertensive therapy should continue, if appropriate, and imaging should be repeated within a few weeks to detect any silent progression of the disease. If the patient with a descending thoracic ulcer develops features of progression, early intervention is indicated. Such features include hemodynamic instability, persisting or recurrent pain, and radiological evidence of deterioration (intramural hematoma expansion, pseudoaneurysm formation, pericardial effusion, or bloody pleural effusion). Embolization from a penetrating ulcer is also considered to be an indication for repair.

Therapeutic options for penetrating ulcers have primarily been open surgical repair, which requires local excision of the ulcer and graft interposition. Over the past decade, there has been a rapid surge in the use of endovascular stent grafts to treat a variety of aortic diseases, including abdominal and thoracic aneurysms. The use of stent graft for aortic ulcers was first described by Dake and colleagues in 1994. For there to be successful exclusion of a penetrating ulcer from the circulation, there must be an adequate length of normal aorta above and below the lesion for the proximal and distal ends of the stent graft to obtain secure purchase. The ulcer, therefore, must not be directly adjacent to the left subclavian artery or the celiac axis. If the ulcer lies within an aneurysm, there must be sufficient proximal and distal aneurysm neck for the stent to fasten to without impinging on these vessels. Early first-generation endovascular devices suffered from complications such as stroke with insertion, ascending aortic dissection or aortic penetration from their metal struts, vascular injury, graft collapse, endovascular leaks, graft material failure, continued aneurysm expansion or rupture, and endograft migration or kinking. Newer devices have been considerably improved. Long-term durability is still not well known, particularly in younger patients. The long-term consequences of repeated radiation exposure received during follow up CT scans to evaluate device integrity and positioning remains a concern in all patients.

Intramural Hematoma

Intramural hematoma of the thoracic aorta is a disease entity that is separate from classic aortic dissection and penetrating aortic ulcers. Aortic intramural hematoma was first described by Krukenberg in 1920 as a “dissection without intimal tear.” CT and MRI findings of this condition were first described in 1988 by Yamada. The overall incidence of intramural hematoma in patients with aortic dissection, from autopsy reports, has ranged from 4% to 13%.

Intramural hematoma is characterized as a concentric aortic wall hematoma without radiographic evidence of an intimal flap or penetrating ulceration. The hematoma is usually located within the media of the aortic wall. Like penetrating ulcers, it is most often found in the descending thoracic aorta. The hematoma may be secondary to hemorrhage, without intimal disruption, from the aortic vasa vasorum as seen in patients with cystic medial necrosis. A true intramural hematoma occurs in absence of identifiable penetrating aortic ulcer (Fig. 11-57). It can, however, be secondary to rupture of an atherosclerotic plaque/ulcer that penetrates into the internal elastic lamina and allows subsequent hematoma formation within the media of the aortic wall (Fig. 11-58). A subacute hematoma in the wall of the aorta can be characterized with MRI by high signal intensity on both T1- and T2-weighted images.

FIGURE 11-57 Intramural hematoma. Coronal reformatted computed tomography demonstrating an acute wall rupture (white arrow) into an existing intramural hematoma (black arrows) of the descending thoracic aorta.

FIGURE 11-58 Intramural hematoma. A, Focal dissection (black arrow) into intramural hematoma of the descending aorta, axial contrast computed tomography. Note the absence of wall calcification. B, Same patient, sagittal plane, showing the dissection to be larger than was depicted in the axial plane. Again, note the absence of calcification. The patient initially refused surgery. C, axial plane, and D, sagittal plane, same patient 3 months later demonstrating enlargement of the dissection (black *). E, Postendograft repair excluding the dissection from the hematoma (black arrow).

The clinical presentation of intramural hematoma is similar to both penetrating aortic ulceration and classic aortic dissection. As with penetrating aortic ulcer and aortic dissection, intramural hematoma with uncontrollable pain is a significant indicator of disease progression. Numerous reports indicate that both intramural hematomas and penetrating aortic ulcers commonly occur in elderly patients with a history of hypertension. The mean age of these patients is older than that of those with classic aortic dissection. The Stanford classification for aortic dissection has been applied to intramural hematoma because of the prognostic implications secondary to location have been found similar to those of classic aortic dissection.

A prognostic indicator in intramural hematoma is the presence or absence of aortic ulcers. Ganaha and colleagues recently demonstrated significant progression of disease in patients with both intramural hematoma and penetrating aortic ulcer. Prognosis of acutely symptomatic hospitalized patients with penetrating aortic ulcers is worse than those with classic aortic dissection because of a higher incidence of aortic rupture. Therefore, patients with both intramural hematoma and penetrating aortic ulcer must be considered to be clinically critical.

Patients demonstrate a relatively stable clinical course when there is no penetrating aortic ulcer associated with intramural hematoma, and it is confined to the descending thoracic aorta. In patients with type B, descending aorta involvement, intramural hematoma can be managed conservatively in the absence of disease progression. Oral beta-blocker therapy may improve long-term prognosis of intramural hematoma regardless of anatomical location. Regardless of the aortic diameter, type A intramural hematoma, involving the ascending aorta, is at high risk for early progression, and surgical intervention is therefore recommended.

Imaging Diagnosis

In current medical practice, the diagnosis of coarctation that is suggested on physical examination is confirmed by imaging. The chest film in the adult frequently shows the notched aortic isthmus, but this sign is usually not seen in the infant. In infants, the evaluation of coarctation is typically made by echocardiography. In children and adults, MRI and occasionally angiography provide additional important information and may modify the medical and surgical management. These additional observations include associated aortic arch anomalies, aberrant subclavian vessels, atypical or long-segment aortic stenoses, and patent ductus arteriosus. At times, abundant collaterals that are evident on angiography were undetected by the physical examination or the chest film. When minimal collaterals are present, the surgical approach may change from a primary repair to a bypass graft around the coarctation to protect the blood supply to the spinal canal.

Classification

There are numerous classifications of coarctation based on the age of the patient, the position of a patent ductus arteriosus in relation to the coarctation, and the length of the coarctation. Most of these schemata, including the classification into infantile or adult types, have limited usefulness in patient management because there is great variability within the categories, and the adult type of coarctation is frequently present in infants. Preductal and postductal coarctation are meaningful if the ductus is patent. Box 11-8 is a useful list of imaging observations that includes ductal patency, extent of collaterals, aortic arch anomalies, and coarctation in unusual locations.

Characteristics

The typical coarctation occurs in the aortic isthmus. This segment of the aorta between the origin of the left subclavian artery and the ductus is normally slightly small in the fetus and newborn. The fetal configuration of the isthmus produces a diameter that is roughly three quarters of the diameter of the descending thoracic aorta. Three months after birth, the fetal configuration of the isthmus is gone and the aortic arch has the same diameter throughout. The coarctation consists of an obstructing membrane on the greater curvature of the aorta opposite the ductus or ligamentum arteriosum. Typically, the lesser curvature of the aorta, which includes the site of the ductus, is retracted medially toward the left pulmonary artery. Beyond the obstruction there is usually a short segment that is dilated and may rarely be aneurysmal. The aorta proximal to the coarctation may be enlarged, either congenitally or from hypertension. The dilatation may include the innominate, carotid, and subclavian vessels. More than half have tubular hypoplasia of the transverse portion of the aortic arch, beginning after the innominate artery and ending at the coarctation. In this configuration, the innominate, carotid, and subclavian arteries are dilated and may be as large as the transverse aortic arch.

The position of a patent ductus arteriosus with respect to the coarctation affects both the clinical presentation and the imaging interpretation. A ductus arteriosus may originate proximal, distal, or adjacent to a coarctation. If the coarctation is distal to the ductus arteriosus, blood flow is initially from the aorta to the pulmonary arteries in a left-to-right direction. If later the pulmonary vascular resistance increases because of an Eisenmenger reaction, the shunt may become bidirectional or reversed. If the coarctation is proximal to the ductus arteriosus, flow through the ductus will depend on the size of the ductus and the difference between the pulmonary and systemic vascular resistances. In this situation, the blood flow is frequently from the pulmonary artery to the descending aorta, a state that produces cyanosis in the lower half of the body. Oxygenated blood from the left ventricle goes to the aortic arch arteries, whereas deoxygenated blood from the right ventricle goes through the ductus to the lower body. A juxtaductal coarctation produces a complex pattern of blood flow, which may vary dynamically as the pulmonary and systemic vascular resistances change with daily activity.

Stenosis or the anomalous origin of a subclavian artery distal to the coarctation results in an inequality in pulses and blood pressures in the two arms. A rare condition that produces equal blood pressures in both arms is the anomalous origin of both subclavian arteries below the coarctation. Coarctation at multiple sites or in the distal thoracic and abdominal aorta probably represents an embryologically different malformation, such as neurofibromatosis, or an acquired disease such as Takayasu aortoarteritis. Mucopolysaccharidosis (Hurler and Scheie syndromes) may have long tubular segmental stenoses in the aorta resembling those seen in Takayasu disease.

Congenital bicuspid aortic valve is frequently associated with coarctation. Between a quarter and half of the patients with aortic coarctation also have a bicuspid aortic valve. Anomalies associated with aortic coarctation are listed in Box 11-9.

Fatal complications of aortic coarctation include bacterial aortitis at the site of the coarctation, aortic dissection, aneurysm of the ductus with rupture, and distal thromboembolism. Fatal left ventricular failure may occur from hypertensive heart disease or from stenosis and regurgitation of a bicuspid aortic valve. Because the carotid arteries are hypertensive, aneurysms in the circle of Willis may develop and rupture.

Chest Film Abnormalities

Plain film findings have their angiographic counterpart and are particularly useful in searching for the extent of collateral supply. The thoracic aorta shows an abnormal contour on the chest film in roughly 60% of patients with coarctation. The “figure 3 sign” is the undulation in the distal aortic arch at the site of the coarctation (Fig. 11-77). The distal convexity in this region represents the poststenotic dilatation. There is considerable variability in the size of the ascending aorta and in the upper half of the figure 3 sign. The ascending aorta may be large, normal, or invisible on the chest film, reflecting the wide morphologic variety of aortic coarctation. Because the left subclavian artery dilates in response to the hypertension on the proximal side of the coarctation, this vessel is frequently visible as it swings from the mediastinum toward the apex of the left lung.

FIGURE 11-77 Coarctation of the aorta. A, Minimal rib notching is present. The arch of the aorta (straight arrow) is unusually large and the left subclavian artery (arrowheads) has elongated into the left apex. The site of the coarctation (curved arrow) is the deep concavity in the descending aorta. B, The para-aortic stripe has a deep indentation (arrow) posteriorly behind the pulmonary artery segment.

Rib notching is the result of enlarged and tortuous intercostal arteries that serve as collateral channels. The notches are an exaggeration of the neurovascular groove in the inferior aspect of the rib (Fig. 11-78). The degree of notching ranges from minimal undulations, which are variations of normal findings without coarctation, to deep ridges in the inferior rib margin. A small notch near the costovertebral joint is normal, so that the more lateral the notching, the more likely it is to be pathologic. Rarely, the intercostal artery is so tortuous that it notches the superior aspect of the adjacent inferior rib. Rib notching is uncommon before the age of 6 years, and its frequency increases with age, so most adults have this sign. The notching may occur at scattered sites and is usually not present on all ribs. After surgical repair of the coarctation, rib notching regresses as the bone is remodeled and the collateral vessels become smaller.

FIGURE 11-78 Coarctation of the aorta. Rib notching from coarctation occurs in the middle and lateral parts of the posterior ribs. Notching only in the medial rib adjacent to the costovertebral junction may be a normal variant.

The intercostal arteries that serve as collateral channels originate from the descending aorta. For this reason, the first and second ribs do not have notches because their intercostal arteries come from the superior intercostal artery, which originates from the subclavian artery, above the coarctated site. Unilateral rib notching implies the presence of an anomalous subclavian artery. Notching of the left ribs only occurs when an aberrant right subclavian artery originates below the coarctated segment. Unilateral notching of the right ribs exists when the coarctation originates between the left carotid and left subclavian arteries. The size and extent of the notching reflects the amount of collateral blood flow through the intercostal arteries. When the coarctation is mild, no notching may be present; conversely, severe stenosis in the adult almost always has some element of rib notching.

In infancy, the abnormal mediastinal contours are invisible because of the overlying thymus. The typical chest film displays signs of congestive heart failure with a large cardiac silhouette and perihilar pulmonary edema (Fig. 11-79). The extent of both of these findings depends on the severity of the coarctation and the patency of the ductus arteriosus. A barium esophagogram may be useful to outline the medial side of the aorta. The barium in the esophagus, when fully distended, has a reversal of the figure 3 sign. The sharp lateral outpouching represents the site of the coarctation and the inferior area of constriction represents the poststenotic dilatation of the aorta.

FIGURE 11-79 Coarctation in a 2-month-old infant. The large cardiac silhouette and the indistinct pulmonary vessels reflect congestive heart failure. The wide mediastinum, particularly on the right side, is the thymus. The site of the coarctation (the “figure 3 sign”) is typically not visible at this age.

Rights were not granted to include this figure in electronic media. Please refer to the printed book.

(From Miller SW: Aortic arch stenoses: coarctation, aortitis, and variants, Appl Radiol 24:15-19, 1995.)

Imaging Examination

In the infant, most coarctations are easily seen with ultrasound. In the suprasternal plane, echodense tissue narrows the aortic isthmus from its posterior aspect. Continuous wave Doppler beam interrogation allows calculation of the pressure gradient across the stenosis.

MRI is the preferred vascular study in older children and adults because it has no ionizing radiation and can image long segments of the aorta (Fig. 11-80). Because the stenosis typically is severe and the aorta tortuous at the poststenotic segment, the technique must be tailored to the pathologic findings. Slice thickness should be about 5 mm. The coronal plane images are useful to show the extent and size of collaterals. A multislice series then is designed from the axial stack to obtain a series of oblique images parallel to the long axis of the aorta centered on the coarctated segment (Fig. 11-81). Gradient echo sequences (Fig. 11-82) in the aortic plane can produce images similar to those of aortography. Visualization of a jet indicates a significant stenosis and pressure gradient across the coarctation. CT and CT angiography with multidetector technology and three-dimensional reformatting continue to rival the resolution of conventional catheter angiography (Fig. 11-83).

FIGURE 11-80 Pseudoaneurysm after surgery for repair of a coarctation. A, A spin echo sequence in the plane of the ascending aorta shows a large saccular aneurysm (A) in the aortic isthmus. B, A parallel slice, which includes the descending aorta, shows the origin of the left subclavian artery (S) at the neck of the aneurysm. The grafted segment (arrows) is intact above a poststenotic dilatation of the aorta.

FIGURE 11-81 Coarctation of the aorta. A gadolinium-enhanced three-dimensional surface rendering of mild coarctation (white arrow) with some tortuosity of the isthmus. There is no blood pressure gradient across this lesion at rest.

(Courtesy Ruchira Garg, MD.)

FIGURE 11-82 Gradient echo image of an aortic coarctation. In the sagittal plane, which contains the right ventricle (RV), left pulmonary artery (P), and left atrium (LA), the aortic isthmus has a long stenosis (arrow) beginning distal to the left subclavian artery.

FIGURE 11-83 Coarctation of the aorta. Reformatted computed tomography angiography of the thoracic and abdominal aorta demonstrating a coarctation (white arrow) of the proximal thoracic aorta with prominent poststenotic dilatation. There is also aneurysmal enlargement of the innominate artery (*).

(Courtesy Ruchira Garg, MD.)

Aortography gives the highest resolution of the coarctated segment, the aortic arch vessels, and the flow through the collateral channels (Fig. 11-84). The catheter from the femoral artery can almost always be advanced through the coarctated segment with a guidewire and positioned in the ascending aorta. Retrograde flow of contrast material then outlines the aortic root and identifies any bicuspid aortic valve. The left anterior oblique projection with cranial angulation projects a ductus inferior to the aortic arch (Fig. 11-85). A delayed imaging sequence of up to 10 to 12 seconds is desirable to include late collateral opacification. At the conclusion of a retrograde aortogram, a measurement of the pressure gradient across the stenotic segment should be recorded. Box 11-10 lists the elements demonstrated in an aortogram.

FIGURE 11-84 Coarctation of the aorta. Aortography of three variations of aortic coarctation filmed in the left anterior oblique projection. A, Aortic valve stenosis is indicated by the domed leaflets of the bicuspid valve and the poststenotic dilatation of the ascending aorta. The transverse arch is frequently hypoplastic before the coarctation. B, The bicuspid aortic valve is oriented in an anteroposterior direction. There is pronounced poststenotic dilatation after the coarctation. Large internal mammary arteries and bridging mediastinal vessels are visible. C, The transverse arch has normal size. A small diverticulum (arrow) represents the obliterated ductus arteriosus.

FIGURE 11-85 Cranial angulation for demonstrating coarctation of the aorta. In this double-outlet right ventricle filmed in the long axial oblique projection, the coarctation (arrow) is projected above the left pulmonary artery. The transverse aortic arch is hypoplastic.

The collateral circulation influences the extent of upper extremity hypertension and the amount of circulation to the lower half of the body. The major routes of collateral flow are through the subclavian arteries and through bridging collaterals in the mediastinum around the coarctated site. These routes vary considerably from patient to patient, even when the degree of coarctation is similar. Numerous bridging mediastinal vessels are frequent when other considerably longer pathways are poorly visualized.

A common collateral channel is for blood to flow from the subclavian arteries to the internal mammary arteries, then in a retrograde direction in the intercostal arteries to the descending aorta (Fig. 11-86). This pathway is responsible for the radiologic signs of large, undulating soft tissue in the retrosternal region on the lateral chest film and for the presence of rib notching. Obviously, if a subclavian artery originates anomalously in the low-pressure region below the coarctation, there will be no collateral flow in that side of the thorax. Another collateral pathway involves the thyrocervical and costocervical arteries, which originate from the subclavian artery. These vessels course through the scapular region to join intercostal arteries in the inferior thoracic region. Collateral pathways that are rarely seen on angiography include the superior and inferior epigastric arteries, which form a bridge from the intercostal arteries to the lumbar and iliac arteries, and the anterior spinal artery and other communicating arteries adjacent to the spinal cord.

FIGURE 11-86 Collateral vessels in coarctation. A, A gradient echo image shows large bilateral internal mammary arteries (arrows) in a coronal plane that also includes the right ventricle. B, Thoracic aortography opacifies large internal mammary arteries (arrows).

The extent and size of the collateral channels that are angiographically visible roughly correspond to the age of the patient and the severity of the stenosis. Large and tortuous intercostal vessels are common in the adult but are rarely seen in infants. When the coarctation is distal to the ductus, collateral circulation forms during fetal life. Collateral circulation may be absent when the coarctation is proximal to the ductus.

Characteristics

Complete interruption of the aortic arch is a rare congenital anomaly characterized by discontinuity of the arch between the proximal ascending aorta and the distal descending aorta. The ductus arteriosus is frequently patent and is the connection to the distal arch and descending aorta. This anomaly usually has three defects:

The DiGeorge syndrome of thymic hypoplasia, bicuspid aortic valve, hypoplastic left ventricle, and truncus arteriosus is frequently associated with aortic arch interruption. Unlike severe coarctation, there is no residual connection between the ascending and descending aorta.

Classifications

The site of the arch interruption determines classification into one of three types (Fig. 11-90). Type A has the interruption distal to the left subclavian artery. In a variation of this type, the right subclavian artery arises from the descending aorta or the pulmonary artery. In type B, the interruption is after the left common carotid artery (Fig. 11-91). The left subclavian artery arises from the descending aorta. This variety is the most common form of interrupted arch; its variations include forms in which the right subclavian artery comes from the right pulmonary artery via a right ductus and another variation in which the right subclavian artery connects to the descending aorta. Type C interruption is a discontinuity of the aortic arch distal to the innominate artery. The left carotid and left subclavian arteries connect to the descending aorta.

FIGURE 11-90 Complete interruption of the aortic arch. A, Type A: Interruption of the aortic arch distal to the origin of the left subclavian artery (LSA) with the descending aorta connecting to the ductus arteriosus (PDA). B, Type B: Interruption distal to the left common carotid artery (LCA) with the LSA arising from the descending aorta. C, Type C: Interruption distal to the right innominate artery with the LCA and LSA arising from the descending aorta. LPA, left pulmonary artery; RCA, right carotid artery; RPA, right pulmonary artery; RSA, right subclavian artery.

FIGURE 11-91 A and B, Type B aortic arch interruption. Sagittal contrast computed tomography. Ascending aorta (AA), descending aorta (DA), right pulmonary artery (PA), and patent ductus arteriosus (*).

(Courtesy Lawrence Boxt, MD.)

Chest Film Abnormalities

The plain chest film is characterized by nonspecific features that include cardiomegaly, increased pulmonary blood flow, and pulmonary edema. Details of the aortic arch are usually invisible even when no obvious thymus is present. In older patients, the trachea is frequently midline, reflecting a hypoplastic ascending aorta. The pulmonary artery is quite large and the aortic arch invisible, creating a deep notch in the aortopulmonary recess. On a well-penetrated film, the descending aorta may appear to end at the level of the main pulmonary artery. In older patients, rib notching, either bilateral or unilateral, depends on the site of the arch interruption and the origin of the subclavian arteries.

Imaging Examination

Because this is mostly a disease of neonates, echocardiography is the modality that ordinarily makes the diagnosis. The aortic arch assessed from the suprasternal area is scanned for continuity and for a large ductus arch.

The characteristic angiographic features depend on the anatomic type of interruption and the collateral flow to arteries not attached to the proximal aorta. In type A interruption with all brachiocephalic vessels arising from the ascending aorta, the angiographic appearance of these vessels resembles the letter V or W. There is a deep notch filled by the left lung between the large main pulmonary artery and the left subclavian artery. In type B interruption, the V configuration is formed by the two carotid arteries (Fig. 11-92).

FIGURE 11-92 Type B aortic arch interruption. The catheter is above the truncal valve (Tr) in an infant with a Van Praagh type 4 truncus arteriosus. The aorta (Ao) is small and is interrupted distal to the left common carotid artery. Both subclavian arteries arose from the descending aorta. The brachiocephalic arteries form the V sign. A large patent ductus arteriosus functions as the aortic arch. PA, pulmonary artery.

Rights were not granted to include this figure in electronic media. Please refer to the printed book.

(From Neye-Bock S, Fellows KE: Aortic arch interruption in infancy: radio- and angiographic features, Am J Roentgenol 135:1005-1010, 1980.)

Collateral circulation is identified by delayed filming and resembles that seen in aortic coarctation. With type A interruption and normal origin of the subclavian arteries, the collateral pathways are identical to aortic coarctation, particularly when the ductus is partly or completely closed. In older children, there may be bilateral rib notching. With type B interruption with the left subclavian artery connected to the descending aorta, collateral flow should promote rib notching only on the right side. A subclavian steal phenomenon may be visible with retrograde flow down the left vertebral artery to opacify the left subclavian artery. In a similar fashion, retrograde flow in any brachiocephalic artery may theoretically be visible if it attaches to the low-pressure side of the aortic interruption.