Aorta, Arteries

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Aorta, Arteries

Aplasia, hypoplasia, and duplication of the aorta are extremely rare and in most cases they will have been diagnosed during the perinatal period. Usually an aplastic aorta results in a fatal defect, and only two cases of aortic duplication have been described in the literature. Artifacts mimicking duplication may arise in the transverse epigastric plane from the prismlike effects of the fatty tissue between the rectus abdominis muscles, resulting in re-

fraction artifacts.4 There is also the possibility of a misdiagnosis due to physical ultrasound if echo reverberation produces an image of multiple aortas. The preferred location of this mirroring is found at especially hard interfaces, e. g., plaque incrustation of the aortic wall; here, a kind of ping-pong effect at the echointensive reflectors increases the transit time, which in turn generates multiple images of the aorta (Fig.1.7).

Congenital circumscribed circular narrowing of the aorta is known as aortic coarctation. It is found at several segments of the aorta: for the

abdomen these are segments IV (from the subphrenium to below the renal arteries) and V (all the way to the aortic bifurcation). Sonograph-

ically these stenoses are best studied by colorflow Doppler imaging and analysis of the flow parameters (see below).

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Oblique/Transverse Course of the Aorta

In case of severe scoliosis or kyphosis of the spine, the aorta will follow this course; the usual longitudinal plane may result in a double lumen, while the transverse view would depict the aorta as a short bandlike structure (Fig.1.8).

Fig. 1.8 Oblique course of the aorta due to kinking.

a Longitudinal subxiphoid plane: because of its oblique course the aorta is visualized twice.

b Oblique subxiphoid plane: the aorta (AO) has been insonated in an almost exactly longitudinal direction. Calipers: aortic ectasia bordering on an aneurysm.

Kinking of theAorta

Hypertension and arteriosclerosis can lead not only to an ectatic but also tortuous aorta. Since the spine does not yield, the aorta becomes displaced in a lateral and/or anterior direction and escapes detection by the standard view in the paramedian plane. If the vessel does not follow a normal straight course, the probe should be angled and shifted laterally in order to demonstrate any kinking (Fig.1.9).

Fig. 1.9 Kinking of the aorta (AO) induced by hypertension and arteriosclerosis (arrows: arteriosclerotic lesions).

Variant and Duplicated Arteries

of cases: here, the left gastric, common hepatic, and splenic arteries arise from a common trunk. Quite often the left gastric artery branches off first, followed by the other two arteries.

Fig. 1.11 Variant anatomy of the celiac axis. AO = aorta; AL = splenic artery; AH = hepatic artery.

a Separate origins of the hepatic and splenic arteries from the aorta.

b Atypical origin of the superior mesenteric artery (AMS) from the celiac trunk (TR): celiomesenteric trunk. V = superior mesenteric vein.

Fig. 1.12 Duplication of the renal artery.

a Longitudinal view: cross-section of two distinct arteries (arrows) posterior to the vena cava (VC).

b Transverse view of the right upper quadrant, color-flow Doppler study. Both renal arteries (A) are depicted; if stenosis of the renal artery is suspected, possible duplication should be ruled out. AO = aorta.

Fig. 1.13 Irregular course of the right renal artery (ARD) anterior to the vena cava (VC). Secondary finding: partial thrombosis (TH) of the vena cava. AO = aorta.

Dilatation

Aortic Ectasia

True Aneurysms

Dissecting Aneurysms

False Aneurysms

Aortic Ectasia

also involved, such as joint hypermobility (found in all forms, in addition to the aortic aneurysm), and, in most cases, thoracic deformations, arachnodactylia, and mitral valve prolapse. Early diagnosis allows preventive or timely surgical treatment (Fig.1.14).

Fig. 1.14

a Marfan syndrome. Ectatic aorta with severe insufficiency of the aortic valve: tortuous ectatic aorta.

b Ectatic aorta. Localized expansion of the ectatic aorta (AO) to 2.7 cm.

c Borderline aortic aneurysm: localized expansion of the ectatic aorta (AO) to 29.5 mm just cephalad of the bifurcation.

An aneurysm is a localized dilatation of the arterial wall. Aneurysms may be classified as follows:

●Etiology

–Congenital

–Atherosclerotic

–Dissecting

–Inflammatory

–Traumatic

●Morphology

–Fusiform

–Pouch-shaped

–Tortuous

–Cylindrical

–Saccular

–Navicular

●Pathogenesis

–True

–False (pseudo-)

–Dissecting

Aortic aneurysms. A practical working definition of an abdominal aortic aneurysm is a transverse lumen diameter of at least 30 mm. Localized atheromatous lesions in the wall facilitate the dilatation of the vessel and impair its contractility, resulting in a weakened aortic wall with aneurysm formation. Small aneurysms do not usually have any thrombotic deposits. Larger aortic aneurysms are characterized by dilatation, arteriosclerosis, and white thrombi, each of these being identifiable by ultrasound. If all three signs can be demonstrated sonographically, the diagnosis of an aneurysm is confirmed (Fig.1.15, Fig.1.16).

Increased size. Aneurysms tend to expand in size over time. The larger the lumen becomes, the less pressure the wall will tolerate before rupturing. According to Laplace’s law the tension in the wall is directly proportional to the radius; thus, small aneurysms with a diameter

Fig. 1.16 Large aortic aneurysm.

a Large aortic aneurysm, centrally perfused, marginal thrombi.

Fig. 1.17

a Thoracic aortic aneurysm (AO). TEE: expansion of the aorta to 40 mm, floating thrombus within the lumen (red thrombus made up of fibrin and red blood cells; arrows). Massive thickening and sclerosis of the wall.

blood jet (“open” rupture) can be demonstrated ( 1.2a,b). In most cases this lifethreatening emergency, requiring emergency repair, does not leave much time for any detailed study.

Other essential parameters to note during ultrasound imaging of abdominal aortic aneurysms are location, length, and the possible involvement of the renal and iliac arteries. With regard to operative possibilities and prognosis, especially when renal arteries are involved, endovascular prosthesis is not possible (

1.2c–i).

Thoracic aortic aneurysm. A true thoracic aneurysm is most often detected by chest ra-

Dissecting Aneurysms

In ultrasonography, dissecting aneurysms are characterized by an echogenic intima floating in synchronous motion with the pulse, or this echogenic intima may be thickened and rigid as a result of atherosclerosis. The vessel itself may be dilated and display all other signs of an aneurysm; however, quite often the artery appears otherwise normal, and the diagnosis is confirmed only by demonstrating the shearedoff intima within the lumen generating the color-flow Doppler image of two distinct lumina.

b All criteria of a true aneurysm are fulfilled in this B- mode image: widening of the vessel, sclerosis of the aorta (arrows), white thrombi (TH). AO = aorta.

b Dissecting aortic aneurysm, Stanford type A. TEE demonstrates the intraluminal hyperechoic intima (arrows) and the thrombosed, nonperfused lumen of the dissected area. (Patient declined surgery, died suddenly 2 weeks later.) AO = aorta.

diograph; it will be confirmed by transesophageal echocardiography (TEE) or CT. Investigation of acute thoracic pathology (often an acute coronary syndrome) should also involve a diagnosis or exclusion of aortic root dissection; sometimes an extension into the abdominal aorta may also be detected here (Fig.1.17).

Nonaortic aneurysms. Aneurysms are not limited to the aorta but may also be found in other intraand retroperitoneal or peripheral (subclavian artery) vessels. However, isolated iliac artery aneurysms without an associated abdominal aortic aneurysm are rare ( 1.1 d,g,h).

In nonaortic aneurysms the actual diameters separating ectatic and aneurysmic arteries

In more than 90% of patients, dissection with its massive, sharp chest pain will commence as thoracic aneurysm and propagate to the abdominal aorta (Stanford classification type B: begins at the ascending aorta or the aortic arch with possible extension to the abdominal aorta). Thoracic aneurysms immediately distal to the aortic valve (Stanford classification type A: involving only the aortic arch and ascending aorta) are diagnosed sonographically by echocardiography or TEE (Fig.1.17b, Fig.1.19).

c Color-flow Doppler: the remaining perfused lumen is defined by the color-coded signal; the color change (from red through black to blue) signifies the change in the flow direction—the flow toward the probe is red, and away from the probe it is blue.

Fig. 1.18 Right subxiphoid view in the longitudinal plane: the vena cava (VC) is insonated through the oblique section of the aneurysm (AN). AR = renal artery.

from normal vessels have not been defined. Diffuse dilatation of the vessel is classified as ectatic, but aneurysms always consist of a localized dilatation of the artery with thinning and structural weakening of the wall. The most common factor in the pathogenesis is atherosclerosis (60%), congenital defects in the wall playing a minor (20%) but still more frequent role than in the aorta where atherosclerosis accounts for the overwhelming majority (95%) of cases. The most frequent location of visceral artery aneurysms is the splenic artery, followed by the hepatic and renal arteries (Fig. 1.18).

The causes of aortic dissection can include damage to the collagen elastic fibrous tissue of the media due to ischemia (arteriosclerosis), inflammation (syphilis), or genetics (Marfan syndrome) (Fig.1.14).

Marfan syndrome and similar diseases are very rare causes of an aortic disorder—ectasia or aneurysm, most often with a dissection. But because there is a possibility of acute dissection, long-term and rigorous follow-up is necessary for these patients.

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Aorta, Arteries