Ultrasound signs of abdominal aortic aneurysm

A true abdominal aortic aneurysm is characterized by a localized bulge or diffuse dilation of the aorta due to disruption of the normal wall structure. Aneurysm diagnostics is based on examination of the aorta in the sagittal, transverse, and coronary scanning planes with measurement of its maximum diameter: distal to the diaphragm, at the level of the visceral arteries, at the level of the aortic bifurcation. Normally, the aortic diameter at these levels is 29-26 mm, 24-22 mm, and 20-18 mm, respectively. It is necessary to analyze the anatomical course and location of the aorta, indicating displacement and bends. The first ultrasound sign of an aneurysm is a segmental increase in the aortic cross-section by 2 times or more. An increase in the aortic cross-section by less than 2 times indicates the presence of an aneurysmal dilation. On the screen, an aneurysm is represented by a cystic formation of a round or, more often, oval shape. In the sagittal scanning plane, a fusiform aneurysm has an oval shape, while a saccular aneurysm is characterized by a bulge of one of the walls of the aorta.

The maximum diameter of the aneurysm is determined by the outer edge of the adventitia of the walls of the aneurysmal sac in the sagittal and transverse scanning planes. The maximum dimensions of the aneurysm are diagnosed more accurately during examination in the transverse scanning plane. It should be noted that deformation of the aorta with a change in its anatomical course, poor resolution at the border of the aortic wall - surrounding tissue are limitations in the correctness of the precise determination of the aneurysm dimensions according to ultrasound examination data.

The state of the aneurysm lumen is assessed in the B-mode and the CDC and EDC modes. Most often, thrombotic masses are visualized inside the aneurysm, represented by hypoechoic, predominantly homogeneous formations in structure, the echogenicity of which is higher than the echogenicity of the residual lumen of the vessel. In the CDC mode, the cavity of the aneurysmal sac is colored with multidirectional flows of red and blue. The spectrum of the Doppler frequency shift is characterized by low systolic velocity and a change in the ratio of the systolic and diastolic peaks.

The aneurysm wall may contain calcium inclusions. The following ultrasound variants of the aneurysm wall condition can be distinguished: unchanged in structure; thickened; thinned; intimal rupture with wall dissection; wall rupture. The ultrasound picture of an aneurysm wall rupture is characterized by the presence of a defect, usually in a thinned wall, and the development of a hematoma, most often in the retroperitoneal space.

It is important to emphasize that the capabilities of color Doppler scanning do not always allow a specialist to solve diagnostic problems in assessing the condition of the aneurysm wall, in particular, in determining an intimal tear. An intimal tear can lead to either wall dissection or rupture. The new method of three-dimensional reconstruction of an aneurysm allows for a more contrasting image of the aortic wall, so its use is advisable in complex diagnostic cases.

In this category of patients, the study of the renal arteries is of great practical importance. Depending on the location of the aneurysm relative to the renal arteries, the following localization of the aneurysm is distinguished: suprarenal, interrenal or infrarenal aorta. There are two approaches to determining the relationship of the aneurysm with the renal arteries. 1st - in the color Doppler or EDC mode in combination with the Doppler frequency shift spectrum, the renal arteries are visualized and the distance from the mouth of the examined arteries to the aneurysm is measured. 2nd - in cases where it is impossible to obtain information on the localization of the renal artery mouth, the distance from the superior mesenteric artery (SMA) to the proximal edge of the aneurysm is measured. The renal arteries are located 1-1.5 cm distal to the SMA. Next, an analysis of the state of the wall and lumen of the renal arteries is carried out with a quantitative assessment of the blood flow. If there is stenosis in the arteries under study, it is necessary to diagnose its degree and localization; if there is an aneurysm, its maximum diameter should be recorded. In addition, it is advisable to pay attention to the presence or absence of additional renal arteries.

Aneurysms of the distal aorta may be combined with aneurysmal dilation or aneurysm of the iliac arteries. Common iliac arteries are most often affected, but in some cases isolated aneurysms of the external iliac artery are also diagnosed. Examination of the iliac arteries begins with measuring the maximum diameter, followed by determining the condition of the wall and lumen of the arteries. If an aneurysm or aneurysmal dilation is present, the maximum diameter, length, condition of the lumen and wall of the aneurysm must be indicated.

The presence of a defect in the intima and its filling with blood contributes to the gradual dissection of the aortic wall and the formation of two lumens - true and false. Such an ultrasound picture indicates the presence of a dissecting aneurysm, which usually begins in the thoracic region. In the lumen of the aorta in B-mode, a membrane is determined, which consists of the intima and / or intima and media, moving synchronously with the pulsation of the aorta. When using the CDC mode, bidirectional flows are recorded in the true and false lumens of the aorta. In the true lumen, antegrade blood flow is recorded. The aortic arteries can depart from both the true and false lumens. If a dissecting aortic aneurysm is detected, a thorough examination of the thoracic aorta is necessary, and then the iliac arteries to determine the boundaries of the spread of this complication.

In the postoperative period, ultrasound examination allows assessing the condition of the prosthesis and the presence of complications. Examination of the periprosthetic area allows diagnosing complications such as infiltrate, abscess or hematoma with determination of their localization, extent and relationship with the prosthesis. Color Doppler scanning provides information on the condition of anastomoses, development of stenosis of the distal anastomosis, thrombosis of the prosthesis or false aneurysm.