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Ultrasound signs of an aneurysm of the abdominal aorta
Last reviewed: 19.10.2021
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The true aneurysm of the abdominal aorta is characterized by local protrusion or diffuse aortic dilatation due to a violation of the normal structure of the wall. Diagnosis of an aneurysm is based on the study of the aorta in the sagittal, transverse and coronary planes of the scan with the 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 diameter of the aorta 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 the displacement and bends. The first ultrasound sign of the presence of an aneurysm is a segmental increase in the aortic cross section in 2 times or more. An increase in the cross section of the aorta is less than 2-fold, indicating the presence of an aneurysmal enlargement. The screen of an aneurysm is represented by a cavity formation of a round or more often oval shape. In the sagittal plane of the scan, the spindle aneurysm has the shape of an oval, the saccate is characterized by the bulging of one of the walls of the aorta.
The maximum diameter of the aneurysm is determined from the outer edge of the adventitia of the walls of the aneurysmal sac in the sagittal and transverse planes of the scan. More precisely, the maximum size of the aneurysm is diagnosed in a study in the transverse plane of the scan. It should be noted that deformity 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 aneurysm size from ultrasound data.
Assessment of the state of the lumen of the aneurysm is carried out in the B-mode and the regimes of the DCC and EHD. More often inside the aneurysm are visualized thrombotic masses represented by hypoechoic, mostly homogeneous structures with an echogenicity higher than the echogenicity of the residual lumen of the vessel. In the DCA mode, the cavity of the aneurysmic sac is colored with differently directed flows of red and blue. The Doppler shift spectrum is characterized by a low systolic rate and a change in the ratio of systolic and diastolic peak values.
The aneurysm wall may contain calcium inclusions. It is possible to distinguish the following ultrasound variants of the condition of the aneurysm wall: it is not changed in structure; thickened; is thinned; tearing of the intima with the separation of the wall; wall rupture. Ultrasound picture of aneurysm wall rupture is characterized by a defect, usually in a thin wall and the development of a hematoma, more often in the retroperitoneal space.
It is important to emphasize that the possibility of color Doppler scan does not in all cases allow solving the diagnostic problems facing the expert in assessing the condition of the aneurysm wall, in particular, in determining the intimal tear. Intimus tearing can lead either to delamination of the wall, or to its rupture. A new technique for the three-dimensional reconstruction of the aneurysm allows a more contrasting image of the aortic wall, so in complex diagnostic cases it is advisable to use it.
In this category of patients, the study of renal arteries is of great practical importance. Depending on the location of the aneurysm relative to the renal arteries, the following aneurysm localization is identified; suprarenal, interrenal or infrarenal aorta. There are two approaches to determining the relationship of an aneurysm with the renal arteries. 1 st - in the CDC or EHD mode, in combination with the Doppler shift spectrum, visualize the renal arteries and measure the distance from the mouth of the examined arteries to the aneurysm. 2 nd - in cases where it is impossible to obtain information about the localization of the mouth of the renal arteries, measure the distance from the superior mesenteric artery (BWA) to the proximal end of the aneurysm. The renal arteries are located 1-1.5 cm distal to the BWA. Further, the condition of the wall and lumen of the renal arteries is analyzed with a quantitative assessment of blood flow. In the presence of stenosis in the examined arteries, it is necessary to diagnose its degree and localization, in the presence of an aneurysm - to fix its maximum diameter. In addition, it is advisable to pay attention to the presence or absence of additional renal arteries.
Aneurysms of the distal aorta can be combined with aneurysmatic enlargement or an aneurysm of the iliac arteries. The common iliac arteries are often affected, but isolated aneurysms of the external iliac artery are also diagnosed in a number of cases. The study of the iliac arteries begins with the measurement of the maximum diameter, followed by the determination of the condition of the wall and the lumen of the arteries. In the presence of an aneurysm or an aneurysmal enlargement, it is necessary to indicate the maximum diameter, extent, lumen and aneurysm wall.
The presence of a defect in the intima and filling it with blood contributes to the gradual stratification of the aortic wall and the formation of two lumens - true and false. This ultrasound pattern indicates the presence of an exfoliating aneurysm, which usually begins in the thoracic region. In the aortic lumen in the B-mode, a membrane is defined that consists of intima and / or intima and media moving synchronously with the pulsations of the aorta. When using the CDM mode, bi-directional flows are recorded in the true and false aortic lumens. In the true lumen, the antegrade direction of the blood flow is recorded. Arteries of the aorta can depart both from the true and false lumens. When revealing an exfoliating aortic aneurysm, a thorough examination of the thoracic aorta and then of the iliac arteries is necessary to determine the extent of this complication.
In the postoperative period, ultrasound examination provides an opportunity to assess the condition of the prosthesis and the presence of complications. Investigation of the periprosthetic area allows diagnosing complications such as infiltrate, abscess or hematoma with the definition of their location, extent and relationship with the prosthesis. Color Doppler scan provides information on the status of anastomoses, the development of stenosis of the distal anastomosis, thrombosis of the prosthesis or false aneurysm.