Ultrasound signs of occlusion of the abdominal aorta

Among the causes of occlusive diseases of the abdominal aorta, atherosclerotic lesion occupies one of the leading places. According to the results of color Doppler scan, the following degrees of aortic lesions can be distinguished: early atherosclerotic changes; stenosis; occlusion.

Early atherosclerotic changes in the aorta are limited to the localization of the process only in the aortic wall. In the study in the B-mode, uneven thickening of the aortic walls, the presence of hyperechoic inclusions corresponding to the deposition of calcium as separate clumps, an uneven internal contour of the aorta with an intact vessel lumen and a major type of blood flow can be noted according to the Doppler spectrogram.

Diagnosis of aortic stenosis is based on visualization in the B-mode of echogenic masses that reduce the aortic lumen. Echogenic masses may be due to the presence of either local, less frequently prolonged atherosclerotic plaques and / or the presence of parietal thrombosis. Atherosclerotic lesion is more often localized in the infrarenal region, in the area of bifurcation of the abdominal aorta, and in a significant number of cases - along the back wall. Atherosclerotic process of this localization is characterized by the presence of high-intensity echo signals in homogeneous and heterogeneous plaques, in some cases accompanied by the presence of an acoustic shade, morphologically corresponding to calcification. The parietal thrombotic masses are represented by hypoechoic, predominantly homogeneous structures, which are usually located along the aortic wall, and have an echogenicity somewhat higher than the lumen of the vessel. Clearly determine the extent and shape of the plaque, as well as the near-wall thrombotic masses, when operating in the DCS and / or EHD regime. The degree of aortic lesion is diagnosed by ultrasound imaging with the calculation of percentage of stenosis using a computer program and supplemented with spectral analysis of blood flow. According to Th. Karasch et al., A local increase in systolic linear velocity of blood flow (LSC) of more than 200 cm / s indicates the presence of hemodynamically significant aortic stenosis. Stenotic lesion of the aorta can be combined with its deviation in a number of cases, especially in patients with arterial hypertension.

By localization, three types of occlusion of the abdominal aorta are distinguished:

1. low occlusion - the occlusion of the bifurcation of the abdominal aorta distal to the divergence of the inferior mesenteric artery;
2. middle occlusion - proximal to the dissection of the inferior mesenteric artery;
3. high occlusion - at the level of the renal arteries ilk within 2 cm distal.

Ultrasound diagnosis of occlusion of the abdominal aorta is based on the following criteria:

1. The presence of echogenic masses, obturating the aortic lumen and the absence of blood flow in the lumen according to the data of the central and / or EHD and the spectrum of the Doppler frequency shift.
2. Reduction of systolic and diastolic blood flow velocity in the aorta is proximal to occlusion.
3. Registration of the collateral type of blood flow in arteries distal to occlusion.

Compensation of blood flow during occlusion of the abdominal aorta is realized by collateral circulation through various anatomical pathways, the course of which, according to the color Doppler scan (DSD), is not always possible to trace. However, in this situation, the CDS allows us to obtain information about the individual components of the collateral circulation system, in particular, the inferior mesenteric artery, the lumbar arteries and the superior mesenteric artery.

Depending on the conditions of the examination, visualization of the inferior mesenteric artery (NBA) is possible in 56-80% of observations. Visualization of NBA in the initial segment is performed when examining in the sagittal or transverse planes of scanning 50-60 mm proximal to the aortic bifurcation at the level of III-IV lumbar vertebrae. Normally, the diameter of the NBA is 2-3 mm. A qualitative characteristic of the blood flow spectrum indicates a high peripheral resistance in the artery involved in the blood supply to the left side of the transverse and descending colon, the sigmoid and proximal portion of the rectum. High peripheral resistance in the NBA is one of the ultrasound criteria for differential diagnosis of NBA and renal arteries, which are characterized by low peripheral resistance.

Lumbar arteries are paired vessels located in the infrarenal aorta. Qualitative evaluation of the spectrum indicates the presence of high peripheral resistance. When performing the function of collateral vessels in the lumbar arteries, the level of blood circulation increases, which improves the possibility of ultrasound imaging of these arteries.

With occlusive lesions of the abdominal aorta, the lower, superior mesenteric arteries, lumbar arteries carry a compensatory load, as a result of which the blood flow increases with a gradual increase in their diameter. A special feature of compensatory blood flow is the recording of an increase in the linear velocity of blood flow throughout the vessel, accessible by ultrasound imaging, while hemodynamically significant stenosis of the lower or upper mesenteric arteries reveals local changes in hemodynamics in the artery narrowing region.

Another cause of occlusive diseases of the abdominal aorta is nonspecific aortoarteriitis. According to A.V. Pokrovsky et al., Depending on the localization of aortic stenosis, three variants of the lesion of the thoracoabdominal segment of the aorta are distinguished. When I variant of the lesion, only the descending thoracic aorta is involved in the process. This type is found in 4.5% of observations. For the second variant of the lesion, the localization of the process in the supra-, inter- and infrarenal segments of the aorta is characterized with a practically obligatory simultaneous involvement of the visceral and renal arteries in various combinations. This most typical and frequently occurring type of aortic lesion was noted by the authors in 68.5% of cases. In type III - 27% of observations - the descending thoracic aorta, its supra-, inter-, and infrarenal segments, as well as visceral and renal arteries, are simultaneously involved in the process.

When performing color Doppler scanning in this patient population, it is advisable to adhere to the following methodological points:

1. To optimize the image of the aorta and a detailed study of the zone of interest, and in this situation it is the aortic wall, it is necessary to use the function of the ultrasound apparatus, which allows obtaining the image of the investigated region in an enlarged size. In addition, to improve the quality of ultrasound images of the aorta in the B-mode, it is advisable to use the tissue harmonic mode.
2. Percentage of stenosis of the aorta according to ultrasound images should be measured based on the calculation of the cross-sectional area.

An increase in the thickness of the posterior and / or anterior wall of the aorta indicates the presence of nonspecific aortoarteriitis. However, the quantitative evaluation of the wall thickness is not a constant value and can vary depending on the activity of the inflammatory process. Ultrasound examination allows to diagnose the extent of changes in the aorta, which are characterized by prolonged lesions, gradually turning into unchanged aortic sites. Echogenicity of the aortic wall can correspond to the norm or be elevated.

To determine the tactics of managing patients and to resolve the issue of indications for surgical treatment, information about the degree of aortic narrowing is important. We distinguish two variants: hemodynamically insignificant stenosis, which is characterized by the presence of wall thickening, the percentage of narrowing according to the ultrasound image data does not exceed 70%, the normal values of LCS indices on the abdominal aorta remain; hemodynamically significant stenosis, which is characterized by a thickening of the aorta wall in combination with an increase in the blood flow velocity, the percent of stenosis according to the ultrasound image data exceeds 70%.

In addition, the obtained data can be supplemented with information on the role of the lower and upper mesenteric arteries, lumbar arteries in the development of collateral circulation.