Ultrasound of the aorta

Visualization of blood flow with the help of ultrasound dopplerography (ultrasound) has expanded the possibilities of the ultrasound method for examination of the abdominal cavity organs. Ultrasonic dopplerography is performed according to certain clinical indications, requiring a specific protocol for the study and quantification of blood flow, for example, after monitoring after interventional interventions for the imposition of a transient intrahepatic portosystemic shunt. Also, the color regime can be applied during an ultrasound examination to identify the vascular nature of undetermined hypoechogenic or anechogenic formations.

When ultrasound examination of the abdominal cavity specialist ultrasound is faced with a large number of clinical problems and the need to visualize all vascular pools. To optimize the image, precise settings are required. Traditional image planes can be changed to examine altered vessels at a convenient Doppler angle.

This chapter presents a normal ultrasound picture of the vascular basins of the abdominal cavity and pathological changes revealed by ultrasound. Parenchymal diseases are limited to neoplasms due to their high clinical significance. The goal is not to fully demonstrate the possibilities of color duplex sonography of the abdominal cavity, but to give an idea of its key aspects and thus help the diagnosticians take the first step in this difficult field.

Ultrasound anatomy of the aorta and its branches

The abdominal aorta is located paravertebrally to the left of the aperture of the diaphragm to the level of the L4 vertebra, where it is divided into common iliac arteries. Its diameter varies from 25 mm or less at the sub-diaphragm level to 20 mm or less at the level of bifurcation.

The first unpaired branch of the abdominal aorta, the celiac trunk, extends to the left of the median line. He deviates somewhat to the right before the departure of the common hepatic artery, a vessel of approximately one caliber, a splenic artery and a small-caliber left gastric artery. The common hepatic artery goes in the hepatic-duodenum ligament to the liver, passing anterior to the portal vein. The splenic artery, accompanied by the eponymous vein, goes along the posterior edge of the pancreas to the gates of the spleen.

The superior mesenteric artery usually departs from the ventral aorta 1 cm distal to the celiac trunk. Its main trunk runs parallel to the aorta, and with the help of an ultrasound method it can be traced over a long distance, when the mesenteric vascular arches are no longer visible.

The inferior mesenteric artery departs approximately 4 cm before bifurcation and for some time goes to the left of the aorta before dividing into branches. Buhler's anastomosis connects the celiac trunk and the superior mesenteric artery through the pancreatic-duodenal arteries. Anastomosis between the superior and inferior mesenteric artery (riolan anastomosis) is accomplished through the middle and left colonic arteries.

Methods of examination

The patient is examined in the supine position using a convection transducer of intermediate frequency (usually 3.5 MHz). The roller under the knee joints allows the patient to feel comfortable and improves the scanning conditions, since the abdominal wall relaxes. The abdominal aorta is fully examined first in the longitudinal and transverse B-mode, after which the color regime is applied.

Normal picture

The picture of blood flow in the aorta is diverse. Above the level, the pseudokistolic peak is replaced by constant direct blood flow to the diastole. Scanning below the level of the kidneys normally reveals an early diastolic reverse flow, as in the peripheral arteries. It should not be considered a pathological blood flow or a "blur".

The blood flow velocity in the abdominal aorta is about 50 cm / m lower than in the peripheral arteries, which is associated with a large caliber of the aorta. The rates and components of the reverse blood flow are variable.

The color mode of aortic scanning below the level of the kidneys when examining the upper abdominal cavity is often unsuccessful, since the angle between the sound track and the direction of blood flow is unacceptable (90 °) when using a convection sensor, and changing the angle has little effect on the situation. The location of the sensor in the caudal direction gives the best Doppler angle, but the gas-filled transverse colon often enters the scanning area at the level of the middle floor of the abdominal cavity, overlaying the image.

The most frequent disease of the aorta is atherosclerosis. Ultrasound can determine the dynamics of the combined changes, such as stenosis, occlusion and aneurysms.

Criteria for aortic enlargement

1. Blood flow laminar or turbulent
2. The maximum diameter of the aorta is less than 2.5 cm. The indication for surgical intervention is the diameter of more than 5 cm, progression of more than 0.5 cm per year
3. Width and localization of perfused, thrombosed or false lumen: eccentric location
4. Defeat of the arteries of the internal organs of the abdominal cavity, the hepatic or iliac arteries? (surgical strategy and choice of implant)
5. Peripheral aneurysmosis?
6. Spectra in the true and false lumen? (threat of ischemia, indications for surgical intervention)

Aneurysms

Aneurysms of the abdominal aorta are usually clinically asymptomatic. The increase in their size and the formation of peripheral emboli lead to the appearance of nonspecific symptoms, such as back pain and abdominal pain.

Classification

Isolated aneurysm occurs quite often and is usually located below the level of the kidneys. The iliac arteries may be involved in the process. The location of the less common thoracoabdominal aneurysm is determined according to the four-stage Crawford classification. Type I (not shown) includes aortic lesion above the level of the kidneys. Stages II-IV determine the level of involvement of the thoracic aneurysm located below the kidneys.

Aneurysm of the abdominal aorta and marginal thrombosis are clearly defined by the ultrasound method. The extent of the lesion of the thoracic aorta and the spatial relationships necessary for the planning of surgical treatment are assessed using Doppler spectra and CT.

With a splitting aneurysm, the blood gets between intima and the media through a gap in the wall of the vessel. The flap of the intima separates the true and false lumens and oscillates when the blood moves. Aneurysm prevalence can be assessed using CT or ultrasound using the Stanford or DeBakey classification. Ultrasound can provide additional information about the condition of the arteries of the internal organs and pelvis, and is also used for dynamic observation at short intervals

Lerish syndrome

Lerish's syndrome is an occlusion of the abdominal aorta in the bifurcation area. Blood flow at the level of the superior mesenteric artery can still be visualized on longitudinal and transverse images. Distal to transverse scans at the level of the mesentery vault and caudal to bifurcation, there is no signal of blood flow. Note that focal color cavities may occur due to an unsuccessful scan angle or because of the shading plaques lying in front. Unsuccessful settings can lead to false positive results.