The normal aorta has clear defined smooth margins and tapers slightly below the level of the renal arteries. The abdominal aorta lies adjacent to the spine throughout its course, slightly to the left of the midline (Fig. 5.1). The inferior vena cava in contrast lies to the right of the midline and gradually moves away from the spine. In contrast to the inferior vena cava, the aorta has a straight course and hard pulsations (Fig. 5.1b). It gives origin to the coeliac trunk and the mesenteric arteries which can simultaneously be shown in longitudinal sections through the abdomen (Fig. 5.1a, b). Colour Doppler displays the artery red (Fig. 5.1c). Pulsed wave Doppler shows a laminar flow characterised by the typical window under the flow curve (Fig. 5.1d). The flow curve is triphasic with a systolic forward flow, an end-systolic negative flow and a very low diastolic forward flow (Fig. 5.1d). This characterises the abdominal aorta as a high-resistance vessel: The abdominal aorta perfuses the low-resistance abdominal organs on one hand and on the other hand, equally important, the high-resistance lower extremities. If flow measurements are performed, flow should be measured at the upper (or lower) end of the picture where the angle of incidence is lowest. The flow in these sections of the artery runs under an angle of 30–50° to the Doppler beam. Correct flow velocities or volume flow can only be calculated if angle corrections are performed.

The descending aorta can be shown on axial sections through the abdomen too (Fig. 5.2). Depending on the height of the section, the origin of different arteries such as the coeliac trunk, the superior mesenteric artery and both renal arteries can be shown. Below the umbilicus the abdominal aorta bifurcates and gives origin to both common iliac arteries (Fig. 5.3). They run in front of the common iliac vein (Fig. 5.3b). Both vessels can be shown in longitudinal sections too (Fig. 5.3c). Flow in the iliac arteries is laminar and triphasic, as peripheral resistance is high (Fig. 5.3d).

Doppler sonographic flow measurements in the descending aorta cannot be performed in transverse sections, as the angle of incidence approximates 90°. With colour-coded Doppler sonography, flow can be seen: If the transducer is slightly angled cranially, the artery is displayed red as the flow runs towards the transducer (Fig. 5.2b). If the transducer is slightly angled caudally, the artery is displayed blue as the flow runs away from the transducer.

The first abdominal branch which originates from the aorta is the coeliac trunk; the second is the mesenteric artery (Figs. 5.1, 5.2, 5.4 and 5.5a, b). Both arteries can be seen in longitudinal sections through the abdomen (Figs. 5.1a, b and 5.5a, b). The third arteries which arise laterally from the aorta below the superior mesenteric artery are the renal arteries (Fig. 5.14). In contrast to the coeliac trunk and the superior mesenteric artery, the renal arteries are best displayed in axial views below the origin of the superior mesenteric artery (Fig. 5.14). Below the umbilicus the abdominal aorta gives origin to both common iliac arteries which can be displayed as round pulsating structures laterally to the midline (Fig. 5.3a). In longitudinal sections, the iliac arteries are displayed as tubular structures (Fig. 5.3c).

The coeliac artery, also called the coeliac trunk or the coeliac axis, is the first branch of the abdominal aorta (Fig. 5.4). It originates from the anterior surface of the aorta, between the diaphragmatic crura. It bifurcates after 0.5–2 cm from its origin into the common hepatic artery and the splenic artery, which can easily be visualised by ultrasound in transverse sections (Figs. 5.2a and 5.5c). The left gastric artery, which originates from the coeliac trunk too, usually cannot be visualised in infancy and childhood. In adolescents however the left gastric artery can be displayed (Fig. 5.5d).

The coeliac artery can be displayed either in sagittal (longitudinal) sections or in axial (transverse) sections through the upper abdomen (Figs. 5.1, 5.2 and 5.5a–c). The T-shaped bifurcation and its branches can best be shown in transverse planes (Figs. 5.2a,b and 5.5c). In longitudinal sections the branches of the artery are not well seen, although in rare cases branches of the coeliac trunk can be demonstrated (Fig. 5.5a, b).

Colour Doppler displays the flow red, as the blood stream is directed towards the transducer (Fig. 5.5a, b).

Pulsed wave Doppler shows a pulsatile flow displayed over the baseline. The flow profile is monophasic with a large amount of continuous forward flow throughout diastole (Fig. 5.6c–d). The monophasic flow is caused by the low peripheral resistance in the perfused organs of the upper abdomen (liver, spleen, pancreas). The splenic and hepatic branches show the same low-resistance flow pattern, as the peripheral resistance within the microcirculation of the liver and the spleen is low. Normal values for the flow velocities in the coeliac artery are helpful for the judgement of pathologic flow (Table 5.3).

The coeliac trunk is the ideal vessel for Doppler sonographic flow measurements in the abdomen:

The common hepatic artery is the limb of the T-shaped coeliac axis that turns to the patient’s right (Figs. 5.2, 5.5 and 5.7). The artery runs a short distance at the superior border of the pancreatic head and gives rise to the gastroduodenal artery which can sometimes be seen at the anterosuperior border of the pancreatic head in older children. Beyond the gastroduodenal artery, the common hepatic artery becomes the proper hepatic artery which follows the portal vein to the porta hepatis. At the entrance to the liver, it divides into the left and right hepatic arteries, which penetrate into the liver. Due to anatomic rules, branches of the hepatic artery, portal vein and bile ducts always run together.

The hepatic arteries can be visualised sonographically from an anterior abdominal approach. The common hepatic artery is most easily identified at its origin from the coeliac artery in transverse sections through the upper abdomen (Figs. 5.5c and 5.7a). Sometimes the origin of the artery can be displayed in longitudinal sections too (Fig. 5.5a, b).

The proper hepatic artery is seen near the porta hepatis that shows the portal vein in short or better long axes. The right and left hepatic arteries can be followed into the liver to a variable distance in children and adolescents (Fig. 5.7b). Due to the small size of the vessels in preterm babies, infants and toddlers, it is often not possible to display the branches of the hepatic artery on two-dimensional images. Using colour Doppler and high flow settings (low sensitivity and high PRF), the flow in the portal veins can be depressed and the high flow in the branches of the hepatic arteries can be seen adjacent to the portal vein branches (Fig. 5.7d). If higher sensitivity (lower PRF) is used and flow in the portal vein and the hepatic artery are simultaneously displayed, aliasing occurs in the hepatic artery (Fig. 5.7c).

Depending on the course of the common hepatic artery, the flow is displayed blue or red if colour-coded Doppler sonography is used (Fig. 5.7d). If the flow is slightly directed towards the transducer, the artery is displayed red; in the other cases (right hepatic artery), it is displayed blue. Flow in the left branch of the hepatic artery runs towards the transducer and is always displayed red (Fig. 5.7d); flow in the right branch of the artery runs away from the transducer and is therefore displayed blue.

As mentioned previously flow in the hepatic arteries is monophasic with high diastolic amplitude, due to low peripheral resistance (Fig. 5.7e).

The splenic artery is the left limb of the coeliac artery. It runs along the posterior superior margin of the pancreatic body and tail before it turns anteriorly to the spleen (Figs. 5.2, 5.5 and 5.7). At the splenic hilus it splits into several branches.

Along its way the splenic artery gives rise to several pancreatic branches, short gastric branches and the left gastroepiploic artery. None of these vessels can be shown sonographically in infancy and childhood.

The splenic artery can be displayed by ultrasound along its complete course. The best images are transverse sections through the upper abdomen which show the artery at the superior border of the pancreas (Figs. 5.7a and 5.8a). The middle portion of the artery and vein can be shown in longitudinal sections too if the transducer is slightly angled to the left side (Fig. 5.8b). The artery always runs together with the splenic vein (Fig. 5.8b). Using 2d images both vessels cannot be distinguished for sure. Usually the artery is the cranially localised vessel. The different Doppler techniques (colour or spectral Doppler) however can easily identify arteries and veins.

The distal branches of the vein can best be shown in transverse or coronal sections through the splenic hilus from a left approach (Fig. 5.9).

Using colour-coded Doppler sonography, the flow in the artery behind the pancreas can be displayed blue as the flow is directed away from the transducer (Fig. 5.10a, b). When the artery has passed the tail of the pancreas and turns towards the splenic hilus, it is displayed red (Fig. 5.10f).

Spectral Doppler shows negative flow behind the pancreatic body and positive flow after the artery has passed the pancreatic tail (Figs. 5.10c and 5.10e, f). Due to low peripheral vascular resistance, the flow profile is monophasic with high diastolic amplitude (Fig. 5.10b, d, e, f).

The left gastric artery is the third branch of the coeliac artery. The left gastric artery is the smallest of the branches. The small artery cannot routinely be shown in infants and young children.

In older individuals and adolescents, the left gastric artery can be displayed cranially of the pancreas. It turns to the left and can be seen at the upper border margin of the stomach in the region of the gastroesophageal communication (Fig. 5.11a). Beside the artery the left gastric vein can sometimes be displayed (Fig. 5.11a). Colour Doppler displays the flow in the artery blue (Fig. 5.11b). Pulsed Doppler reveals as systolic-diastolic forward flow with low diastolic amplitude due to intermediate peripheral vascular resistance (Fig. 5.11c).

The superior mesenteric artery arises as the second branch from the anterior surface of the aorta, immediately distal to the coeliac trunk (Figs. 5.1a, 5.4, 5.5a, b and 5.12a). The SMA consists of a short, anteriorly directed segment and a longer inferiorly directed segment that ends in the region of the ileocaecal valve (Fig. 5.12a). SMA branches supply the jejunum, ileum, caecum and ascending colon, as well as the proximal two-thirds of the transverse colon and portions of the duodenum and pancreatic head.

The artery can be displayed in longitudinal and transverse sections through the upper abdomen (Figs. 5.1a, b, 5.5a and 5.12a, b). In transverse planes the artery is displayed between the splenic vein anteriorly and the aorta posteriorly. The SMA is surrounded by an echogenic halo of fat (Fig. 5.12b). The SMA is an important anatomic landmark for scanning of upper abdominal vessels. The SMA lies to the left of the superior mesenteric vein. It lies behind the body of the pancreas and the splenic vein. The left renal vein lies posterior to the SMA. It runs between the aorta and the SMA.

Colour Doppler reveals the flow in the SMA. It runs best in longitudinal sections. The artery is displayed red as the flow is directed towards the transducer (Figs. 5.1b and 5.6a).

Measurements of flow in the SMA are best performed in the proximal section of the SMA where the angle of incidence is low. The angle of incidence in the section where the artery parallels the aorta approximates 90°. Flow measurements cannot be performed in this section. The flow in the SMA depends highly on the fasting status of the patient. In contrast to the flow in the coeliac artery, a high-resistance flow pattern with a sharp systolic peak and low diastolic amplitude can be found in the fasting patient (Fig. 5.13a, b). Sixty minutes after a meal, the diastolic amplitude increases to a low-resistance flow profile with a high diastolic amplitude similar to the flow in the coeliac trunk (Table 5.4).

The renal arteries arise from the aorta, slightly below the SMA. The right renal artery arises from the anterolateral aspect of the aorta before it passes under the inferior vena cava and then enters the right renal hilus (Fig. 5.14a). The left renal artery originates from the left lateral or posterolateral aspect of the aorta before it follows a posterolateral course to the left hilus (Fig. 5.30c).