Ultrasound of the portal vein system

Ultrasound anatomy

The portal vein is formed from the fusion of the superior mesenteric vein and the splenic vein. The latter departs from the gates of the spleen and goes along the posterior edge of the pancreas, accompanying the same artery. The pattern of intrahepatic branching and hepatic veins is determined by the segmental structure of the liver. The anatomical diagram shows the type of liver in front. MP angiography in the coronal plane is an alternative technique for visualization of the portal vein system.

Methodology of research

Extrahepatic segments are visualized on the expanded intercostal image. If this technique is unsuccessful due to superposition of gas in the large intestine or an unacceptable Doppler angle, the extrahepatic branches of the portal vein can be scanned from the right anterior intercostal access with the right arm raised, which makes it possible to increase the intercostal spaces. Often the main periportal trunk is visualized only in this plane due to the fact that the acoustic window due to the liver is the best. The course of the intrahepatic branches is such that they are best visualized on the subcostal scythe. After scanning in B- and color modes, Doppler spectra are recorded for quantitative estimation of periportal blood flow in the portal vein.

Normal picture

Ultrasonic dopplerography of the portal vein shows a steady flow of blood to the liver, giving a single-phase Doppler spectrum in the form of a band. Changing the position of the body and breathing mode, you can control the blood flow. The velocity of blood flow in the portal vein, for example, significantly decreases in a sitting position and on a full breath.

Ultrasonic dopplerography in the diagnosis of portal vein pathology in various diseases

Portal hypertension

The color regime for portal hypertension demonstrates a decrease in blood flow or even a significant change, such as the flow of blood from the liver through the portal vein or splenic vein and helps visualize the collaterals.

Thrombosis of the portal vein leads to an increase in resistance in the circulation system of the portal vein. It can be the result of cirrhosis, tumor invasion, increased blood coagulability or inflammation. Blood flow in the main hepatic artery is strengthened to compensate for oxygen deficiency caused by impaired perfusion in the portal vein. In the course of the thrombosed portal vein, a cavernous transformation can occur, leading to the onset of hepatopetal blood flow.

Indirect signs of portal hypertension by ultrasound dopplerography

• Reduction of blood flow velocity less than 10 cm / s
• Thrombosis
• Cavernous transformation of the portal vein

Direct signs of portal hypertension by ultrasound dopplerography

• Portocaval anastomoses
• Blood flow from the liver

Intrahepatic intrahepatic portosystemic shunt

The installation of a transient intrahepatic portosystemic shunt became the primary method of decompression of the vein system. The catheter is inserted through the internal jugular vein into the right hepatic vein and then through the liver tissue into the periportal portal portal segment. This message is kept open due to the metal stent. One of the results of this procedure is compensatory intensification of blood flow in the common hepatic artery. Recurrent stent stenosis or occlusion of the stent are frequent complications and require repeated intervention.

Ultrasonic dopplerography, especially in the energy regime, plays an important role in the control after the implementation of the intervention procedure.

Intrahepatic Tumors

Ultrasonic dopplerography helps in the differential diagnosis of vascular and solid liver formations. Adenomas, focal nodular hyperplasia and hemangiomas can be distinguished from malignant tumors by characteristic features. The absence of blood flow in the hyperechoic homogeneous formation allows one to suspect hemangioma. This diagnosis can be clarified by determining additional characteristics of blood flow when using contrast agents.

The use of contrast agents

In recent years, the use of Doppler and energy Doppler regimens has improved the differential diagnosis of intrahepatic formulations in comparison with the traditional B-regimen, but even experienced specialists still have problems.

First, some deeply located liver formations, as well as education in very complete people, can only be visualized with an unacceptable Doppler angle, which limits the accuracy of the study. Secondly, very slow blood flow, which is often observed, especially with small tumors, gives inadequate frequency shifts. Third, in some areas of the liver, it is very difficult to avoid artifacts from movement due to the transfer of heart beats to the liver parenchyma.

Ultrasound contrast media in combination with a modified scanning technique helps to solve these problems. They significantly increase the intravascular signal, improving the detection of even slow blood flow in small tumor vessels.

When bolus injection of contrast agents in the enhancement pattern, several phases are isolated. They may to some extent vary depending on the individual circulatory features of the patient.

Gain phases after intravenous administration of a contrast agent

• Early arterial: 15-25 seconds after administration
• Arterial: 20-30 seconds after administration
• Gate: 40-100 s after administration
• Late venous: 110-180 s after administration

Benign liver formation: focal nodular hyperplasia and adenoma

Benign liver formations, unlike malignant ones, do not contain pathological shunts. As a result, they remain strengthened, even in the late venous phase. This is typical for focal nodular hyperplasia and hemangioma. Focal nodal hyperplasia most often affects women who are constantly using oral contraceptives. Liver adenomas have an almost identical pattern in B-mode, and differentiation often requires a histological evaluation. With the use of color and energy Doppler modes with focal knotty hyperplasia, a typical pattern of blood flow is determined, which allows differential diagnosis.

The vascular plexus in focal ganglion hyperplasia diverges from the central artery , demonstrating centrifugal blood flow with the formation of the symptom of "spokes of the wheel." Focal nodular hyperplasia and adenoma can be characterized by similar symptoms due to an increase due to growth or bleeding. With CT, focal nodular hyperplasia and adenomas are most clearly defined in the early arterial phase of amplification. In the parenchymal phase, they are hyper- or isoechoic with respect to the surrounding liver tissue.

Hemangiomas of the liver

Unlike focal knotty hyperplasia, hemangiomas are supplied from the periphery to the center. In the arterial phase, the outer regions of education are strengthened, while the center remains hypoechoic. The central part becomes much more echogenic in the subsequent gates, and the entire formation acquires a hyperechoic character in the late venous phase. This picture of amplification from the periphery to the center, also called the "iris diaphragm" symptom, is typical of liver hemangiomas. It is also determined by CT.

Hepatocellular carcinoma

Detection of intra- and near-tumorous arterial Doppler signals, vascular breaks, vascular invasion, spiral configurations and an increase in the number of arteriovenous shuntoees are considered as criteria of malignancy in ultrasound dopplerography. Hepatocellular cancer usually has a heterogeneous picture of signal amplification in the arterial phase after the administration of the contrast agent. It remains hyperechoic in the gate phase and takes an isoechogenic character with respect to the normal liver parenchyma in the late venous phase.

Metastasis in the liver

Metastases in the liver can be hypo- or hypervascular. Although the exact location of the primary tumor along the vascular picture of hepatic metastasis can not be determined, it was found that some primary tumors are characterized by a certain degree of vascularization. Neuroendocrine tumors, such as C-cell thyroid cancer or carcinoid, tend to form hypervascular metastases, whereas metastases of primary colorectal tumors are usually hypovascular.

In the arterial phase after the administration of the contrast preparation with the standard scanning technique, metastases have a small contrast enhancement, depending on the degree of vascularization. They usually remain hypoechoic to the liver parenchyma in the late venous phase or can become isoechoic. This low echogenicity in the late venous phase after the administration of the contrast preparation is the key criterion for the differential diagnosis of metastases from the above-described benign liver formations. What follows from this? A distinctive characteristic of metastases is their tendency to form arteriovenous shunts. This may explain why contrast preparations are more rapidly excreted from hepatic metastases than from normal liver parenchyma, which is why in the late phase of contrast perfusion the picture of metastases is relatively hypoechoic.

Typical signs of hepatic metastases are an uneven amplification pattern, a spiral or corkscrew configuration of the vessels and the presence of a large number of arteriovenous shunts. Due to the latter aspect, the contrast agent enters the hepatic veins within 20 seconds instead of 40 seconds in normal. A clinical picture can help in the differential diagnosis between hepatocellular cancer and metastases: patients with hepatocellular carcinoma often suffer from cirrhosis of the liver, chronic hepatitis and / or have an elevated level of alpha-fetoprotein in the blood. This combination is much less common in patients with hepatic metastases.

Special scanning techniques

When scanning with a low mechanical index (MI ~ 0.1), often combined with phase inversion, small microbubbles are immediately destroyed during the initial passage of the bolus. This increases the contrast gain. At the same time, the use of a low mechanical index reduces the sensitivity of the study. For example, using a low mechanical index, the posterior acoustic enhancement is no longer an effective criterion for differentiating cysts from other hypoechoic formations. In some cases, the back acoustic gain reappears only when the mechanical index rises to "normal" values from 1.0 to 2.0.

Variable transmission of two ultrasonic pulses per second instead of 15 (alternating harmonic visualization) makes it possible to visualize even the smallest capillaries, since a longer intermicpulse delay leads to less destruction of microbubbles. As a result, their high concentration leads to capillary signal amplification, when the delayed impulse passes through the tissue.

When applying the variable pulse transfer technique with a low mechanical index, even hypovascular metastases become hyperechoic in the early arterial phase (within the first 5-10 seconds from the passage of the contrast medium), thus creating a visible difference between the early arterial and arterial phases of contrast enhancement.

An important rule of differential diagnostics of liver formations

The use of contrast agents allows the use of the following differential-diagnostic rule: formations with longer duration of signal amplification are likely to be benign, whereas metastases and hepatocellular carcinoma are often hypoechoic compared to the surrounding parenchyma of the liver, even in the late venous phase.

Inflammatory bowel disease

Despite the difficult conditions for scanning the gastrointestinal tract, some pathological conditions can be detected and evaluated using an ultrasound method. B-mode allows to suspect the inflammatory process by the presence of exudate and thickening of the intestinal walls. The detection of hypervascularization makes it possible to presume a chronic or acute inflammatory bowel disease. With fluoroscopic enterography (contrast study of the small intestine using the technique of Sellink) the segment of the residual lumen is determined. Acute enteritis and radiation enteritis are also characterized by nonspecific hypervascularization, which leads to an increase in the velocity of the blood flow and its volume in the superior mesenteric artery. When appendicitis is also determined nonspecific hypervascularization of the thickened and inflamed intestinal wall.

Critical Assessment

Ultrasonic dopplerography is a non-invasive technique of investigation with various possibilities for evaluating the organs and vascular systems of the abdominal cavity. The liver is easily accessible to ultrasound examination even in difficult clinical conditions. To assess focal and diffuse changes in the parenchyma and blood vessels of the liver, specific indications have been determined. Ultrasonic dopplerography became a method of choice in the diagnosis and evaluation of portal hypertension, as well as in the planning and control of the setting of a intrahepatic intrahepatic portosystemic shunt. Ultrasonic dopplerography allows non-invasive measurement of the speed and volume of blood flow, revealing complications such as stenosis and occlusion.

Ultrasonic dopplerography is used for the postoperative control of liver transplants to determine organ perfusion. However, there are no standard criteria for diagnosing liver transplant rejection.

The characteristic of focal formations of the liver is based on the degree of vascularization. Some criteria for malignancy are known, which help to more accurately diagnose the volume formation of the liver. The use of ultrasound contrast preparations improves the imaging of vascularization and assesses changes in the pattern of perfusion in different phases of contrast.

In the study of the vessels of the abdominal cavity, ultrasonic dopplerography is used for screening and evaluating aneurysms. For the planning of therapeutic and surgical treatment, additional methods, such as CT, MRI and DSA, may be required. Ultrasonic dopplerography is also a method of screening for chronic intestinal ischemia.

The ability of ultrasound dopplerography to detect increased vascularization in inflammatory diseases, such as appendicitis and cholecystitis, has increased the possibilities of ultrasonic diagnostics.

An experienced ultrasound specialist can determine specialized non-standard indications for ultrasound dopplerography using a sensor with a high spatial resolution. However, there are certain limitations of this method. For example, a full survey may take a considerable amount of time. Moreover, the dependency of ultrasound dopplerography in examining the abdominal cavity is quite high. Thanks to advances in electronic data processing, the results of the research will continue to improve, becoming more detailed and easily interpretable, for example, using panoramic SieScape technique and 3D reconstructions.

Tissue harmonic visualization is a new technique that is used in diagnostically complex cases, allowing to improve visualization in poor conditions of abdominal scanning. The use of various contrast preparations significantly improved the possibilities of ultrasound diagnostics, especially in patients with volumetric liver formations. Thus, ultrasonic dopplerography is a non-invasive diagnostic technique with a high development potential, which, when examining the abdominal cavity, must necessarily be applied much wider than at present.