Abdominal ultrasound of the digestive system

2021-07-02 09:17 AM

The normal liver has a uniform, gray-white structure, interspersed with tubular structures of the portal vein and the hepatic vein.

Technical requirements for abdominal ultrasound examination

Prepare the patient: Usually, an ultrasound exam can be done right away without any preparation. However, for good results, the disease must have fasted, or some patients need to drink water before ultrasound examination of the stomach, pancreas, pelvis, and urogenital tract.

Patient position: The patient is lying supine, comfortable. There is a pillow for the head and maybe a knee pillow at the knee.

Probe selection: Type 3.5 MHZ for adults and 5 MHZ for children or thin people, transducer (sector ) for general assessment, hepatobiliary; or a flat probe (linear) to evaluate the superficial, gastrointestinal tract.

Scanning technique: After putting a little gel on the patient's abdomen, gently put the transducer from the midline of the abdomen to the right, to the left, up and down the subframe, rotate the angle, tilt the transducer in the areas to be examined. Examine, including through the intercostal space, to view parts close to the diaphragm and to ensure a complete examination of the abdomen.

The basic image of the gastrointestinal ultrasound

Normal liver

The normal liver has a homogenous, gray-white structure, interspersed with tubular structures of the portal vein (TMC) and hepatic vein (TMG). The intrahepatic biliary tract and hepatic artery are often barely visible.

The liver is divided into two lobes: the right liver and the left liver. Each hepatopancreas is further divided into 2 segments and each segment is further divided into 2 subsegments. A total of 8 subsegments. Detail:

Left liver:

Middle segment: subsegment IV and subsegment I.

Lateral segments: subsegment II and subsegment III.

Right liver:

Anterior segment: lower segment V and lower segment VIII.

Posterior segment: lower segment VI and lower segment VII.

The portal vein branches from the pedicle, the hilum of the liver, into the middle of the lower segments, while the hepatic vein (also known as the suprahepatic) runs at the boundary between the segments, emptying into the inferior vena cava.

Figure: Correlation between the liver, stomach, and surrounding organs.

Figure: Schematic image of liver segments.

Normal bile duct

The normal intrahepatic bile duct is usually not visible, because the bile duct is normally less than 3 mm. At the hepatic peduncle on the cross-section of the 3-component hepatic peduncle, there will be a "Mickey mouse head" image: posterior portal body, anterior and left hepatic artery, anterior and right main bile duct. The common bile duct posterior to the head of the pancreas is usually more visible in the trans pancreatic view.

The gallbladder is a negative empty sac, located in the fossa on the visceral surface of the liver, between the lower segment V on the right and the lower segment IV on the left, the inferior border of the liver anterior and the hilum posteriorly. The most common shape is pear-shaped. Size varies a lot, 6 - 8cm long, 3cm wide when fully stretched.

Figure: Trans-gallbladder ultrasound cut.

Pancreas is normal

The normal pancreatic structure is uniformly hypoechoic compared with the acoustic structure of the liver.

The pancreas can be visualized in the retroperitoneal space, with its anatomical landmarks conspicuous in the cross-sections along the aorta with the superior mesenteric artery (SMA), the pancreas above the mesenteric artery. on.

Figure: Peripancreatic computed tomography.

Normal digestive tract

When there is fluid in the digestive tract, with a flat probe with good resolution, we can see that the wall of the digestive tract has a fairly clear layer structure from the inside out, including:

The lumen of the gastrointestinal tract contains fluid with a negative hollow structure (black).

The wall of the digestive tract has 5 layers with alternating gray-white sound structure:

Mucosal layer and glands: hypoechoic gray color, thickness < 1mm.

Submucosa: white hyperechoic, <1mm thick.

Muscle layer: hypoechoic layer < 2mm thick.

Subserosa layer: mild hyperechoic is very thin, often indistinguishable.

Serous layer: very thin hypoechoic layer, often surrounded by fat.

Image: Stomach wall on ultrasound.

Image: Intestinal wall on ultrasound.

Some pathological signs on gastrointestinal ultrasound images

Liver - congestive heart

The liver structure is unchanged, the liver size is large.

Dilated hepatic veins.

The inferior vena cava does not change with the respiratory cycle.

Pleural effusion can be seen above the diaphragm.

Acute Jaundice Hepatitis

There is no specific image on hepatobiliary ultrasound.

Can increase or decrease the sound.

Normal or increased size.

Cirrhosis ascites

The liver is small, with irregular margins.

Amplification structure.

The hepatic vein and the portal vein zigzag due to the pulling and pushing of fibrous nodules.

The portal vein in the lobes is normal or small, strongly echogenic, possibly with thrombosis (with the echogenic image in the portal vein lumen).

Reconstruction of the umbilical vein.

Ascites around the liver, "iceberg-shaped".

Figure: Ascites around the liver.

Liver abscess

Abscesses are usually solitary, but can also be multifocal, varying in size. It is more common in the right lobe than in the left lobe.

In the early stages, the abscess may be hyperechoic, but sometimes the homonym is invisible.

In the later stage, the hypoechoic fovea has irregular margins, posterior hyperechoic.

It is difficult to distinguish between amoebic and bacterial liver abscesses.

At the stage of complete necrosis, we can see the foci of the tumor, with a few scattered echoes inside.

After stable treatment, we can see the cystic cavity, with calcified walls, persisting for many years.

Figure: Hypoechoic necrotic foci.

Hemangioma in the liver

It is a common benign liver tumor, which can be solitary or multifocal, most often small < 4 cm, asymptomatic, detected only incidentally on ultrasound.

Microscopically, hemangiomas are often divided into two types: capillary hemangiomas and cavernous hemangiomas.

The ultrasound image is very variable, usually hyperechoic, rare hypoechoic, mixed form is common in large hemangiomas > 4 cm in diameter. The typical hyperechoic form has a well-defined border, rounded shape, and sometimes lobes; There is no transition zone between tumor and healthy tissue.

Most hemangiomas are located peripherally or with access to a hepatic vein

Liver Cancer

It is a common primary malignancy in patients with cirrhosis, with a history of viral hepatitis, more male than female.

There are 3 types: solitary nodular form, multinodular form, and diffuse infiltrative form.

The solitary nodular form in the early stage is small, round, hypoechoic. This stage is difficult to diagnose, requiring biopsy under the guidance of ultrasound. In later stages, the size increases with central necrosis, surrounding the mass with a hypoechoic border. Doppler ultrasound will detect both peripheral and central angiogenesis.

Diffuse infiltrates are difficult to diagnose, are heterogeneous hypoechoic, and angiogenesis difficult to detect.

Diagnosis is also based on indirect signs such as liver rough sound structure, irregular border, portal vein thrombosis, intrahepatic biliary dilatation.

Figure: Inhomogeneous sound reduction, no fringing.

Liver metastasis

Typical hyperechoic form, poor pulse on Doppler, no posterior echogenicity. There is a hypoechoic border around, creating a "Bull eye" shape, which is a metastasis of the gastrointestinal tract.

The vascular hyperechoic form, which is difficult to distinguish from intrahepatic hemangiomas, is metastasis of endocrine tumors.

Homogeneous hypoechoic form, metastasis of breast K.

Gallstones

The direct sign is the "clamshell" sound reinforcement border, the back has a back shadow.

The gallbladder wall may be irregularly thickened but may be normal.

An image with a slurred echo in the bile can also be seen bile mud

Some pathological signs on pancreatic ultrasound images

Acute pancreatitis

There are two types of acute pancreatitis: mild or edematous, severe, or hemorrhagic necrosis. Ultrasonography is usually limited, due to distended bowel loops.

Pancreatic enlargement, homogeneous hypoechoic in edematous form; or the pancreas is not enlarged, the acoustic structure is not uniform, the structure is empty in necrotic pancreatitis; hypoechoic with mild hyperechoic foci in hemorrhagic form.

There may be fluid accumulation around the pancreas.

Ascaris, stones can be seen in the pancreatic duct, bile duct.

Chronic pancreatitis

Pancreas normal or atrophied, hyperechoic, border unclear

The appearance of many calcified nodules dilated Wirsung duct,

Pancreatic pseudocyst

Some pathological images on ultrasound of the digestive tract

Inflammation of the appendix

The longitudinally resected appendix (RT) is a closed, single-ended tubular structure that does not collapse (normally visible only 2% in adults, 50% in children);

The cross-section is a target shape with diameter > 6mm (81%), wall thickness > 2mm.

Diffuse hyperechoic (more likely to perforate)

The appendix lumen is tight and hollow; Stones can be seen in the lumen of the appendix.

Accumulation of fluid is localized around the appendix.

The elevation is dominant in the mesentery, around the cecum.