Ultrasound signs of gastrointestinal pathology

Fluid in the abdominal cavity (ascites)

The patient should lie on his back, the entire abdomen is examined, then each side is examined in a tilted position or in a position on the right or left side. In the presence of pronounced flatulence, the patient is in the knee-elbow position. When searching for fluid, scan the lowest parts of the abdomen in all projections. The fluid is visualized as an anechoic zone.

Small amounts of fluid will collect in two places in the abdomen:

1. In women, in the retro-uterine space (in the space of Douglas).
2. In men, in the hepatorenal recess (in Morrison's pouch).

Ultrasound is an accurate method for detecting free fluid in the abdominal cavity.

If there is more fluid, the lateral pockets (the recesses between the parietal peritoneum and the colon) will be filled with fluid. As the amount of fluid increases, it will fill the entire abdominal cavity. The intestinal loops will float in the fluid, and the gas in the intestinal lumen will collect at the anterior abdominal wall and move when the patient's body position changes. If the mesentery thickens as a result of tumor infiltration or inflammation, the intestine will be less mobile, and fluid will be detected between the abdominal wall and the intestinal loops.

Ultrasound cannot differentiate between ascites, blood, bile, pus and urine. Fine needle aspiration is required to determine the nature of the fluid.

Adhesions in the abdominal cavity may form partitions, and the fluid may be shielded by gas inside the intestine or by free gas. It may be necessary to conduct the examination in different positions.

Large cysts may simulate ascites. Examine the entire abdomen for free fluid, especially in the lateral canals and pelvis.

Small amounts of fluid can be aspirated under ultrasound guidance, but aspiration requires some skill.

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Intestinal formations

1. Solid intestinal masses may be tumors, inflammatory masses (e.g., amoebic) or ascariasis masses. Intestinal masses are usually kidney-shaped. Ultrasound reveals thickening of the wall, unevenness, swelling and blurred contours. Inflammation or tumor infiltration may cause intestinal fixation, and fluid may be due to perforation or bleeding. Determining the organ of origin may be difficult.

When a bowel tumor is detected, it is necessary to exclude liver metastases, as well as enlarged anechoic mesenteric lymph nodes. Normal lymph nodes are rarely visualized by ultrasound examination.

2. Extra-intestinal solid masses. Multiple, often confluent, and hypoechoic masses are suggestive of lymphoma or lymph node enlargement. In children in the tropics, Burkitt lymphoma may be suspected, and the kidneys and ovaries should be examined for similar tumors. However, ultrasonographic differentiation of lymphoma from tuberculous lymphadenitis can be very difficult.

Retroperitoneal sarcoma is uncommon and may be a large, solid structure of varying echogenicity. Necrosis may occur in the center of the tumor. In this case, it is determined as a hypoechoic or mixed echogenic zone due to liquefaction.

3. Complex structures of formation

• Abscess: can be located anywhere in the abdomen or pelvis. It often causes pain, is accompanied by fever, and has unclear contours. In addition to appendicular abscess, the following may be detected:
  • colonic diverticula with perforation: the abscess is usually localized in the left lower abdomen;
  • amoebiasis with perforation: the abscess is usually located in the right lower abdomen, less often in the left half or somewhere else;
  • tumor perforation: an abscess can be detected anywhere;
  • tuberculosis or any other granulomatous inflammation: the abscess is usually found in the right half of the abdomen, but can be located anywhere else;
  • regional ileitis (Crohn's disease), ulcerative colitis, typhoid or other intestinal infection: abscesses can be found anywhere;
  • perforation by parasites such as Strongyloides, Ascaris or Oesophagostomum: the abscess is usually found in the right side of the abdomen, but can be found anywhere. (Ascaris can appear in cross-section as long tubular structures)

It is not difficult to detect an abscess, but it is rarely possible to determine the cause of the abscess.

4. • The hematoma appears as a cystic or mixed echogenicity structure similar to an abscess, but it does not cause fever. A history of trauma or anticoagulant therapy is important. There may be a suspension or liquefaction zone in the center of the hematoma, and septa may be visible in it. Also look for free fluid in the abdominal cavity.
5. Fluid containing formations. Most of them are benign, they are either congenital, parasitic or have an inflammatory genesis).

4. • Duplication of the intestine. This congenital anomaly is often identified as fluid-containing structures of varying shapes with a clearly defined wall. They may be small or large and may have an internal echotexture due to the presence of suspension or partitions.
   • Lymphatic or mesenteric cysts. Although they are usually anechoic, septations may be seen, and internal echotexture may or may not be detectable. They may be located anywhere in the abdomen and vary in size up to 20 cm or more in diameter.
5. Intestinal ischemia. Ultrasound can reveal a solid thickening of the intestinal wall, sometimes localized, but more often extended. In this case, mobile gas bubbles can be detected in the portal vein.
6. Echinococcal cysts (parasitic disease). Cysts in the abdominal cavity have no special characteristics and resemble other visceral parasitic cysts, especially liver cysts. They are almost always multiple and are combined with cysts in other organs. (Conduct an ultrasound of the liver and chest X-ray.) If a cluster of multiple small cysts is detected, one may suspect alveococcosis (Echinococcus multHoculoris), which is not so common.

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Suspected appendicitis

Ultrasound diagnosis of acute appendicitis can be difficult and even impossible. It requires some experience.

If acute appendicitis is suspected, examine the patient in the supine position using a 5 MHz transducer. Place a pillow under the knees to relax the abdomen, apply gel randomly to the lower right abdomen and begin scanning longitudinally with light pressure on the transducer. Use more noticeable pressure to move the intestine. If the intestinal loops are inflamed, they will be fixed and no peristalsis will be detected: pain will help to determine the site of the lesion.

The inflamed appendix is visualized in cross-section as a fixed structure with concentric layers ("target"). The internal lumen may be hypoechoic, surrounded by a zone of hyperechoic edema: a hypoechoic intestinal wall is visualized around the edema zone. In longitudinal sections, the same structure has a tubular shape. When the appendix is perforated, an anechoic or mixed echogenicity zone with unclear contours may be determined near it, extending into the pelvis or somewhere else.

It is not always easy to visualize the appendix, especially if it is in the abscess stage. Other causes of abscess in the right lower abdomen include intestinal perforation due to amebiasis, tumors, or parasites. Careful comparison of the echographic picture with the clinical picture is necessary, but even in this case it is not always possible to make a diagnosis using ultrasound examination.

Symptoms of gastrointestinal diseases in children

Ultrasound examination is very effective in the following pediatric diseases.

Hypertrophic pyloric stenosis

The diagnosis can be made clinically in most cases by palpation of the olive-shaped thickening of the pylorus. It can also be easily detected and accurately diagnosed by ultrasound examination. As a result of the thickening of the muscular layer of the pylorus, which normally does not exceed 4 mm in thickness, a hypoechoic zone will be detected. The transverse internal diameter of the pyloric canal should not exceed 2 mm. Gastrostasis will be detected even before filling the child's stomach with warm sweet water, which must be given to the child before further examination.

On longitudinal sections, the length of the child's pyloric canal should not exceed 2 cm. Any excess of this size causes a strong suspicion of the presence of hypertrophic pyloric stenosis.

Intussusception

If the clinician suspects intussusception, ultrasound may in some cases reveal a sausage-shaped intussusception: in cross-sections, the presence of concentric rings of intestine is also very characteristic of intussusception. A hypoechoic peripheral rim of 8 mm or more in thickness with a total diameter of more than 3 cm will be determined.

In children, ultrasound diagnosis of pyloric hypertrophy and intussusception requires some experience and careful clinical correlations.

Ascariasis

The appearance of a formation in any part of the intestine may occur as a result of ascariasis: in this case, transverse scanning visualizes typical concentric rings of the intestinal wall and the bodies of helminths contained in the lumen. Ascarids can be mobile, their movements can be observed during real-time scanning. Perforation into the abdominal cavity may occur.

Human immunodeficiency virus infection

HIV-infected patients often have fever, but the source of infection cannot always be determined clinically. Ultrasound can be useful for detecting abdominal abscesses or enlarged lymph nodes. In intestinal obstruction, overstretched loops of the small intestine with pathologically altered mucosa can be detected already at an early stage by ultrasound.

Ultrasound examination should include the following standard set of organ examination techniques:

1. Livers.
2. Spleen.
3. Both subdiaphragmatic spaces.
4. Kidneys.
5. Small pelvis.
6. Any subcutaneous mass with bulging or pain.
7. Paraaortic and pelvic lymph nodes.

When an HIV-infected patient begins to have a fever, an ultrasound examination of the abdominal and pelvic organs is necessary.

Ultrasound will not help differentiate between a bacterial and fungal infection. If gas is present in the abscess, it is most likely a predominantly bacterial infection, although a combination of bacterial and fungal infections may also occur.