Sonography Intestinal Assessment, Protocols, and Interpretation

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Continuing Education Activity

Intestinal or bowel ultrasound is a non-invasive examination method of the gastrointestinal tract. It acts as a complementary examination of the abdominal ultrasound to providers that use ultrasound as part of their practice. This activity highlights the role of the interprofessional team in incorporating intestinal ultrasound in clinical practice and reviews its technique, equipment used, and limitations.

Objectives:

  • Describe the importance of intestinal ultrasound and its use in clinical practice and the technique used in screening by ultrasound.
  • Summarize the anatomical landmarks of the intestinal ultrasound.
  • Review the different indications for using intestinal ultrasound and the pathological picture seen in different diseases.
  • Outline the importance of interprofessional team strategies for effectively using intestinal ultrasound to diagnose chronic diseases requiring a long-term follow-up and management plan.

Introduction

Intestinal or bowel ultrasound is a non-invasive examination method of the gastrointestinal tract. It acts as a complementary examination of the abdominal ultrasound, taking only a few added minutes to the formal ultrasound exam, offering a tremendous amount of clinical data that are beneficial to the patient and cost-effective to the healthcare system when used by expert gastroenterologists or radiologists.[1] Intestinal ultrasound also offers the option of being portable to those patients who cannot move to radiological scans or are contraindicated to certain devices due to weight or body prosthesis.[2]

As a hollow organ, the gastrointestinal system contains air and fluid. Fluid is considered a good acoustic medium. However, the air will impair visualization. Thus preparing the patient will improve the data yield from the ultrasound examination.

Bowel ultrasound can be used in the detection, diagnosis, and follow-up of many gastrointestinal illnesses. Ultrasound does not involve radiation, so it is the safest for pregnant women and children and for patients that require repeated radiological examination. The only setback is that it requires specialized training, requiring time allocation for further learning, including reading and hands-on practice. However, once the advanced training is provided, the benefits are significant for providers and patients.[3][4]

Anatomy and Physiology

The normal bowel anatomy as determined by the intestinal ultrasound is different from other radiological and histological visualization. Multiple diagnostic scoring systems are present to detect gastrointestinal diseases with various levels of efficiency and accuracy.[5]

  • Normal bowel wall: It consists of five layers, each differing in its echogenicity, which makes distinguishing each layer easier. The normal bowel diameter depends on the part of the intestine. Although no average is determined, it is well accepted that the small intestine diameter may not exceed 2.5 cm.
  • Echo pattern: Although the arrangement of layers does not match the histological layers exactly, this stratification is important in identifying diseases by detecting "loss of stratification."
    1. The lumen of the gut interface: hyperechoic
    2. The mucosa: hypoechoic
    3. The submucosa: hyperechoic
    4. The muscularis propria: hypoechoic
    5. The serosa: hyperechoic
  • Thickness: This is the most important feature in intestinal ultrasound assessment and the most common parameter used for detecting intestinal diseases in clinical studies. Thickness is determined by measuring all of the wall layers from the lumen interface to the serosa. Usually, between 3 to 4 mm is considered normal, except for the gastric wall, which could range up to 5-6 mm.
  • Vascularity: Determining abnormal vascularity, such as hyperemia or neovessels, is important in diagnosing different intestinal diseases such as edema or inflammation. This is usually assessed by color doppler during the ultrasound examination. Another important feature is determining the condition of large vessels supplying the gastrointestinal system, including; superior mesenteric artery, inferior mesenteric artery, celiac trunk, and their corresponding veins; superior and inferior mesenteric veins, and portal and splenic veins.
  • Motility: Is one of the most subjective measures and is operator-dependent. Peristalsis is limited in cases of inflammation of the bowel or fibrous strictures. Increased peristalsis is present in diarrhea, celiac disease, and intestinal obstruction, among other causes.
  • Compressibility: This is important to diagnose abnormal patterns, as non-compressible bowel could indicate an inflammatory or malignant change in the bowel wall.

Other important signs that could be found on the intestinal ultrasound and be an indication of the underlying disease:

  • Mesenteric Fat: mainly assessed from the epigastrium to the right iliac fossa. Increased thickness >6mm is associated with an abnormality, such as an inflammatory process like diverticulitis.
  • Small air bubbles: usually indicate perforation around the affected area.

Different scoring systems used in intestinal ultrasound:[2][6]

The use of regular ultrasound or bubble contrast (contrast-enhanced ultrasound CEUS) is a common medical practice in Europe and North America. Different scoring systems were evaluated, but no universal scoring system has been proven effective at present. Most of the scoring systems include bowel wall thickness, stratification, detection of fistula formation, ascites, mesenteric fat, lymph nodes, compressibility, peristalsis, and inflammatory signs in the bowel wall with color doppler.

A simple ultrasound score that can be used for Crohn disease monitoring was validated through clinical studies. The authors claimed that it could be used in follow-up instead of the repeated invasive endoscopy for Crohn's disease patients.[7]

The difference in wall thickness in children with Crohn disease:[8]

The normal bowel thickness in children is normally less than 2 mm, which is similar to that of adults. Intestinal ultrasound is helpful in the detection and follow-up of Crohn disease in children.

Indications

Intestinal ultrasound is a non-invasive procedure that could be a part of the normal abdominal ultrasound. Radiologists and clinicians use it as the first examination method after history and clinical examination due to its feasibility and non-invasiveness.

Intestinal Ultrasound Could Be of Great Benefit in the Following Conditions [9][10][11]

Acute Abdomen

  1. Acute appendicitis:[12] Different compression techniques are used to visualize acute appendicitis. The diagnostic signs on ultrasound are an uncompressible, enlarged blind-ended organ present in the right iliac fossa.
  2. Acute diverticulitis:[13] Ultrasound shows bowel wall thickening, diverticula, and foci of varying echogenicity, along with hyperechoic pericolic inflammatory fat.
  3. Ischemic colitis:[14] An increase in the colon wall diameter >5mm (mostly in the left colonic area), with loss of bowel wall stratification, is observed, and absent signs of wall-flow on color doppler.
  4. Intestinal obstruction:[15] Intestinal ultrasound is not the most conclusive method for diagnosing intestinal obstruction due to the gaseous distension associated with obstruction. Still, if the bowel loops are filled with a larger amount of fluid, the bowel could form an acoustic shadow to visualize the lesion and bowel abnormalities. The bowel diameter is >2cm, while the length of the obstructed segment is >10cm, with the bowel distended with either fluid or debris.
  5. Enlargement of mesenteric lymph nodes.

Chronic Diseases or Non-urgent Conditions

  1. Crohn disease:[16] Bowel wall thickening is observed mainly in the intestine, creeping fat (inflammation of the transmural fat), hyperemia as shown by power doppler, mucosa abnormalities (indicating adhered bowel, fistulas, polyps, etc.). Fistulas associated with Crohn's disease could be internal or external, symptomatic or asymptomatic. They appear in the intestinal ultrasound as fluid or air-filled duct-like structures connecting the loops of the bowel. Also, intestinal ultrasound can visualize the abscess associated with fistulas or inflammation.
  2. Ulcerative colitis:[17] Increased bowel wall thickness of the colon >4mm is visualized, with loss of wall haustrations, loss of stratification of bowel wall layers, hyperemia as shown in the power color doppler, enlarged mesenteric fat, and ascites.
  3. Infectious diseases (bacterial enteritis, tuberculous enteritis, pseudomembranous colitis, amebic or parasitic enteritis, ascariasis)
  4. Colorectal and gastric cancers.
  5. Peritoneal metastasis.

Contraindications

There are no contraindications to this non-invasive procedure.

Equipment

In the bowel-ultrasound, the sonographer uses the same equipment as the normal abdominal ultrasound but requires more experience to detect abnormalities in the intestinal wall. The bowel screening can start with the common convex low-frequency probe (3.5 to 5MHz) with normal abdominal ultrasound examination. Then details can be visualized using the linear high-frequency (4 to 13 MHz) probe, as it possesses high resolution.[18]

When possible, it is always better to use tissue harmonic imaging (THI) because its visualization is better regarding the wall, lumen, and fluid content.

Personnel

Radiologists or clinicians that use ultrasound as part of their practice, such as with gastrointestinal specialties.

Preparation

The patient should be fasting for at least 8 to 10 hours. Food could induce gaseous distension, which makes the visualization of the bowel difficult. Ingestion of a large amount of fluid could fill the bowel with water and mimic an intestinal obstruction. Thus, patients should be fasting for better intestinal visualization. Although fasting is preferable, it is not mandatory if there is an acute intestinal injury suspected.

Technique

The Sequence of Intestinal Ultrasound Examination

In chronic conditions: as ulcerative colitis, Crohn disease follow-up, coeliac disease, etc., it is preferred to start from the epigastric area or the left iliac (sigmoid) quadrants and then proceed to examine the rest of the intestine and colon, along with the terminal ileum and appendix in the right iliac quadrant.

While the sequential examination is a good reminder to the operator to examine every area, it is not mandatory and could differ between assessors as long as all required areas are examined.

In acute conditions: as acute intestinal obstruction, acute appendicitis or diverticulitis, etc., the examiner should start with the area most tender and pointed out by the patient to establish a diagnosis quickly and decrease the time of reaching the diagnosis.

Limitations

If the intestine visualization cannot be accomplished due to gaseous distension, then "graded compression" of the bowel will help to shift gaseous shadows and clarify the visualization. Another maneuver is to turn the patient on his/her side (right or left according to the bowel examined). This will shift the gasses, allowing for better visualization of the intestines.

Complications

There are no complications to this non-invasive procedure.

Clinical Significance

The Impact of Intestinal Ultrasound on the Medical Care of Inflammatory Bowel Disease[19][20][17]

Intestinal ultrasound could be used in the diagnosis of multiple gastrointestinal diseases (acute and chronic). Inflammatory bowel diseases could be diagnosed and followed up by intestinal ultrasound, as these patients need close monitoring and follow-up. Using a cost-effective, non-invasive method with no radiological hazard such as intestinal ultrasound is of great benefit to the patients.

Enhancing Healthcare Team Outcomes

Intestinal ultrasound as a part of the follow-up for patients with inflammatory bowel diseases (Crohn disease and ulcerative colitis) is very satisfactory in the hands of efficient physicians, such as gastroenterologists and radiologists, because it decreases the need for repeated CT scans or MRI of the abdomen. An interprofessional team approach where the family clinicians, specialists, nurses, mid-level practitioners, and ultrasound techs exercise open communication regarding conducting the examination and the finding that result can help the team guide patient care leading to better outcomes. [Level 5]


Article Details

Article Author

Sarah El-Nakeep

Article Editor:

Alexander Pozun

Updated:

9/2/2021 9:54:48 AM

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