Gastro-intestinal Ultrasound: Much has long been known and proven!Gastrointestinale Sonografie: Vieles ist seit langer Zeit bekannt und bewährt!
14 June 2017 (online)
Contrary to numerous assumptions, sonographic examination of the gastrointestinal tract has been performed since the beginning of the 1970 s, making this one of the early clinical indications of diagnostic ultrasound imaging.
Radiologists and endoscopists at that time seemed to have found their “ideal” examination methods. Endoscopy with viewing and targeted biopsy of the mucosa of the upper GI tract and colon along with the terminal ileum was state of the art, and radiologists dominated the small intestine with the Sellink technique. While competetive endoscopists were fixated on the mucosa, the radiologists insisted on the use of double contrast to visualize the stomach, duodenum, small bowel, and colon.
Diagnostic ultrasound was ridiculed by the proponents of endoscopy and radiology and even many sonographers did not see much of a chance of success due to the limited resolution of 2 – 2.5 MHz at that time and the overestimation of the air and gas content of the GI tract as an obstacle to examination.
A further enduring argument against ultrasound of the GI tract is the subjectivity of the method. The use of the terms objective and subjective serves to perpetuate preconceived notion here. The evaluation criteria are objective; the method can be taught and learned. Moreover, almost all medical examination results depend on the limits of the method and the expertise of the operator.
The most important and unique features of ultrasound in the GI tract, such as noninvasiveness, the lack of contraindications, the availability and repeatability of the examination at any time without preparation, and the ability to evaluate peristalsis without the effect of contrast agent or air insufflation, were not taken into account. Furthermore, ultrasound visualizes the area surrounding the GI tract and can also be used when radiological or endoscopic examinations cannot be used or are inconclusive.
Ultrasound was used with astonishing success as early as the start of the 1970 s at some ultrasound centers. News of the method spread primarily "verbally" in ultrasound courses, at conferences, and in barely noticed papers in conference publications.
The first publication on ultrasound of the GI-tract is in PubMed 1972 and interestingly relates to the determination of stomach volume , which was often an important component of functional examination of the GI tract in the workgroup of the main authors of the available guidelines  .
The early publications including individual case reports all addressed clinically important aspects. Diagnosis of the GI tract with B-mode ultrasound was based on the “cockade phenomen” (which was later on called “target sign“ in the angloamerican literature) introduced by Lutz and Rettenmaier , which corresponded to a cross section of a bowel wall thickening and was first described in the case of stomach cancer. This sign was able to be used to different extents for all inflammatory and tumorous diseases associated with intestinal wall thickening and resulted in a series of systematic studies starting in 1976       . Two studies regarding diagnosis of the GI tract also appeared in the first issue of the UiM/EJU  . The breakthrough in Germany brought the first prospective studies with large case numbers in chronic inflammatory intestinal diseases  . One of the first diagnoses based on the pathognomonic image of the concentric ring sign was intussusception  , which was subsequently able to be treated with a water enema under ultrasound guidance  . Even a special procedure for the study of the stomach was established .
Starting in 1980, the use of 5 – 15 MHz transducers revolutionized B-mode ultrasound. Additional important information was provided by publications about the detection of small quantities of free air in gastrointestinal perforations, fistulas in Crohn's disease, obstructions, and small bowel volvulus in pediatrics           .
The final missing milestones were reached with the diagnosis of appendicitis in 1986   and colon diverticulitis in 1992     . The very successful use of ultrasound for these diseases was substantiated in numerous subsequent studies. The use of ultrasound for the diagnosis of diverticulitis was introduced last and was only accepted with difficulty . However, it has become the method of choice in the new German diverticulitis guidelines .
In addition, the integration of the Doppler and color Doppler technique  into B-mode ultrasound improved differential diagnosis, for example in the differentiation between inflammatory and fibrotic stenoses or in the detection of (bleeding) vessels, which can now be performed more reliably with CEUS.
While radiologists soon switched to CT and MRI for diagnosis, endoscopists discovered endoscopic US as a new tool. It was originally intended for "seeing" through the gastric or intestinal wall, for example to the pancreas. However, it was soon realized that it could be used to differentiate gastric and intestinal wall layers to determine the depth of infiltration of a lesion. Already in 1976 a prototype of an ultrasonic endoscope was introduced  and 10 years later the stomach wall layers on ultrasound were defined with a decisive effect on clinical application .
While endosonography developed into an established part of diagnostic imaging of the gastrointestinal tract, many sonographers and gastroenterologists are still uncomfortable with B-mode imaging of the GI tract.
Many ultrasound users are unaware of the largely scientific abdominal ultrasound studies on gastrointestinal peristalsis. Abnormal GI motility can have different causes and result in symptoms that are difficult to classify. Real-time ultrasound can visualize GI contractions and the transport of gastrointestinal contents in a 2 and 3-dimensional manner. Moreover, with the Doppler and color Doppler technique functional disorders of the GI tract can be examined and the distribution and emptying of stomach contents can be visualized      . Therefore, (patho)physiological mechanisms in patients with functional dyspepsia, gastroparesis in diabetes, sclerodermia, celiac disease, Crohn's disease, etc. can be examined after the intake of various soups. Ultrasound is also useful for evaluating peristalsis of the small intestine and examining emptying and reflux, e. g. at the ileocecal valve and at the distal esophagus.
Although the current EFSUMB guidelines include knowledge that was primarily acquired between 1980 and 1990 and found its way into textbooks and a series of guidelines, they are still significant since the potential and clinical use of gastrointestinal ultrasound is far from exhausted and the deficits in training and knowledge present major opportunities for reducing the use of X-rays. The “newly discovered” emergency ultrasound or point of care ultrasound (POCUS) can easily exacerbate this issue of insufficient training particularly in the GI tract. By using the already available knowledge, we can avoid having to reinvent the wheel and can prevent any wrong turns.
Elastography, CEUS and DE-CEUS can actually be considered new and are largely a “work in progress”. It remains to be seen what additional benefits these techniques will bring. However, the most important task is still to establish a comprehensive training program.