Diagnostic Imaging Europe
October, 1999

Ultrasound:
Don’t neglect ultrasound in gastrointestinal cases

Robert Peck, FRCR

Ultrasound is an essential element of esophageal and rectal imaging. In the staging of esophageal cancer, endoscopic ultrasound is ranked by many as equivalent or superior to CT scanning, and it should be situated in the endoscopy suite directly next to (if not within) the endoscope.^1,2 Ultrasound can be used when stricture prevents endoscopic passage and evaluation,³ and is used to assess conditions such as Barrett’s esophagus and esophageal varices.

The value of ultrasound in assessing nodal involvement and tumor extension into the esophageal wall is proven, and its potential in real-time image-guided biopsy and cytology is now being realized.⁴In addition, ultrasound has played an important role in evaluating sphincter abnormality, especially post-childbirth. It has had limited use with an endoluminal or transperineal approach to anal abscesses and fistulas.⁵

The area of transabdominal gastrointestinal (GI) ultrasound, however, appears to merit a much wider role and use than it has at present. Twelve years after Puylaert first described the use of simple gray-scale ultrasound with graded compression in appendicitis, GI ultrasound still seems novel.⁶The technique of ultrasound scanning may not have undergone a revolution in the same way that CT has with the advent of rapid spiral scanning, but probe technology has improved and there have been significant advances in resolution that allow detailed assessment and analysis of bowel disease. Color and power Doppler have also contributed to the development of standard transabdominal bowel sonography.

Why there has been a reluctance to look with intent at 50% of the abdominal cavity between the diaphragm and the pubis symphysis must be questioned. The acceptance of ultrasound as a major part of GI imaging and assessment is for the most part confined to specialist GI units, although there is hardly any bowel problem that has not been described using ultrasound. The technique is increasingly requested for assessment of acute and chronic abdominal pathology. Yet GI ultrasound is not part of the syllabus in many imaging teaching centers. An ability to recognize and interpret abnormal bowel ultrasound is essential. With the continuing need to minimize diagnostic radiation, ultrasound must play an important intermediate role between plain film and contrast/CT imaging.

DIAGNOSTIC ROLE

A 35-year-old woman presented with possible acute cholecystitis. This diagnosis was excluded by ultrasound. But an awareness of GI pathology prompted a look at the adjacent bowel, which clearly revealed a nearby peptic ulcer (Figure 1), confirmed at laparotomy. There is no reason an ultrasonologist should not be able to make this diagnosis as simply as the diagnosis of gallstones and thick-walled gallbladder if the patient indeed had cholecystitis.

An elderly infirm patient presented with iron-deficiency anemia. If the patient is too frail for anything other than palliative surgery to control anemia and prevent obstruction, ultrasound clearly has a role in establishing the diagnosis of carcinoma. The alternative would be to subject the patient to bowel preparation (often incomplete in the elderly) and the difficulty of the subsequent barium enema. Figure 2 shows a mass consistent with a carcinoma in this patient’s colon.

A young patient with known but recently quiescent Crohn’s disease returned with a recurrence of abdominal pain. Ultrasound of the abdomen showed bowel wall thickening, but in addition there was involvement of the anterior abdominal wall (Figure 3). This can indicate pericolic extension of the disease, which has significant implications if conservative therapy is unsuccessful and surgical intervention is required.

A 50-year-old female patient with a history of pain and bloating was referred for lower abdominal/pelvic ultrasound by her general practitioner, who suspected gynecological pathology. The ovaries and uterus were normal but routine examination of the sigmoid colon showed sigmoid diverticulosis with bowel wall thickening and muscle hypertrophy (Figure 4).

Ultrasound has been shown to be of value in a multitude of diverse intestinal conditions, such as appendicitis, intussusception, ascariasis, and necrotizing enterocolitis. Ultrasound of the bowel should thus be part of the routine examination of the abdomen.⁷

TECHNIQUE

It is simple to identify the site of the disorder, whether stomach, small bowel, appendix, or large bowel, because wall thickening or edema causes focal or diffuse abnormalities to stand out. Like all forms of imaging, ultrasound may indicate the pathological process, but cannot be tissue-specific. Some diagnoses, such as the ulcer case described above, are clear as to their nature, but differentiating between the bowel wall thickening of diverticular disease and colon carcinoma can be as unrewarding with ultrasound as it is with barium studies, CT, and even surgery. In these cases, clinical or pathological information is crucial.

Some researchers have suggested filling the bowel with fluid and then carrying out “colonic hydrosonography” with careful examination of the whole bowel by ultrasound.⁸This technique has not caught on in ultrasound, but it presaged the development of virtual 3-D colonoscopy.

There can be “blind” areas, such as the rectosigmoid region and the hepatic and splenic flexures, in anatomic evaluation by ultrasound, but even these areas can be assessed with careful technique. Overlapping loops of small bowel, particularly when there is partial or complete small bowel obstruction, can hinder the identification and evaluation of the source of the obstruction, but again, careful evaluation often permits a diagnosis to be made. A retrocecal appendicitis, for example, can usually be identified when specifically sought by a posterolateral approach to the cecum.

Chronic or low-grade problems can be approached with ease, but an inexperienced operator might occasionally hesitate when examining a painful acute abdomen because of patient discomfort. This is especially the case with junior or relatively inexperienced staff who tend to “poke” the abdomen. The more experienced sonographer is often able to press or gently apply compression that allows better visualization of the disease process. An ultrasonologist or sonographer will know, for example, when a certain part of the pancreas that the trainee thought invisible can actually be viewed; this is particularly true in the acute abdomen.

There are no particular situations in which abdominal sonography is unable to provide adequate results. No technique is 100% sensitive or specific, but there is no individual area of bowel imaging that is recurrently or persistently difficult in terms of actual pathology. In my experience, however, the one pathological process or appearance that is often confused is perforation. The free gas in the abdominal cavity is misinterpreted as bowel gas, but closer inspection may reveal that there is no bowel enclosing the gas and that it lies truly against the peritoneum. Further examination and probe manipulation will reveal that the gas is lying on top of a fluid layer and will confirm a perforation (Figure 5).

All processes are operator-dependent, whether it is a mechanic fixing a car or a surgeon removing a gallbladder. In imaging there are good CT radiologists and good interpreters of plain chest x-rays, just as there are those who are less good. The interpretation of an MRI of the knee is “observer-dependent,” but the images are usually provided in standard format for all to see. Obtaining them is one step removed from the interpretation.

I would contend that producing an ultrasound image, however, requires a type of skill that not all can achieve. The skill required involves an integration of manual and visual processes. Producing an image on the ultrasound monitor that is clear and demonstrates the relevant pathology can be likened to painting: the probe can be compared to the brush, the patient to the palette, and the monitor to the canvas. Some people simply do not have the aptitude to perform ultrasound, and others will not be able to extend the technique to scanning the bowel. Most people who do scanning are able to do so, but like all techniques, it must be practiced and refreshed constantly.

FUTURE DEVELOPMENTS

Inflammatory bowel disease is an area in which clinicians require information that we are currently unable to deliver. There are, however, a number of reports of Doppler ultrasound of mesenteric vessels related to disease activity.⁹Biopsy of bowel pathology has always been avoided but has been shown to be feasible and safe under ultrasound guidance.¹⁰

Ultrasound has frequently underdiagnosed malignancy that has spread from bowel tumors into the omentum and peritoneum, and although CT and MRI can be more informative, pathology may be revealed only at laparotomy or, as is now becoming more routine, laparoscopy. Higher resolution scanning with particular attention to the omentum and peritoneum and the advent of tissue harmonic imaging may afford new information.

The extra yield from these additional refinements is likely to be substantial, but many clinical questions can be answered with the technology and techniques now available.

GI ultrasound is currently not part of the working practice at most general ultrasound departments. The biggest development will occur when this changes and we begin to report on small bowel or colon as normally as we do the gallbladder, kidneys, and ovaries.

DR. PECK is a consultant radiologist at the Royal Hallamshire Hospital in Sheffield, U.K.

References

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