Diagnosis of Appendicitis
Abdominal Film (KUB)
An x-ray of the abdomen may be augmented by another film of the abdomen taken while the patient is sitting or lying on his or her left side. It is very unlikely that the diagnosis of appendicitis will be made by x-ray, but there is one exception. One third of patients have small stones in the appendix, which are visible on x-ray. These so-called appendicoliths develop inside the appendix and when they are large enough, they can actually block the channel.
Appendicoliths generally appear in the right lower abdomen, where they may be confused with other stones, such as those in the kidneys, ureters, bladder, and ones that form inside veins (phleboliths). Still, if the radiologist can be reasonably certain that the stone represents an appendicolith, chances are that the patient has appendicitis.
There are a few other "softer" findings on plain film. The bowel may appear to be dilated just in the area of the appendix, which suggests that there is something causing trouble there, but generally these findings are pretty nonspecific.
A barium enema (BE) may be the last thing a patient with an acute appendicitis would want, but most patients can actually tolerate a BE fairly well. The point of this test is to fill the large bowel with contrast solution; the normal appendix will also fill with the barium.
If the appendix is inflamed and its channel is obstructed, the appendix will not fill and there will be a prominent impression on part of the right colon at the base of the appendix. The appendix and all the inflammation around it form a fistful of tissue that pushes right up against the tip of the colon.
One problem is that barium enemas entail some radiation. In the younger age group in which this disease is most prevalent, especially in younger women, physicians try to limit abdominal radiation. Although barium enema has generally been overtaken by newer tests, such as ultrasound and CT scan, the barium enema is almost always safe and not a bad alternative.
Wouldn't a completely noninvasive test—no enema, no dye, no radiation—be nice? Ultrasound is almost the perfect test, but not quite. The problem is that the bowel is just not a very good ultrasound subject. There is always gas in the bowel, and gas reflects sound waves. With no sound waves passing through, there is no image. To see the gallbladder and to avoid the bowel in the upper abdomen, we image through the liver, an excellent sound transmitter; in the lower abdomen and pelvis, we use the fluid-filled urinary bladder. To look at the bowel, it is best to use x-rays or CT scan.
But there is an exception as far as the appendix is concerned. Imagine the appendix as a sack of inflammatory debris (pus), the size of a thin pinky finger, that is sitting there in the lower abdomen appearing on ultrasound, like a sausage. When you push down gently with the ultrasound transducer on sections of the bowel, they compress easily. Not so with the inflamed appendix, which causes pain when it is compressed.
One of the great advantages of real time ultrasound is that the radiologist gets a moving picture of what is going on in real time. Generally, the small bowel is in a constant state of motion as materials are propelled through. A section of the tube squeezes down on itself and then relaxes and the next section does the same and so on in what is known as peristaltic motion.
If the appendix is inflamed, it will essentially turn off any peristalic activity. Finding peristaltic activity therefore would tend to diminish the likelihood of appendicitis.
So what is the problem? Sounds like a pretty good test. If you see an inflamed appendix, you could be very suspicious, especially if other symptoms associated with appendicitis are present. This means the test is very specific for appendicitis, but is not very sensitive. The patient may have acute appendicitis, but it may be missed because the appendix is not visualized. For example, if the appendix is retrocecal (behind the right side of the colon), or if the patient is too obese to scan accurately, it may not be seen and another test may be needed.
In many places CT scan has become the test used most often to make the definitive diagnosis of appendicitis. Until recently, obese patients and elderly patients with other conditions would undergo CT scans of the abdomen instead of ultrasound. As the scanners got faster and as the technology improved, CT generally replaced ultrasound, which is relegated to subsections of patients (e.g., young women of childbearing age, pregnant women, claustrophobic patients, thin patients). Others will probably get a CT scan.
If you ask ten radiologists the best way to do a CT scan looking for acute appendicitis, you will get ten different answers. The optimal procedure has yet to be worked out. Most of the controversy has to do with the use of dyes. Is it best to use intravenous contrast with the concurrent issues? Is oral contrast needed? What about introducing contrast into the rectum just before or during the CT scan?
Here is what seems to be true: intravenous contrast does improve the image of the abdomen by highlighting the kidneys, ureters, and vascular structures. It also enhances the imaging of small tumors and sharpens the image surrounding the appendix. But, intravenous contrast does pose a very small risk and it is timeconsuming. The use of oral contrast is less clear, but it does allow the radiologist to see bowel loops better. When contrast fills the tubes, it is much easier to figure out what is going on inside.
The CT KUB is a relatively new approach to imaging the acute abdomen. It involves no contrast, does involve low-dose radiation, so it is not ideal for pregnant women. The test is fast and easy especially with the newer CT scanners. But does it provide the information needed?
CT KUBs are used to screen for a variety of intra-abdominal conditions, including appendicitis, kidney stones, diverticulitis, and others. Just as with the KUB, finding an appendicolith confirms the diagnosis with CT. When they are dense enough, appendicoliths are seen on abdominal x-rays and may be seen on ultrasound, but they are easier to detect using CT KUB. CT is more sensitive in picking out the density and showing it on the image. Also, because it is cross-sectional, overlapping and confusing shadows are eliminated. Anything that looks like an appendicolith in the right lower quadrant probably is just that. Fortunately, there are other signs, such as thickening of the appendix wall, fluid collections, inflammatory infiltration of the mesenteric fat in the region, that help nail down the diagnosis. At the same time, the radiologist can look for other conditions (e.g., kidney stones, diverticulitis).
Most appendicitis patients are diagnosed on the basis of clinical findings and do not require imaging.