This page is presented in the context of imaging services provided to an Emergency Department. Some of the content may not apply in a different context.

The abdominal plain film examination is possibly the least understood procedure in medical imaging. The confusion regarding the role of the supine abdominal plain film is surpassed only by the erect abdominal plain film.

I strongly suspect that over a working lifetime as a radiographer I have commonly performed erect abdominal plain films on patients when it was not indicated and not performed one when it was indicated. This page considers why this happens.

The difference between the supine abdominal plain film and the erect abdominal plain film has plenty to do with gravity and not much else. Not to put too fine a point on it, the AP supine abdominal plain film and the erect AP abdominal plain film are the same projections of the same anatomy under the same gravitational forces. The difference lies in the fact that a contained air/fluid filled structure will have an interface that is imaged en face in the supine projection and in profile in the erect projection.

There are, of course, other more subtle benefits of the erect plain film as follows

• potential to include all of the upper abdomen (centre slightly more superiorly)
• in a gasless obstruction, loops of fluid filled small bowel can be seen to drop under the effect of gravity
• others I'm sure

The Thermometer Analogy The abdominal plain film has been suggested to provide information which is akin to taking a patient's temperature. A patient with a high temperature might suggest to you that the patient is unwell, but would not throw up a diagnosis in the absence of other contextual information such as patient history, clinical examination and blood results. The Poster I have placed a poster on the wall of the X-ray viewing area in the Emergency Department as shown below This is a quotation from the abdominal plain film bible by Stephen R. Baker. His book titled The Abdominal Plain Film is out of print but second hand copies are available from Amazon. In my opinion, it's well worth the money. We have a copy in our Radiology library but it is continuously out on loan.

Case1

Case2

The left image (case1) demonstrates small bowel loops (probably ileum and jejunum) to be dilated with air to 53mm. The dilated jejunal loops have a pattern known as coiled spring sign. I emphasise that you have now diagnosed that the small bowel is abnormally dilated and it contains large volumes of air. How important is it to also establish whether the small bowel also contains fluid? Will this information assist in confirming the diagnosis? The answer of course is no- whether the small bowel contains fluid as well as air is, under normal circumstances, highly irrelevant.

Consider the image on the right (case 2). You might notice that this patient appears to have gastrografin in their small bowel. This is not correct. The patient has fluid-filled small bowel and this is suggestive of a gasless small bowel obstruction... but you want to be sure. A person who has recently overeaten might have a similar appearance. I would definitely perform an erect abdominal film in the hope of demonstrating a string of pearls sign.

To summarise, both patients are likely to have a small bowel obstruction. The difference is that one patient has a firm diagnosis on the supine image and the other has a strong suggestion. Which patient would you have chosen to perform an erect abdominal film on?