The Abdominal Plain Film- Ileus

Introduction

The abdominal plain film is often the first port of call in imaging of the acute abdomen. It can be somewhat of a gatekeeper in deciding who proceeds to CT or Ultrasound or for other procedures. A definitive diagnosis of ileus can be particularly difficult. This page examines aspects of diagnosis of ileus on plain films.

Definition of Terms

Ileus

The term ileus appears to have undergone a subtle change in meaning/usage. The term Ileus originally was used to denote stasis of bowel contents. The term had two common uses Adynamic Ileus ( syn paralytic ileus, non-obstructive ileus) This referred to non-functioning bowel for reasons other than obstruction Obstructive Ileus This referred to stasis of bowel contents for reasons related to obstruction It appears, for reasons of economy, the terms where abridged as follows Adynamic Ileus ----------> was shortened to ----------> Ileus Obstructive Ileus----------> was shortened to ----------> obstruction Thus, with its current meanings, you will hear a clinician ask a radiologist whether he/she thinks a patient has ileus or obstruction. To make matters even more complicated, some countries still use the original meanings of these two terms. Some radiologists avoid the issue by describing an appearance as demonstrating a "motility disorder".

Motility Disorder

This term refers to abnormal motility of bowel contents without specifying whether it is obstructive or non-obstructive in nature.

Can a SBO be Differentiated from an Ileus on Plain Film?

The hallmark of small bowel obstruction is the presence of gaseous loops of small bowel which are distended over 30mm. The absorptive capacity of the small bowel is so great that even extreme amounts of air swallowing will not distend normal small bowel.

The presence of dilated loops of small bowel is not a guarantee that the patient is obstructed. Correlation with patient history and clinical signs can assist in arriving at a more specific diagnosis. The difficulty in differentiating obstruction from ileus has led some radiologists to use the blanket term "motility disorder" when describing dilated loops of bowel.

There is a very good discussion on obstruction vs ileus in paediatrics here <a class="external" href="http://www.hawaii.edu/medicine/pediatrics/pemxray/v3c18.html" rel="nofollow" target="_blank">http://www.hawaii.edu/medicine/pediatrics/pemxray/v3c18.html</a>
Note the logical process of arriving at a probable diagnosis.

Generalised Adynamic Ileus

	The bowel could reasonably be said to be a very sensitive organ. It has a propensity to stop functioning with little provocation. Amongst the possible causes are infection (anywhere), abdominal inflammation, chemical/pharmacological causes, post-operation peritonitis, electolyte imbalance, and trauma. Abdominal surgery commonly results in generalised adynamic ileus in which the bowel is temporarily non-functioning. This typically manifests on around day 4 post-op. In response, the patients are often referred for abdominal plain film imaging to rule out obstruction. The appearance of generalised adynamic ileus on plain film is quite characteristic (see left). The large and small bowel are extensively airfilled but not dilated. I have heard this described as the large and small bowel "looking the same".

Reflex Ileus

Reflex ileus refers to a secondary ileus in response to some type of insult. The causes of reflex ileus are numerous including abdominal inflammations and infections, chemical and pharmacological causes, trauma and abscess.

Clinical Context Patient has renal colic Other Imaging The patient proceeded to have a CT abdomen where a 5.4cm left renal stone was found with left upper renal tract obstruction with moderate left hydronephrosis. Comment In the absence of any other patient information, this image suggests nothing specific. Knowing that the patient has renal colic raises the possibility that the patient has a reflex ileus which is causing the prominent central small bowel loops. The renal stone and hydronephrosis found on CT support this finding. Normal air-filled bowel tends to have a random, faceted, tessellated appearance rather than an organised non-random appearance Check here for more information on the normal appearances of small bowel

Localised Ileus (Sentinel Sign)

	This patient has a segment of inflamed transverse colon (white arrow). The cause of the inflammation is unknown but would be typical of ulcerative colitis or Crohn's disease. This appearance is known as "thumbprinting". Just inferior to the diseased segment of colon are a few prominent air-filled loops of jejunum. It is possible that this is localised ileus of the jejunum associated with the diseased colon. This is known as "sentinel sign".

Summary

Ileus can be a difficult diagnosis on abdominal plain film, particularly if the clinical context is not known. Distinguishing between ileus and obstruction is not always possible on plain film. Knowldge of the appearances of ileus will engender greater meaning to the abdominal plain film examination for the radiographer and improve the likelihood of him/her performing appropriate supplementary views when required.

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