A patient with abdominal trauma does not require a plain abdominal radiograph (AXR). The AXR will not contribute to the clinical diagnosis and should be avoided.

The AXR is of limited value as a diagnostic tool in the evaluation of many patients presenting with an acute abdomen. This is largely because the abdominal contents are composed of soft tissue. Plain film radiography does not provide adequate soft tissue contrast discrimination to detect and differentiate between many of the numerous inflammatory and neoplastic intra-abdominal soft tissue pathologies. The AXR is not the right tool for the job. Consequently, it has been superseded by ultrasound and CT scanning which are highly accurate in terms of evaluating the various intra-abdominal soft tissues.

In present day clinical practice, the AXR is in the main limited to confirming a clinical suspicion of large or small bowel obstruction (as illustrated below), and demonstrating dangerous swallowed foreign bodies. Even so, CT will be selected as the first line imaging test in many cases of suspected intestinal obstruction, and also as the preferred and only imaging examination when renal colic is suspected.

What if the preferrred imaging investigations are not immediately available? Is there any point in requesting an AXR as a substitute imaging test? On the whole, no. You risk obtaining false reassurance from a seemingly normal AXR appearance. It is safer to rely on a detailed clinical history and a careful physical examination. Furthermore, an experienced pair of examining hands from a member of the surgical team will recognise the emergency case that needs to go to theatre.

The table on the right indicates the relatively few occasions when an AXR can be useful.

Distended small bowel. No large bowel gas. Diagnosis: small bowel obstruction.

Gross distention of the large bowel extending as low as the sigmoid colon. Diagnosis: large bowel obstruction.

Radiology and abdominal pain

Clinical problem	The best tests	Is an AXR useful?
Small bowel obstruction	▪ CT—will often show the point of obstruction/cause

Yes. It will confirm the clinical impression in most cases. Large bowel obstruction

▪ CT—will often show the point of obstruction/cause

Yes, to confirm the clinical impression. Perforation

▪ Erect CXR

▪ CT

No Appendicitis

▪ Clinical examination

▪ Ultrasound

▪ CT

No Biliary Colic

▪ Utrasound

No Cholecystitis

▪ Ultrasound

No. Will show calcified gallstones occasionally, but will not show wall thickening/inflammation. Diverticulitis

▪ CT

No Pancreatitis

▪ CT

No Haematemesis

▪ Endoscopy

No Acute lower gastrointestinal bleeding

▪ CT angiogram

No Bowel ischaemia

▪ CT

No Aortic aneurysm

▪ Clinical examination

▪ Ultrasound

▪ CT

No Acute colitis

▪ Sigmoidoscopy

Yes. Will exclude toxic megacolon. Constipation

▪ Clinical history & examination; rectal examination

No Renal colic

▪ CT KUB

No. On its own it is imprecise and non-specific.

Analysis: plain film checklists

Erect CXR

In the context of a patient attending the Emergency Department with abdominal pain there are just two questions to ask of the CXR:

1. Does the erect CXR show any evidence of free air under the diaphragm?

2. Is there any evidence of pneumonia?

This erect CXR shows: normal lung bases and no free air under the diaphragm. The normal appearance of each lung is described on pp. 308–313.

Abdominal pain. No specific diagnostic features from the history and clinical examination. The erect CXR reveals an extensive pneumonia in the right lower lobe.

Supine AXR

When analysing an AXR some normal features can be listed:

▪ Gas within the stomach may be seen as gas outlining the gastric folds in the left upper quadrant; there is rarely any gas seen in the small bowel.

▪ Normal gas patterns in the colon and rectum will vary. Sometimes segments of gas will be seen but no long continuous segments that are distended.

▪ No calcification overlying the liver or gall bladder, nor over the pancreas, kidney, ureters or urinary bladder.

▪ Calcification in the aorta may be age related and is common in the elderly; it will not show any localised bulge.

Supine AXR.

Normal features on this AXR: gastric folds/rugae outlined; faeces in the ascending colon; no bowel distension; no pathological calcification.

Supine AXR.

Elderly patient. Predominantly normal features on this AXR. Gas in an undistended large bowel (ascending, transverse, and descending colon); some age related calcification in the aorta. (The liver shadow might be prominent, but possible hepatomegaly is better assessed on palpation during the clinical examination.)

The common problems¹^–¹⁰

Both the likelihood of a particular diagnosis and the level of clinical concern will determine the specific radiological investigation that is selected. In some instances no imaging will be requested. The local availability of equipment or particular skills may also influence the choice of the first line test.

The following descriptions refer solely to plain film radiography; ie when a supine AXR or a CXR is obtained in the Emergency Department.

Non-specific abdominal pain

An erect CXR is primarily obtained in order to exclude a basal pneumonia or free air under the diaphragm. A supine AXR is not a useful test, because:

▪ A normal AXR does not exclude serious pathology.

▪ A good clinical history and physical examination are more useful than an AXR.

Following clinical examination the most useful imaging tests are CT or ultrasound. In the absence of these facilities, an AXR is unlikely to be better than the clinical examination performed by an experienced member of the surgical team.

Erect CXR. Extensive pneumonia in the left lower lobe.

Erect CXR. Free air below both domes of the diaphragm (arrows). The lung bases are clear.

Pneumonia diagnosis

Pneumonia is a well recognised cause of acute abdominal pain, particularly in children. It might be unwise to place too great a reliance on the clinical examination of the chest alone as a means of excluding a pneumonia. A prospective survey¹ concluded:

“the traditional chest physical examination is not sufficiently accurate on its own to confirm or exclude the diagnosis of pneumonia”.

Suspected perforation

The most useful radiograph is a well-penetrated erect CXR. An erect AXR is not indicated as the CXR is much more reliable in detecting free air. Very small quantities (as little as 1.0 ml) of free air can be demonstrated on an erect CXR².

If a patient is unable to sit up for an erect CXR then an alternative technique is employed: the patient reclines in the left-side-down decubitus position and a cross table AXR is obtained using a horizontal X-ray beam.

Other options:

▪ In some centres in North America, CT is requested as the first line investigation. CT is the most sensitive imaging test for diagnosing pneumoperitoneum. It is highly accurate, and it will often indicate the precise site of the perforation.

▪ In a few centres sonography is utilized for the detection of free intraperitoneal air ³. Practitioners tend to follow a step by step protocol. As follows: plain radiography first; then ultrasound only in those in whom the plain radiograph (usually an erect CXR) is normal. CT is thus reserved for those occasions when ultrasonograhy still fails to make the diagnosis⁶.

Suspected perforation. Patient too unwell to sit up. A lateral decubitus AXR with the patient lying on the left side. A large amount of free intraperitoneal air is shown (between the arrowheads) above the lateral surface of the liver. The air outlines the undersurface of the right dome of the diaphragm (arrows).

Suspected intestinal obstruction

The options:

1. CT.
CT is highly accurate in demonstrating or excluding obstruction ⁴^,⁵. In addition, the precise site and probable cause of the obstruction can usually be defined. In an individual patient, the surgical team may well prefer CT as the first line imaging test, because of the excellent detail and additional information that will be provided.

2. Supine AXR.
Some basic features will assist with diagnosis.

□ Dilated small bowel with an absence of colon gas suggests a complete, or a nearly complete mechanical obstruction to the small bowel.

□ Dilated small bowel with gas in an undistended colon suggests either an incomplete mechanical obstruction to the small bowel, or a localised adynamic (ie paralytic) ileus.

□ Dilated large bowel but no small bowel dilatation suggests mechanical obstruction to the large bowel with a competent ileo-caecal valve.

□ Dilated large bowel with dilated small bowel suggests either mechanical large bowel obstruction with an incompetent ileo-caecal valve, or a generalized adynamic (ie paralytic) ileus. The distinction is usually clinically obvious.

Pitfalls.

The supine AXR may appear normal—to the inexperienced observer—in two circumstances:

1. A very high small bowel obstruction.

2. Very occasionally the obstructed small bowel will distend with fluid and not with gas. Consequently there will not be the usual finding of multiple loops of bowel distended with gas.

Colicky abdominal pain.

Dilated loops of small bowel (arrows). Some loops measure 50 mm in diameter (the upper limit of normal is 30 mm). Almost no gas within the large bowel. Mechanical small bowel obstruction.

Colicky abdominal pain.

Transverse colon and descending colon are dilated (arrowheads). A small amount of gas in the distal sigmoid. The caecum and ascending colon are also distended and contain faecal residue (arrows). These findings indicate a high grade mechanical obstruction in the distal descending colon or in the sigmoid colon. The absence of small bowel dilatation is due to a competent ileo-caecal valve. If the obstruction persists, then the small bowel will eventually become distended with gas.

Suspected constipation

The plain AXR is rarely of help in reaching a diagnosis of constipation as being the likely cause of abdominal pain. Because:

▪ The clinical history in relation to a change in stool frequency and consistency, together with a rectal examination, is usually diagnostic.

▪ The normal quantity of formed stool in the colon varies from person to person. A subjective quantification on the basis of the AXR appearances can be erroneous.

Suspected renal colic

The options:

1. Unenhanced multidetector CT, often referred to as a CT KUB.
The CT KUB is now established as the preferred imaging test when renal colic is suspected ⁵^–⁹. It is an accurate and quick examination and there is no need for intravenous contrast medium injection.

2. Sonography.
A case has been made that in female patients presenting with flank pain and suspected renal colic, sonography should be the initial examination in order to detect the presence of hydronephrosis ⁶. This alternative approach is (a) based on consideration of the CT radiation dose to the ovaries and (b) because sonography is so good at detecting other pathologies deep in the female pelvis that may account for the patient’s symptoms.

3. AXR plus sonography.
Others have suggested that patients should have an AXR and ultrasound as a combination examination and if negative that CT should be reserved for the patient who does not subsequently improve on conservative management ¹⁰. The addition of the AXR has been found to improve the accuracy of diagnosis of renal colic,ie when compared with ultrasound as the solitary examination¹⁰.

4. Limited intravenous urography.
Carried out as a two film examination: A plain AXR will be diagnostic when there is an obvious opaque calculus in the line of the renal tract. It is less helpful if the film (image) appears normal. A calculus might be obscured by superimposed bone, or confused with a pelvic phlebolith, or might simply be insufficiently radio-opaque to be seen. Although 90% of renal calculi contain calcium, less than 50% are visible on an AXR. Consequently, a single additional AXR at 10 minutes after the intravenous injection of contrast medium will be highly accurate in confirming or excluding the presence of a ureteric calculus. Normal excretion of the contrast medium together with undilated calyces and ureter will exclude the diagnosis of renal colic; delay in excretion on the painful side and/or calyceal/ureteric dilatation will confirm the diagnosis of renal colic.

Clinical suspicion: acute left sided ureteric colic.

The patient was referred directly for a CT examination. The obstructing calculus in the lower third of the ureter is shown on this coronal reconstruction.

Clinical suspicion: acute left sided ureteric colic. Faint calcification in the true pelvis was seen on the supine AXR. This single radiograph obtained 10–20 minutes after the injection of contrast medium confirms that a calculus is causing ureteric obstruction.

Suspected acute biliary disease

Sonography is the first line imaging procedure whenever the suspicion is that of biliary colic or gall bladder disease.

Suspected abdominal aortic aneurysm/rupture

Sonography is the first line investigation.

Suspected foreign body ingestion

The important roles of the CXR, the AXR and hand held metal detector scanning are described in Chapter 21 (Swallowed Foreign Bodies).

Infrequent but important problems

Blunt trauma to the abdomen

In patients who have sustained abdominal or pelvic trauma the rapid assessment of the injury is critical. Delay increases mortality and morbidity¹¹.

▪ Plain abdominal radiography is not indicated when investigating a blunt or penetrating injury. Obtaining an AXR is strongly discouraged—it delays the useful investigations.

▪ Recommendations in relation to imaging ¹¹:

□ Haemodynamically stable patient: the need is to demonstrate or exclude an intra-abdominal injury. CT is the examination of choice.

□ Haemodynamically unstable patient: the need is to establish that the assumed bleeding is intra-abdominal. A FAST ultrasound examination is indicated. This test can be performed very quickly. If free fluid (blood) is detected then the patient can proceed to theatre for surgery.

Focussed abdominal sonography for trauma (FAST).

FAST is an abbreviated and protocol-designated form of ultrasound assessment that seeks only to demonstrate whether intraperitoneal or pericardial fluid is present or is increasing. It does not seek to define the exact site of injury. Carrying out a FAST study (after appropriate training) has been shown to be well within the capabilities of residents and registrars working in the Emergency Department¹²^–¹⁴.

Penetrating injury to the abdomen

▪ Haemodynamically stable patient: If the surgeon does not elect to proceed immediately to surgery for wound exploration then CT is the most useful imaging test. CT will demonstrate organ damage.

▪ Haemodynamically unstable patient: requires immediate surgery not imaging.

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Abdominal pain & abdominal trauma

The AXR—its usefulness