Core Topics in General & Emergency Surgery: Companion to Specialist Surgical Practice (24 page)
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Authors: Simon Paterson-Brown MBBS MPhil MS FRCS
With advances in technology and improved radiological techniques, the radiologist is playing an ever more important role in the diagnosis of patients with acute abdominal pain. Furthermore, abdominal ultrasonography and plain radiography evaluated by senior radiologists substantially enhance senior surgical assessment of patients with acute abdominal pain, resulting in reduced surgical admissions.
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The role of plain radiology in the investigation of the acute abdomen has been extensively examined. Until recently there was general consensus that the erect chest radiograph was the most appropriate investigation for the detection of free intraperitoneal gas, with use of the lateral decubitus film if either the erect chest film could not be taken (due to the patient's condition) or was equivocal. This no longer seems to be true following a report from Taiwan, where ultrasonography was shown to be superior to the erect chest radiograph, with a sensitivity of 92% in the detection of pneumoperitoneum compared with only 78% for plain radiology.
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Undoubtedly there will be operator dependence and for now the erect chest radiograph should still be the initial test for suspected perforation (
Fig. 5.1
). Failure to detect free gas under the diaphragm in a patient with suspected intestinal obstruction can then be further investigated by US, CT or contrast radiology, as discussed below. The erect chest radiograph remains important for excluding chest conditions such as acute lobar pneumonia that can present as acute upper abdominal pain (
Fig. 5.2
).
Figure 5.1
Erect chest radiograph in a patient with a perforated duodenal ulcer. Note the free intraperitoneal air under both hemidiaphragms.
Figure 5.2
Erect chest radiograph in a patient with acute right-sided pneumonia.
Plain abdominal radiography is still carried out unnecessarily in a large number of patients,
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and it could be significantly reduced if its use is limited to those patients where it might provide some diagnostic help, such as suspected intestinal obstruction, suspected perforation (
Fig. 5.3
) and exacerbation of colitis.
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Figure 5.3
Plain supine abdominal radiographs demonstrating free intraperitoneal air
(a)
in a patient with a perforated duodenal ulcer and retroperitoneal air
(b)
in a patient with perforated diverticular disease.
The use of the supine abdominal radiograph should be limited to patients with suspected intestinal obstruction, suspected perforation and exacerbation of colitis, as indicated in the guidelines produced by the Royal College of Radiologists.
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Similar controversy exists in the use of erect abdominal radiographs for the assessment of patients with suspected intestinal obstruction. Most surgeons still prefer both views (erect and supine) on the basis that in those patients in whom the supine radiograph is normal or equivocal the erect film may be helpful.
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It has been recognised for many years that gastrointestinal contrast studies can be used to evaluate acute gastrointestinal conditions.
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Its main function remains the assessment of both large- and small-bowel obstruction and possible gastrointestinal perforation. However, with the increasing availability of multi-slice CT (see below) this role is dwindling.
Although the erect chest radiograph is recognised as the most appropriate first-line investigation for a suspected perforated peptic ulcer, in approximately 50% of patients no free gas can be identified on the radiograph.
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This leaves the emergency surgeon with three options: (i) to review the diagnosis, such as reconsidering acute pancreatitis; (ii) to proceed to laparotomy based on the clinical findings alone; or (iii) particularly if there are reasonable grounds for uncertainty, to arrange for either a CT with oral contrast or a water-soluble contrast study. The latter will confirm or refute the presence of an ongoing leak (
Fig. 5.4
), but will not differentiate between the patient without a perforation and one in whom the perforation has sealed. The addition of US,
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as already discussed, and increasingly CT in this scenario may help by revealing free abdominal air and fluid in the patient whose perforation has sealed spontaneously. As has been well understood for quite some time now, many patients with perforated peptic ulcers can be managed non-operatively;
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with this knowledge, the assessing surgeon has plenty of time to resuscitate the patient and make efforts to confirm or refute the diagnosis before rushing to emergency surgery. Patients who might be considered for non-operative treatment of their perforation should have a contrast meal to confirm spontaneous sealing of the perforation. This topic is discussed in more detail in
Chapter 6
.
Figure 5.4
Supine abdominal radiograph taken 20 minutes after the oral administration of 50 mL of water-soluble contrast material in a patient with a suspected perforated peptic ulcer in whom the erect chest radiograph was normal. Note the small trickle of contrast through the perforation. These findings were confirmed at laparotomy.
Reproduced from Ellis BW, Paterson-Brown S (eds). Hamilton Bailey's emergency surgery, 13th edn. London: Hodder Arnold, 2000. With kind permission from Taylor Francis.
Surgery for small-bowel obstruction is performed for one of two reasons: first, there has been failure of non-operative management; second, there is clinical suspicion of impending strangulation. Although plain abdominal radiographs are useful in establishing the diagnosis of small-bowel obstruction, they cannot differentiate between strangulated and non-strangulated gut. The criteria on which strangulated intestine must be suspected are well established: peritonism, fever, tachycardia and leucocytosis.
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However, even when the diagnosis is suspected, the changes at operation are often irreversible and resection required. Some workers have looked at serum markers such as phosphate and lactate concentrations
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to help identify patients with possible strangulation in order to allow earlier surgery, but unfortunately they are unreliable. As in other areas of acute abdominal imaging, US also appears to be able to contribute to the diagnosis of intestinal obstruction,
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but the problem of detecting early ischaemic changes in small-bowel obstruction remains largely unsolved. There is little doubt that water-soluble contrast studies in patients with small-bowel obstruction are useful in detecting those patients who are not likely to settle with non-operative management.
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A randomised trial comparing water-soluble contrast follow-through versus conventional management in patients with suspected adhesive small-bowel obstruction demonstrated a significantly shorter time to surgery and therefore overall hospital stay in the group receiving the contrast study.
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Water-soluble contrast material also allows quicker resolution of symptoms.
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In general, failure of water-soluble contrast to reach the caecum by 4 hours strongly suggests that surgical intervention is likely to be required, and better sooner than later (
Fig. 5.5
). Water-soluble contrast follow-through is also useful in the assessment of early postoperative obstruction in order to identify those patients with an ileus from those with mechanical obstruction who need re-operation.
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Figure 5.5
Supine abdominal radiograph in a patient with adhesive small-bowel obstruction
(a)
, 90 minutes
(b)
and 4 hours
(c)
after oral administration of 50 mL of water-soluble contrast material. Note failure of contrast to reach the caecum and the obvious small-bowel obstruction. Laparotomy confirmed small-bowel obstruction due to adhesions.
(d)
A post-contrast 4-hour film in a patient with suspected small-bowel obstruction from the plain abdominal radiograph but on this occasion contrast has reached the colon by 4 hours and no surgery was required.
In patients with small-bowel obstruction early administration of a water-soluble contrast material should be considered as it allows those patients who require surgery to be identified sooner and those that will settle non-operatively to do so quicker than patients managed conventionally.
79,
80
A systematic review and meta-analysis of the diagnostic and therapeutic role of water-soluble contrast in adhesive small-bowel obstruction found that it was effective in predicting the need for surgery, as well as actually reducing the need for operation and shortened hospital stay.
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A recent clinicopathological score has been developed to predict the risk of strangulated small-bowel obstruction
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and is discussed in more detail below under CT imaging. More detailed information on the surgical management of small-bowel obstruction is provided in
Chapter 9
.
The management algorithm for large-bowel obstruction has now become well established following the more widespread recognition that colonic pseudo-obstruction could not be distinguished from mechanical obstruction on plain radiographs alone (
Fig. 5.6a,b
).
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The decision that all patients with suspected large-bowel obstruction should now undergo a contrast enema (
Fig. 5.6c,d
) before laparotomy has probably been the most important factor in reducing not only the unnecessary operation rate for pseudo-obstruction, but also the associated mortality. Patients with acute colonic pseudo-obstruction present with similar history and clinical signs to the patient with a mechanical obstruction. Although factors recognised as precipitating pseudo-obstruction, such as dehydration, electrolyte abnormalities, pelvic and spinal surgery, acid–base imbalance and so on, may alert the clinician as to the possible cause, it cannot be confirmed without further investigation. As the treatment for one is non-operative and for the other is usually operative, accurate assessment is essential.
Figure 5.6
Supine abdominal radiographs in two patients with large-bowel obstruction.
(a)
Patient A has pseudo-obstruction.
(b)
Patient B has mechanical obstruction.
(c,d)
Water-soluble contrast enema confirmed pseudo-obstruction in patient A
(c)
and an obstructing carcinoma of the sigmoid colon in patient B
(d)
.
All patients with a suspected large-bowel obstruction should undergo some form of contrast examination to exclude pseudo-obstruction.
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The surgical management of both large-bowel obstruction and the next topic, acute diverticulitis, is covered in more detail in
Chapter 10
.