Core Topics in General & Emergency Surgery: Companion to Specialist Surgical Practice (25 page)
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Authors: Simon Paterson-Brown MBBS MPhil MS FRCS
The majority of patients who present with symptoms and signs of acute diverticulitis can be managed non-operatively, with the exception of those patients who have overt peritonitis from perforation. Although US in experienced hands might identify a thickened segment of colon, perhaps with an associated paracolic collection of fluid, invariably there is too much gas for adequate assessment and quite significant collections can go unnoticed. For this reason clinicians have attempted to evaluate other modalities, such as water-soluble contrast radiology and CT. The former has the ability to identify an ongoing ‘leak’, the latter a perforation and collection. Both of these pieces of information may be of use to the surgeon in reaching a decision to operate, even though the ultimate decision must be based on clinical rather than radiological criteria. Overall, CT has been shown in a prospectively randomised trial to be superior to contrast enemas in both the evaluation of inflammation and identification of a collection.
84
The use of US is now one of the mainstays of investigation of the acute abdomen. Accurate detection of small amounts of intraperitoneal fluid associated with conditions such as perforated peptic ulcer, acute cholecystitis, acute appendicitis, strangulated bowel and ruptured ovarian cysts can be very helpful in alerting the clinician to the possible severity of the patient's symptoms. Furthermore, reports on the accuracy of US in the detection of specific conditions such as acute cholecystitis and appendicitis are impressive. The presence of free fluid, gallstones, a thickened gallbladder wall and a positive ultrasonographic Murphy sign are all good indicators of acute cholecystitis.
85
US is the first-line investigation for acute biliary disease, with a sensitivity greater than 95% for the detection of acute cholecystitis.
86
As the most appropriate management of these patients is now laparoscopic cholecystectomy during the same admission, and if possible within 48 hours,
87
early US examination on any patient with suspected acute biliary disease should be undertaken soon after admission (see also
Chapter 8
).
In experienced hands US has been shown to be able to detect an acutely inflamed non-perforated appendix with a sensitivity of 81% and specificity of 100%.
88
Because the technique relies on visualising a non-compressible swollen appendix (
Fig. 5.7
), the sensitivity for perforated appendicitis is much lower (29%). When a scoring system is used for both clinical diagnosis and ultrasonographic findings, the addition of the latter increases the diagnostic accuracy for acute appendicitis.
89,
90
Clearly, it would be inappropriate to scan everyone with suspected appendicitis, but where the diagnosis is uncertain, particularly in women, the case for US scanning is strong, as many alternative diagnoses can be detected.
91
Figure 5.7
Ultrasound examination on a patient with acute appendicitis. Note the non-compressible thick-walled hollow organ (appendix) beneath the probe.
Other areas where US is specifically used to assess the acute abdomen are abdominal aortic aneurysms, renal tract disease and acute gynaecological emergencies. US may also have a role to play in the diagnosis of strangulated small-bowel obstruction, by detecting dilated non-peristaltic loops of bowel in association with free intraperitoneal fluid.
92
US can also be useful in detecting acute abdominal wall problems, such as rectus sheath haematoma (
Fig. 5.8
), and differentiating them from intra-abdominal pathology.
93
US also has a role in the early assessment of patients with blunt abdominal trauma,
94
and this is covered in detail in
Chapter 13
.
Figure 5.8
Ultrasound of the abdominal wall demonstrating a rectus sheath haematoma.
The place of CT in the early assessment of the acute abdomen has received wide attention over the last few years following the introduction of multislice CT and recognition of the excellent images that can be produced, especially if intravenous (i.v.) contrast is used. Its role in the investigation of the severity of acute diverticulitis has already been discussed
84
and it can also be used to identify miscellaneous intra-abdominal collections resulting from other conditions. Attempts to improve the diagnostic accuracy of acute appendicitis using CT have been impressive, with 98% accuracy in 100 consecutive patients with suspected appendicitis (
Fig. 5.9
), of whom 53 had acute appendicitis.
95
However, irrespective of the cost and availability issue, the diagnosis of acute appendicitis can usually be made without the aid of imaging studies and care must be taken to ensure that such investigations are used to complement rather than to replace the clinical assessment of patients with suspected appendicitis.
96
Because of the associated risks of i.v. contrast in some individuals as well as excessive radiation exposure, particularly in the younger patients, the role of non-contrast CT has been examined in a systematic review of seven studies.
97
This review concluded that non-contrast helical CT provides an acceptably high accuracy (sensitivity of 92.7% and specificity of 96.1%) for the diagnosis of acute appendicitis in adult patients.
Figure 5.9
CT image with intravenous contrast demonstrating perforated appendicitis.
A randomised study from Cambridge that examined the effect of early CT (within 24 hours of admission) compared to standard investigations on patients with undifferentiated acute abdominal pain demonstrated an improvement in diagnostic accuracy in patients undergoing early CT, but no difference in length of stay or mortality.
98
Further analysis of the same data demonstrated that another advantage of early CT was in the detection of unexpected significant primary and secondary diagnoses.
99
These findings were confirmed in another more recent randomised trial comparing plain radiology with early low-dose abdominal CT.
100
In addition to its overall role in the investigation of the acute abdomen, CT is also extremely useful specifically in the detection of gastrointestinal obstruction (
Fig. 5.10
), perforations (
Fig. 5.11
), along with indications of the site of perforation,
101
intestinal ischaemia (
Fig. 5.12
)
102
and bleeding (
Fig. 5.13
), as well as abdominal wall problems (
Fig. 5.14
). Multislice CT with intravenous and rectal contrast can also be useful in the detection and differentiation of different types of colitis, including ulcerative, Crohn's, pseudo-membranous and
Clostridium difficile
colitis.
103
A clinicoradiological score has recently been developed to predict the risk of strangulated small-bowel obstruction using duration of pain (lasting 4 days or more), elevated C-reactive protein (> 75 mg/L), leucocyte count (> 10 × 10
9
/L), the presence of guarding, at least 500 mL of fluid as seen on CT and reduced enhancement of the small bowel on CT. The risk of ischaemia in 233 consecutive patients studied with small-bowel obstruction was 6% in patients with a score of 1 or less (one point for each variable) compared to a sensitivity of 67.7% and specificity of 90.8% in requiring resection for a score of 3 or more.
66
Overall, 138 of the patients in this study underwent surgery, of whom 45 required intestinal resection.
Figure 5.10
CT image with intravenous contrast demonstrating small-bowel obstruction due to an incarcerated inguinal hernia.
With thanks to Dr Dilip Patel, Consultant Radiologist, Royal Infirmary, Edinburgh.
Figure 5.11
(a)
Sagittal view of a CT scan with intravenous contrast demonstrating free intraperitoneal gas from a perforated peptic ulcer. Note the free air anterior to the liver.
(b)
Axial view of the same patient showing free air above the liver.
With thanks to Dr Dilip Patel, Consultant Radiologist, Royal Infirmary, Edinburgh.
Figure 5.12
CT angiogram demonstrating coeliac axis thrombus.
Figure 5.13
CT angiogram demonstrating contrast in the mid descending colon from bleeding diverticular disease.
Figure 5.14
CT image with intravenous contrast demonstrating a large rectus sheath haematoma.
Despite the relatively high diagnostic accuracy of CT in the assessment of the acute abdomen, and particularly acute appendicitis, the main drawbacks remain cost and radiation exposure.
104
As a result the role of CT in the early assessment of patients with acute abdominal pain should still be limited to those in whom there remains uncertainty as to either diagnosis or decision to operate after initial assessment.