Is Contrast Needed for CT in the Diagnosis of Appendicitis?

A Systematic Review of the Literature<sup type="ref">1</sup>

Christian Molstrom, MD, PGY2; Sandeep Johar, DO, MS

Disclosures

AccessMedicine from McGraw-Hill 

Background

It can be argued that in US Emergency Departments, the diagnosis of acute appendicitis has shifted from clinical impression to radiographic confirmation, even for patients for whom the diagnosis is relatively certain on clinical grounds alone. The reasons for this are varied: desire to make prompt diagnosis by imaging rather than observing in today's busy ED, wide-spread 24/7 availability of CT, desire to reduce negative appendectomy rate, and medico-legal concerns over a missed diagnosis.[2]

Given its speed and accuracy, CT has become the definitive imaging choice for most ED patients. However, there are several contested questions regarding CT in acute appendicitis. First is the issue of whether CT should be routine in all patients suspected with appendicitis. Studies have been mixed, with some showing significant reduction in negative appendectomies and others claiming that imaging is costly and delays care when the diagnosis is clinically obvious.[3,4] A second question regards the role of contrast. A multitude of studies have looked at the use of CT with IV, PO, rectal contrast, combinations of these three, or without contrast. Currently, institutions use different protocols, with no clear expert consensus on what type of contrast, if any, should be used.[5]

Noncontrast CT in the emergency diagnosis of appendicitis is attractive for several reasons. Administration of oral contrast consumes valuable time in today's fast-paced and overcrowded ED. The contrast may taste unpleasant, and may be aspirated in patients who are actively vomiting. Intravenous contrast carries the risk of contrast-induced nephropathy and allergic reactions, and is contra-indicated in many patients with poor renal function.

Methods

This paper was a systematic review of studies on the diagnostic accuracy of noncontrast helical (multi-slice) CT for acute appendicitis in adults (age > 16) who presented to the ED. To be included in the review, studies needed to meet two key inclusion criteria: (1) a patient spectrum representative of the ED, and (2) a diagnosis confirmation by surgery or pathology, or uneventful clinical follow-up for at least 2 weeks. The quality of each study was assessed using the QUADAS tool.

Results

Of 1,257 studies meeting search criteria in EM Abstracts, MEDLINE, Cochrane, and EMBASE, 32 underwent full review and 7 were included in final analysis. All 7 studies had a patient spectrum representative of the ED, reported an acceptable reference standard (diagnosis by surgery or pathology), had an acceptably short delay between CT and measurement of reference standard, and reported that the radiologists reading the CTs had been blinded to the results of reference standard. Respective pooled estimates for sensitivity and specificity of these 7 studies were 92.7% (95% CI 89.5% to 95.0%) and 96.1% (95% CI 94.2% to 97.5%), with a positive likelihood ratio of 24 and negative likelihood ratio of 0.08.

Relevance to Emergency Medicine

The utilization of CT scanning in the emergency department has increased significantly over the past 20 years, along with the associated risks of radiation exposure and adverse reactions to CT contrast.[6] Minimizing these risks requires development of evidence-based diagnostic imaging strategies to avoid CTs when possible in younger patients, and to minimize the use of contrast agents. One development to emerge from this type of research is the use of noncontrast CT instead of IVP for the diagnosis of kidney stones,[7] (which does help reduce the use of IV contrast in at risk patients, but may actually lead to increased radiation risks in the long term). In the case of abdominal CT for the diagnosis of appendicitis, the evidence is that the varied modalities of contrast (IV, PO, rectal, combination) may simply add risk, time, and complexity without increasing diagnostic accuracy.

This systematic review adds evidence that noncontrast helical CT provides sufficiently high accuracy in the diagnosis of acute appendicitis in adult ED patients. Potential advantages of noncontrast scanning in today's overcrowded ED include rapid diagnosis, early disposition, cost savings, and higher patient satisfaction, as well as the elimination of contrast-related adverse affects.

Nevertheless, there is still a role for clinical judgment in deciding when to use contrast. For example, contrast is more likely to be of benefit in the patient with undifferentiated abdominal pain where acute appendicitis is a less likely diagnosis, since alternative diagnoses may be more easily identified with contrast enhanced CT. The bottom line: There is a role for noncontrast CT in the diagnosis of acute appendicitis in adults. If your institution doesn't have such a protocol, it may be time to sit down with radiologists and surgeons and develop one.

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