All current incorporates the prospective acquisition of thin section less than 5mm images. Thin slices improve the z axis resolution by reducing partial volume averaging, thereby improving the visualization of appendiceal abnormalities. There is considerable variation in appendicitis CT scan protocol use different combinations of oral, rectal, intravenous or no contrast materials as enumerated on the table below.
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| Examples of Different CT Protocols for the Diagnosis of Acute Appendicitis |
On the table above this study includes various group of patient examined with different kinds of techniques of intravenous (IV), oral and rectal contrast agents administration. The figures reported above are for the majority subset that include both oral and intravenous contrast agents.
Protocols also differ regarding the anatomic area to be included of the technique used the reported accuracy in diagnosing appendicitis is high. The various technique differs in their rater of providing alternative diagnoses when the appendix is found to be normal. However, the related studies have also varied in the selection criteria and other important design criteria, so it is difficult to draw definite conclusions by simply comparing results. Consequently, debate still exist over the optimal appendicitis in CT scan protocol.
Focused Appendiceal CT Scan Exam
Some investigators advocate a protocol that limits the scan area to the lower abdomen and upper pelvis. This technique is referred to as focused appendiceal CT scan and has the advantage of reducing the patient’s radiation exposure. The disadvantage of a focused technique is the potential for incomplete visualization of non-visualization of the appendix. This is of particularly concern because the appendix can vary considerably in length and position.
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| Contrast-filled appendix located in the pelvis. Image courtesy of the University of Michigan Health Systems. |
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| Unusual right upper quadrant location of an inflamed appendix indicated by arrow. (L = liver). Image courtesy of the University of Michigan Health Systems. |
In addition, limiting the scan area to the lower abdomen and upper pelvis may reduce the ability to provide alternative diagnoses when the appendix is normal.
Focused appendiceal CT scan protocol have been proposed with the range of contrast media choices seen in table picture above. When contrast is given orally, adequate opacification of ileocecal bowel may take 45 to 90 minuted. Raoet al. have suggested a technique designed to reduce this wait time. In this protocol, a limited CT scan study of the right lower quadrant is performed after the rapid administration of rectal contrast material. A limitation if this technique is that some patients will require additional scanning of the proximal abdomen or the distal pelvis to identify disease not included in the initial scan range. In addition, other researchers express doubt that rectally administered contrast material provides sufficient added benefit to warrant its use.
Procedure Preparation and Duration
A CT scan protocol has also been advocated that includes the entire abdomen and pelvis but does not incorporate any contrast media agents. This examination can typically be performed in 10 minutes or less, does not expose the patient to the potential risk associated with IV iodinated contrast agent, and require no bowel preparation. This CT scan technique is often favored in patients with large body habitus, because diagnostic accuracy may be compromised in patient who have little abdominal and intrapelvic fat.
Probably the most widespread CT approach is to scan the entire abdomen and pelvis with both intravenous and oral contrast material. Those who use this method believe that contrast material. Those who use this method believe that contrast enhanced CT scan is essential to diagnose many of the other conditions that cause acute abdominal pain and may stimulate appendicitis. Jacobs et al. state that “our study findings demonstrate that use of intravenous contrast material significantly improved the reader’s ability to identify the inflamed appendix, to diagnose acute appendicitis, and to establish alternative diagnoses..” Finally, diagnosis of appendicitis may be missed with a focused helical CT scan technique it the inflamed appendix lies outside the limited scanning field of view.
Opacification of the terminal Appendix and Cecum
Enhancement of the terminal ileum and cecum with oral contrast material has been advocated to avoid a false positive result, a scenario in which fluid filled terminal ileal loops are misdiagnosed as a distended, inflamed appendix. The oral administration of up to 800mL of contrast medium during a minimum of 1 hour before scanning enables the opacification of both the small bowel and right colon in most patients. Water soluble agents such as diatrizoate sodium (Hypaque, GE Healthcare) mixed with sorbitol (an osmotic laxative) tend to stimulate peristalsis and thus move through the small intestine more quickly than do barium suspensions.
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