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Imaging for Diagnosis of Appendicitis
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- Appendiceal CT allows for rapid and accurate diagnosis of appendicitis
- Appendiceal CT can be modified to a full abdominal and pelvic examination to detect alternate pathologies
- Appendiceal CT is cost effective because it avoids unnecessary appendectomy and/or hospitalization for observation
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In
the past decade, the clinical evaluation of patients with suspected
appendicitis has dramatically improved in speed and accuracy due to the
focused appendiceal CT developed at Massachusetts General
Hospital. Clinical signs and laboratory tests are not
sufficiently accurate to unequivocally diagnose or rule out
appendicitis. Because of the seriousness of a perforated appendix,
prior to the availability of appendiceal CT, appendectomy or in
hospital observation was routine for those with suspected appendicitis.
As many as 15-20% of appendectomies resulted in the removal of a normal
appendix; and since the annual number of appendectomies performed in
the United States exceeded 250,000, both the monetary and personal
costs of unnecessary surgery and/or hospitalization were considerable.
Thus, appendiceal CT has not only improved the quality but decreased
the cost of caring for patients with suspected appendicitis.
Imaging for Appendicitis
Appendiceal CT is a highly accurate radiological diagnosis of
appendicitis when conducted by an experienced radiologist (Table 1).
Ultrasonography can be used to aid in the diagnosis of appendicitis and
has the advantage of avoiding any ionizing radiation. Although it
has been used effectively in small children, it is only moderately
accurate in adults and adolescents (Table 1). It is often difficult or
impossible to characterize the normal appendix with ultrasonography and
rule out appendicitis, especially if the appendix in located in a
retrocecal position, if there is overlying bowel gas, or in obese
patients.
Because the radiation dose from appendiceal CT can be minimized by a
computerized dose reduction technique and by performing a focused lower
abdominal scan, appendiceal CT can be performed relatively safely on
pregnant women and children. Ionizing radiation can be avoided with
MRI; but this modality produces lower resolution images. Although there
are some preliminary studies demonstrating that it can be used to
evaluate pregnant women in whom appendicitis is suspected and to
diagnose other causes of right lower quadrant pain, the accuracy of
this technique is yet to be determined.
Economic Impact of Appendiceal CT
In 1997, two years after the introduction of appendiceal CT at
Massachusetts General Hospital, the rate of negative appendectomies was
found to be to 7% and the appendiceal perforation rate was 14%.
In comparison, in the three years prior to the introduction of
appendiceal CT the rates were 20% and 22%, respectively. This
significant
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Figure 1. Normal appendix. Contrast is seen filling a normal appearing appendix (arrows) demonstrating a thin wall.
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improvement was achieved even though only 59% of patients who
received appendectomies had their diagnoses confirmed by
appendiceal CT. In addition, for about half those patients in whom no
evidence of appendicitis was found, specific alternative conditions
were diagnosed (Table 2). The overall cost savings from unnecessary
surgery and in hospital observation attributable to appendiceal CT were
estimated to be $45,000 for the 100 patients in the study.
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| Figure 2. Appendicitis with appendicolith. An enlarged appendix (solid arrows) is seen with an appendicolith (dashed arrows) at the base. |
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| Figure 3. Appendicitis.
The appendix (solid arrows) is abnormally dilated and demonstrates a
thickened enhancing wall and no filling with contrast. |
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| Figure 4. Perforated
appendicitis. The appendix (solid arrows) is abnormally dilated with a
thickened enhancing wall. Small pockets of extraluminal air (dashed
arrows) indicate perforation. |
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Appendiceal CT Procedure
The appendiceal CT protocol in use at Massachusetts General Hospital
Emergency Department uses intravenous contrast material and rectal
contrast to opacify the bowel. The rectal contrast agent used is a
solution of up to 1500 mL of iodinated contrast agent in saline,
administered by gravity from an IV bag via a pediatric rectal tube
while lying on the CT table. Most patients tolerate this
procedure well; but if cramps develop, administration of contrast may
be halted temporarily until the symptoms subside. A scout image
is taken to observe whether the contrast agent has reached the right
colon. If not, more rectal contrast may be instilled and another scout
image obtained. A focused abdominal CT scan is then performed, which
gives high-resolution images of the right lower quadrant. When the
appendix is normal, the radiologist may choose to extend the anatomic
range of the scan to search for alternate diagnoses.
In the emergency room, rectal rather than oral contrast administration
is preferred for several reasons. First, the contrast quickly passes
through the colon and reaches the appendix within minutes, whereas oral
contrast may take 1-2 hours. Second, it is easier to predict the time
of optimal cecal opacification. Third, rectal rather than oral contrast
is preferred in case of emergency surgery requiring general
anesthesia. Finally, some patients find administration of rectal
contrast preferable to drinking a large volume of oral contrast when
feeling unwell.
However, in a non-emergent setting, rectal contrast is usually not
preferable to oral contrast. First, oral contrast opacifies the
small bowel, which allows for more accurate diagnoses of other
bowel-related cases of abdominal pain, e.g. inflammatory bowel disease,
bowel obstruction. Second, in many patients, especially the
elderly and the hospitalized who have poor anal sphincter control,
retention of rectal contrast for adequate opacification of the cecum is
often difficult to achieve and causes patient discomfort.
Thus, for non-emergent patients with abdominal pain where
appendicitis is only one of several diagnoses under consideration, or
in patients where rectal contrast is unlikely to achieve adequate cecal
opacification, oral contrast is used. Oral contrast is typically
administered as 300-500 cc or dilute barium sulphate suspension
ingested over 1-2 hours.
Intravenous contrast is also administered unless contraindicated
because it makes it easier to visualize the normal appendix, especially
in children and in older and/or thin patients. The contrast agent
highlights the dilated vasculature in inflamed tissue and also make it
easier to characterize complications such as appendiceal perforation
and extra-appendiceal abscess formation, as well as for diagnosing
alternate causes of abdominal pain, such as inflammatory bowel disease,
pancreatitis, pelvic inflammatory disease, and pyelonephritis.
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Table 1. Diagnostic Performance of Imaging
Studies for Appendicitis |
| Imaging Technique |
Sensitivity |
Specificity |
| Appendiceal CT with rectal contrast (adults) |
100% |
95% |
| Appendiceal CT with rectal contrast (children) |
97% |
99% |
| Abdominal CT with oral contrast |
93-95% |
88-96% |
| Appendiceal CT with no bowel opacification |
90-96% |
94-97% |
| Ultrasonography (adults and adolescents) |
83-88% |
78-84% |
| Ultrasonography (children) |
85% |
92% |
| MRI |
Not available |
Not available |
| Table 2. Alternate Appendiceal CT Diagnoses |
| Diverticulitis |
| Renal calculi |
| Pyelonephritis |
| Epiploic appendagitis |
| Omental infarction |
| Adnexal conditions |
Scheduling
Acutely ill patients with suspected appendicitis should be sent to the
Emergency Department for clinical evaluation where a focused
appendiceal CT may be performed. For patients who have been
clinically evaluated, an abdominal CT to look for appendicitis can be
ordered for the same day through ROE (http://mghroe
) (at the Main
Campus, Waltham, and Chelsea), or by telephone for Mass General West
Imaging Waltham (781-895-1199) and Mass General Imaging Chelsea
(617-887-3500).
Further Information
For further questions, please contact Robert Novelline, M.D.
, Director of Emergency Radiology, at 671-726-8796.
We would like to thank Robert Novelline, M.D., Peter R. Mueller, M.D., Director of Abdominal
Imaging and Interventional Radiology and Matthew Hutter, M.D., General
Surgeon, for his assistance and advice for this issue.
This article provided useful information about the appropriate use of imaging studies:
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References
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Old, JL, Dusing, RW, Yap, W and Dirks, J. (2005) Imaging for suspected appendicitis. Am Fam Physician 71: 71-8
Oto, A, Ernst, RD, Shah, R, Koroglu, M, et al. (2005) Right-lower-quadrant pain and suspected appendicitis in pregnant women: evaluation with MR imaging--initial experience. Radiology 234: 445-51
Pinto Leite, N, Pereira, JM, Cunha, R, Pinto, P and Sirlin, C. (2005) CT evaluation of appendicitis and its complications: imaging techniques and key diagnostic findings. AJR Am J Roentgenol 185: 406-17
Rao, PM, Rhea, JT, Novelline, RA, Mostafavi, AA and McCabe, CJ. (1998) Effect of computed tomography of the appendix on treatment of patients and use of hospital resources. N Engl J Med 338: 141-6
Rao, PM, Rhea, JT, Rattner, DW, Venus, LG and Novelline, RA. (1999) Introduction of appendiceal CT: impact on negative appendectomy and appendiceal perforation rates. Ann Surg 229: 344-9
Terasawa, T, Blackmore, CC, Bent, S and Kohlwes, RJ. (2004) Systematic review: computed tomography and ultrasonography to detect acute appendicitis in adults and adolescents. Ann Intern Med 141: 537-46
Sivit CJ, Siegel MJ, Applegate, KE, Newman, KD. When Appendicitis Is Suspected in Children RadioGraphics 2001; 21:247–262
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