Thursday, October 14, 2004

Nonvisualization of Appendix on CT Linked With Low Rate of Appendicitis

Nonvisualization of Appendix on CT Linked With Low Rate of Appendicitis

Nonvisualization of the appendix on helical computed tomography (CT) examination is associated with low incidence of acute appendicitis in the absence of secondary inflammatory changes, according to the results of a retrospective study published in the October issue of the American Journal of Roentgenology. Appendicitis may be safely ruled out given the visualization of more than a scant amount of pericecal fat.
"CT has become part of the standard of care in managing patients with suspected acute appendicitis," writes Paul Nikolaidis, MD, from the Department of Radiology at Northwestern University Feinberg School of Medicine in Chicago, Illinois, and colleagues. "Sometimes, however, the appendix is not visualized on CT examination despite the use of optimal imaging parameters."
To assess the significance of nonvisualization of the appendix in the absence of secondary inflammatory changes, the investigators retrospectively reviewed CTs taken to rule out appendicitis in 366 consecutive patients presenting with symptoms of lower abdominal or right lower quadrant pain.
Original CT reports included 56 CTs (15%) in which the original reviewer was unable to visualize the appendix in the absence of secondary inflammatory changes, including abscess formation, localized perforation, periappendiceal fat stranding, or appendicolith.
The investigators were able to visualize appendices in 10 of these CTs upon review, yielding 46 CTs (13%) in which nonvisualization of the appendix was agreed upon. Pericecal fat was evaluated on a scale of 0 (scant, n = 8), 1 (n = 20), and 2 (abundant, n = 28).
In 12 patients (26%), CT indicated gastrointestinal (n = 8) and genitourinary (n = 4) symptom sources. Of 34 remaining patients, 11 (24%) were diagnosed through further imaging or clinical evaluation. One patient (2%) with a scant amount of pericecal fat (score = 0) was diagnosed with acute appendicitis that was confirmed by surgical pathology.
"The amount of fat surrounding the cecum influences our ability to visualize the appendix and therefore more confidently exclude the possibility of acute appendicitis," the authors write, pointing out the scant amount of pericecal fat (score of 0) in the patient with the missed diagnosis.
Study limitations include its retrospective nature and the lack of follow-up information for a relatively large number of patients (50%).
"In the absence of a distinctly visualized appendix and secondary inflammatory changes, the incidence of acute appendicitis is low (2%)," the authors conclude, adding that acute appendicitis may be safely excluded with CT visualization of more than a scant amount of pericecal fat.



Am J Roentgenol. 2004;183:889-892

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