Imaging description

The primary CT signs of acute appendicitis are appendiceal dilatation (the upper limit of appendiceal dilatation has been variably reported, but is generally regarded as between 6 and 10 mm) with or without periappendiceal fat stranding or fluid [1]. Occasionally, such CT findings are due to other causes, including normal variation in appendiceal diameter, appendiceal dilatation associated with malignancy, hematoma, spontaneously resolving acute appendicitis, Crohn's appendicitis, ischemic appendicitis, granulomatous appendicitis, lymphoid hyperplasia, mucocele, appendiceal tumor, and right-sided colon cancer (Figures 63.1–63.9) [2–10]. In such settings, the term pseudoappendicitis can be appropriately applied to the imaging findings.

Importance

A false positive diagnosis of acute appendicitis may lead to unnecessary appendectomy.

Typical clinical scenario

Pseudoappendicitis is rare. In patients with abdominal pain, spontaneously resolving acute appendicitis, Crohn's appendicitis, ischemic appendicitis, and granulomatous appendicitis should be considered as potential additional causes of appendiceal dilatation with or without periappendiceal fat stranding or fluid. In patients without abdominal pain, considerations include lymphoid hyperplasia, mucocele, appendiceal tumor, and right-sided colon cancer.

Differential diagnosis

There are several forms of pseudoappendicitis:

• Appendiceal diameter is variable, and a diameter over 6 mm has been reported to occur in up to 42% of normal appendixes, either with visible or indiscernible content [2]. Such variation may account for a contemporary false positive rate of 3% for the diagnosis of acute appendicitis by CT [11]. It is also possible that a dilated appendix on CT in patients in whom a diagnosis of acute appendicitis is rejected after surgical consultation is still due to spontaneously resolving acute appendicitis, because up to 38% of these patients ultimately require appendectomy [5].

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