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E2303. The Knowns and Unknowns of Appendix
Authors
  1. Deanna Thorson; Loyola University Medical Center
  2. Tucker Burr; Loyola University Medical Center
  3. Sudeep Soni; Loyola University Medical Center
  4. Erin Werhun; Loyola University Medical Center
  5. John Hibbeln; Loyola University Medical Center
  6. Anugayathri Jawahar; Loyola University Medical Center
Background
The vermiform appendix is a vestigial organ, but it is a frequent cause of emergency room visits when it is inflamed. Acute appendicitis (AA) is the most common consideration when an abnormal appendix is identified on imaging. The lifetime risk for appendicitis is 1 in 15 in the United States. Although rare, appendiceal neoplasms may demonstrate imaging and clinical features that overlap with AA and may even be found concomitantly with appendicitis. The purpose of this educational exhibit is to illustrate and discuss choice of various imaging studies in the different age groups and genders, and imaging findings of common and uncommon pathologies of the appendix that mimic AA.

Educational Goals / Teaching Points
Acute appendicitis can demonstrate a variety of imaging appearances on computed tomography, often related to the severity of the inflammation and/or presence of complications. While identification of an uncomplicated appendicitis demonstrating multiple classic features is often straightforward, complicated appendicitis may be more challenging to accurately characterize. An intentional search for certain imaging findings can be helpful in evaluating these more complicated cases. Appendiceal neoplasm should be considered in the differential for an abnormal appendix, as these clinically present with symptoms of AA in 30-50% of patients, and are often only identified upon surgical excision.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Uncomplicated AA may be characterized by increased appendiceal diameter, intraluminal appendicolith, and appendiceal wall thickening, hyperenhancement or mural stratification. Increased bacterial proliferation and intraluminal pressure may lead to obstructed lymphatic and venous drainage, whereby bacteria may invade the appendiceal wall leading to hemorrhage and eventually perforation. Clinically, this manifests as intense peritonitis and shift of pain from the umbilicus to the right lower quadrant. It is important to thoroughly evaluate for signs of perforation including abscess, phlegmon, and extraluminal air, enteric contrast, or appendicolith. Neuroendocrine tumors represent the most common type of appendiceal tumor, and may be particularly difficult to accurately diagnose on imaging due to their indolent presentation. Imaging diagnosis may be further complicated if presenting with concurrent appendicitis. These tumors manifest as enhancing submucosal masses or nodular thickening of the appendiceal wall, most commonly measuring <1 cm in diameter, and more frequently involving the distal appendix than the base. Appendicular lymphoma is rare but can share overlapping imaging features with appendicitis, including diffuse wall thickening, appendiceal enlargement with preserved vermiform shape, and regional adenopathy.

Conclusion
Acute appendicitis is a common cause of right lower quadrant pain and diagnosis is often straightforward for the radiologist in uncomplicated presentation. It is important, however, to consider a broader differential and guide the clinician in the setting of perforated appendicitis, hemorrhage/suppuration, and suspected neoplasm.