Appendicitis Mimics, Thompson et al. Mimickers of Acute Appendicitis Joel P. Thompson, M.D., MPH, Dhana Selvaraj, M.D., Refky Nicola, D.O. Department of Imaging Sciences, University of Rochester Medical Center, Rochester, NY Introduction of patients.2,3 The presence of intravenous and enteric contrast aids in identification of the appendix.3 Acute abdominal pain is the most common reason The appendix arises from the cecum inferior to the for an emergency department visit among patients age ileocecal junction (Fig. 1). MDCT signs of acute 15 and older, a large portion of them will complain of 1 appendicitis include appendiceal diameter > 7 mm pain localizing to the right lower quadrant. While with peri-appendiceal stranding of the mesenteric fat appendicitis is the most common cause of the surgical (Fig. 2A).4 Both findings are present in up to 93% of abdomen, a wide variety of acute gastrointestinal, appendicitis cases identified on MDCT.5 The diagnosis genitourinary, and gynecological pathologic processes of appendicitis should not be made using appendiceal can present in similar fashion (Table 1). Acute diameter alone; wall thickening and increased gastrointestinal diseases, such as Crohn’s disease, enhancement should also be present.6 Additional infectious enterocolitis, mesenteric adenitis, cecal findings include the presence of an appendicolith, diverticulitis, Meckel’s diverticulitis, epiploic cecal apical thickening (“arrowhead sign”), mesenteric appendagitis, and omental infarcts can present with adenopathy, fluid in the paracolic gutter, and the right lower quadrant. In addition, acute genitourinary presence of phlegmon.5 A focal wall defect, diseases, such as pyelonephritis and ureterolithiasis, extraluminal air, or presence of an abscess are signs of can present with similar symptoms. In a young perforation.5 While MDCT is currently the preferred woman, acute gynecological disease processes, such as imaging modality, in the pediatric and pregnant ovarian torsion, hemorrhagic ovarian cyst, pelvic patient ultrasound as well as MRI has been shown to inflammatory disease, and ectopic pregnancy, should perform comparable to CT.7 also be considered within the differential diagnosis. Ultrasound has a sensitivity and specificity of 78% Imaging modalities utilized in the emergency setting and 83%, respectively.8 The most common findings in to evaluate right lower quadrant pain include appendicitis are diameter > 6 mm, lack of computed tomography (CT), ultrasound (US), and compressibility, hyperemia of the appendiceal wall on magnetic resonance imaging (MRI). These modalities Doppler imaging, peri-appendiceal inflammatory may be value-added for patients with nonspecific changes, and the presence of peritoneal fluid (Fig. symptoms, thus it is useful to triage surgical and non- 2B). Occasionally, a calcified appendicolith may be surgical patients. It is important for the practicing seen with posterior shadowing (Fig. 2C). However, radiologist to be familiar with the various acute ruling out appendiceal pathology is often difficult with disease entities which can cause right lower quadrant US if the appendix cannot be visualized. One study pain in order to determine the best approach or reported positive ultrasound findings for appendicitis modality to make an accurate diagnosis. in about 20% of cases, but equivocal findings in almost 50% of cases (i.e. inability to identify the appendix).7 Imaging of the appendix Evaluation of the right lower quadrant is particularly difficult in pregnant women due to distorted The most common imaging modality for the abdominal and pelvic anatomy (particularly in the third evaluation of the right lower quadrant pain is MDCT. trimester). MRI has been shown to be superior at MDCT has a sensitivity of 97%, specificity of 98%, and localizing the appendix in comparison to ultrasound, accuracy of 98% in diagnosing acute appendicitis, with with a sensitivity and specificity of up to 89% and the additional benefit of suggesting an alternative 99%.8,9 diagnosis for acute abdominal pain in up to two-thirds Page 10 J Am Osteopath Coll Radiol 2014; Vol. 3, Issue 4 Appendicitis Mimics, Thompson et al. Pathology Imaging Appearance Treatment Gastrointestinal Crohn’s Disease Bowel wall thickening and mural stratification, most commonly involving Initially medical. Indications for surgery the terminal ileum. Chronic inflammation may result in fibrofatty include obstruction due to fibrotic stricture, proliferation along the mesenteric side of the bowel wall. Fistulas and perforation, abscess formation, and fistulas abscesses may form. not able to be managed medically. Diverticulitis Thick-walled diverticulum with adjacent infiltrative changes; short or long Medical. Surgical intervention may be -segment bowel wall thickening. Abscesses may form. necessary for medically refractory cases, large abscesses, and fistula formation. Infectious Long-segment circumferential wall thickening, usually without Medical. Enterocolitis mesenteric fat stranding. Mesenteric Adenitis Cluster of 3 or more right lower quadrant lymph nodes >5 mm in shortest Medical. diameter, without identifiable cause. Neutropenic Colitis Distended and thick-walled cecum, infiltrative changes, pericolic fluid. Medical. High risk of bowel perforation; CT (Typhlitis) may be used to monitor treatment response. Meckel’s Blind-ending tubular structure in the right lower quadrant arising from Surgical resection. Diverticulitis the distal ileum; infiltrative changes, wall thickening, and hyperenhancement may be seen. Epiploic Appendagitis Pericolic fatty mass with surrounding inflammatory changes, most Medical. commonly in the transverse and descending colon. A central thrombosed vein may be identified. Omental Infarct Pericolic fatty mass with surrounding inflammatory changes, most Medical. commonly in the right hemiabdomen between the colon and the anterior abdominal wall. Genitourinary/Gynecological Urolithiasis Obstructing calculus with hydronephrosis +/- hydroureter. Medical, unless calculus large. Pyelonephritis Imaging most often normal. May see striated nephrogram or delayed Medical. contrast excretion on CT. US may show loss of corticomedullary differentiation. Ovarian Torsion US: Enlarged and heterogeneous ovary; may be midline. May see Surgical detorsion. reduced or absent venous flow. Hemorrhagic Ovarian US: Finely septated “fishnet” pattern of fibrin bands; retractile clot or None. Cyst avascular peripheral nodule non-acutely. Pelvic Inflammatory Dilated tubular structures representing Fallopian tubes with wall Medical. Disease thickening. Ipsilateral ovary may be enlarged. Ectopic Pregnancy Non-visualization of an intrauterine pregnancy with positive beta-hCG. Medical but may require surgical US: May see yolk sac, detect fetal heartbeat, or see “ring of fire” sign of intervention. peripheral hypervascularity around adnexal mass. Mittelschmerz Normal. May see physiologic fluid in the pelvis. None. Table 1. Overview of gastrointestinal and genitourinary causes of right lower quadrant pain. J Am Osteopath Coll Radiol 2014; Vol. 3, Issue 4 Page 11 Appendicitis Mimics, Thompson et al. Figure 1. Normal appendix. Coronal MDCT with IV and enteric contrast (A) demonstrates a normal appendix (white arrow) arising from the cecum inferior to the ileocecal junction (yellow arrow). Longitudinal ultrasound image (B) shows a normal appearance of a blind-ending appendix, which measures 4 mm in diameter (caliper 2). A B A B C Figure 2. Acute Appendicitis. Axial MDCT image with oral contrast (A) demonstrates an enlarged appendix, measuring up to 14 mm in diameter (white arrow), wall thickening, and adjacent inflammatory changes with phlegmon formation (yellow arrow). Surgical pathology demonstrated appendicitis. Longitudinal ultrasound images in a different patientB ( ) demonstrate an enlarged appendix, measuring up to 10 mm, that is noncompressible, consistent with appendicitis. Ultrasound image at a different level in the same patient demonstrates a hyperechoic focus with posterior shadowing, consistent with an appendicolith (C). On MRI, the appearance of acute appendicitis Differential Diagnosis includes an appendiceal diameter > 7 mm and adjacent fat stranding that is often best appreciated Crohn's Disease on T2 fat saturated sequences.10 An inflamed Crohn's disease can involve any segment of the appendix demonstrates restricted diffusion.10 The gastrointestinal tract, but the most common location is appendix may be filled with high T2 fluid or edema, within the terminal ileum. Patients often present with which decreases in signal intensity if the fluid is abdominal cramps localized within right lower purulent (higher debris and protein quadrant and bloody stools. The initial presentation content). Appendicoliths are low in T1 and T2 signal typically occurs between 15 and 30 years of age. intensity, with blooming artifact on GRE images. A The imaging features of Crohn's disease consist of periappendiceal abscess is identified as a walled-off bowel wall thickening (greater than 4 mm), mural high T2 fluid collection with restricted diffusion. An stratification ("target" or stratified appearance of the appendix filled with high T2 fluid and diameter of 6-7 bowel wall due to submucosal edema), and abnormal mm is indeterminate (if no adjacent fat stranding of 11 10 enhancement (Fig. 3). Active inflammation leads to fluid) and should be closely followed up. engorgement of vasa recta (the "comb sign"). Chronic inflammation results in fibrofatty proliferation