KEY FACTS
Terminology
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Acute inflammation of appendix, which may be precipitated by obstruction of lumen
Imaging
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Blind-ended, aperistaltic, thick-walled tubular structure with gut signature
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Length ranges between 2-20 cm; base between ileocecal valve and cecal apex
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Noncompressible appendix with outer diameter ≥ 7 mm; single wall thickness > 3 mm
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Increased caliber alone is not reliable indicator
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Mural stratification seen in early stages, absent in gangrenous appendicitis
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Periappendiceal edema seen as echogenic fat
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Additional findings: Appendicolith, periappendiceal fluid
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Perforated appendicitis: Periappendiceal abscess or phlegmon, free appendicolith
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Increased vascularity on color Doppler
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US: 1st choice in children, thin young adults, and pregnancy
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CT performed for patients with inconclusive US, if complications suspected, or in obese patients
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MR: Useful in pregnancy
Top Differential Diagnoses
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Appendiceal mucosal lymphoid hyperplasia
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Appendicular mucocele
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Mesenteric adenitis
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Cecal diverticulitis/ileocolitis
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Appendiceal/cecal carcinoma
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Pelvic inflammatory disease
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Segmental omental infarction/epiploic appendagitis
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Meckel diverticulitis
Pathology
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Can be obstructive (appendicolith) or nonobstructive
Clinical Issues
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All ages affected, M = F
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Periumbilical pain migrating to RLQ; peritoneal irritation at McBurney point; atypical signs in 1/3 of patients
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Anorexia, nausea, vomiting, diarrhea, fever
Scanning Tips
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Scan over area of pain, use graded compression and color/power Doppler, consider decubitus positioning
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Use combination of linear and curved transducers
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Transvaginal US: For visualization of pelvic appendix
. The direction of the tip of the appendix and length can vary.
appearance due to the preservation of mural stratification. Note the surrounding echogenic, inflamed fat 
and a thickened, inflamed parietal layer 
of the peritoneum, which is in contact with the inflamed appendix.
