Appendicitis represents acute inflammation of the vermiform appendix, most commonly due to luminal obstruction by fecalith, lymphoid hyperplasia, or neoplasm. It constitutes a surgical emergency with classic right lower quadrant pain migrating from periumbilical region.

Lifetime risk approaches 7-8% with peak incidence in second and third decades. Male predominance (3:2). Seasonal variation absent but increased incidence during summer months reported.

Classic triad: periumbilical pain migrating to right lower quadrant, anorexia, nausea/vomiting. Fever typically low-grade (<38°C). Rebound tenderness at McBurney point. Rovsing, psoas, and obturator signs variably present.

Obstruction leads to mucus accumulation, bacterial overgrowth, and ischemia. Progression: mucosal ulceration → transmural inflammation → gangrene → perforation (24-72 hours). Common pathogens: E. coli, Bacteroides fragilis.

• Non-compressible diameter >6 mm (most specific)
• Target/pretzel sign: hypoechoic lumen + echogenic mesentery + hypoechoic wall
• Appendicolith: hyperechoic focus with posterior shadowing
• Periappendiceal fluid collection, hyperemia on color Doppler
• Sensitivity 75-90%, specificity 86-95% (operator dependent)

• Appendix diameter >6-7 mm with wall thickening (>2 mm)
• Periappendiceal fat stranding
• Appendicolith (central hyperdensity)
• Wall hyperenhancement
• Complications: phlegmon, abscess, free air, extraluminal fluid
• Sensitivity 94-98%, specificity 95-99% (gold standard)

• T2: fluid-filled distended appendix (>6 mm), periappendiceal high signal
• T1 post-contrast: wall hyperenhancement
• Useful in pregnancy/children (sensitivity 97%)

Appendectomy (open/laparoscopic) remains gold standard. Antibiotics for uncomplicated cases or percutaneous drainage for abscess. Perforation risk 30-40% if >36 hours from onset. Mortality <1% with early surgery.

• Gastroenteritis (diffuse symptoms)
• Meckel diverticulitis (mesenteric location)
• Epiploic appendagitis (oval fat density lesion)
• Right ovarian torsion/cyst (adnexal mass)
• Crohn ileitis (skip lesions, fistulae)

* LITFL: Abdominal CT Appendicitis * AJR 2005: CT Evaluation of Appendicitis * AAFP: Radiologic Evaluation * Insights Imaging 2016: Ultrasound First * Radiology Assistant: US Findings

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