====== Appendicitis ======

**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.

===== Epidemiology =====
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.

===== Clinical presentation =====
**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.

===== Pathology =====
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.

===== Radiographic features =====

==== Ultrasonography ====

  * **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)

==== Computed tomography ====

  * **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)

==== Magnetic resonance imaging ====

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

===== Treatment and prognosis =====
**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.

===== Differential diagnosis =====

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

===== References =====
* [[https://litfl.com/abdominal-ct-appendicitis/|LITFL: Abdominal CT Appendicitis]]
* [[https://ajronline.org/doi/10.2214/ajr.185.2.01850406|AJR 2005: CT Evaluation of Appendicitis]]
* [[https://www.aafp.org/pubs/afp/issues/2005/0101/p71.html|AAFP: Radiologic Evaluation]]
* [[https://pmc.ncbi.nlm.nih.gov/articles/PMC4805616/|Insights Imaging 2016: Ultrasound First]]
* [[https://radiologyassistant.nl/abdomen/acute-abdomen/appendicitis-us-findings|Radiology Assistant: US Findings]]

> **Medical Disclaimer**: Portions of this content were AI-generated to facilitate rapid knowledge synthesis. Radiologists and clinicians must independently verify all information against peer-reviewed literature, institutional protocols, and patient-specific factors before clinical application.