Acute appendicitis is inflammation of the appendix vermiformis and the most common surgical cause of acute abdominal pain. It typically develops following luminal obstruction (fecalith, lymphoid hyperplasia, tumor) leading to increased intraluminal pressure, mucosal ischemia, and bacterial superinfection. CT is the gold standard for diagnosis, characteristically showing a dilated appendix (>6 mm), periappendiceal fat stranding, and wall enhancement. Early diagnosis is critical to prevent perforation and complications.
Age Range
5-50
Peak Age
25
Gender
Male predominant
Prevalence
Common
The pathophysiology of acute appendicitis begins with luminal obstruction, most commonly caused by a fecalith (30-40%), followed by lymphoid hyperplasia, and rarely tumor. After obstruction, continued mucus secretion increases intraluminal pressure, impairing venous and lymphatic drainage. This leads to mucosal ischemia, allowing bacterial invasion (E. coli, Bacteroides) through the edematous wall. Inflammation spreads transmurally causing serosal irritation and periappendiceal fat stranding — forming the basis of the characteristic CT finding. If untreated, gangrenous changes and perforation develop, potentially resulting in free fluid, abscess, and even diffuse peritonitis.
On portal venous phase CT, appendix outer diameter >6 mm with wall thickening and enhancement combined with periappendiceal fat stranding represents the most reliable diagnostic combination for acute appendicitis. This triad of findings provides 94-98% sensitivity and 95-97% specificity.
Appendix outer diameter >6 mm, typically measuring 8-15 mm. The lumen is dilated with fluid or fecal material. Specificity increases significantly when diameter exceeds 10 mm.
Report Sentence
The appendix is dilated with an outer diameter measuring ... mm, consistent with acute appendicitis.
Increased density (stranding) in the mesenteric fat surrounding the appendix indicates spread of inflammation to the peritoneal surface and surrounding tissues. This is the most sensitive CT finding and increases diagnostic confidence over isolated appendiceal dilatation.
Report Sentence
There is prominent periappendiceal fat stranding supporting acute inflammation.
The appendiceal wall is thickened (>3 mm) and shows marked enhancement on portal venous phase. Wall thickening reflects edema and inflammatory infiltration, while enhancement reflects increased vascularity. Stratified (layered) enhancement = submucosal edema ('target sign').
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The appendiceal wall is thickened with marked enhancement.
Calcified fecalith (appendicolith) within the appendiceal lumen, typically appearing as a round or oval high-density (>100 HU) structure. Found in 25-30% of appendicitis cases and indicates the cause of luminal obstruction. Presence of appendicolith increases perforation risk.
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A ... mm calcified appendicolith is identified within the appendiceal lumen.
Localized free fluid is seen surrounding the appendix and in the right lower quadrant. The fluid amount is limited and typically accumulates in the periappendiceal region and pelvic floor. Diffuse free fluid raises suspicion for perforation.
Report Sentence
A small amount of free fluid is noted in the periappendiceal region and right lower quadrant.
On ultrasound, the appendix is non-compressible with graded compression technique, measuring >6 mm in outer diameter. The lumen may be filled with anechoic fluid or hyperechoic fecal material. The wall layered structure is preserved but thickened (target sign).
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A non-compressible tubular structure measuring ... mm in outer diameter in the right lower quadrant is consistent with acute appendicitis.
Color Doppler ultrasound demonstrates increased vascularity (hyperemia) in the appendiceal wall. Increased blood flow may also be detected in periappendiceal fat. Hyperemia indicates active inflammation.
Report Sentence
Color Doppler demonstrates increased vascularity in the appendiceal wall.
On MRI, the appendix shows T2-hyperintense lumen (fluid) and periappendiceal edema with hyperintense fat stranding on T2-weighted sequences. Periappendiceal edema is more conspicuous on T2 fat-suppressed sequences. DWI diffusion restriction supports inflammation.
Report Sentence
The appendix demonstrates T2-hyperintense lumen and periappendiceal edema consistent with acute appendicitis.
Criteria
Dilated appendix, wall enhancement, periappendiceal stranding; no perforation, abscess, or free air
Distinct Features
Wall integrity preserved, surrounding organs normal, minimal or no free fluid. Treated with antibiotic therapy or appendectomy.
Criteria
Focal wall enhancement defect, wall irregularity, or intramural air in appendix; full perforation not yet developed
Distinct Features
Wall necrosis has begun but free perforation has not yet occurred. CT may show segmental wall enhancement loss and intramural air focus. This is the final stage before perforation and requires emergent surgery.
Distinguishing Feature
In chronic appendicitis, appendix diameter is less dilated (<10 mm), wall thickening is milder, and periappendiceal stranding is minimal or absent; clinical symptoms are mild and recurrent
Distinguishing Feature
In perforation, wall defect, extraluminal air, periappendiceal collection/phlegmon, and diffuse free fluid are seen; these findings are absent in uncomplicated acute appendicitis
Distinguishing Feature
Appendiceal abscess shows organized periappendiceal collection (rim enhancement + central low density); simple acute appendicitis lacks organized collection
Urgency
emergentManagement
surgicalBiopsy
Not NeededFollow-up
no-follow-upAcute appendicitis is a surgical emergency. Standard treatment is laparoscopic appendectomy. Antibiotic therapy may be applied as an alternative in uncomplicated cases, but carries a 30-40% recurrence risk. Delayed diagnosis increases the risk of perforation, abscess, sepsis, and peritonitis. Surgery is recommended within 24 hours of diagnosis.
Acute appendicitis is the most common indication for emergency surgery. Treatment is appendectomy (open or laparoscopic). Delayed diagnosis can lead to perforation, abscess formation, and peritonitis. Antibiotic therapy is discussed as an alternative in uncomplicated cases. The presence of an appendicolith increases perforation risk.