Acute appendicitis is acute inflammation of the vermiform appendix and one of the most common indications for emergency surgery. Lifetime risk is 7-8%. Most common between ages 10-30. Luminal obstruction (fecalith, lymphoid hyperplasia, tumor) is the initiating factor. Complications include perforation, abscess, peritonitis, and pylephlebitis. CT has 94-98% sensitivity and 95-99% specificity for diagnosis and is the gold standard for emergency evaluation.
Age Range
5-50
Peak Age
25
Gender
Male predominant
Prevalence
Common
Appendicitis typically begins with obstruction of the appendiceal lumen — most common causes are fecalith (35%), lymphoid hyperplasia (60%, especially in children), and rarely tumor or parasite. Luminal obstruction increases intraluminal pressure, mucosal barrier disrupts, and bacterial translocation occurs. Venous and lymphatic drainage is impaired — first edema and congestion (catarrhal phase), then transmural inflammation and necrosis (gangrenous phase) develop. Perforation risk increases in gangrenous wall — after perforation, localized abscess or diffuse peritonitis may develop. On CT, this pathophysiology is sequentially visualized: dilated appendix (>6 mm) → periappendiceal fat stranding → wall thickening and enhancement → perforation findings (free fluid, abscess, extraluminal air). Fecalith (appendicolith) appears as calcified structure on CT and provides a diagnostic clue.
The combination of a dilated appendix >6 mm with surrounding fat stranding is pathognomonic for acute appendicitis. This two-finding combination has 98% sensitivity and 95% specificity. When combined with clinical history (right lower quadrant pain, McBurney point tenderness), diagnosis is confirmed.
Appendix diameter >6 mm (normal <6 mm). Dilation reflects increased intraluminal pressure. May be filled with fluid or fecal material.
Report Sentence
The appendix is dilated, measuring approximately ___ mm in diameter; consistent with acute appendicitis.
Increased density in fat tissue surrounding the appendix (fat stranding). Indicates spread of inflammation to periappendiceal tissues. Most sensitive secondary finding.
Report Sentence
Significant periappendiceal fat stranding is observed surrounding the appendix.
Calcified structure in appendix lumen (appendicolith/fecalith). Density ranges from 100-600 HU. Found in 25-30% of cases. Increases perforation risk.
Report Sentence
A calcified appendicolith measuring approximately ___ mm is seen within the appendix lumen.
Appendiceal wall thickening (>3 mm) and increased enhancement. Reflects transmural inflammation. Target sign — inner ring enhancing mucosa, outer ring edematous submucosa.
Report Sentence
Appendiceal wall thickening and increased enhancement are observed, consistent with transmural inflammation.
Perforation findings: periappendiceal free fluid, extraluminal air, abscess formation (rim-enhancing fluid collection), appendiceal wall discontinuity.
Report Sentence
Free fluid/air surrounding the appendix and a rim-enhancing collection measuring ___ cm are seen, consistent with perforated appendicitis.
Non-compressible tubular structure on US, diameter >6 mm. Target sign — concentric wall layers. Periappendiceal hyperechoic fat tissue (inflammation). Primary imaging modality in children and pregnant women.
Report Sentence
A non-compressible tubular structure measuring ___ mm in diameter with surrounding hyperechoic fat tissue is seen in the right lower quadrant, consistent with acute appendicitis.
Criteria
Dilated appendix, fat stranding, wall thickening present. No perforation, abscess, or free air.
Distinct Features
Treated with antibiotics or laparoscopic appendectomy. Conservative (antibiotic) approach may suffice in some cases.
Criteria
Wall discontinuity, extraluminal air, periappendiceal free fluid. Develops in 20-30% of cases.
Distinct Features
Requires emergency surgery. Risk of diffuse peritonitis. Perforation rate is higher in children and elderly.
Criteria
Periappendiceal rim-enhancing fluid collection. Localized infection contained by omentum and bowel adhesion after perforation.
Distinct Features
May be treated with percutaneous drainage + antibiotics. Interval appendectomy planned 6-8 weeks later. CT-guided drainage is safe and effective.
Distinguishing Feature
Cecal diverticulitis may show similar fat stranding but appendix is normal and inflamed diverticulum is seen in the cecum. In appendicitis, the appendix is dilated and inflamed.
Distinguishing Feature
Crohn disease shows terminal ileum thickening, skip lesions, comb sign, and fistula tracts. Isolated appendiceal involvement is rare. In appendicitis, findings are localized to the appendix.
Distinguishing Feature
Mucinous neoplasm may show low-density (mucinous) dilation, wall calcification, and peritoneal spread. Acute appendicitis has prominent inflammatory findings (fat stranding, wall enhancement).
Distinguishing Feature
Cecal adenocarcinoma shows mass formation, apple-core appearance, and lymphadenopathy. Appendicitis is characterized by dilated appendix and periappendiceal inflammatory changes.
Urgency
emergentManagement
surgicalBiopsy
Not NeededFollow-up
no-follow-upAcute appendicitis is an emergency surgical indication. Laparoscopic appendectomy is the gold standard for uncomplicated appendicitis — some centers offer conservative (antibiotic) treatment. Treatment strategy changes for complicated appendicitis (perforation, abscess): diffuse peritonitis→emergency surgery, localized abscess→percutaneous drainage + antibiotics + interval appendectomy 6-8 weeks later. CT findings guide treatment decisions: complicated vs uncomplicated distinction is critical. Pathologic examination of the appendix is mandatory for exclusion of tumor (carcinoid, mucinous neoplasm).
Requires emergency surgery (appendectomy). Complicated appendicitis (abscess, phlegmonous) may be treated with percutaneous drainage and delayed surgery. Perforation and peritonitis are life-threatening.