Appendicitis

• Incidence
  
  
  • 7-12% in Western world population
  • Peak age
    • 2nd-3rd decade
      
      
• Etiology
  
  
  • Obstruction of appendiceal lumen by
    • Lymphoid hyperplasia
    • Fecolith
    • Foreign bodies
    • Stricture
    • Tumor
    • Parasite
    • Crohn’s disease
      
      
• Clinical findings
  
  
  • RLQ pain over appendix is a positive McBurney sign
  • Leukocytosis
  • Fever
  • Nausea and vomiting
  • Relatively higher rate of misdiagnosis in women between ages 20-40
    • May have an atypical location
      
      
• Imaging Findings
  
  
  • Abdominal plain film (abnormalities seen in <50%)
    • Plain-film findings become more distinctive after perforation, while clinical findings subside
      • May simulate other diseases
    • Calcified, frequently laminated, appendicolith in RLQ (in 7-15%)
      • Appendicolith and abdominal pain = 90% probability of acute appendicitis
      • Appendicolith in acute appendicitis means a high probability for perforation
    • "Cecal ileus" = local paralysis
    • Small bowel obstruction pattern
    • Soft-tissue mass and paucity or absence of intestinal gas in RLQ (more often with perforation)
    • Extraluminal gas bubbles (again more often in perforation)
    • Large pneumoperitoneum  is rare because etiology of appendicitis involves obstruction of a very small lumen
    • Focal increase in thickness of lateral abdominal wall
    • Loss of properitoneal fat line on right side
  • BE / UGI (accuracy 50-84%):
    • Failure to fill appendix with barium (normal finding in up to 35%)
    • Indentation along medial wall of cecum (from edema at base of appendix / matted omentum / periappendiceal abscess)
  • US (77-94% sensitive, 90% specific, 78-96% accurate)
    • Useful in ovulating women (false-negative appendectomy rate in males 15%, in females 35%):
    • Visualization of noncompressible appendix as a blind-ending tubular aperistaltic structure (seen only in 2% of normal adults, but in 50% of normal children)
    • Target appearance of  >6 mm in total diameter on cross section (81%)
      • Mural wall thickness >2 mm
    • Diffuse hypoechogenicity (associated with higher frequency of perforation)
    • Lumen may be distended with anechoic / hyperechoic material
    • Loss of wall layers
    • Visualization of appendicolith (6%)
    • Localized periappendiceal fluid collection
    • Prominent hyperechoic mesoappendix / pericecal fat
  • Color Doppler US:
    • Increased conspicuity from increase (in size + number) of vessels in and around the appendix
    • Decreased resistance of arterial waveforms
    • Continuous / pulsatile venous flow
  • CT (87-98% sensitive, 83-97% specific, 93% accurate)
    • Distended lumen
    • Circumferentially thickened and enhancing wall
    • Appendicolith = homogeneous / ringlike calcification (25%)
    • Periappendicular inflammation-linear streaky densities in periappendicular fat
    • Pericecal soft-tissue mass
    • Abscess
      • Poorly encapsulated
      • Single or multiple fluid collection(s) with air
      • Extraluminal contrast material
    • Focal cecal wall thickening (80%)
    • "Arrowhead" sign = funnel of contrast medium in cecum centering about occluded orifice of appendix

Yellow arrowheads point to appendicolith (upper) and appendix
with thickened and enhancing wall and peri-appendiceal stranding (lower)

• Complications
  
  
  • Perforation (13-30%)
    
    
• Differential diagnosis (DDx)
  
  
  • Colitis
  • Diverticulitis
  • Epiploic appendagitis
  • Infectious enteritis
  • Intussusception
  • Crohn’s disease
  • Mesenteric lymphadenitis
  • Ovarian torsion
  • Pelvic inflammatory disease
    
    
• Treatment
  
  
  • Appendectomy
  • Finding of appendicolith is sufficient evidence to perform prophylactic appendectomy in asymptomatic patients (50% have perforation / abscess formation at surgery)