Appendicitis

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)